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Theses and Dissertations
2005
The effect of carbon dioxide on hydroformylation
of 1-Hexene by an immobilized rodium catalyst
Selma Bektesevic
The University of Toledo
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Recommended Citation
Bektesevic, Selma, "The effect of carbon dioxide on hydroformylation of 1-Hexene by an immobilized rodium catalyst" (2005). Theses
and Dissertations. 1407.
http://utdr.utoledo.edu/theses-dissertations/1407
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A Dissertation
Entitled
The Effect of Carbon Dioxide on Hydroformylation of 1-Hexene by an Immobilized
Rhodium Catalyst
By
Selma Bektesevic
Submitted as partial fulfillment of the requirements for
The Doctor of Philosophy Degree in
Engineering
______________________________________
Advisor: Dr. Martin A. Abraham
______________________________________
Graduate School
The University of Toledo
August 2005
i
The University of Toledo
College of Engineering
I HEREBY RECOMMEND THAT THE DISSERTATION PREPARED UNDER MY
SUPERVISION BY
Selma Bektesevic
ENTITLED
The Effect of Carbon Dioxide on Hydroformylation of
1-Hexene by an Immobilized Rhodium Catalyst
BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF
DOCTOR OF PHILOSOPHY IN ENGINEERING
Dissertation Advisor: Dr. Martin A. Abraham
Recommendation concurred by
Dr. Sudhir N. V. K. Aki
Committee
Dr. Mark R. Mason
On
Final Examination
Dr. Constance A. Schall
Dr. Sasidhar Varanasi
Dean, College of Engineering
ii
An Abstract of
The Effect of Carbon Dioxide on Hydroformylation of 1-Hexene by an Immobilized
Rhodium Catalyst
Selma Bektesevic
Submitted as partial fulfillment of the requirements for
The Doctor of Philosophy Degree in
Engineering
The University of Toledo
August 2005
In
situ
high-pressure
Diffuse
Reflectance
Infrared
Fourier
Transform
Spectroscopy was performed to investigate the hydroformylation of 1-hexene in
supercritical carbon dioxide. A rhodium complex was immobilized on phosphinated
silica and used as a catalyst. The changes in the infrared spectrum over time showed the
reaction profile, which was used to evaluate the effect of pressure on the reaction
mechanism. Increasing the reaction pressure by adding carbon dioxide increased 1hexene conversion and hydroformylation activity. Specific changes observed in the
infrared spectrum when the supported complex interacted with carbon monoxide,
hydrogen and/or mixture of carbon monoxide and hydrogen in the presence and absence
of carbon dioxide at elevated pressures revealed the nature of the reacting species over
iii
time and pressure, and clearly demonstrated the role of carbon dioxide when it was used
as the solvent. The catalyst activity and structure were compared for reaction in
supercritical carbon dioxide with that in nitrogen in order to more completely delineate
the role of the supercritical solvent on the reaction mechanism. It was found that the
resting state of the catalyst was HRh(CO)2Lx, L=PPh2CH2CH2 bound to silica,
independent of the reaction pressure and the presence of carbon dioxide or nitrogen.
iv
Acknowledgements
Dr. Martin A. Abraham has been my research advisor and I thank him for his
guidance and assistance. His technical expertise helped me improve my skills as a
chemical engineer. Dr. Abraham supported me and encouraged me to complete this
dissertation. I would also like to thank to Dr. Mark R. Mason for his insight and patience.
He has been a great teacher and I will sure remember our discussion about metal
complexes. The assistance of Dr. Sudhir Aki, Dr. Constance A. Schall and Dr. Sasidhar
Varanasi as part of my examination committee is greatly appreciated.
I am also grateful to the Department of Chemical and Environmental Engineering
for the teaching assistantship and the Environmental Protection Agency for partially
supporting my research. My thanks go to Mr. Robert Dunmyer and Mr. Donald
Mockensturm for their assistance.
I would also like to thank to past and current lab members and other graduate
students. It is always good to have friends to talk and work with.
My mother, Enisa Bektesevic, has been my greatest supporter. She always
encouraged me to go further and if I was about to give up she would always say “little bit
more”. Thank You Mom.
Finally, I would like to thank Haris Ligata for cheering me up, supporting me and
being there for me no matter what.
v
Table of Contents
Page
Abstract
iii
Acknowledgments
v
Table of Contents
vi
List of Tables
xi
List of Figures
xii
List of Abbreviations
xxiii
Chapter
1.
2.
Introduction
1
1.1
Background Information
1
1.2
Motivation
5
Literature Survey
10
2.1
Homogeneous Catalysis
10
2.1.1
Ligand Effects
10
2.1.2
Mechanism
16
2.1.3
Stability
29
2.2
Heterogeneous Catalysis
31
2.2.1
Organic Supports
32
2.2.2
Inorganic Supports
34
2.2.3
Mechanism
41
2.2.4
Stability
47
vi
2.3
3.
4.
Reactions in Benign Solvents
49
2.3.1
Homogeneous Catalysis
51
2.3.2
Heterogeneous Catalysis
58
Experimental Section
63
3.1
Introduction
63
3.2
Experimental Equipment
64
3.3
Experimental Setup
66
3.4
Experimental Procedure
68
3.5
Catalyst Preparation
69
Characterization of Reaction Intermediates
72
4.1
Characterization of the Support and the Catalyst
73
4.1.1
Characterization of Phosphinated Silica Support
73
4.1.2
Characterization of Rh Catalyst Immobilized on
75
Phosphinated Silica Support
4.2
Characterization of the Immobilized Rh Catalyst Under
76
Different Environments
4.2.1.1
Nature of the Immobilized Rh Catalyst Under CO
76
4.2.1.2
Nature of the Immobilized Rh Catalyst Under CO/CO2
80
4.2.2.1
Nature of the Immobilized Rh Catalyst Under H2
81
4.2.2.2
Nature of the Immobilized Rh Catalyst Under H2/CO2
83
4.2.3.1
Nature of the Immobilized Rh Catalyst Under CO/H2
84
4.2.3.2
Nature of the Immobilized Rh Catalyst Under
85
CO/H2/CO2
vii
4.2.4
Nature of the Immobilized Rh Catalyst Under CO2
88
4.2.5
The Behavior of the Immobilized Catalyst Under C6H12
89
and CO2
4.2.6
Identification of the Bands due of Heptanal
91
4.3
Characterization of RhCl(PPh3)3
92
4.4
Hydroformylation of 1-hexene with the Immobilized Rh Catalyst
95
in CO2
4.4.1
Identification of the Species Formed Under Reaction
95
Conditions
4.5
4.4.2
Assignment of the Band at 1710-1730 cm-1
103
4.4.3
Assignment of the Band at 1800 cm-1
107
Investigation of the Reaction Intermediates
112
4.5.1
116
Investigation of the Acylrhodium Complex
Immobilized on Silica Support
4.6
4.5.2
Hydroformylation of 1-hexene with RhCl(PPh3)3
131
4.5.3
Rate Determining Step
133
Hydroformylation of 1-Hexene with the Immobilized Rh
134
Catalyst in the Absence of CO2
5.
Effect of CO2
142
5.1
The Effect of Total Pressure by Addition of CO2
144
5.1.1
145
The Species Present Under Hydroformylation
Conditions
viii
5.1.2
The Species Present After Reaction/ Resting State of
157
the Catalyst
5.2
The Effect of Total Pressure by Addition of N2
163
5.2.1
163
The Species Present Under Hydroformylation
Conditions
5.2.2
The Species Present After Reaction/ Resting State of
173
the Catalyst
5.3
The Effect of Additional Gas on Hydroformylation Reaction
178
5.3.1
178
Species Formed at ~ 500 psig in the Presence of
Different Additional Gas
5.3.2
Species Formed at ~ 840 psig in the Presence of
181
Different Additional Gas
5.3.3
Species Formed at ~ 1040 psig in the Presence of
183
Different Additional Gas
5.3.4
Species Formed at 1250 psig in the Presence of
186
Different Additional Gas
6
Conclusions and Recommendations
193
6.1
Conclusions
193
6.2
Recommendations
194
References
196
Appendix
218
A.1
ChemCAD Output for the Phase behavior in the presence of CO2
219
A.2
ChemCAD Output for the Phase behavior in the presence of N2
232
ix
A.3
Stability of Rh complex immobilized on Phosphinated Silica and
247
MCM-41 Supports
A.3.1
Introduction
247
A.3.2
Experimental Equipment
248
A.3.3
Experimental Procedure
249
A.3.4
Results and Discussion
250
x
List of Tables
Page
Table
4.1
Volume adsorbed during pulse chemisorption
79
4.2
Reported IR vibrations for Rh carbonyl complexes
95
4.3
Reported C=O stretch for acyl metal complexes
116
5.1
The number of moles of reactants present initially at given total
145
pressures and 100 °C in reactions carried out in the presence of CO2
5.2
Estimated rate constants for 1-hexene disappearance
152
5.3
The calculated angles between two carbonyls in the possible dicarbonyl
159
metal complexes observed after hydroformylation carried out in the
presence of CO2 at different total pressures.
5.4
The number of moles of reactants present initially at given total
163
pressures and 100 °C in reactions carried out in the presence of N2
5.5
The calculated angles between the two carbonyls for possible
175
dicarbonyl metal complexes observed after hydroformylation carried in
the presence of N2 at different total pressures
A.3.1
Elemental analysis of fresh and used catalysts
xi
247
List of Figures
Page
Figure
1.1
Order of activity of metals and ligands used in hydroformylation 2
reaction [2]
1.2
The order of reactivity of alkene substrates [2]
3
1.3
Structure of TPPTS
5
2.1
Structure of triphenylphosphine
11
2.2
Representation of cone angle (θ)
12
2.3
Structures of DPPE and DPPB
13
2.4
Structure of xantphos ligand prepared by Kranenburg et al. [29]
14
2.5
Structure of BISBI
15
2.6
Structure of thixantphos used by van der Veen et al. [30]
16
2.7
Hydroformylation mechanism for cobalt catalysts as proposed by Heck 17
and Breslow [34].
2.8
Associative mechanism for hydroformylation proposed by Evans et al. 18
[25]
2.9
Dissociative mechanism for hydroformylation cycle proposed by Evans 19
et al. [25]
2.10
Mechanism for ethylene hydroformylation, L=PPh3 [26]
21
2.11
Isomeric forms of RhH(CO)2(PPh3)2; a) ea: b) ee [37]
23
2.12
Structure of dimeric species observed by Evans et al. [36]
27
2.13
Structure of [Rh(CO)(PPh3)2,S] [36]
27
xii
2.14
Structure of orange dimer (a) and phosphido-bridged dimer (b) as 30
reported by Moser et al. [49]
2.15
Deactivation route of phosphine-modified Rh catalyst [3]
31
2.16
Structures proposed by Luchetti and Hercules for Rh complexes
35
supported on silica and alumina [68]
2.17
Structure of the catalyst prepared by Standfest-Hauser et al. [69]
36
2.18
Structure of the complexes formed on zinc aluminate spinel [70]
37
2.19
Structure
of
4-[bis(2-diethylaminoethyl)aminomethyl]diphenyl 38
phosphine, N3P [72]
2.20
Structure
of
N-(3-trimethoxysilane-n-propyl)-4,5- 39
bis(diphenylphosphino)phenoxazine [74]
2.21
Hydroformylation on heterogeneous catalysts; modified from [88]
42
2.22
Changes in the structure of rhodium dimers attached on SiO2 [92]
45
2.23
Structure of the rhodiumacyl complex as reported by Rode et al. [95]
46
2.24
Structure of the catalyst used by Lin and Akgerman [128]
54
2.25
Structure of the ligand used by Franció et al. [129]
55
2.26
UCC liquid recycle process [3]
58
2.27
Structure of the ligand used by Bronger et al. [140]
61
2.28
Structure of the catalyst used by Shibahara et al. [141]
62
3.1
Change in dipole moment due to bending vibration [143]
64
3.2
Stretching and bending modes of the molecule [142]
64
3.3
Collector and high pressure/high temperature chamber assembly for 66
DRIFTS studies
xiii
3.4
Experimental Setup for DRIFTS studies
67
3.5
Schematic overview of the procedure for the catalyst synthesis
71
4.1
Structure of phosphinated silica support
73
4.2
IR spectra the support at room temperature and at 100 °C
74
4.3
IR spectra of the catalyst and the support at room temperature and at 76
100 °C
4.4
IR spectra of the catalyst after exposure to CO
77
4.5
Structure of the supported carbonyl complex reported by Luchetti et al. 78
[148]
4.6
Structures of immobilized rhodium carbonyl complexes
78
4.7
TCD response during CO pulse chemisorption
79
4.8
IR Spectra of the catalyst and the support after being exposed to 100 80
psig CO in CO2, P=1100 psig
4.9
IR Spectra of the catalyst under 200 psig of hydrogen and after being 82
exposed to carbon monoxide at 100 °C
4.10
IR spectra of the catalyst under H2/CO2; P=1190 psig, T=100 °C
83
4.11
IR spectrum of the catalyst after being exposed to CO/H2, P=450 psig,
85
T=100 °C
4.12
IR spectra of the catalyst under CO/H2/CO2; P= 1140 psig, T=100 °C
86
4.13
IR spectrum of the catalyst after exposure to CO/H2 in CO2, P=1140 86
psig, T=100 °C
4.14
IR spectrum of the catalyst after treatment with CO and the changes
observed after being exposed to H2
xiv
88
4.15
IR spectra of the catalyst under CO2, P=1220 psig, T=100 °C
89
4.16
IR spectra of the catalyst before, during and after exposure to mixture 90
of 1-hexene and carbon dioxide, P=1100 psig, T=75 °C
4.17
IR spectra under and after exposure of the catalyst to mixture of 01
heptanal and carbon dioxide, T=100 °C, P=1200 psig
4.18
IR spectra of RhCl(PPh3)3 after different pretreatments
93
4.19
Comparison of the IR spectra of Wilkinson’s catalyst and TPP
93
4.20
IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
96
P=1250 psig
4.21
IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C, 97
P=1250 psig; bands due to 1-hexene vibrations
4.22
IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C, 98
P=1250 psig; bands due to 1-hexene and aldehyde vibrations
4.23
IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C, 100
P=1250 psig; bands due to 1-hexene and 2-hexenes vibrations
4.24
IR spectrum of the 2-hexenes in CO2
100
4.25
IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
101
P=1250 psig; bands due to 2-hexene and/or aldehyde vibrations
4.26
IR spectrum of the catalyst after hydroformylation mixture was 103
removed by nitrogen, T=100 °C, P=1250 psig
4.27
IR spectra of the catalyst under different atmospheres, region ~ 1720 104
cm-1
xv
4.28
IR spectra of the support and different catalysts at room temperature 105
and at 100 °C
4.29
IR spectra of the different catalysts after hydroformylation reaction was 106
completed
4.30
IR spectra of the catalyst and the support under hydroformylation 107
conditions
4.31
The spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C, 108
P=1250 psig; bands in the bridging carbonyl region
4.32
Structure of dimer reported by Luchetti et al. [148]
109
4.33
Structure of Rh dimer reported by Haji and Erkey [11]
109
4.34
IR spectra of the catalyst after different pretreatments, bridging 110
carbonyl region.
4.35
Structure of the dimer, [Rh(CO)2L]2, formed on the phosphinated silica 111
support
4.36
Structure of the dimer, (Rh(CO)2L2)2, formed on the phosphinated 111
silica support
4.37
Mechanism proposed for hydroformylation by immobilized Rh catalyst
112
4.38
Structures of possible Rh complexes immobilized on phosphinated 113
silica support during hydroformylation
4.39
Comparison of IR spectra obtained under hydroformylation conditions 117
and under CO/H2/CO2, T=100 °C, P=1250 psig
4.40
Comparison of the difference spectra obtained under hydroformylation
conditions and under CO/H2/CO2
xvi
118
4.41
IR spectra of the pretreated catalyst under mixture of CO, 1-hexene and 119
CO2, T=100 °C, P=1160 psig
4.42
IR spectra of the catalyst under mixture of CO, 1-hexene and CO2, 121
T=100 °C, P=1120 psig
4.43
The difference of the spectra taken at 5th minute and the time indicated 122
under conditions as specified in Figure 4.42
4.44
IR spectra of the catalyst under PCO=15 psig; PC6H12=25 psig, T=100 °C 123
4.45
IR spectra of the catalyst under CO, H2, 1-hexene and CO2 (CO:H2:1-
124
hexene=2.5:2.5:1), T=100 °C
4.46
IR spectra of the catalyst taken under mixture of CO, H2, 1-hexene and 126
CO2, T=100 °C, P=1030 psig
4.47
IR spectra of the catalyst taken under mixture of CO, H2, 1-hexene and 127
CO2, T=100 °C, P=1200 psig, CO:H2:C6H12=24:24:1
4.48
IR spectra of the catalyst with Rh:P=1:1 under hydroformylation 129
conditions (nCO=nH2=1*10-2, n1-hexene=1*10-3, T=100 °C, P=1240 psig)
4.49
Comparison of the spectra of the catalyst with Rh:P=1:1 under 130
hydroformylation conditions and under CO/H2
4.50
IR spectra of Wilkinson catalyst under reaction conditions stated in the 132
text
4.51
IR spectra of the catalyst under 2*10-2 mol CO/H2 (1:1), 9.7*10-4 mol 135
C2H12 and N2
4.52
IR spectra of the catalyst under conditions reported in Figure 4.52, 136
1700-1750 cm-1 region
xvii
4.53
IR spectra of the catalyst under conditions reported in Figure 4.52, 137
2990-3100 and 850-1050 cm-1 regions
4.54
Comparison of IR spectra of the catalyst under hydroformylation 138
conditions in the presence of CO2 and N2
4.55
Comparison of IR spectra of the catalyst after hydroformylation 139
reaction in the presence of CO2 and N2
4.56
IR spectra of the catalyst under hydroformylation conditions in the 140
presence of N2, 2400-2250 and 700-600 cm-1 regions
4.57
IR spectra of the catalyst under different environments; 2250-2450 141
region
5.1
IR spectra of the catalyst 5 minutes upon the onset of hydroformylation
146
reaction at varying total pressures in the presence of CO2
5.2
IR spectra of the catalyst under hydroformylation conditions at varying 147
total pressures in the presence of CO2; 1600-1800 cm-1 region
5.3
IR spectra of the catalyst 600 minutes upon the onset of 148
hydroformylation reaction at varying total pressures in the presence of
CO2
5.4
Comparison of the spectra taken at varying total pressures in the 149
presence of CO2; 1600-1800 cm-1 region
5.5
Area counts vs. time for 1-hexene disappearance during reactions 152
carried out in the presence of CO2 at varying total pressures
5.6
Effect of total pressure on rate of 1-hexene disappearance in
hydroformylation accomplished in the presence of CO2
xviii
153
5.7
IR spectra of the catalyst at 5th and 600th minute of hydroformylation 154
reaction at varying total pressures in the presence of CO2, 100-850 cm-1
region
5.8
IR spectra of the catalyst during hydroformylation reaction at varying 155
total pressures in the presence of CO2, 1850-1750 cm-1 region.
5.9
Pressure vs. integrated area under the band at 1800 cm-1 observed at 156
600th minute of reactions carried out at different total pressures in the
presence of CO2.
5.10
IR spectra of the catalyst after hydroformylation carried out in the 157
presence of CO2 at different total pressures
5.11
Comparison of IR spectra obtained shortly after hydroformylation 160
reaction and aged catalyst (Reaction carried in presence of CO2)
5.12
IR spectra of the catalyst one day after hydroformylations carried out in 161
the presence of CO2 at different total pressures
5.13
Area counts vs. total pressure for bands at 1800 and 1710 cm-1 162
observed after reaction accomplished in the presence of CO2
5.14
IR spectra of the catalyst 5 minutes upon the onset of hydroformylation
164
reaction at varying total pressures in the presence of N2
5.15
IR spectra of the catalyst under hydroformylation conditions at varying 165
total pressures in the presence of N2, region 1800-1600 cm-1
5.16
IR spectra of the catalyst 600 minutes upon the onset of 166
hydroformylation reaction at varying total pressures in the presence of
N2
xix
5.17
The difference of the spectra obtained under hydroformylation 166
conditions in the presence of N2
5.18
Comparison of the spectra taken at varying total pressures in the 167
presence of N2 in the 1600-1800 cm-1 region
5.19
Area counts vs. time for 1-hexene disappearance during reactions 168
carried out in the presence of N2 at varying total pressures
5.20
Effect of total pressure on rate of 1-hexene disappearance in
169
hydroformylation carried out in the presence of N2
5.21
The difference of the spectra obtained under hydroformylation 171
conditions in the presence of N2, 3100-300- and 1000-850 cm-1 regions
5.22
The difference of the spectra obtained under hydroformylation 172
conditions in the presence of N2, 1850-1750 cm-1 region
5.23
Pressure vs. integrated area under the band at 1800 cm-1 observed at 173
600th minute of reactions carried out in the presence of N2 at different
total pressures
5.24
IR spectra of the catalyst shortly after being used for hydroformylation 174
of 1-hexene in the presence of N2 at different total pressures
5.25
Comparison of IR spectra obtained shortly after reaction is carried in 176
the presence of N2 and of aged sample
5.26
IR spectra of the catalyst 1 day after being used for hydroformylation 177
of 1-hexene in the presence of N2 at different total pressures
5.27
Area counts vs. pressure plot for bridged carbonyls observed after 177
reaction carried out in the presence of N2
xx
5.28
The difference of the spectra obtained under hydroformylation 178
conditions in the presence of N2, 2450-2250 cm-1 region
5.29
IR spectra of the catalyst 5 minutes after the onset of hydroformylation 179
reaction at ~ 500 psig in CO2 and N2
5.30
IR spectra of the catalyst 600 minutes after the onset of 179
hydroformylation reaction at ~ 500 psig in CO2 and N2
5.31
IR spectra of the catalyst under hydroformylation conditions in the 180
presence of N2 and CO2, 1800-1600 cm-1 region
5.32
IR spectra of the catalyst after hydroformylation reaction carried at 181
~500 psig in the presence of CO2 and N2
5.33
IR spectra of the catalyst 5 minutes after the onset of hydroformylation 182
reaction at ~ 840 psig in CO2 and N2
5.34
IR spectra of the catalyst 600 minutes after the onset of 182
hydroformylation reaction at ~ 840 psig in CO2 and N2
5.35
IR spectra of the catalyst after hydroformylation reaction carried at 183
~840 psig in the presence of CO2 and N2
5.36
IR spectra of the catalyst 5 minutes after the onset of hydroformylation 184
reaction at ~ 1040 psig in CO2 and N2
5.37
IR spectra of the catalyst 600 minutes after the onset of 184
hydroformylation reaction at ~ 1040 psig in CO2 and N2
5.38
IR spectra of the catalyst under hydroformylation conditions in the 185
presence of N2 and CO2 at ~1040 psig, 1800-1600 cm-1 region
xxi
5.39
IR spectra of the catalyst after hydroformylation reaction carried at 186
~1040 psig in the presence of CO2 and N2
5.40
IR spectra of the catalyst 5 minutes after the onset of hydroformylation 187
reaction at 1250 psig in CO2 and N2
5.41
IR spectra of the catalyst 600 minutes after the onset of 187
hydroformylation reaction at ~ 1250 psig in CO2 and N2
5.42
IR spectra of the catalyst under hydroformylation conditions in the 188
presence of N2 and CO2 at 1250 psig, 1800-1600 cm-1 region
5.43
IR spectra of the catalyst after hydroformylation reaction carried at 189
1250 psig in the presence of CO2 and N2
5.44
IR spectra of the catalyst under hydroformylation conditions in the 191
presence of He, N2 and CO2, 1800-1600 cm-1 region
A.3.1
Experimental setup for stability studies
249
A.3.2
Aldehyde yield and selectivity during hydroformylation of 1-hexene on 251
rhodium anchored on phosphinated silica
A.3.3
Yield and selectivity of Rh anchored on phosphinated MCM-41
253
A.3.4
pathway for 1-hexene hydroformylation and isomerization
253
xxii
List of Abbreviations
acac
acetylacetonate
BET
Brunauer-Emmett-Teller
BISBI
[2,2’-bis(diphenylphosphino)methyl]-1,1’-biphenyl
COD
cyclooctadiene
CP
cross-polarization
DPPB
1,4-bis(diphenylphosphino)butane
DPPE
1,2-bis(diphenylphosphino)ethane
DRIFTS
diffuse reflectance infrared spectroscopy
DVB
divinylbenzene
Et
ethyl
EXAFS
extended X-ray absorption fine spectroscopy
FTIR
Fourier transform infrared spectroscopy
GC
gas chromatography
IR
infrared spectroscopy
L:B
ratio of linear aldehyde to branched aldehyde
LHHW
Langmuir-Hinshelwood-Hougen-Watson
MAS
magic angle spinning
MCM
Mobil Corporation materials or Mobil crystalline materials
MS
mass spectroscopy
xxiii
NMR
nuclear magnetic resonance
PPh3
triphenylphosphine
PS
polystyrene
Rh:P
rhodium-to-phosphorus molar ratio
scCO2
supercritical carbon dioxide
TCD
thermal conductivity detector
TOF
turnover frequency
TPP
triphenylphosphine
SCF
supercritical fluid
xxiv
CHAPTER 1
INTRODUCTION
1.1 Background Information
The hydroformylation reaction was discovered by Otto Roelen of Ruhrchemie AG
in 1938. The reaction, also called “oxo synthesis”, adds one mol of each CO and H2 to an
olefinic substrate to produce an aldehyde. The reaction proceeds in the presence of a
catalyst to yield both linear and branched aldehydes, as depicted by the reaction below.
CHO
catalyst
R
+ CO + H2
CHO
R
+
R
Commercially, both cobalt and rhodium catalyst are used to produce approximately 7
million tons of oxo products [1] per year.
Aldehydes are used for the production of alcohols, carboxylic acids, aldol
products, diols, acetals, ethers, acroleins and esters [2]. Economically, the most important
substrate is propene [3]. Its hydroformylation product, butanal, is converted to 2ethylhexanal by aldol condensation and then to 2-ethylhexanol by hydrogenation [3]. The
plasticizer dioctyl phthalate is manufactured from 2-ethylhexanol and is used by polymer
industry [3]. Detergent products can also be made from long chain aldehydes.
1
While both plasticizer and detergent manufacturing require linear aldehydes,
branched aldehydes are also valuable products. They can be used in the pharmaceutical
and agrochemical industries, and in particular, in cases in which the desired intermediate
is a branched aldehyde with an asymmetric carbon atom. The two most common
examples are ibuprofen and naproxen, inflammatory agents that can be produced from
branched aldehydes [4].
As evident from above, selectivity is an important parameter in hydroformylation
chemistry. The selectivity can be partially controlled through the choice of the catalyst.
The efficient hydroformylation catalyst will lead to formation of aldehydes in significant
yield (chemoselectivity) and will have high selectivity toward desired aldehyde.
Therefore, regioselectivity or ratio of linear aldehyde to branched aldehyde (L:B) is an
important parameter for hydroformylation reaction. For asymmetric reactions,
enantioselectivity is also an important parameter.
The catalyst used in hydroformylation has a general composition of
HxMy(CO)zLn. Several metals (M) and ligand combinations can be used as the catalyst.
The order of reactivity is shown in Figure 1.1.
M=Rh>>Co>Ir, Ru>Os>Pt>Pd>Fe>Ni
L=PPh3, P(OR)3> P(n-C4H9)3>>NPh3>AsPh3,SbPh3> BiPh3
Figure 1.1: Order of activity of metals and ligands used in hydroformylation reaction [2].
2
Rhodium is more active than cobalt, but is also more expensive. Rhodium is the
catalyst of choice for conversion of low molecular weight alkenes, while cobalt based
catalysts are used for conversion of high molecular weight alkenes. For example,
Ruhrchemie/Rhone-Poulenc (RCH/RP) process is used for hydroformylation of propene
by Rh based catalysts.
Cobalt based catalysts are used for hydroformylation of 1-octene in the BASF
process, and C6-C12 olefins in the Exxon process [3]. However, high pressure of 39154350 psi is applied. Reaction temperature between 120-175 °C is used. At first no ligands
were added so that n in HxMy(CO)zLn was 0 and therefore, the catalysts were unmodified.
However, addition of phosphine-based ligands allowed milder reaction conditions and
increased selectivity.
Ligands change the electronic and steric properties of the catalyst complex.
Because of their importance in affecting activity and selectivity, extensive research has
occurred in ligand design. Some representative examples are given in Chapter 2 and
additionally by Marteel [4], but the general trend of activity as reported by Trzeciak et al.
is shown in Figure 1.1 [2].
Another key parameter is the choice of the alkene. The order of the reactivity is as
depicted in Figure 1.2 [2].
>
>
>
Figure 1.2: The order of reactivity of alkene substrates [2].
3
>
So, the highest reactivity is achieved with unbranched, terminal alkenes while the
reactivity decreases as the degree of branching increases.
Commercially, 73% of alkene feed is comprised of propene followed by C4-C12
alkenes (19%), while ethylene and alkenes higher than C12 comprise 2 and 6%,
respectively [3]. As stated above, propene is hydroformylated mostly by Rh, even though
Co based processes are still in use. This is due to infrastructure based on high pressure as
well as catalyst separation thereafter being available [3]. Additionally, Rh has low
reactivity for branched alkenes and separation becomes difficult when higher alkenes are
hydroformylated because the boiling points of aldehydes with increased carbon number
are high.
Hydroformylation is conducted in a mixture of reactants and products, and as of
1984 in biphasic aqueous media to allow dissolution of Rh catalyst and reactants in a
homogeneous liquid phase. The catalysts used are homogeneous in nature, dissolved into
the solvent or reactant/product mixture. This poses significant challenges related to
separation, which is simplified in the biphasic RCH/RP oxo-process. This process is
based on aqueous biphasic catalysis and uses tri(m-sulfonyl)triphenylphosphine (TPPTS),
depicted in Figure 1.3, as the ligand and a water soluble Rh metal as the catalyst. Even
though this process is extremely regioselective for propene hydroformylation, it is not
suitable for alkenes such as C5 and higher, because the solubility of these substrates in
water is too low for significant activity to be achieved.
Several solutions to the poor solubility of higher alkenes in water are proposed in
the literature. They are based on addition of co-solvents to increase solubility of alkenes
in biphasic process. Additionally, alternate solvent systems such as polyethylene glycol,
4
water, or fluorous solvents are proposed to ease separation due to immobilization of the
catalyst in a phase other than that in which the product is dissolved. Other solutions
involve the use of ionic liquids and supercritical fluids. All the proposed solutions seek to
use a homogeneous metal complex to maximize the metal availability. There have also
been attempts to anchor metal complexes on inorganic supports and achieve separation
by purely mechanical (filtration) means.
NaSO3
SO3Na
P
SO3Na
Figure 1.3: Structure of TPPTS.
1.2 Motivation
Hydroformylation is an economically important process since the production
volume is so large. Even though significant improvements have been made, there is still
room for changes. For example, plasticizers based on C10 alcohols are now desired, as
they are less volatile than the C8 alcohols currently used [3].
Asymmetric
hydroformylation is also a field of great potential.
Green chemistry is the design of chemicals and processes that decrease or
eliminate the utilization and generation of hazardous materials [5]. Principles of green
5
chemistry include the design of a process and/or product which is based on biodegradable
materials, which saves energy, uses less toxic materials, is more efficient and causes less
pollution, and the use of the reactions that are atom economical. The term atom economy
was used by Trost to emphasize efficient synthesis [6]. For a well-conceived
hydroformylation process, 100% atom economy is possible, since all materials used in
the process can end up in the final product. Lately, ideas such as “Green Chemistry” and
sustainability have been embraced by more and more companies.
Tadd et al. [7, 8] and Marteel et al. [9] have used hydroformylation as an example
process to demonstrate the opportunities for catalyst in a benign reaction medium. The
catalyst used by this group was a Rh complex (Rh2Cl2(COD)2) immobilized on a
phosphinated silica support and the reaction was carried in supercritical CO2. Detailed
catalyst preparation method as well as characterization by nuclear magnetic resonance
spectroscopy (NMR) was reported by Marteel [4]. Tadd et al. studied 1-hexene
hydroformylation at 75 °C and 2700 psig in scCO2 [8]. Both hydroformylation and
isomerization of 1-hexene occurred under reaction conditions. Linear aldehyde and
branched aldehydes were observed hydroformylation products, while isomerization
reaction produced cis- and trans-2-hexene. In some cases product mixture also contained
small amounts of 1-heptanol [7]. When the ratio of rhodium to phosphorus was 1 to 2,
yield was 14000 mol of all aldehydes per mol rhodium [4]. Initial regioselectivity of
about 2.3 was found to decrease with time as isomerization products were
hydroformylated [4].
1-Hexene hydroformylation in scCO2 with Rh complex anchored on phosphinated
silica was reported to follow Langmuir-Hinshelwood type kinetics [8]:
6
(rHF )0 =
K A [1 − hexene]0 [ H 2 ]0 [CO ]0
1 + K C [1 − hexene]0 + (1 + K B [CO ]0 )
2
The good fit of experimental data to the rate expressions for homogeneously and
heterogeneously catalyzed hydroformylation, suggested that the heterogeneous catalyst
system was behaving like an immobilized homogeneous system.
Temperature and pressure effects were also studied [7]. Conversion increased as
reaction temperature was increased from 60 to 90 °C, but the ultimate yield was similar
in all cases. Regioselectivity at the end of reaction was greatest at 60 °C and decreased as
temperature increased. An increase in the rate of the hydroformylation reaction was also
correlated with an increase in the total reaction pressure [7].
The effect of modifying the support of the immobilized catalyst was studied by
Tadd et al. [7]. Three supports were prepared and tested: phosphinated support produced
with Ph2P(CH2)2 side-chains, hydrophobic support with CH3(CH2)9 and Ph2P(CH2)2 sidechains, and CO2-philic with CF3(CF2)7(CH2)2 and Ph2P(CH2)2 side-chains. The catalyst
immobilized to hydrophobic support showed highest yield and selectivity, which was
attributed to higher concentration of 1-hexene in proximity of catalyst surface.
Further work compared a tethered catalyst with a homogeneous catalyst prepared
from Rh(acac)3 and ethyldiphenylphosphine [10]. The rate of aldehyde formation was
greater for the homogeneous catalyst in liquid phase toluene, but the immobilized catalyst
in scCO2 had higher L:B ratio (4.5).
The research on immobilized catalyst was continued by comparing the activity
and selectivity (L:B) for Rh complexes anchored on low surface area phosphinated silica
7
(8.6 m2/g) with those anchored on higher surface area supports such as phosphinated
MCM-41 (642.1 m2/g) and MCM-20 (829.5 m2/g) [9]. The activity of Rh complex
anchored on MCM type support was higher than that of Rh complex anchored on silica,
with the yield of Rh complex on MCM and silica being around 35000 and 13000 mol
aldehyde per initial mol 1-hexene per mol Rh, respectively. This was thought to be due to
the larger surface area of MCM type support which in turn led to better dispersion of the
catalyst. The highest initial selectivity (L:B = about 2.7) was found for Rh tethered on
MCM-20 support, while the lowest regioselectivity (L:B = less than 2) ratio was seen
when Rh complex was anchored on silica. The improved selectivity using MCM-20
support was attributed to the smaller pore, which minimized the formation of undesired
branched aldehydes.
Tadd et al. tested the stability of a Rh catalyst covalently bonded to the support
[8]. Even though losses of approximately 20% and 33% were observed for phosphorus
and rhodium, respectively, the catalyst was active through three cycles (24 hours total)
and aldehyde yield appeared to have increased with repeated catalyst use. Researchers
proposed that activity was due to rhodium chemically bound to the support through a
phosphorus anchor site, while leaching was due to inactive rhodium physically adsorbed
onto the support [8].
The results obtained by the cited groups showed the potential of combining the
immobilized catalyst and use of scCO2 as a solvent. They, therefore, demonstrated a
process that generates less waste and uses an environmentally benign reaction solvent.
The current work is extension of the research reported by cited groups. The
research seeks to develop additional details for the catalytic hydroformylation of 1-
8
hexene to heptanal in the presence of CO2 using a supported rhodium catalyst. The
catalyst is Rh complex (Rh2Cl2(COD)2) immobilized on phosphinated silica support
where the ratio of phosphorus to rhodium is 2. Infrared (IR) spectroscopy has been used
to study homogeneous reactions in presence [11] and absence [12, 13] of CO2.
Heterogeneous reactions have also been studied by IR spectroscopy [14]. This study
seeks to probe the behavior of the Rh complex immobilized on phosphinated silica in
CO2 by IR spectroscopy. This entail identification of species formed during
hydroformylation of 1-hexene in the presence of CO2. Additionally, the study seeks to
find out the role of CO2 in hydroformylation of 1-hexene by an immobilized Rh complex.
9
CHAPTER 2
LITERATURE SURVEY
2.1 Homogeneous Catalysis
2.1.1 Ligand Effects
Hydroformylation reactions can be catalyzed by various metal complexes.
Initially, unmodified cobalt catalyst obtained either from Co2(CO)8 or from cobalt salts
were used [15]. For example, the BASF process uses a cobalt based catalyst for
hydroformylation of propene or higher olefins [3]. Similarly, cobalt-catalyzed
hydroformylation of C6-C12 alkenes is also carried out in the Exxon process [3].
However, both of these processes require elevated temperatures (120-175 °C) and high
pressures (3915-4350 psi). Slaugh and Mullineaux reported on tertiary phosphine, arsine
or phosphite modified cobalt catalysts [15]; cobalt phosphine is used for
hydroformylation of C7-C14 alkenes in the Shell process [3]. Even though the reaction
temperature is still high (150-190 °C), pressures of 580-1160 psi are applied.
The introduction of modified catalysts led to considerable research on ligand
effects. Triphenyl phosphine (TPP) ligand, shown in Figure 2.1, has been studied
extensively [16, 17, 18] since it modified a metal complex to yield an active and selective
hydroformylation catalyst under milder reaction conditions.
10
P
Figure 2.1: Structure of triphenyl phosphine (PPh3).
Phosphine ligands (TPP) are also applied commercially in the Union Carbide
Corporation (UCC) process [3], in which propene is hydroformylated by Rh catalyst
modified by TPP. The temperatures and pressure are 85-90°C and 261 psi in UCC liquid
recycle process.
Phosphite ligands were reported by Pruett and Smith [19]. They are efficient
ligands for Rh catalyzed hydroformylation since they allow for higher reaction rates
compared to TPP, but they are less selective than TPP ligand [20].
The activity and selectivity of phosphine and phosphite based catalyst complexes
depend on steric and electronic properties. The electronic properties of the organometallic
complex are determined by electron donating and/or accepting ability of the ligand.
Electron withdrawing ligands will prevent excess negative charge buildup on the metal,
in which case the formation of the linear metal alkyl complex might be favorable [20].
Moser et al. studied the electronic effects on hydroformylation rates and selectivity [13].
11
Electron density on Rh was varied by using p-N(CH3)2, p-OCH3, p-H, p-F, p-Cl and pCF3 as substituents Z in RhH(CO)2(P(C6H4Z)3)2. They found that reaction rate and
regioselectvity increased as the electron withdrawing properties of the ligand increased.
Highest rate and L:B ratio were reported for the case where Z was p-CF3
The cone angle (θ) is used to determine the steric properties. It is defined as “the
apex angle of a cylindrical cone, centered at 2.28 Å from the center of the P atom, which
touches the van der Waals radii of outermost atoms” [21]. Figure 2.2 is a pictorial
representation of the cone angle, where R are the substituents attached to the phosphorus
atom.
R
R
R
P
θ
M
Figure 2.2: Representation of cone angle (θ).
Phosphite and phosphine ligands are more bulky than carbonyl ligands and create
sterically demanding environment around the metal. The bulkiness of the ligand will
impede the coordination of the alkene. As a result, the rate of the reaction will decrease
while selectivity to linear aldehyde will increase because the linear aldehyde is less bulky
than the branched aldehyde.
12
Suomalainen et al. studied 1,2-bis(diphenylphosphino)ethane (DPPE) and 1,4bis(diphenylphosphino)butane (DPPB), depicted in Figure 2.3, as ligands for
hydroformylation of propene by rhodium phosphine catalysts [22]. At 145 psi and 100
°C, the yield of butanal was near 0 for DPPE and 73 % for DPPB modified catalyst, with
regioselectivity (L:B) of 0 and 2.7, respectively. The change in the steric bulk of the
ligand affected the activity and selectivity.
PPh2
PPh2
PPh2
PPh2
DPPE
DPPB
Figure 2.3: Structures of DPPE and DPPB.
Rhodium complexes of phosphites were also studied [23, 24]. Comparison of
monodentate phosphite ligands such as tris(o-tert-butylphenyl)phosphite and PPh3 for
hydroformylation of 2-methyl-1-hexene revealed that the former was more active than
Rh/PPh3 system [23].
Higher concentration of free PPh3 led to higher selectivity toward linear aldehyde
which suggested that an active species contained two triphenylphosphine ligands [17,
25]. One of the ways to achieve formation of this species is to use excess ligand or to use
bidentate ligands [26]. Introduction of bidentate ligands would ensure that rhodium atom
13
is coordinated to two phosphorus atoms and would additionally provide control of the
metal-ligand geometry [26]. The coordination mode is important as it can impact the
catalytic cycle by stabilizing/destabilizing the complex formed during reaction [27].
Casey and Whitaker introduced the concept of “natural bite angle”, estimated using
molecular mechanics, to determine the preferred chelation angle of diphosphine ligands
[28].
Kranenburg et al. developed bidentate diphosphines, based on xanthene-like
backbones to study the effect of bite angle on the regioselectivity in rhodium-catalyzed
hydroformylation of 1-octene [29]. They observed that the regioselectivity increased with
increasing bite angle. However, when the calculated bite angle was so large (131.1 °),
chelation was no longer possible and the L:B ratio was low. A xantphos-based rhodium
complex with a bite angle of 111.7°, Figure 2.4, was the most active (TOF=800 mol
aldehyde per mol Rh per hour) and most selective (L:B=53.5) for hydroformylation of 1octene at 80 °C and 145 psi CO/H2.
O
PPh2
PPh2
Figure 2.4: Structure of xantphos ligand prepared by Kranenburg et al. [29].
14
The same group also studied BISBI ligand (Figure 2.5) whose natural bite angle
was 122.6° for hydroformylation of 1-octene at the same conditions as for
hydroformylation with xantphos-based Rh complex [29]. BISBI-Rh complex was more
active (TOF=850) and more regioselective (L:B=80.5) than xantphos-Rh complex but
BISBI based system was also more active for isomerization. The authors concluded that
rigidity of the ligand was important to obtain stable chelated complexes.
PPh2
PPh2
Figure 2.5: Structure of BISBI.
Van der Veen et al. studied the electronic effect in the Rh-diphosphine catalyzed
hydroformylation [30], by using p-(CH3)2N, p-CH3O, p-H, p-F, p-Cl or p-CF3 as the
substituents (R groups) on the phenyl rings. The natural bite angle of the thixantphos
ligands (Figure 2.6) was varied between 106.4° for p-H and 109.3° for p-CF3. For
hydroformylation of 1-octene at 80 °C and 290 psi, the highest activity and
regioselectivity were observed for ligand-Rh system with p–CF3 as a substituent
15
(TOF=158 mol aldehyde per mol Rh per hour, L:B=86.5). Data obtained also indicated
that the L:B ratio increased as basicity of the ligand decreased.
S
Ar =
R
O
PAr2
PAr2
Figure 2.6: Structure of thixantphos used by van der Veen et al. [30].
Several groups have studied hydroformylation of internal alkenes [31, 32, 33].
Internal alkenes are more stable than terminal alkenes and therefore harder to
hydroformylate. Therefore, a catalyst that can isomerize internal alkene to terminal
alkene, which can then be hydroformylated has to be designed.
2.1.2 Mechanism
The main steps occurring during hydroformylation of alkenes by unmodified
rhodium (and cobalt) catalysts are thought to be those proposed by Breslow and Heck [3].
The cycle involves coordinatively unsaturated tricarbonyl species as an active catalyst.
The mechanism of Co catalyzed hydroformylation is given in Figure 2.7. Coordination of
alkene followed by hydride transfer generates a 16 electron alkylcobalt carbonyl species.
CO coordination and alkyl transfer to CO leads to a 16 electron, acylcobaltcarbonyl
species.
16
CO
RCH = CH2 + HCo(CO)3 → RCH2CH2Co(CO)3 → RCH2CH2CO(Co)(CO)3
H2
→ HCo(CO)3 + RCH2CH2CHO
Figure 2.7: Hydroformylation mechanism for cobalt catalysts as proposed by Heck and
Breslow [34].
The reduction of acyl complex to aldehyde, according to Breslow and Heck [34], is by
hydrogen rather than HCo(CO)4.
In 1965, Osborn et al. reported that hydroformylation of olefins can be
accomplished at mild conditions (55 °C; 1322.3 psi) by rhodium phosphine catalysts
[16]. Hydroformylation of alkenes by modified Rh catalysts is thought to follow the
Heck-Breslow
cycle
with
slight
modification.
Evans
et
al.
suggested
that
hydroformylation can proceed through two different pathways, as depicted in Figures 2.8
and 2.9 [25].
The associative route begins with coordination of the alkene to the dicarbonyl
species (Figure 2.8, 1B). The dissociative route involves dissociation of one of the
ligands (PPh3 or CO) and is similar to Heck-Breslow cycle. After the initial steps, the
following steps in the associative and dissociative mechanisms are similar; following
alkene coordination, an alkyl species (Figure 2.8, 1D, Figure 2.9, 2D) is formed. Alkyl
migration to CO leads to acyl formation (Figure 2.8, 1E, Figure 2.9, 2F). Hydrogen
addition produces dihydrido acyl species (Figure 2.8, 1F, Figure 2.9, 2G). Finally,
17
[Rh(CO)2(PPh3)2]2
R
R
H
H
CH2CH2R
Ph3P
Ph3P
Rh
CO
Ph3P
Ph3P
Rh
Ph3P
CO
Rh
Ph3P
CO
CO
1B
CO
CO
1D
1C
CO
CH2CH2R
H
H
PPh3
Ph3P
Rh
CO
H
H2
PPh3
Rh
-RCH2CH2CHO Ph3P
Ph3P
Rh
COCH2CH2R
Ph3P
CO
CO
CO
1A
1F
1E
CO
+PPh3
CH2CH2R
H
Ph3P
Ph3P
Rh
PPh3
CO
Rh
Ph3P
CO
Ph3P
CO
CO
1G
Figure 2.8: Associative mechanism for hydroformylation proposed by Evans et al. [25].
18
R
H
H
Ph3P
H
CO
-PPh3
Rh
CO
Rh
Ph3P
Rh
Ph3P
CO
OC
CO
2B
2A
R
Ph3P
CO
2C
CO
H
CH2CH2R
PPh3
CO
Rh
Rh
Ph3P
Ph3P
CO
CO
2D
-RCH2CH2CHO
CH2CH2R
H
Ph3P
H
CO
H2
Rh
Ph3P
PPh3
+PPh3
Ph3P
Rh
COCH2CH2R
CH2CH2R
Rh
CO
Ph3P
Ph3P
CO
CO
CO
2G
2F
2E
CO
COCH2CH2R
Ph3P
Rh
CO
Ph3P
CO
2H
Figure 2.9: Dissociative mechanism for hydroformylation cycle proposed by Evans et al.
[25].
19
elimination of the aldehyde and addition of CO regenerates the active catalytic species
HRh(CO)2L2.
Yagupsky et al. argued that hydroformylation proceeded through both
mechanisms [35]. The associative mechanism would be more regioselective due to the
presence of bulky PPh3 ligands which create sterically demanding environment around
metal, while the dissociative mechanism through RhH(CO)2PPh3 would be less selective
but more active [35]. The associative mechanism is the preferred path when excess PPh3
is added to the system as dissociation of ligand is suppressed [35].
The associative mechanism involves 20-electron intermediates and is often
rejected on the grounds that Rh should form 16 or 18 electron complexes. Also, initial
attack of alkene onto the trans-Rh(CO)(PPh3)2 was discounted by Evans et al. [25]. So,
instead, hydroformylation is usually accepted to follow the dissociative mechanism, as
depicted in Figure 2.10 [26]. In order to avoid referring to two figures depicting
mechanism as proposed by Evans et al., the subsequent literature review discussion will
refer to Figure 2.10, as it is much simpler to follow.
20
O
C CO
L
Rh
H
L
H2
H
L
Rh
Rh
CO
L
CO
Rh
CO -H2 OC
L
H
L
CO
Rh
L
C
L
2ae
CO
2ee
CO
H
9
OC
Rh
1
L
CO
O
H
L
L
Rh
L
CH3
O
L
L
L
CO
3c
3t
C2H4
CH2
C
H
L
Rh
H
OC
L
H2
CH3
O
CH3
CH2
O
C
CH3
CH2
H2C
C
OC
Rh
4ae 4ee
L
CO
L
L
Rh
Rh
L
L
OC
CO
L
8ee 8ae
CO
CO
7c 7t
CH3
5t 5c
CH3
CH2
CH2
L
L
Rh
OC
CO
Rh
CO
L
L
6ae
CO
6ee
Figure 2.10: Mechanism for ethylene hydroformylation, L=PPh3 [26].
The mechanism of hydroformylation has been studied by infrared (IR) and
nuclear magnetic resonance spectroscopy to gain insight into the species formed during
21
reaction. Evans and coworkers studied the interaction of CO and RhH(CO)(PPh3)3 [36].
This species has Rh-H stretch at 2000 and Rh-CO stretch at 1920 cm-1 [36]. Addition of
CO at 25 °C, led to disappearance of the bands due to RhH(CO)(PPh3)3 and appearance
of peaks at 2038, 1980 and 1939 cm-1. These peaks were associated with the formation of
RhH(CO)2(PPh3)2. Subsequently, under further exposure to CO, the bands due to
RhH(CO)2(PPh3)2 decreased and bands at 2005, 1985, 1790 and 1765 cm-1 appeared.
These bands were assigned to the dimer [Rh(CO)2(PPh3)2]2. However, if the catalyst was
held under a 1:1 mixture of CO and H2 at 20 °C and 14.7 psi, RhH(CO)2(PPh3)2 was
predominant species with only small amounts of dimer formed.
Industrially applied hydroformylation employs high pressures and high
temperatures. Morris and Tinker carried out IR studies at elevated temperature and
pressure using RH(CO)(PPh3)3 as a catalyst precursor [12]. The IR spectrum of
RhH(CO)(PPh3)3 at 25 °C and 200 psig CO/H2 showed bands at 2030 (m), 1980 (s), 1940
(m) and 1770 (m) cm-1. They ascribed the bands to a mixture of RhH(CO)2(PPh3)2 and
the dimer [Rh(CO)2(PPh3)2]2. However, heating the solution to 80 °C led to the
disappearance of bands at 2030, 1940 and 1770 cm-1 and the appearance of bands at 1980
and 1950 cm-1. They reported that at high temperature dicarbonyl and dimer were not
present in high amounts. The findings of Morris and Tinker contradict those of Moser et
al. [13], who found that at 200 psi CO/H2 and 70 °C, RhH(CO)2(P(C6H5)3)2
was
observed with IR bands in the 2000 cm-1 region.
Brown et al. studied the behavior of triphenyl complexes under a CO atmosphere
by NMR spectroscopy [37]. They found that HRh(CO)(PPh3)3 was in equilibrium with
isomeric forms of HRh(CO)2(PPh3)2, as depicted in Figure 2.11.
22
H
H
CO
PPh3
Rh
Ph3P
Rh
Ph3P
CO
CO
PPh3
CO
(a)
(b)
Figure 2.11: Isomeric forms of RhH(CO)2(PPh3)2; a) ea: b) ee [37].
Isomer (a) has hydrogen trans to a phosphine ligand so the two phosphine ligands
are in apical-equatorial (ae) coordination while ee coordination has hydrogen trans to CO
and two equatorial phosphine ligands (ee), as indicated by isomer (b). The ratio of
diequatorial (ee) isomer to equatorial-apical isomer was 85:15 [37]. The stereochemistry
is important as it is one of the factors that determine the regioselectivity of the
hydroformylation reaction [26]. When two PPh3 ligands are trans to each other and each
of them is cis to hydrogen, the steric effects is maximized [25].
The
[Rh2{µ-S(CH2)3N(Me2)}2-(COD)2]/PPh3
system
was
studied
under
hydroformylation conditions (80 °C, 72.5 - 435 psi) by Diégues et al [38]. Under 72.5 psi
CO/H2 at 80 °C, peaks at 2054, 2040, 1989, 1977, 1965 and 1946 cm-1 were observed.
Bands at 2040 and 1946 cm-1 were attributed to two isomers of RhH(CO)2(PPh3)2.
Additional bands at 1992 cm-1 and 1981 cm-1, due to above mentioned isomers, were
overlapped
by
the
signals
at
1989
and
1979
cm-1,
assigned
to
Rh2{µ-
S(CH2)3N(Me2)}2(CO)4(PPh3)2. Based on the above mentioned results, as well as the
23
observation of similar regioselectivity of [Rh2{µ-S(CH2)3N(Me2)}2-(COD)2]/PPh3 and
Rh(acac)(CO)2/PPh3 systems, the researchers concluded that catalytic activity was due to
a mononuclear hydrido species.
It was argued that hydrogenation was connected to RhH(CO)(PPh3)2 while
RhH(CO)2(PPh3)2 was connected to hydroformylation [25, 39]. Moreover, in another
study Evans et al. reported that only RhH(CO)2(PPH3)2 reacted with ethene, so it was
possible to differentiate between monocarbonyl- and dicarbonylrhodium species [36].
The next step in the hydroformylation cycle would be coordination of alkene and
formation of alkyl species RhR(CO)L2 (Figure 2.10, 5). Since reaction of
RhH(CO)(PPh3)3 with 1-hexene was too fast and generated acyl species, Yagupsky et al.
studied reaction of RhH(CO)(PPh3)3 with C2F4 [35]. They observed that reaction of the
catalyst with tetrafluoroethylene yielded Rh(C2F4H)(CO)(PPh3)2 (νCO=1990 cm-1). They
argued that this fluoroalkyl species was stable since Rh-C bond was stronger, in part due
to the electronegativity of F atoms.
Whyman studied the hydroformylation reaction with HIr(CO)3P-i-Pr3 at 50° C in
heptane solution [40]. Reaction of HIr(CO)3P-i-Pr3 (νCO=1970 and 2038 cm-1) with 200
psi ethylene produced alkyl species, C2H5Ir(CO)3P-i-Pr3 (νCO=1957, 1954, 2030 and
2025 cm-1). Alkyl complex was also observed when the pre-formed active catalyst,
RhH(CO)2L2 (L=PPh3) was reacted with 1-hexene in dichloroethane under nitrogen at
room temperature [13]. The RhR(CO)2L2 species formed had IR peaks at 1987 and 1939
cm-1.
In the rhodium-catalyzed mechanism, alkyl migration to carbon monoxide
generates the acyl intermediate (Figure 2.10, 7). Existence of this intermediate was
24
suggested by observations of the IR bands corresponding to functional group (C=O) of
the acyl complex. Baird et al. observed the formation of acyl complex,
RhCl2(COEt)(PPh3)2 [41] by interaction of RhCl2(Et)(PPh3)2 with CO; identified through
an IR band at 1701 cm-1 and a weak band at 1762 cm-1, thought to be due to presence of
rotational or geometrical isomer. Yagupsky et al. [35] observed acyl formation upon
reaction of CO and RhH(CO)(PPh3)3 in the presence of liquid 1-hexene, identified by two
bands in terminal carbonyl region (1900-2000 cm-1) and an acyl band at 1620-1660 cm-1.
Whyman found that exposure of fairly stable species such as HIr(CO)3P-i-Pr3 in
n-heptane to ethylene, followed by venting of the excess ethylene and the addition of 200
psi of CO at 50° C generated acyl, C2H5COIr(CO)3P-i-Pr3 with bands at 2041, 1978 and
1671 cm-1 [40]. Liu et al studied hydroformylation of several alkenes using Rh4(CO)12 as
the catalyst precursor at 20 °C, PH2=290 psi, PCO=290 psi in n-hexane [42]; as a
representative terminal alkene, the acyl complex formed from 1-hexene showed bands at
2110.5, 2064.2, 2038.2, 2020.2, 1702.9 cm-1. In addition to the band at ~1703 cm-1 from
coordination at the α carbon, a weak sideband at 1694 cm-1 was observed and assigned to
coordination at the β carbon. In further studies with the same catalyst and ethylene as a
substrate, Liu and Garland observed the formation of ethyl Rh tetracarbonyl,
[CH2CH3Rh(CO)4], (νCO=2089, 2038, 2017 cm-1) at low partial pressure of CO (43.5 psi
CO, 43.5 psi H2 and 580 psi ethylene), while the acyl complex, [CH2CH3CORh(CO)4]
was formed at higher partial pressures of CO [43].
Yagupsky et al. [35] observed formation of species analogous to complex 8 in
Figure 2.10 upon exposure of trans-Rh(C2F4H)(CO)(PPh3)2 to CO. The first reaction gave
Rh(C2F4H)(CO)2(PPh3)2 (νCO=2005, 1958 cm-1). However, further reaction led to
25
formation of tricarbonyl species Rh(C2F4H)(CO)3PPh3 that has IR bands at 2075 and
2020 cm-1.
Hydroformylation of 1-hexene by RhH(CO)(PPh3)3 was studied by NMR at 580
psi (1:1) CO/H2 and 30 fold excess of 1-hexene (75 µL; 0.6 mmol) [44]. At room
temperature, the acyl complex [Rh(CO(CH2)5CH3)(CO)2(PPh3)2] was formed. However,
upon depressurization, the signal due to the acyl complex disappeared, indicating that this
intermediate was only stable under CO atmosphere. Adeyemi and Coville reported that
(η5-C5H5)Mo(CO)3COMe could be formed by reaction of (η5-C5H5)Mo(CO)3Me and CO
in the absence of solvent at 80 °C and 145 psi of CO [45].
The final step in the hydroformylation cycle involves formation of the aldehyde
product. Prior to elimination of aldehyde, a dihydrido acyl species (Figure 2.8, 1F, Figure
2.9, 2G) is formed by hydrogen addition to the monocarbonyl acyl. Propanal band was
observed at 1730 cm-1 in organic solvent such as heptane [40].
Formation of the hydrido rhodium carbonyl complex under CO/H2 is usually
accompanied by formation of the Rh-dimer. Evans et al. observed that upon addition of
CO, RhH(CO)(PPh3)3 was carbonylated to RhH(CO)2(PPh3)2, (νCO=2038, 1980, 1939
cm-1), but further exposure led to appearance of bands at 1765, 1790, 2005 and 1985 cm-1
[36] that were assigned to the rhodium dimer, [Rh(CO)2(PPh3)2]2, depicted in Figure
2.12.
26
O
C
(Ph3P)2(OC) Rh
Rh(CO)(PPh3)2
C
O
Figure 2.12: Structure of dimeric species observed by Evans et al. [36].
Bianchini et al. reported formation of Rh(0) dimers of the formula
Rh2(CO)4+x(PPh3)4-x, x = 0 or 1 [44]. The dimer formation was influenced by CO pressure
and presence of free PPh3. Morris and Tinker observed that upon addition of H2, the
dimer was converted back to HRh(CO)2(Ph3P)2 [12].
Evans et al. suggested that
[Rh(CO)2(PPh3)2]2 was converted to a different dimer, depicted in Figure 2.13, which in
the presence of solvent (S) such as CH2Cl2 has IR bands at 1980 and 1740 cm-1 [36].
O
C
(Ph3P)2(S) Rh
Rh(S)(PPh3)2
C
O
Figure 2.13: Structure of [Rh(CO)(PPh3)2,S]2 [36].
27
Another important factor in determining selectivity is the rate determining step.
The rate determining step during hydroformylation depends on several factors. For
example, for unmodified carbonyl catalysts and bulky phosphite liganded catalysts, the
resting state of the catalyst is a dicarbonyl acyl complex and therefore the rate
determining step is addition of H2 [26]. Evans et al. suggested that the rate determining
step was the oxidative addition of molecular hydrogen to acyl species [25], as this step is
the only one in hydroformylation cycle in which a change in oxidation state of metal and
its coordination number occurs [25].
Because the concentration of acyl species increased with an increase in partial
pressure of CO at constant total pressure during hydroformylation of 1-octene with
Co2(CO)8 as catalyst precursor, Whyman suggested that the rate determining step was
hydrogenolysis of acyl cobalt carbonyl species [46]. However, Whyman also reported
that when cobalt catalyst was modified with PBu3, no acyl was observed [46]. Addition
of alkene to HIr(CO)3P-i-Pr3 was suggested to be the rate determining step in 1-heptene
hydroformylation as only observable species during reaction was HIr(CO)3P-i-Pr3 [41].
Even though these studies refer to Co and/or Ir, it shows that the rate determining step
depends on presence of ligand.
Van Rooy et al., determined that the reaction was negative order in CO, first
order in 1-octene and independent of
H2 for hydroformylation of 1-octene using
diphosphite modified Rh catalyst [47], and suggested that the rate determining step was
exchange of a CO ligand for a π - coordinated alkene.
It was argued that under standard conditions (T=70-120 °C, PCO=72.5-362.5 psi,
PH2=72.5-362.5 psi, Rh~1mM, alkene =0.1-2 M), the rate type I applies [26]
28
Rate (type − I) =
A[alkene][Rh]
B + [L ]
where L is proportional to concentration of PPh3 or CO and A and B are constants that do
not refer to specific rate constants. Thus, for phosphine modified catalyst with kinetics of
type I, the rate determining step was proposed to be insertion of the alkene into Rh-H
bond [26]. However, under conditions where the concentration of Rh is kept low by using
RhH(CO)(PPh3)3 without excess PPh3, dissociation of PPh3 occurs leading to type II
kinetics [26].
Rate (type - II) =
C[ H 2 ][ Rh]
D + [CO ]
2.1.3 Stability
Catalyst performance factors including activity, selectivity, and stability
determine the commercial development of the catalytic process. Since the metal complex
is composed of metal and ligand, loss of either could be important. Preventing
degradation or deactivation through catalyst loss minimizes the cost of the
hydroformylation process.
Rhodium loss occurs primarily through two routes:
•
Chemical loss through the formation of inactive rhodium complexes, such as
Rh dimers or Rh6(CO)16. High ligand concentrations minimize formation of
inactive Rh-complexes [48].
•
Physical loss, also called “Rh leaching”, which occurs as the catalyst is drawn
out along with the liquid product [48].
29
Moser et al. evaluated the formation of Rh-carbonyl complexes during
deactivation of RhH(CO)2(P(C6H4Z)3)2 (Z=p-N(CH3)2 and p-OCH3) [49]. They observed
the formation of yellow dimer (νCO=1968 cm-1) at 35.6% conversion; the dimer is similar
to that of the dimer shown in Figure 2.12. At 50.5% conversion, orange dimer (νCO=1960
cm-1), Figure 2.14, structure (a), was observed, while concentration of yellow dimer and
alkyl complex, RhR(CO)2L2, decreased. At 60% conversion phosphido bridged dimer,
depicted in Figure 2.14, structure (b), was observed.
R
L
OC
Rh
Rh
L
P
L
L
R
Rh
CO
L
OC
Rh
P
R
(a)
CO
L
R
(b)
Figure 2.14: Structures of orange dimer (a) and phosphido-bridged dimer (b) reported by
Moser et al. [49].
Loss of ligands can also cause degradation of the catalyst. Phosphine degradation
can take place through:
•
Oxidation of ligand by reaction with oxygen, water, or carbon dioxide [48].
Even though this usually occurs during separation steps where contact with air
is most probable, the presence of impurities in synthesis gas can also lead to
ligand decomposition.
30
•
P-C bond cleavage, which leaves inactive rhodium complexes, or formation of
undesirable phosphorus ligand structures [48].
Abatjoglou et al. found that the extent of orthometallation was small and that
phosphorus-phenyl bond cleavage was the main reaction of triphenylphosphine during
propene hydroformylation by phosphine modified rhodium catalyst [50]. The
deactivation mechanism of phosphine modified Rh catalyst is depicted in Figure 2.15.
Arylrhodium species C in Figure 2.15 is formed by insertion of Rh into P-C bond [3].
Lx(CO)Rh
PPh2
Lx(CO)Rh
A
PPh2
Lx(CO)Rh
B
PPh2
C
Figure 2.15: Deactivation route of phosphine-modified Rh catalyst [3].
2.2 Heterogeneous Catalysis
Catalyst
recovery
represents
a
major
cost
in
commercially
applied
hydroformylation. This is especially a concern when expensive Rh is employed as the
catalyst and much effort must be expended to recover used catalyst. Development of a
heterogeneous catalyst would eliminate the need for costly separations.
Most heterogeneous catalysts use inorganic support materials such as silica [51,
52, 53, 54, 55, 56, 57], alumina or carbon [58]. These traditional catalysts are usually
prepared by impregnation technique. Immobilized catalysts may be formed from
31
inorganic materials such as silica or alumina, or from polymer supports that are usually
prepared by sol-gel or ion exchange methods.
Immobilized (anchored, heterogenized) catalysts were originally developed to
combine the advantages of homogeneous and heterogeneous catalysts. They are metal
complexes (metal and ligands) chemically bonded to a polymeric or inorganic support. In
this way the metal complex is attached to a solid support for ease of separation and
recovery. The difficulty in obtaining a uniform structure [59, 60] and expensive
preparation techniques are disadvantages of these catalysts.
2.2.1 Organic Supports
Polymeric supports are widely used for immobilized catalysts due to ease of
functionalization. Hydroformylation of 1-pentene by RhH(CO)(PPh3)3 catalyst anchored
on
phosphinated
resin-A
(P/Rh=19)
was
more
selective
than
homogeneous
RhH(CO)(PPh3)3 catalyst (at 96% yield, selectivity was 6.1 for polymer anchored catalyst
vs. 2.4 for homogeneous catalyst) [61]. A high catalyst-ligand concentration within the
volume of resin was considered to be the source of this behavior. At high phosphorus
loading the predominant species was RhH(CO)2(PPh3)2, which gave higher selectivity
than RhH(CO)2(PPh3) found at lower phosphine loading. Moreover, the authors
suggested that in the polymer matrix, the close proximity of Rh and P increased the
collision rate, leading to higher selectivity [61]. Pittman et al. also found that the rate of
hydroformylation of methyl methacrylate with RhH(CO)(PPh3)3 was faster than that of
its polymer-supported analogue, but RhH(CO)(PPh3)3 was less selective for the branched
product [62].
32
Hydroformylation of propylene over polymer-immobilized RhCl(CO)(PPh3)2 was
studied by Ro and Woo [63]. It was found that the largest initial activity was displayed by
20% cross-linked macroreticular type phosphinated polystyrene – divinylbenzene (PSDVB) while initial activity of 8% cross-linked gel-type PS/DVB (PS8/Rh), 4% crosslinked PS/DVB (PS4/Rh) and 2% cross-linked PS/DVB (PS2/Rh) was similar. The
selectivity (L:B) of the catalysts decreased in order of PS2/Rh>PS4/Rh>PS8/Rh. The
increase in selectivity with decreasing crosslink ratio was described by change in the
internal mobility of the polymer chain. The increase of polymer chain mobility with time
and with decreasing crosslink ratio was thought to provide greater sterically demanding
environment and an increase in the number of phosphine ligands free to coordinate to Rh
carbonyl species, leading to an increase in the phosphorus to rhodium ratio, and thus an
increase in selectivity.
Propene hydroformylation was catalyzed by a cationic rhodium carbonyl complex
anchored on a cross-linked co-polymer that was prepared from 2-vinylpyridine (25 mol
%), methyl acrylate (70%) and ethene diacrylate (5%) [64]. The catalyst was prepared
from [RhCl(CO)2]2 anchored on polymer and chloride exchanged with tetraphenylborate.
It was found that at 130°C and 159.5 psi (C3H6:CO:H2 = 2.4:2.2:1.0) the L to B ratio was
about 1. Mdleleni et al. anchored rhodium on poly(4-vinylpyridine) for hydroformylation
of 1-hexene in ethoxyethanol-water under varying PCO at 100°C [65]. A
hydroformylation turnover frequency of 4.5 d-1 was observed, with the L:B ratio
increasing from 0.6 at PCO = 4.4 psi to 1.3 at PCO = 22 psi. Stille and Parrinello reported
on styrene hydroformylation by platinum-tin chloride supported on polymer bound chiral
33
phosphine [66]. Optical yields of 70% and the B to L ratios in range 0.45 to 0.6 were
reported.
2.2.2 Inorganic Supports
Organic polymers are not mechanically stable and their structure is influenced by
the reaction temperature, pressure and solvent [60]. This, in turn, restricts their use in
commercial processes where the long tubular reactors are employed. Inorganic supports,
most notably silica, on the other hand are mechanically stable, and are thus a versatile
substitute for polymeric supports.
Zhang et al. studied propene hydroformylation by Rh-phosphine complex
supported on carbon nanotubes [67] at 120 °C and 145 psi (C3H6:CO:H2=1:1:1) and
found activities similar to that of Rh/SiO2 (TOF=0.12 s-1), but with higher
regioselectivity (11.2 for nanotubes compared to 8.2 for silica). Luchetti and Hercules
studied liquid phase hydroformylation of 1-hexene by analogues of RhCl(CO)(PPh3)2
anchored on alumina and silica [68]. At 80°C and 661.2 psi CO/H2 (1:1), selectivity
(L:B) was 0.8 for Rh anchored on silica and 1.3 for Rh on alumina It was also reported
that the rate was higher using the silica anchored catalyst and that isomerization was
lower for the alumina anchored catalyst. One of the reasons for higher reaction rates of
silica based catalyst over alumina supported catalyst was thought to be due to higher
stability of the R(C=O)Rh(CO)(PPh3)2 complex on silica than on the alumina support.
Isomerization behavior was explained in terms of species formed on different
supports. A monophosphine cis-dicarbonyl complex, Figure 2.16, structure A, was
formed under hydroformylation conditions on silica, and was responsible for
34
isomerization and low selectivity [68]. On the other hand, a Rh complex supported on
alumina was transformed to both structure A and a penta-coordinated diphosphine
dicarbonyl complex such as depicted in Figure 2.16, structure B. The species that has
structure B was thought to be responsible for lower isomerization rates.
O
Si
O
CH2 CH2 P Ph2
Si
CH2 CH2 P Ph2
CO
Cl
Cl
Rh
Rh
CO
CO
CO
O
Si
CH2 CH2 P Ph2
B
A
Figure 2.16: Structures proposed by Luchetti and Hercules for Rh complexes
supported on silica and alumina [68].
Hydroformylation of 1-hexene was also reported by Standfest-Hauser et al. [69],
using a catalyst prepared by reacting [Rh(acac)(CO)2] with Ph2PCH2CH2Si-(OMe)3,
which was then grafted onto the silica surface. On the basis of
31
P CP/MAS NMR
spectroscopy and GC-MS analysis, the researchers argued that the catalyst as depicted in
Figure 2.17 was obtained. At 80 °C and 146.9 psi CO/H2, conversion of 98% was
obtained with an L:B ratio of 2.0; 81% of 2-hexenes were also detected. The yield of
aldehydes increased as excess phosphinated silica P-{SiO2} or free PPh3 were added.
35
CO
Rh
PPh2
HO
OH
Si
O
O
O
O OH
Figure 2.17: Structure of the catalyst prepared by Standfest-Hauser et al. [69].
The heterogenization of a homogeneous rhodium catalyst on zinc aluminate spinel
(ZnAl2O4) was reported by Wrzyszcz et al. [70]. For this purpose, rhodium (I)
complexes, Rh(acac)(CO)2, Rh(acac)(CO)(PPh3) and RhCl(CO)(PPh3)2 supported on the
spinel
were
prepared
to
obtain
Rh(CO)2/spinel,
Rh(CO)(PPh3)/spinel
and
Rh(CO)(PPh3)2/spinel. The catalyst Rh(CO)2/spinel under N2 or CO atmosphere showed
IR bands at 2015 and 2088 cm-1 and Rh(CO)(PPh3) on spinel had an IR band at 1992 cm1
, leading the researchers to propose the structures shown in Figure 2.18. No activity of
Rh(CO)2 supported on spinel at 145 psi of CO/H2 and 83 °C for 1-hexene
hydroformylation was observed. However, addition of excess of 15 mol PPh3 per mol of
supported Rh led to aldehyde yields of 96% and L:B ratio of about 3.
36
CO
CO
CO
Rh+
O-
PPh3
Rh+
O-
O
O
spinel
spinel
(a)
(b)
Figure 2.18: Structure of the complexes formed on zinc aluminate spinel [70].
Rhodium catalyst can be linked to an inorganic support via ligands other than
phosphorus. Allum et al. compared the activity of rhodium complexes linked to silica via
phosphorus, nitrogen, oxygen and sulfur [71]. At 631.8 psi CO/H2 (1:1) and 100-120 °C,
the catalyst linked to silica through phosphorus ligands was the most active for 1-hexene
hydroformylation ( 99 % conversion, 96% yield of heptanals) and selective (L:B =2.2:1).
The catalyst linked through nitrogen and oxygen were less active while Rh complex
linked through the sulfur ligand were the least active (yield of heptanal was about 8 wt %
at 140-150 °C).
Karlsson et al. prepared α-zirconium phosphate supported rhodium-phosphine
complex [72] with N3P ligand, as depicted in Figure 2.19. Hydroformylation of 1hexene at 80 °C and 290 psi (1:1) CO/H2 in the liquid phase resulted in a selectivity of 3
with a TOF of 110 h-1.
37
Et2N
N
NEt2
P
Figure 2.19: Structure of 4-[bis(2-diethylaminoethyl)aminomethyl]diphenyl phosphine,
(N3P) [72].
The
catalyst
prepared
by
anchoring
thiopyrimidine
complex
[Rh(SPymMe2)(CO)2] onto SiO2 was tested for hydroformylation of 1-heptene [73]. The
tethered catalyst was active at 70 °C and 435 psi CO/H2 (TOF=28.6 mol aldehydes per
mol Rh per hour). Addition of free PPh3 led to increase in selectivity, but TOF was 2.5
mol aldehydes per mol Rh per hour.
Homogeneous catalyst containing bidentate ligand showed high selectivity [30].
Sandee et al. [74] prepared five different immobilized catalysts from xanthene based
diphosphine ligands, depicted in Figure 2.20.
38
PPh2
(MeO)3Si
N
O
PPh2
Figure 2.20: Structure of N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine [74].
Catalyst 1, prepared using a sol-gel method wherein [Rh(acac)(CO)2], tetramethyl
orthosilicate (TMOS) and ligand were mixed in THF/H2O, was most active (TOF=18.3
mol product per mol catalyst per hour) and most selective (L:B=65) for 1-octene
hydroformylation at 725 psi CO/H2 (1:1) and 80 °C. Catalyst 2, prepared by first
anchoring the ligand to silica and then mixing it with [Rh(acac)(CO)2] in THF showed
the lowest selectivity, thought to be due to existence of ligand-free Rh. Sandee et al.
further studied immobilized catalyst [75], anchoring the ligand depicted in Figure 2.20 on
Si (120 m2/g) and SiC (0.5 m2/g) monoliths. Hydroformylation of 1-octene at 80 °C and
725 psi CO/H2 gave selectivity of 14 and 46 for Si and SiC monoliths, respectively, with
TOF of 3 and 2 mol aldehyde per mol catalyst per hour. Compared to the sol-gel
analogue [74], the activities of monolith-supported catalysts were lower (18.3 vs. 2-3).
39
Zeolites have also been used as catalyst and/or catalyst support. Zeolite supported
catalysts are prepared by ion exchange. Davies et al. studied liquid phase
hydroformylation of 1-hexene at 293.8 psi H2/CO and 50 °C with Rh zeolite A catalyst
[76]. Even though conversion was low, 21.3 %, the L:B ratio of RhCaA catalyst was
2.73. Davies et al. further studied zeolite supported Rh catalysts for hydroformylation of
1-hexene at 50 °C and 300 psig H2/CO (1:1) [77]. The conversion for the catalyst with 3
wt% Rh was about 85%, but L:B ratio was 2.68. Addition of PPh3 increased selectivity to
2.88 and decreased conversion, suggesting that catalysis was due to Rh present in
solution and/or on the surface and not due to Rh found inside the zeolite pores [77].
Beck and coworkers [78] reported on a new family of silicate/aluminosilicate
mesoporous molecular sieves, M41S, with large surface areas. Variation of surfactant
chain length led to the pore size variation. The MCM supported catalysts have been
studied for oxidation of alkenes [79], olefin polymerization [80, 81, 82], and
hydrogenation of arenes [83]. These materials have larger pores than zeolites so that
diffusional limitations can be overcome, however, due to the same pore effect, selectivity
may be induced.
Mukhopadhyay et al. studied HRh(CO)(PPh3)3 encapsulated in zeolite, MCM-41
and MCM-48 supports [84] for 1-octene hydroformylation. At 591.6 psi (1:1) CO/H2 and
100 °C in toluene as a solvent, TOF were 141, 216 and 270 h-1 for Rh on zeolite, MCM41 and MCM-48, respectively. All catalysts were stable (less than 0.01 % of Rh leaching)
and L:B ratios reported were 1.5, 1.7 and 1.7 for Rh on zeolite, MCM-41 and MCM-48,
respectively. With 1-hexene as the reactant, TOF of 338 h-1 and L:B of 2.33 were
reported for MCM-48 supported catalyst. The higher selectivity obtained for 1-hexene
40
than for 1-octene might have been due to greater size of 1-octene. As for the difference
between the activity of zeolite and MCM supports, the authors reported that this might be
due to larger pore size of MCM supports leading to easier access to the active sites
located inside the pores.
Hydroformylation of cyclohexene with MCM-41 tethered Rh complexes was also
studied by Huang et al. [85]. They compared the activities of Rh4(CO)12 anchored on
MCM-41 through amine, phosphine, and thiol ligands. The activity of the catalysts
decreased in the following order: Rh4(CO)12/MCM-41> Rh4(CO)12/MCM-41(NH2)>
Rh4(CO)12/MCM-41(PPh2) while no activity was observed for Rh4(CO)12/MCM-41(SH).
The unfunctionalized Rh4(CO)12/MCM-41 leached almost all Rh (0.04 % remained)
which implied that the catalyst behaved as a homogeneous catalyst. Based on the studies
of Allum et al. [71] and Huang et al. [85], it appears that immobilization of rhodium
complex through a sulfur ligand does not lead to high activities.
2.2.3 Mechanism
The mechanism of heterogeneously catalyzed hydroformylation has also been
studied [14, 86, 87]. Figure 2.21 describes the reaction pathway for ethylene
hydroformylation on a heterogeneous catalyst. Hydrogenation of adsorbed ethylene leads
to adsorbed ethyl species. Insertion of adsorbed CO leads to formation of C2H5CO*, an
adsorbed acyl species. Finally reaction between adsorbed hydrogen and the acyl species
leads to formation of propanal and recovery of the active site.
41
CO + *
CO*
C2H5CHO*
C2H5CO*
H*
*C2H5
-*
C2H5CHO + *
*C2H5
C2H4
H*
* ~ active site
½ H2 + *
Figure 2.21: Hydroformylation on heterogeneous catalysts; modified from [88].
Chuang and Pien studied reactions of adsorbed CO with C2H4/H2 and ethylene
hydroformylation over reduced (pre-treated with H2), oxidized (air) and sulfided (pretreated with H2S) Rh/SiO2 catalyst by in situ IR spectroscopy [14]. The authors reported
that reaction of ethylene and hydrogen with pre-adsorbed CO on the oxidized catalyst at
28 °C produced propanal (νC=O=1732 cm-1), but no acyl complex was observed. It was
observed that the intensity of the band at 1732 cm-1 increased as the intensity of the band
at 2106 cm-1 decreased. In a different experiment the authors observed that under
hydroformylation conditions (100 °C, 14.7 psi) with oxidized Rh/SiO2, bands at 2083 and
2025-2033 cm-1, assigned to RhI(CO)2 and bands at 1881-1886 cm-1, assigned to bridged
carbonyl species, were also formed. The authors concluded that linear CO adsorbed on
RhI was involved in CO insertion on the oxidized Rh/SiO2, while the dicarbonyl and
bridged CO did not take part in the reaction. On reduced Rh/SiO2, linear CO that was
adsorbed on the Rh0 sites took part in propanal formation. Hydroformylation activity and
selectivity were found to be higher on the oxidized Rh/SiO2 than on the reduced support.
42
Ethylene hydroformylation catalyzed by silica supported {Rh12(CO)30]2-} cluster
anion [89] produced ethane and propanal with a selectivity, defined as the % mol ratio of
propanal to a mixture of propanal and ethane, of 52.6 when counteraction was Na. IR
analysis showed that prior to exposing the catalyst to the hydroformylation mixture, only
RhI(CO)2 was observed, whereas only CO linearly bonded to small metallic particles was
present under hydroformylation conditions.
Coronado et al. studied styrene hydroformylation over modified Rh/SiO2·Al2O3
catalysts [90]. Exposure of the reduced catalyst to 21.8 psi of CO/H2 and styrene at 85 °C
led reduction of the bridge CO band (1882 cm-1). Bands due to dicarbonyl species had a
very weak intensity in the resulting spectrum and the change in the band due to linearly
adsorbed CO (νCO=2064 cm-1) was small. Exposure of used catalyst to CO/H2 led to
reappearance of dicarbonyl bands (νCO=2098, 2039 cm-1).
Park and Ekerdt studied Rh(CO)(PPh3)3 bound to phosphinated gel-form
polystyrene-divinylbenzene beads [91]. At ambient temperature and 264.5 psi total
pressure (CO/H2=0.67), the bis(phosphine)dicarbonyl complex and the dimer were the
major immobilized species.
Ro
and
Woo
studied
behavior
of
RhCl(CO)(PPh3)2
immobilized
on
polystyrenedivinylbenzene membrane by subjecting the catalyst to 1.9 psi CO, 1.9 psi H2
and 1.9 psi propylene at 100 °C for 4 hours [63]. Under this condition, Rh(CO)2Cl(PPh3)2
was formed, identified through bands at 2019 and 2083 cm-1. Increasing temperature to
120 °C led to disappearance of the bands due to Rh(CO)2Cl(PPh3)2 and transRhCl(CO)(PPh3)2 and the appearance of a new band at 2069 cm-1. Comparison of the
results with the results obtained in the liquid phase (homogeneous system), where
43
acylcarbonyl and hydridocarbonyl rhodium complexes were formed, led to the
conclusion that immobilization of RhCl(CO)(PPh3)2 to a polymer affected the activity of
Rh carbonyl complex and suppressed “liquid phase chemistry” [63].
Asakura et al. studied behavior of the immobilized catalyst obtained by anchoring
trans-[Rh(C2Me5)(CH3)]2(µ-CH2)2 onto SiO2 surface [92]. The catalyst obtained had a
structure depicted as complex 3A in Figure 2.22. When catalyst 3A was exposed to 5.8
psi of CO at room temperature, two peaks appeared at 2032 and 1969 cm-1 upon which it
was concluded that a complex of structure 3B was obtained. Upon heating to 150 °C
under vacuum, the peaks at 2032 and 1969 cm-1 disappeared and peaks at 1710 and 1394
cm-1 appeared. The bands at 1710 and 1394 cm-1 was assigned to ν(CO) and δ(CH) of the
acyl group, respectively. Moreover, exposure of acyl complex 3C to H2 led to formation
of propanal. Additional EXAFS study showed that Rh-Rh bond was broken by CO but
was reformed once the acyl complex was formed. Since no CO insertion took place on
Rh monomers 3B and 3D, the authors concluded that Rh-Rh bond formation promoted
insertion of CO.
Transient response of propanal formation during reaction of CO, H2 and C2H4 on
Rh/SiO2 was studied [88]. It was found that an increase in total reaction pressure
increased the rate constant for hydrogenation of acyl intermediate and this was related to
the decrease in the overall activation energy for formation propanal.
Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics were used to describe
the rates of formation for propanal and ethane formation [93]. Hydrogenation of acyl
species was proposed as the rate determining step for propanal formation. It was
44
concluded that the LHHW model described the reaction kinetics with high accuracy
based on the quality of fit to rate and coverage data.
C5 Me5
C2 H5
Rh
CH2
O
C5 Me5
2CO
Rh
Rh
313 K
O
O
C
Rh
CH2
O
O
C
SiO2
SiO2
3A
3B
C2 H5
O
423 K
evacuation
O
C
C5 Me5
Rh
O
C
Rh
CO, 313 K C5 Me5
C2 H5
Rh
423 K
O
O
COC2 H5
Rh
O
O
SiO2
SiO2
3D
3C
C2 H4
H2
2CO
C5 Me5
C2 H5
Rh
C2 H5 CHO
Rh
O
O
SiO2
3E
Figure 2.22: Changes in the structure of rhodium dimers attached on SiO2 [92].
45
Rode et al. studied propylene hydroformylation on rhodium zeolites X and Y [94].
Both catalysts were active for hydroformylation once they were pretreated with CO, air
or N2. The activity was the lowest when Rh/NaY was pretreated with H2/N2. The authors
suggested that activation process involved formation of hydridorhodium species rather
than reduction of rhodium. In further studies it was observed that the spectra of the
catalysts pretreated by different methods were similar; in all cases Rh6(CO)16 was formed
[95]. The authors suggested that the Rh6(CO)16 was not responsible for hydroformylation.
Propene hydroformylation on rhodium Y zeolite was studied by IR spectroscopy [95]. IR
spectra under hydroformylation conditions revealed that apart from formation of
aldehyde (at 1721 cm-1, shifted to 1691 cm-1 at steady state), adsorbed propylene (1455,
1442 and 1380 cm-1), Rh6(CO)16 (2093, 2067 and 1763 cm-1), the bands at 1290, 1660
and 2042 cm-1 also formed. The band at 1290 cm-1 was attributed to the rocking
deformation mode of rhodium alkyl species while a band at 1660 cm-1 was assigned to
rhodium acyl complex. The band at 2042 cm-1 was assigned to the structure depicted in
Figure 2.23.
CO
Z
O
Rh
CO
C3H6
Z=zeolite
Figure 2.23: Structure of the rhodiumacyl complex reported by Rode et al. [95].
46
Takahashi et al. studied activity of Rh-Y zeolite for ethylene hydroformylation
[96]. IR studies revealed that Rh(CO)2 was not an active species for hydroformylation,
but rather it could have been metallic rhodium particles or HRh(CO)x.
Although zeolites are mainly used as inorganic supports due to the small pore size
and therefore possibility to increase linear to branched aldehyde ratio, another material
that might have such properties is pillared smectite clay. Vapor phase hydroformylation
of ethylene and propylene catalyzed by a rhodium containing aluminum pillared smectite
clay was studied by Lenarda et al. [97]. Reaction occurred after the catalyst was activated
by CO/H2 at 220 °C. Regioselectivity was 3.65 at 125 °C for propene hydroformylation.
Linear and bridged CO species both took part in the hydroformylation while gemdicarbonyl did not, the investigators concluded.
2.2.4 Stability
Catalyst leaching is often a substantial problem in the use of heterogeneous
catalysts. Leaching had been reported for immobilized catalysts [73]. If a catalyst can be
designed that does not leach, then the lower activity normally associated with
heterogeneous catalysts can be compensated for by easier separation.
Hydroformylation of 1-hexene over Rh/C in liquid phase was studied by
Kainulainen et al. [98]. They observed conversion of 1-hexene between 48 and 92 % but
high levels of leaching, indicating that some of the activity was due to homogeneous
catalysis. Hjortkjaer et al. studied the stability of silica supported HRh(CO)(PPh3)3 [99].
The catalyst was active for 144 hours after which selectivity decreased from 9.6 to 4.9
while activity decreased by 50%. Zhang et al. reported that the catalyst made by
47
supporting Rh-phosphine complex on silica deactivated over 30 hours during which
selectivity decreased from 7.9 to 6.4 [67]. However, there are also cases where low [100]
or zero [75] leaching was observed. For example, Rh thiolate complex anchored onto a
silica support was studied for 1-octene hydroformylation [101] and was found to be
active through three cycles amounting to a total of 69 hours, and total turnover number
reported was 1273 mol aldehyde per mol rhodium.
Allum et al. studied hydroformylation of 1-hexene at 80-90 °C and 617.1 psi
CO/H2 (1:1) by Rh anchored polymer [71]. In 9 hours on stream the conversion
decreased from 86 to 36 wt% while yield of heptanal decreased from 85 to 35 wt %.
Product solution contained 78 ppm of the catalyst. Allum et al. anchored a Rh complex
on a different polymer that was insoluble in both the reactants and products and found
that still 90 ppm of Rh was leached [71]. Using the same catalyst under oxygen free
conditions, 1 ppm of Rh was detected in solution during 87 hours on stream and the
conversion of 1-hexene was 97 wt% throughout the run.
Huang and Kawi tested a Wilkinson complex tethered to SiO2 via amine,
phosphine and thiol ligands for cyclohexene hydroformylation at 100 °C and 406 psi
CO/H2 (1:1) [102]. The SiO2(NH2)-tethered catalyst was the most active with the lowest
leaching (9%). PPh2 tethered catalyst was of intermediate activity with 41 % Rh leaching.
RhCl(PPh3)3/SiO2(S-H) catalyst was the least active but fairly stable (~13% Rh leaching).
The authors proposed that the behavior was due to the strength of chemical bonds formed
between the ligands and Rh. The thiol liganded system showed no leaching because of
strong bonding between S and Rh; however, the strong bonding precluded formation of
rhodium hydride complex so limited reactivity was observed. In the phosphine ligand
48
system, the Rh-P bond was very weak and easily cleaved by CO, leading to leaching of
the Rh. Based on these results, the authors concluded that the amine ligand was the most
suitable for immobilization of RhCl(PPh3)3.
2.3 Reactions in Benign Solvents
The hydroformylation reaction is carried out in the mixture of reactants and
products and/or in organic solvents in order to provide dissolution of the catalyst and
bring reactants and the catalyst into a homogeneous phase. However, organic vapors lead
to hazardous air pollutants in the environment. Incomplete separation of the organic
solvent from the catalyst or reaction products accounts for a substantial process cost and
the loss of valuable products into the waste stream.
One of the principles of Green Chemistry is that the waste formation should be
prevented [5]. Modern hydroformylation processes, such as Ruhrchemie/Rhone-Poulenc
oxo-process, which employ biphasic hydroformylation, are more environmentally
appropriate than earlier processes employing organic solvents and/or reactants and
products. However, they are not suitable for alkenes C5 and higher because of limited
solubility in the aqueous phase, so higher alkenes are still hydroformylated using
traditional organic solvents.
Lately, there has been interest in employing supercritical fluids as a medium for
conducting reactions. Supercritical fluids are compounds at a temperature and pressure
higher than their critical point. Supercritical fluids have properties intermediate to those
of gases and liquids and as a result are interesting as a solvent. Supercritical water and
CO2 have both been used as solvents, but the critical properties of CO2 (T=31.1°C and
49
P=1084.3 psi) are milder, making it easier to handle. Supercritical CO2 has several
advantages; for example, many gases have higher solubility in scCO2 than in organic
liquids. Because of the increased concentrations of the reactants relative to traditional
liquid-phase chemistry, the rate of reaction is expected to increase in scCO2. Another
advantage is that viscosity of scCO2 is low and diffusivity is higher than in liquid so that
mass transfer problems can be minimized. When all reactants are soluble in scCO2, a
reaction can be accomplished in single phase. Further process simplifications include
separation and product recovery that can be achieved rather easily through a decrease of
temperature and/or pressure. Decrease of either leads to a decrease in the solubility of the
reaction products and therefore eliminates energy-intensive separation techniques such as
distillation. Lastly, but importantly, scCO2 is considered as a benign solvent since it is
non-toxic, non-flammable, environmentally acceptable, cheap, available in large
quantities, and its utilization, rather than production, falls within the Green Chemistry
principles.
The decaffeination of coffee and tea and the extraction of hops, spices and drugs
with scCO2 are some examples of industrial applications of supercritical processes [103].
Reviews on homogeneous [104, 105] and heterogeneous [105, 106] catalysis in scCO2
are already available. Many catalytic reactions have been evaluated in scCO2, and include
hydrogenation of cyclohexene [107] and 1-octene [108], alkylation [109], esterification
[110], and hydroformylation of alkyl acrylates [111], ethylene [112], 1-octene [113],
styrene [114], 1,5-hexadiene and 1,7-octadiene [115].
50
2.3.1 Homogeneous Catalysis
Rathke and coworkers first studied propylene hydroformylation in supercritical
CO2 [116] using cobalt carbonyl complexes and observed that rates of hydroformylation
were comparable to those obtained in organic solvents. Hydroformylation of propene in
scCO2 was studied by Guo and Akgerman [117] with Co2(CO)8 as the catalyst precursor.
Authors observed that the rate constant at 88 °C doubled and L:B ratio increased from 2.7
to 4.3 as pressure was increased from 1350 to 2700 psig. Regioselectivity decreased from
4.2 at 78 °C to 2.7 at 108 °C at 2400 psig. Activation energy was also calculated at 1650
and 2400 psig and obtained value of 23.3 kcal/mol was found to be comparable to values
obtained in organic solvents. Later experiments with rhodium-based catalysts evaluated
ligand modifications, since phosphine based complexes have very low solubility in
scCO2.
Bach and Cole-Hamilton used triethylphosphine and Rh2(OAc)4 as a catalyst
precursors in the hydroformylation of 1-hexene in scCO2 [118]. Reactions in toluene and
scCO2 showed similar activities but slightly improved regioselectivity for the reaction in
scCO2 relative to toluene (2.4 vs. 2.1). The authors also reported that using trioctyl
phosphine as a ligand gave lower rates but higher regioselectivity.
Hydroformylation of 1-hexene by phosphite-modified rhodium catalysts insoluble
in scCO2 was studied by Sellin and Cole-Hamilton [119]. Using Rh2(OAc)4 and
P(OC6H4-4-C9H19)3 as the catalyst precursors, the yield was found to be higher in toluene
than in scCO2, but the L:B ratio was higher in scCO2. Catalyst stability was also tested.
As the catalyst was insoluble in scCO2, flushing the reactor with scCO2, led to separation
51
of the catalyst and the products. The decrease in regioselectivity after five runs was
ascribed to hydrolysis of the phosphite ligand.
Even further improvements in compatibility with scCO2 were obtained by using
fluorinated analogues of phosphine ligands [120, 121, 122]. Koch and Leitner studied
unmodified and modified Rh catalysts for hydroformylation of 1-octene in scCO2 [123]
and found that unmodified Rh catalyst provided the highest rate (TON=2440 mol
aldehyde per mol Rh) but that the regioselectivity (L:B) increased when the CO2-philic
triarylphosphine or triarylphosphite ligands were used. Using trans-RhCl(CO)(P(pCF3C6H4)3)2, Palo and Erkey found that at 70 °C and 4011 psi, 1-octene was
hydroformylated to C9 aldehydes [113]. Regioselectivity was 2.4 and was comparable
with results obtained with non-fluorinated analogue of the catalyst in benzene.
Palo and Erkey studied the effect of ligand modification on Rh catalyzed
homogeneous hydroformylation of 1-octene in scCO2 [124]. The activity increased as
basicity of phosphine ligand decreased. Linear relationship between activity of Rh
complexes and their carbonyl stretch frequencies was found. The highest activity was
found for a system with [3,5-(CF3)2C6H3]3P as the ligand. However, regioselectivity did
not change significantly as basicity of the phosphine ligand was changed.
Even though fluorinated ligands are efficient in providing a soluble Rh complex,
they are expensive. Hu et al. reported on combination of rhodium complexes with
alkoxycarbonylated arylphosphines as an alternative for fluoroalkylated ligands [125].
Incorporation of one methoxycarbonyl unit into PPh3 increased the TOF for 1-decene
hydroformylation at 80 °C from 174 to 535 mol aldehyde per mol catalyst per hour. The
L:B ratio decreased from 3.3 to 3.1. However, further addition of methoxycarbonyl
52
groups (two units) led to a decrease of TOF to 390 mol aldehyde per mol catalyst per
hour even though the L:B ratio increased to 3.4. The authors also reported that
homogeneous phase existed when one methoxycarbonyl unit was incorporated into PPh3,
but on further addition of methoxycarbonyl units, single phase behavior ceased to exist.
Palo and Erkey found that total pressure did not affect reaction rate or selectivity
when the catalyst was RhH(CO)(P(p-CF3C6H4)3)3 [120]. This study was contradictory to
the findings of Guo and Akgerman [126], who reported that in homogeneously catalyzed
propene hydroformylation in scCO2 with Co2(CO)8 as the catalyst precursor, at constant
temperature, the L to B ratio increased as pressure increased. The change in the L:B ratio
was described using the differences in partial molar volume of the linear and the
branched aldehyde.
Pressure effect was also studied by Lopez-Castillo et al. [127]. Rhodium based
catalyst attached to a polymer backbone that had fluoroacrylate branches, providing
solubility in scCO2, was used for hydroformylation of 1-octene. At 50 °C, higher rate was
obtained at 3500 than at 2500 psi. Fujita et al. observed that an increase in CO2 pressure,
increased the yield of aldehydes obtained from 1-hexene hydroformylation when the
catalyst precursors were Rh(acac)(CO)2 and diphenyl(pentafluorophenyl)phosphine
[121]. However, when the catalyst precursors were Rh(acac)(CO)2 and tris(ptrifluoromethylphenyl)phosphine, little variation in aldehyde yield was observed.
Styrene hydroformylation in scCO2 was investigated by Lin and Akgerman [128].
The catalyst used was [(COD)Rh(Et-DuPHOS)]+BARF-, depicted in Figure 2.24. BARF
anion was employed to increase the solubility of the catalyst in scCO2. Major products
detected at 65 and 80 °C and pressures from 2094 to 2900 psi were 2-
53
phenylpropionaldehyde and 3-phenylpropionaldehyde. Desired product, branched
aldehyde, was predominant as evident from high B to L ratio, but decreased as pressure
increased. At constant pressure, the B to L ratio was higher at 65 °C than at 80 °C. The
authors also reported that there was no enantioselectivity.
+
H5 C 2
C2H5
F3C
-
CF3
F3C
CF3
P
Rh
B
P
C 2 H5
H5C2
CF3
F3C
F3C
CF3
Figure 2.24: Structure of the catalyst used by Lin and Akgerman [128].
Enantiomeric excess of 92% and B:L ratio of 93:7 was reported by Franció et al.
[129] for asymmetric hydroformylation of styrene in scCO2 at 60 °C and 3509 psi.
Catalyst used was Rh complex of (R, S)-3-F(CF2)6-(CH2)2-BINAPHOS, depicted in
Figure 2.25. When the substrate was styrene, the reaction rate and selectivity of the
catalyst derived from BINAPHOS in benzene were comparable to those of fluorinated
analogue in scCO2.
Palo
and
Erkey
studied
the
kinetics
of
homogeneously
catalyzed
hydroformylation of 1-octene in scCO2 with HRh(CO)[P(p-CF3C6H4)3]3 [130]. They
observed that the reaction rate was 0.5 order in 1-octene, 0.48 order in H2, and negative
order in CO. It was also noted that the L:B ratio decreased as concentration of CO
54
increased. According to the authors, increasing CO concentration led to preferential
formation of RhH(CO)2L over RhH(CO)L2. Formation of branched aldehyde was
enhanced as CO created less steric bulk in the rhodium complex than phosphine ligand.
In studies with HRh(CO)[P(3,5-(CF3)2C6H3)3]3 [131], the authors found the rate to be
nearly first order in hydrogen concentration, suggesting that the rate determining step at
low phosphine concentrations was oxidative addition of H2 to an acyl complex.
F F
F
F
F F
F
F
F
F
F
F
F
F
F
F
F
P
O
P
O
O
Figure 2.25: Structure of the ligand used by Franció et al. [129].
55
F
F
F
F
F
F
F
F
F
Mechanistic studies on hydroformylation at supercritical conditions are scarce due
to the limited availability and high cost of high pressure analytical equipment. However,
some reports have recently appeared. Using FTIR spectroscopy [11], it was found that
RhH(CO)L3 {L=P(3,5-(CF3-C6H3)3} did not dissociate in scCO2. In the presence of CO
and CO2, the catalyst was converted to RhH(CO)2L2 (νRh-H=2076, νCO=2056 and 2034
cm-1) and to [RhH(CO)2L2]2 with νCO=1827 and 1799 cm-1. Addition of H2 led to the
appearance of bands at 2066 cm-1 (νRh-H) and 2027 cm-1 (νCO), assigned to RhH(CO)L2,
and a decrease in the intensity of the bands assigned to
RhH(CO)2L2 and
[RhH(CO)2L2]2.
Haji and Erkey observed three peaks in the acyl region upon exposing
RhH(CO)(P(3,5-(CF3)2C6H3)3)3 to ethylene (45.7 psi, 140 mM), CO (45.7 psi , 140 mM)
and CO2 (PT=609 psi) at 1.5° C [11]. Peaks at 1645 and 1975 cm-1 were attributed to the
monocarbonyl acylrhodium, Rh(CO)L2(COEt), bands at 1673, 2014 and 2051 cm-1, were
assigned to dicarbonyl acylrhodium Rh(CO)2L2(COEt), and bands at 1695, 2008, 2033
and 2086 cm-1 were attributed to tricarbonyl acylrhodium species, Rh(CO)3L(COEt).
Yonker and Linehan investigated ethylene hydroformylation in liquid CO2 by
NMR spectroscopy [132] and found that at 22.8 °C and 3233.5 psi, under H2 and CO in
CO2, both HRh(CO)((p-CF3C6H4)3P)3 and HRh(CO)2((p-CF3C6H4)3P)2 were formed from
(p-CF3C6H4)3P and Rh(CO)2(acac). In situ formation of HRh(CO)((p-CF3C6H4)3P)2(η2C2H4) was also reported.
Extended X-ray absorption fine structure (EXAFS) was employed to study
hydroformylation of 1-octene by catalyst precursors Rh(CO)2(acac) and triethylphosphine
(PEt3) in liquid and scCO2 [133]. In liquid CO2, (room temperature, 145 psi each CO and
56
H2 and 1740 psi CO2), the resting state of the catalyst was found to be RhH(CO)2(PEt3)2
when Rh:P was 1:3. At supercritical conditions (T=43 °C), the resting state was
RhH(CO)(PEt3)3. When Rh to P ratio was changed to 1:1, it was found that Rh dimer was
formed in both liquid and scCO2.
Carbon dioxide can also be used as a co-solvent or transporting medium.
Homogeneously catalyzed hydroformylation of 1-octene in a supercritical fluid – ionic
liquid biphasic mixture was studied in a continuous flow reactor by Sellin et al. [134].
PhP(C6H4SO3)2-[PMIM]2, (PMIM = 1-propyl-3-methylimidazolium), and Rh(OAc)4
were dissolved in 1-butyl-3-methylimidazolium hexafluorophosphate,[BMIM]PF6, and 1octene and products were transported in and out of the reactor by scCO2. Regioselectivity
observed at 100°C and 2900 psi was 3.1 over 33 hours of run time, with rhodium
leaching of less than 1 ppm. Using Rh(acac)(CO)2 and [OctMIM][Ph2PC6H4SO3], where
[OctMIM] is 1-octyl-3-methylimidazolium, as a ligand at 2030 psi and with CO2 as a
flowing phase, Webb and Cole-Hamilton [135] reported a TOF of 239 mol aldehyde per
mole Rh per hour in 12 hour reaction with a L:B ratio of 3.2. Only 5-10 ppm of Rh
leaching was noted.
Jin
and
Subramaniam
reported
on
hydroformylation
of
1-octene
by
Rh(acac)(CO)2 in CO2-expanded solvent [136]. Rate of reaction was greater in CO2
expanded solvent than in pure acetone at 60 °C. The L:B ratio was 1.5 in both acetone
and CO2-exapanded solvent. At 30 °C, turnover number was 106.4 mol aldehyde per mol
Rh complex in acetone but it increased to 140.9 mol aldehyde per mol Rh complex when
75 % of acetone was replaced with CO2. In liquid CO2, 31.6 mol aldehyde per mol Rh
complex was obtained. Higher solubility of synthesis gas in CO2-exapanded solvent was
57
thought be the reason for higher turnover numbers in CO2-exapanded solvent than in
acetone.
2.3.2 Heterogeneous Catalysis
From a commercial standpoint, one major concern in homogeneously catalyzed
reactions is catalyst recovery. UCC liquid recycle is an example of a process that
employs homogeneous catalyst. This process uses Rh/TPP as a catalyst which is
dissolved in high boiling aldehyde condensation products [3]. Figure 2.26 shows the
description of the UCC liquid recycle process.
Vent
1
2
7
3
4
5
6
H2 /CO
Propene
25 °C
14.5-29 psi
Figure 2.26: UCC liquid recycle process [3].
58
130 °C
2.18 psi
The reactants and recycled gas are fed into a well mixed reactor. The outlet stream
containing aldehydes, Rh phosphine complex, dissolved gases and heavy ends is sent to a
separator (2), depressurized (3) and then introduced into flash evaporator (4). The
unconverted reactants are separated, condensed and recycled to the reactor. Liquid
products are sent to first distillation column (5). The aldehydes are separated and
removed at the column overhead. The bottom stream, however still contains significant
aldehyde product, so a second distillation column (6) is used. The column operates at
subatmospheric pressures to concentrate the catalyst solution. The temperature and
pressure of the UCC liquid recycle process are 85-90 °C and 261 psi, respectively.
As evident from the above description, most of the unit operations in a
commercial hydroformylation process deal with catalyst separation and/or recovery.
While the use of a heterogeneous catalyst would minimize catalyst recovery concerns, its
use leads to lower selectivity and lower yield. Previous researchers have attempted to
combine the use of a heterogeneous catalyst with a supercritical fluid, attempting to
improve yields by exploiting properties of supercritical fluids, namely high diffusivity
leading to lower mass transfer limitations, as well as higher concentrations of reactants.
Dharmidhikari and Abraham used rhodium supported on activated carbon for
hydroformylation of propylene in scCO2 [137]. Propylene adsorbed on both Rh/Centaur
and Rh/PCB without substantial conversion to the butanal. Selectivity reported was 1.5.
Differences in rate of adsorption on the two supports revealed that adsorption was
kinetically controlled and not mass transfer controlled. Thus, it was concluded that
reaction was affected by choice of the support. Snyder et al. used Rh-Fe supported on
modified and unmodified silica for hydroformylation of propylene in scCO2 [138]; the
59
catalysts were active but leaching of the rhodium from the support occurred leading to
catalyst deactivation.
Hydroformylation of 1-octene in scCO2 was investigated by Meehan et al. [139].
A Rh complex of N-(3-trimethoxysilyl-n-propyl)-4,5-bis(diphenylphosphino)phenoazine
immobilized on silica was used as a catalyst. At 90 °C, TOF reported was 160 moles
aldehyde per mol catalyst per hour. The L:B ratio was 33 at these conditions. Increasing
the CO2 pressure led to lowering of the TOF, possibly due to higher solvent density (and
thus lower rates of mass transport) obtained at higher CO2 pressure. The catalyst was
reported to be active with no selectivity variation for six non-consecutive days (30 hours).
Bronger et al. covalently anchored phenoxaphosphino-modified xantphos-type
ligand (Figure 2.27) to commercially available silica and used it for 1-octene
hydroformylation in scCO2 [140]. At 80 °C, TOF reported were 44.1, 126.6 and 54 mol
aldehyde per mol catalyst per hour at 1160, 1740 and 2320 psi of CO2. Regioselectivity
was the highest, 19.6, at 1160 psi. Increasing the flow rate of CO2 from 0.65 to 1.4 L/min
led to decrease in conversion from 2.94 to 1.23. Effectively, a decrease in the residence
time led to a decrease in conversion. Using the same catalyst at 120 °C, no
hydroformylation activity was reported for trans-2-octene. However, the catalyst was
stable and no rhodium leaching was reported.
Hydroformylation of styrene, vinyl acetate, 1-octene, 1-hexene and fluorinated
alkenes by (R, S)-BINAPHOS-Rh (I), depicted in Figure 2.28, covalently anchored to a
highly cross-linked polystyrene support in scCO2 was reported by Shibahara et al. [141].
At 60 °C and 1293 psi, 35% conversion, 82% iso-selectivity and 82% enantiomeric
excess was reported for styrene hydroformylation. Increasing the pressure led to increase
60
in conversion (91%). At 1763 psi, iso-selectivity and enantiomeric excess were 80.3 and
85 %, respectively.
O
C6H13
(OEt)3Si
3 N
H
N
H
5
O
POP
P
POP =
O
Figure 2.27: Structure of the ligand used by Bronger et al. [140].
61
POP
O
Ph2P
O
P
Rh(acac)
O
Figure 2.28: Structure of the catalyst used by Shibahara et al. [141].
62
CHAPTER 3
EXPRIMENTAL SECTION
3.1 Introduction
Infrared (IR) spectroscopy is a powerful technique that can be used to determine
the functional groups present in the sample. When a molecule is subjected to infrared
radiation, it will either absorb or transmit the energy, depending on the frequency and the
structure of the molecule. Molecule will absorb only the certain energy and will be
excited to a higher energy state. Energy changes involved in absorption of IR radiation
are in the range of 8 to 40 kJ/mol and correspond to stretching and bending vibrations
[142]. However, the fact that the frequency of radiation corresponds to the energy of a
vibration does not mean that the bond will absorb the energy. A change in the dipole
moment has to be created as a result of a vibrational motion if IR radiation is to be
absorbed. Molecules such as H2 and Cl2 do not absorb IR radiation. Molecules such as
CO2 posses no permanent dipole moment because of molecular symmetry; however, as
depicted in Figure 3.1, a bending vibration provides an induced dipole response.
63
O
δC
O
C
O
O
δ+
Figure 3.1: Change in dipole moment due to bending vibration [143].
The infrared absorption spectrum of the molecule will depend on the type of bond
within the molecule and the atoms in the molecule. As a result, it is possible to relate
specific IR responses to the structure of the molecule. The stretching and bending modes
are the major types of vibration motion.
C
O
H
C
stretching
H
bending
Figure 3.2: Stretching and bending modes of the molecule [142].
Stretching vibrations can be symmetric and asymmetric while bending vibrations can be
in-plane and out-of-plane.
3.2 Experimental Equipment
Absorption spectra were measured by infrared spectrometry. A Fourier transform
infrared (FTIR) spectrometer was used to generate the absorption spectra. The instrument
64
generates interferogram which is a plot of time vs. intensity and contains all the
frequencies in the infrared spectrum. Since the interferogram has wave-like signal, the
Fourier transform can be applied so that individual frequencies are obtained. Nicolet
Avatar 370 DTGS optical bench (Thermo Electron Corporation) was used to collect the
absorption spectra.
The diffuse reflectance technique was used for acquiring spectra of supported
catalysts. Diffuse Reflectance Infrared Fourier Transform (DRIFTS) technique is suitable
for powders and solid samples. A picture of the collector and the high pressure, high
temperature chamber assembly (SpectraTech) for the DRIFTS study is shown in Figure
3.3. A laser beam was sent from the optical bench. Through the system of adjustable
mirrors and crystal windows, the laser beam reaches the surface of the catalyst sample.
The laser beam reflected from the sample then reaches the ellipsoidal mirrors. The
ellipsoidal mirrors are designed to collect and refocus the diffusely scattered energy. The
laser beam is then sent back to the optical bench for analysis. DTGS KBr detector was
used. 7.03 EZ Omnic software was used to control the optical bench and analyze infrared
spectra.
DRIFTS technique is an alternative to pressed-pellet and mull techniques which
require a special procedure for preparing the sample. However, DRIFTS technique also
has drawbacks. Due to specular component of the reflected energy, the IR spectra can be
distorted. Because the light is scattered, much of the energy is lost so that signal is low
and the signal to noise ratio is small.
65
Ellipsoidal mirrors
Laser beam to
the detector
Laser beam
in
Gas inlet
Gas outlet
Catalyst bed
Mirrors
Figure 3.3: Collector and high pressure/high temperature chamber assembly for DRIFTS
studies.
3.3 Experimental Setup
The setup used for DRIFTS studies is shown in Figure 3.4. The feed gas consisted
of a mixture of CO/H2 (1:1, O.E. Meyer), 1-hexene (Sigma Aldrich) and CO2 (Airgas).
The reactants were loaded in sample cylinder (Swagelok) 1 or 1 and 2, as appropriate.
The sample cylinders were heated by heating tapes (Cole-Parmer). An Omega
temperature controller was used to maintain the temperature of the heating tapes. Ultra
pure grade N2 (Airgas) was used for collecting background spectrum.
66
N2
T
P
P
67
To vent
T
T
2
IR
1
Cooling water
Figure 3.4: Experimental setup for DRIFTS studies
3.4 Experimental Procedure
Approximately 25 mg of catalyst powder was loaded in the sampling cup. The
chamber was closed, and N2 (O.E. Meyer) gas was introduced onto catalyst and spectra
taken at room temperature. The catalyst cup was then heated to 100 °C under the flow of
nitrogen. When the system was stable at 100 °C, a spectrum labeled “high T” was
recorded. In order to truly monitor changes occurring on the catalyst surface, this
spectrum was then subtracted from each subsequent spectrum. Unless otherwise indicated
all the spectra represent the difference between the spectrum shown and the “high T”
spectrum. Nitrogen gas was then released and the chamber closed.
Two different procedures were followed. The first procedure was used for the
results obtained from the experiments in the Chapter 4. A predetermined amount of 1hexene was introduced into 150 mL sampling cylinder 2 by a syringe. The cylinder was
then sealed and CO/H2 added to a predetermined pressure. Finally, the CO2 or N2 was
added. The weight of the single components was determined by weighing the cylinder
following each species addition. Additionally, each cylinder was weighed after the
components were introduced into the system to determine the actual amount of material
added into the system. The cylinder was then heated to 100 °C. After reaching the stable
temperature, the feed mixture was introduced into the DRIFTS chamber and the inlet and
outlet valve closed. The spectra were taken at certain intervals without removing the gas
phase. After the experiment, the contents of the DRIFTS cell were vented and N2 was
passed through the catalyst bed for 10 minutes to remove the gas phase reactants and/or
products. The spectrum called “post” was then taken under nitrogen at the reaction
pressure.
68
The second procedure, used for the results in Chapter 5, involved loading of 1hexene and CO/H2 into the 150 mL sampling cylinder (cylinder 1 in Figure 3.4), while
CO2 or N2 was loaded into sampling cylinder 2. Both cylinders were then heated. Upon
reaching desired temperature, the contents of the cylinder 1 were first added to the
predetermined pressure followed by addition of the contents of the cylinder 2 to
predetermined pressure.
3.5 Catalyst Preparation
The catalysts used in this study were prepared by the Department of Chemistry at
The University of Toledo. The synthesis of the Rh complex immobilized on phosphinated
silica support required the synthesis of the catalyst support and Rh precursor separately.
Details of the catalyst synthesis procedure are provided by Marteel [4].
The catalyst support was modified silica synthesized by a sol gel technique.
Figure 3.5 provides a schematic representation of the catalyst synthesis procedure. The
1,2-(diphenylphosphino)ethyltriethoxysilane and tetraethoxysilane were mixed in the
ratio of 1 to 9 and were added to a 95:5 ethanol/water solution at a pH of 5.5.
Si(OCH2CH3)4 + Si(OCH2CH3)3(CH2)2PPh2 + H2O → (SiO2)n—(CH2)2PPh2
The mixture was stirred for 48 hours at room temperature. Ethanol was then removed
under vacuum. The product of the reaction was a solid nonporous silica with phosphine
groups available as anchor sites.
69
The rhodium precursor was prepared by mixing rhodium trichloride and
cyclooctadiene (COD) in ethanol and water (5:1) according to the procedure reported by
Giordano and Crabtree [144]. The mixture was refluxed for 18 hours and subsequently
washed with pentane and methanol/water to yield the product as a yellow orange solid.
Rh
precursor,
di-µ-chloro-bis(η4-1,5-cyclooctadiene)rhodium (I),
and
the
phosphinated support were mixed in ethanol under nitrogen atmosphere. The ethanol was
evaporated under vacuum after reaction was completed.
[RhCl(COD)]2 immobilized on phosphinated silica support was characterized by
cross-polarization and magic angle spinning (CP/MAS)
[4]. The
31
31
P and
13
C NMR spectroscopy
P NMR spectrum showed two resonances which were assigned to
uncoordinated phosphorus and rhodium to phosphorus couplings and/or oxidized
phosphorus species. The 31C NMR spectrum revealed resonances of phosphinated support
and of COD. Elemental analysis indicated that the content of the metal was 3.78-4.59
wt% and that of phosphorus 2.91-2.88 wt%.
Surface area and pulse chemisorption experiments were carried using AutoChem
2910 analyzer (Micromeritic). The catalyst had a BET surface area of 8.66 m2/g.
70
Si(OEt)4 + Si(OEt)3(CH2 CH2PPh2)
9eq
eq
2RhCl3
+ 2
Cl
P
Rh
Cl
CH2
CH2
Si
71
SiO2
Phosphinated Support
Rh
Rh Precursor
COD
Cl
Rh
P
CH2
CH2
Si
SiO2
Catalyst
Figure 3.5: Schematic overview of the procedure for the catalyst synthesis
CHAPTER 4
CHARACTERIZATION OF REACTION INTERMEDIATES
The first goal of this study was to determine the nature of the species present
when the hydroformylation reaction is catalyzed by phosphinated silica immobilized Rh
catalyst in CO2. The characterization results related to the phosphinated silica support and
immobilized rhodium complex are first presented. The subsequent text of this chapter
deals with the results and the discussion of the in situ reactions. The text in Chapters 4
and 5 will refer to [Rh(COD)Cl]2 immobilized on phosphinated silica as the catalyst.
Even though this is not exactly correct, as the active species is hydridorhodiumcarbonyl
complex, the term is used as it provides consistency with the previous reports with this
system. FTIR spectroscopy is used as the analysis tool. In situ FTIR spectroscopy is well
suited for such investigations since intermediates can be identified and monitored under
reaction conditions.
72
4.1 Characterization of the Support and the Catalyst
4.1.1 Characterization of Phosphinated Silica Support
Phosphinated silica support was used for anchoring the catalyst, as shown in
Figure 4.1. In Figure 4.1 and thereafter Ph stands for phenyl group (C6H5-).
Ph
Ph
P
CH2
CH2
Si
O
Figure 4.1: Structure of phosphinated silica support.
The IR spectrum of the phosphinated silica support at room temperature is shown
in Figure 4.2. Bands due to phenyl (C6H5-), methylene (CH2), P-CH2, Si-CH2 as well as
Si-O are observed, as expected. C-H stretching vibrations of phenyl and CH2 can be seen
in the region 2880-3090 cm-1. Aromatic out-of plane C-H deformation vibrations can be
seen in the region 700-800 cm-1. Two to three bands are observed in the region 16251430 cm-1 due to the ring C=C stretching vibration for 6 member rings [145]. The bands
that are observed at 1438, 1483 and 1591 cm-1 are assigned to aromatic C=C stretch.
Overtone and combination bands due to C-H out of plane bending vibrations can be used
to assign the structure to mono-, di-, tri-, tetra-, penta-, or hexasubstituted aromatic ring
[142, 145]. These absorptions are found in the region 2000-1667 cm-1 [142]. The three
73
bands observed at 1967, 1893, 1828 and a weaker band observed at 1776 cm-1 suggests
benzene ring is monosubstituted. This is expected since the support contains C6H5-P
group.
3
2.5
Absorbance
2
high T (phosphinated silica)
1.5
room T (phosphinated silica)
1
0.5
0
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
Wavenumber (1/cm)
Figure 4.2: IR spectra of the support at room temperature and at 100 °C.
P-CH2 vibration is observed at 1410 cm-1. The spectra also reveal the broad and
very strong band centered at 1234 cm-1. The band actually spreads from 1070-1380 cm-1.
The bands due to several functional groups can be observed in this region. For Si-CH3 a
band due to bending vibration of CH3 is observed at 1280-1250 cm-1 [145]. Si-CH2 is
expected to absorb at slightly higher frequencies, which falls in the range where the broad
band is observed. Other groups of relevance are Si-O stretch which give band in the
region 1100-1000 cm-1, P-Ph with the band in the range 1130-1090 cm-1 and P=O
vibration in the region 1350-1150 cm-1 [145]. Marteel characterized Rh immobilized on
phosphinated silica support by NMR spectroscopy and suggested that oxidized
74
phosphorus species might be present on the support [4]. All of the above species are
possible since the bands appear rather broad.
Figure 4.2 also shows spectra of the support after being heated under N2 to 100°C.
The spectrum taken at 100 °C appears similar to the spectrum taken at room temperature
except that the band present at 1633 cm-1 at room temperature decreased in intensity. The
bending vibrations of H-O-H are found in the region 1630-1600 cm-1 [145], suggesting
that absorbed water might have been removed by heating the catalyst to 100 °C in
flowing N2.
4.1.2 Characterization of Rh Catalyst Immobilized on Phosphinated Silica Support
The spectrum of the Rh complex immobilized on phosphinated silica support is
presented in Figure 4.3. Comparison with the spectra for a phosphinated silica support
reveals that the only changes are the presence of additional bands in the region 28003000 cm-1, 700-800 cm-1 and around 1550 cm-1. These bands are attributed to C-H
stretch, C-H deformation and C=C stretch of cyclooctadiene, respectively. After heating
under an atmosphere of nitrogen, similar changes occur as observed for the support.
75
4
3.5
3
high T (Rh:P=1:2)
Absorbance
2.5
room T (Rh:P=1:2)
2
high T (phosphinated silica)
1.5
room T (phosphinated silica)
1
0.5
0
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
Wavenumber (1/cm)
Figure 4.3: IR spectra of the catalyst and the support at room temperature and at 100 °C.
4.2 Characterization of the Immobilized Rh Catalyst Under Different Environments
4.2.1.1 Nature of the Immobilized Rh Catalyst Under CO
The nature of the species formed when [RhCl(COD)]2 immobilized on
phosphinated silica was investigated by exposing the catalyst held at 100 °C to 100 psi of
flowing CO. After 1 hour the gas phase CO was removed by flowing N2 for 10 minutes.
The spectrum taken after this period is shown in Figure 4.4.
Two bands are observed at frequencies 2085 and 2010 cm-1. Additionally, a band
at 1716 cm-1 is observed. The bands at 2085 and 2010 cm-1 are characteristic of carbonyl
species with linear CO bonded to Rh [146]. The nearly equal intensity of the symmetric
(2085 cm-1) and asymmetric vibration (2010 cm-1) bands suggest that two carbonyls
are cis to each other [147]. Therefore, a cis-RhCl(CO)2Lx, (L=PPh2 ligand attached to
silica by CH2CH2 spacers) is present on the surface of the catalyst.
76
1.2
1
Absorbance
0.8
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 4.4: IR spectrum of the catalyst after exposure to CO.
Several groups have characterized the species formed on immobilized catalyst by
IR technique. Silica supported analogue of RhClCO(PPh3)2 was characterized by Luchetti
et al. [148]. At 1200 psi CO and 100 °C, bands at 2082 and 2012 cm-1 were observed.
The bands were assigned to a cis-Rh(CO)2 moiety as depicted in Figure 4.5. Bands at
2090 and 2018 cm-1 were also observed by Allum et al. and were assigned to RhCl(CO)2
on phosphinated silica [60]. Based on the literature reports, the Rh complexes that exist
on the surface of the phosphinated silica are suggested to be as depicted in Figure 4.6.
77
CO
O
Si CH2 CH2 PPh2
Rh
CO
Cl
O
Si CH2 CH2 PPh2
Figure 4.5: Structure of the supported carbonyl complex reported by Luchetti et al. [148].
OC
CO
Rh
Ph
P
Ph
CO
Cl
Ph
P
OC
Ph
Rh
Ph
P
CH2
CH2
CH2
CH2
CH2
CH2
Si
Si
Si
Cl
Ph
(S1)
(S2)
Figure 4.6: Structures of immobilized Rh carbonyl complexes.
Reaction of CO with [Rh(COD)Cl]2 immobilized on phosphinated silica support
was further confirmed by CO pulse chemisorption. Figure 4.7 shows TCD signal vs. time
78
plot obtained when the catalyst was pulsed with 10 % CO in helium. From area under the
peaks, the amount of adsorbed CO could be calculated. The amount adsorbed is given in
Table 4.1. Therefore, CO uptake occurs when the catalyst was exposed to CO.
0.07
0.06
TCD Signal
0.05
0.04
0.03
0.02
0.01
0
0
5
10
15
20
25
Time (sec)
Figure 4.7: TCD response during CO pulse chemisorption.
Table 4.1: Volume adsorbed during CO pulse chemisorption.
Peak Number
1
Volume Adsorbed (ml/g)
0.00000
2
3
4
5
6
7
8
9
10
0.02723
0.00285
0.00000
0.00045
0.00000
0.00037
0.01075
0.00000
0.00000
79
30
35
4.2.1.2 Nature of the Immobilized Rh Catalyst Under CO/CO2
Because of the interest in understanding the influence of scCO2 on species formed
on the support, the IR spectrum of [RhCl(COD)]2 immobilized on phosphinated silica and
exposed to a mixture of CO and CO2 was obtained. The catalyst was heated to 75°C in
flowing N2. The catalyst was then exposed to the CO/CO2 mixture at 75 °C and total
pressure of 1100 psig. After 1 hour the gas phase CO and CO2 were removed by flowing
N2 for 10 minutes. The spectrum taken after this period is shown in Figure 4.8.
Two broad bands appear at 2080 and 2006 cm-1 with a shoulder at 2100 cm-1,
consistent with CO interaction with Rh anchored on the catalyst surface. Therefore,
presence of CO2 does not change the nature of the species present and the bands at 2080
and 2006 cm-1 are assigned to cis-RhCl(CO)2Ly.
0.4
Rh on silica
0.35
Silica without metal
Absorbance
0.3
0.25
0.2
0.15
0.1
0.05
0
2200
2100
2000
1900
1800
1700
Wavenumber (1/cm)
Figure 4.8: IR Spectra of the catalyst and the support after being exposed to 100 psig CO
in CO2, P=1100 psig.
80
During the formation of Rh carbonyl complexes, it is expected that
cyclooctadiene (COD) is replaced by CO. When the gas phase mixture of CO and CO2 is
removed by N2, COD is removed from the catalyst. Cauzzi et al. prepared supported
rhodium catalyst [149]. The support was benzoylthiourea-functionalized silica xerogel.
The precursor for rhodium was [Rh(COD)Cl]2. The IR spectrum of used catalyst showed
two bands at 2023 and 1969 cm-1. The authors concluded that the initially immobilized
complexes were converted into carbonyl species and therefore COD was replaced by CO.
To confirm that observed CO species were formed through the interaction of CO
with rhodium complex, the phosphinated silica support was also probed with CO and
CO2 mixture. As in the case of supported catalyst, the phosphinated silica was exposed to
mixture of CO and CO2 at 100 °C and total pressure of 1100 psig. The resulting spectrum
is also presented in Figure 4.8. No carbonyl bands can be detected in terminal or bridging
carbonyl region. Therefore, it can be concluded that CO binds to Rh complex and does
not adsorb onto the surface of phosphinated silica.
4.2.2.1 Nature of the Immobilized Rh Catalyst Under H2
Rh immobilized on phosphinated silica was exposed to 200 psig of pure H2 at 100
°C. As can be seen from Figure 4.9, initially (spectra H2, 5 min), no bands are present in
the 1990-2100 cm-1 region. However, after being held under hydrogen for 2 hours
(spectra H2, 120 min), a band at 1990 cm-1 developed. Yagupski and Wilkinson [150]
reported that the complex IrH(CO)2(PPh3)2 has band due to Ir-H at 2029 cm-1 (Nujol
mull), while Li et al. [151] reported the metal-hydrogen vibration for HCo(CO)4 at 1993
cm-1. Bands at 2015 cm-1 (νRh-H), 2080 and 2040 cm-1 and a weak band at 1844 cm-1
81
were also observed when Rh(acac)(CO)(P), (P=Ph2PCH2CH2Si(OMe)3), immobilized on
SiO2 was exposed to 146.9 psi of H2 at 80 °C for 2 hours [70].
The spectra obtained suggests that band at 1990 cm-1 might be due to Rh-H
vibration. However, some CO2 was also formed in the cell after 120 min exposure of the
catalyst to H2, as evident from doublet at 2340 cm-1. The fact that CO2 was formed
suggests that exposure to hydrogen might have lead to destruction of the catalyst so that
carbon present in the catalyst reacted with surface water to form carbon dioxide. This in
turn suggests that band at 1990 cm-1 might be due to Rh-CO bond. Exposure of Rh/SiO2
to CO2 led to appearance of the band at 2033-2025 cm-1 that was assigned to Rh-CO
stretch [152]. Even though the wavenumber reported in literature and in this study differ
appreciable it can be inferred that it is possible to obtain CO stretch upon exposure of Rh
Absorbance
based catalyst to CO2.
2.4
2.4
2.2
2.2
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
post CO
post first H2 treatment
H2, 120 min
0
2400
2200
H2, 5 min
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 4.9: IR spectra of the catalyst under 200 psig of H2 and after being exposed to CO
at 100 °C.
82
4.2.2.2 Nature of the Immobilized Rh Catalyst Under H2/CO2
Interactions of the catalyst with H2 were further studied by exposing the catalyst
to mixture of H2 (100 psig) and CO2 at 100 °C and total pressure of 1190 psig. The
changes produced by mixture of H2 and CO2 are represented in Figure 4.10. The bands at
2073 and 1710-1730 cm-1 are formed within 5 minutes of exposure. As the time of
exposure increases, the peak at 2073 cm-1 increases and a peak at 1996 cm-1 appears and
grows with time. After 2 hours, peaks at 2073, 1996 with the shoulder at 2025 cm-1, as
well as peak at 1730 cm-1 were developed. These peaks are retained after the gas phase
mixture of H2 and CO2 was removed by flowing N2.
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
120 min
Absorbance
Absorbance
post exposure
1
0.8
1
30 min
0.8
15 min
0.6
0.6
0.4
0.4
0.2
0.2
0
3100
3000
2900
2800
Wavenumber (1/cm)
2700
60 min
5 min
0
2200 2100 2000 1900 1800 1700 1600
Figure 4.10: IR spectra of the catalyst under H2/CO2; P=1190 psig, T=100 °C.
Ro and Woo studied interactions of RhCl(CO)(PPh3)2 immobilized on
polystyrene/divinylbenzene membrane with 14 psi of H2 [63]. They observed that H2 did
not interact with the metal complex below 100°C. However, at 120 °C, bands at 2073,
83
2140 and 1796 cm-1 appeared. The authors purposed that these bands were due to
formation of the hydrocarbonyl and rhodium carbonyl clusters.
The resemblance of the peaks formed under H2/CO2 with those formed under
CO/CO2, suggest that rhodium carbonyl complexes are formed under H2. Even though a
Rh-H band was not observed, it might be obscured by overlapping CO bands. Yang and
Garland observed a band in the range 2062-2045 cm-1 and assigned it to single linear CO
bonded to one Rh atom since the band was positioned between the two bands assigned to
two COs bonded to Rh atom (Rh dicarbonyl) [146]. Even though the study involved a
heterogeneous catalyst, it is proposed that the band at 2025 cm-1 might be due to Rh-CO
stretch. It can be speculated that hydridocarbonyl species, HRh(CO)xLy, x=1 or 2, is
formed under H2/CO2.
Figure 4.10 also displays the 3100-2700 cm-1 region. Bands at 2931 and 2963
appear under H2/CO2 atmosphere. These bands can arise due to C-H stretch of the
product formed by hydrogenation of COD or from the formation of methane by reaction
of CO with H2 [146].
4.2.3.1 Nature of the Immobilized Rh Catalyst Under CO/H2
The species present on the surface of the phosphinated silica was also studied
under atmosphere of CO and H2 mixture. Rh on phosphinated silica was exposed to 450
psig (1:1) of syn gas at 100 °C. After 1 hour, the gas phase was removed by flowing N2
for 10 minutes. The spectrum obtained is shown in Figure 4.11.
After exposure to CO/H2, the bands appear at 2081, 2023 and 2007 cm-1. The
spectra suggest that apart from Rh-dicarbonyl complex, additional species might be
84
present. Even though the three bands observed might be due to two carbonyl and
hydrido-metal stretch, it is also possible that apart from dicarbonyl rhodium complex,
RhH(CO)2Lx, monocarbonyl complex, RhH(CO)Lx is formed.
2
1.8
1.6
Absorbance
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2200
2100
2000
1900
Wavenumber (1/cm)
Figure 4.11: IR spectrum of the catalyst after being exposed to CO/H2, P=450 psig,
T=100 °C.
4.2.3.2 Nature of the Immobilized Rh Catalyst Under CO/H2/CO2
The behavior of the catalyst under a mixture of CO, H2 and CO2 at 100 °C and
total pressure of 1140 psig was also studied. The spectra taken during exposure of the
catalyst to this mixture are shown in Figure 4.12.
Bands are observed at 1720 cm-1 and 1800 cm-1 and increase with time of
exposure. The peaks in terminal carbonyl region (2100-1990 cm-1) are obscured by gas
phase CO. Upon the removal of gas phase mixture, bands at 2078, 2001, 1799 and 1720
85
cm-1 remain as presented in Figure 4.13. Peaks at 2078 and 2001 cm-1 are assigned to
HRh(CO)yLx.
1
120 min
0.8
Absorbance
60 min
0.6
30 min
0.4
15 min
0.2
5 min
0
2000
1800
1600
Wavenumber (1/cm)
Figure 4.12: IR spectra of the catalyst under CO/H2/CO2; P= 1140 psig, T=100 °C.
2
1.8
1.6
Absorbance
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.13: IR spectrum of the catalyst after exposure to CO/H2 in CO2, P=1140 psig,
T=100 °C.
86
Luchetti et al. reported that presence of H2 did not affect the species formed on
the surface [148]. In other words when an immobilized Rh catalyst was treated with CO
the species formed was the same as when treated with a mixture of CO/H2 (1:1). A
similar result is observed in the present case as Rh dicarbonyl complex, evident from the
twin bands at ~2080 and 2000, is formed under both CO and CO/H2 atmosphere. It is
evident from Figures 4.8 and 4.13 that bands formed under CO/CO2 mixture and those
formed under the atmosphere of CO, H2 and CO2 mixture are similar in appearance.
Since the band due to Rh-H vibration could not be observed and assigned with
confidence, an experiment was performed where the catalyst was exposed to 100 psig of
CO for 30 minute followed by exposure to hydrogen.
The Figure 4.14 shows the spectrum obtained after exposure to CO, while the
other spectra are the changes produced as a function of time under H2. Bands at both
2084 and 2009 cm-1 decrease with time as the band at 1990 cm-1 increases. This suggests
that indeed the band at 1990 cm-1 might be due to Rh-H vibration.
87
1.2
1
Absorbance
0.8
post H2-post CO
H2-30 min-post CO
0.6
H2-15 min-post CO
H2-5 min-post CO
post CO
0.4
0.2
0
2200
2100
2000
1900
Wavenumber (1/cm)
Figure 4.14: IR spectrum of the catalyst after treatment with CO and the changes
observed after being exposed to H2.
4.2.4 Nature of the Immobilized Rh Catalyst Under CO2
The nature of the catalyst in the presence of CO2 was also tested. To this end, the
catalyst was exposed to pure CO2 at 100 °C and 1220 psig. The changes were followed
by taking spectra at certain time intervals. The spectra obtained are shown in Figure 4.15.
At the 5th minute, apart from peaks at 2350 (not shown), peaks at 2072 and broad
band at ~1730 cm-1 (not shown) are present. The peak at 2072 cm-1 increase with time
and peak at 2017 with a shoulder at 1990 cm-1 appear and also grow with time. Because
these bands were observed under CO, it can be concluded that CO is formed and taken as
proof that CO2 dissociation occurs. The spectra of the catalyst after removal of the gas
phase CO2 (post CO2 in Figure 4.15) shows that Rh(CO)2Lx is formed under CO2.
88
2.6
2.4
2.2
post CO2
2
Absorbance
1.8
under CO2-240 min
1.6
1.4
under CO2-120 min
1.2
1
under CO2-30 min
0.8
0.6
under CO2-5 min
0.4
0.2
0
2200
2100
2000
1900
Wavenumber (1/cm)
Figure 4.15: IR spectra of the catalyst under CO2, P=1220 psig, T=100 °C.
4.2.5 The Behavior of the Immobilized Rh Catalyst Under C6H12 and CO2
Interactions of 1-hexene in CO2 with the catalyst were also studied. The catalyst
was exposed to a mixture of 1-hexene (Aldrich) and CO2 at 75 °C and total pressure of
1100 psig. The spectra taken before, during and after catalyst exposure are shown in
Figure 4.16. Upon exposure of catalyst to 1-hexene/CO2 mixture, bands due to gas phase
1-hexene at ~ 2800-3090, 1828, 1643, 1455, 1384, 993 and 914 cm-1 can be observed.
The band at 1643 cm-1 is assigned to C=C stretch, while peaks at 1455 and 1384 cm-1 are
assigned to C-H bending vibrations of methylene and methyl, respectively. The peaks at
3090-2800 cm-1 are assigned to C-H stretch and peaks at 993 and 914 cm-1 are due to out
of plane C-H bending vibrations. The peak at 1828 cm-1 is the overtone of the peak at 914
cm-1.
89
0.6
After exposure
0.6
0.6
0.6
0.4
0.4
0.4
0.4
0.2
0.2
0.2
0.2
During exposure
Kubelka- Munk
Before exposure
0
3100
0
3000
2900
2800
0
2100 2000 1900 1800 1700 1600
1500
1400
0
1050
950
850
Wavenumber (1/cm)
Figure 4.16: IR spectra of the catalyst before, during and after exposure to mixture of
C6H12 and CO2, P=1100 psig, T=75 °C.
Upon sweeping the mixture of 1-hexene and CO2 with N2, bands due to 1-hexene
are no longer present and the spectrum appears similar to spectrum taken before the
catalyst was exposed to 1-hexene/CO2 mixture. Thus, it can be concluded that 1-hexene
does not interact with the catalyst.
This is in contrast to observations reported by Wrzyszcz et al. [70]. The
researchers reported that IR spectra of Rh(acac)(CO)2 and Rh(acac)(CO)(PPh3)
complexes supported on ZnAl2O4 spinel that were used in hydroformylation reaction,
each exhibited a band at 2053 cm-1, in addition to bands at 2088 and 2015 cm-1 assigned
to Rh(CO)2. It was suggested that the band at 2053 cm-1 was due to Rh(I) complex
immobilized on the spinel that was modified by reactant 1-hexene.
90
4.2.6 Identification of the Bands due to Heptanal
One of the products expected for hydroformylation of 1-hexene is heptanal. In
order to identify the bands due to product formation, heptanal (Aldrich) was mixed with
CO2 and heated to 100 °C. The catalyst was then exposed to this mixture. The
temperature and pressure were 100 °C and 1200 psig. The spectra obtained during the
Absorbance
exposure are presented in Figure 4.17.
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
3100
3000
2900
2800
2700
2600
post exposure to Heptanal/CO2
under Heptanal/CO2
0
2200 2100 2000 1900 1800 1700 1600
Wavenumber (1/cm)
Figure 4.17: IR spectra under and after exposure of the catalyst to mixture of heptanal
and carbon dioxide, T=100 °C, P=1200 psig.
Under the atmosphere of heptanal and CO2, a band at 1737 cm-1 is observed. It
was assigned to the C=O stretch of aldehyde. The C-H stretch for aldehyde (-CHO) is
observed at 2715 cm-1 as well as C-H stretches at 2880, 2935 and 2962 cm-1. The bands
at 2071 and ~ 2000 cm-1 are also present. These are CO bands which probably arise due
to CO2 dissociation. The spectrum obtained after the mixture was removed shows no
91
band due to the presence of heptanal. The only bands present are bands at 2071 and
~2000 cm-1 and a band centered at 1711 cm-1.
4.3 Characterization of RhCl(PPh3)3
Hydroformylation has been widely studied with Wilkinson catalyst, RhCl(PPh3)3.
The catalyst is transformed into HRh(CO)y(PPh3)x under an atmosphere of CO/H2. Since
the IR studies of this catalyst in solution are widely reported, the behavior of this catalyst
under atmosphere of CO2 was also studied. It was thought that some of the changes that
could not be observed with the immobilized catalyst would be observed if this catalyst is
studied. Wilkinson catalyst was prepared by Nick Kingsley at Chemistry Department at
The University of Toledo.
Figure 4.18 shows IR spectra of Wilkinson catalyst, red solid, under the
atmosphere of nitrogen at room temperature. Since the important changes can be
observed in 2100-1600 cm-1, only this region is shown. The bands can be observed at
1963, 1892, 1821, 1772, 1666 and ~1590 cm-1.
Bands at 1963, 1892, 1821 and 1772 cm-1 are assigned to overtone and
combinations bands of C-H out of plane deformations. The bands for C-H out-of plane
deformations are observed in 900-700 cm-1 region and are not shown in Figure 4.18. The
four bands observed are characteristic of monosubstituted benzenes as previously
discussed. The band at 1590 cm-1 is due to aromatic C=C stretch. The band at 1666 cm-1
could not be assigned. Figure 4.19 shows comparison of PPh3 and RhCl(PPh3)3. The
spectra of the PPh3 (TPP) are better resolved but other than that all bands appear similar
92
confirming the assignment of the bands to ligand, PPh3. The band at 1666 cm-1 also
appears in the spectra of the PPh3 which was obtained from Sigma-Aldrich.
7.5
Absorbance
7
post rxn, after flowing N2
6.5
post rxn at 100 C, gas phase vented
after being exposed to Syn for 90 min at 90 C
6
under N2, room T
5.5
5
2100 2000 1900 1800 1700 1600
Wavenumber (1/cm)
Figure 4.18: IR spectra of RhCl(PPh3)3 after different pretreatments.
4
3.5
Wilkinson's catalyst under N2
3
Absorbance
2.5
TPP after Syn, 50 C
2
TPP after Syn, room T
1.5
1
TPP under N2, room T
0.5
0
2100 2000 1900 1800 1700 1600
Wavenumber (1/cm)
Figure 4.19: Comparison of the IR spectra of Wilkinson catalyst and TPP.
93
Figure 4.18 also shows the spectra obtained after the catalyst was pretreated with
CO/H2 mixture (1:1, 500 psig, and 90°C). The bands are observed at ~2040, 2007, 1977,
1960, 1916, 1886, 1812, 1768 and 1665 cm-1. The bands at ~2040, 2007 and 1916 cm-1
are clearly new bands but have very low intensity. Evans et al. assigned the band at 2040
cm-1 to Rh-H stretch [36]. In agreement with Evans et al., the band at 2040 cm-1 is
assigned to Rh-H stretch. Assignment of other bands is rather difficult because of overlap
of phenyl bands with low intensity carbonyl stretching vibrations.
A clearer picture can be obtained after the pretreated catalyst was used for
hydroformylation reaction for approximately 10 hours at 100 °C and 1250 psig. The
spectrum obtained after a reaction mixture consisting of 1-hexene, CO, H2 and CO2 was
vented is also presented in Figure 4.18. The band ~2040 cm-1 has higher intensity
suggesting that RhCl(PPh3)3 was converted to hydridorhodium complex. The other bands
that can be observed are at ~2000, 1962, ~1940, 1918, 1888, 1769 and 1667 cm-1. The
bands at 1888, 1820, 1769 and 1667cm-1 were observed for Wilkinson catalyst before
exposure to Synthesis gas.
Table 4.2 gives vibrations for rhodiumcarbonyl species
reported by various groups.
Examination of Table 4.2 reveals that the medium under which spectra are taken
affects the spectra. It also suggests that ligand has an effect on position of carbonyl
bands. This is actually expected since fluorinated ligand is strongly withdrawing group so
that back donation of metal to CO will decrease so that CO band will appear at higher
frequency. Also, the terminal carbonyl-stretching frequencies of the dimer are higher than
the carbonyl-stretching frequency of dicarbonylrhodium species.
94
Table 4.2: Reported IR vibrations for Rh carbonyl complexes.
Compound
IR vibrations
Solvent
Reference
RhH(CO)(PPh3)3
2040*, 1923
Nujol mull
36
RhH(CO)(P(3,5-(CF3)2C6H3)3)3
2041*,1964
CO2
11
RhH(CO)2(PPh3)2
2038*, 1980, 1939
Hexane
36
RhH(CO)2(P(3,5-(CF3)2C6H3)3)2
2076*, 2056, 2034
CO2
11
Nujol mull
36
CO2
11
2017, 1992, 1800,
[Rh(CO)2(PPh3)2]2
1770
[Rh(CO)2(P(3,5-(CF3)2C6H3)3)2]2
1827, 1799
* Rh-H stretch
Since the media in which spectra are taken is different than the media under
which the catalyst is tested in the current study, the wave numbers will not match each
other. So, the shoulder at ~2000 and the band at 1962 cm-1 are assigned to terminal
carbonyl vibrations of [Rh(CO)2(PPh3)2]2. The bands at 1940 and 1918 cm-1 are assigned
to νCO of RhH(CO)2(PPh3)2. The bridging carbonyl band cannot clearly be seen in the
spectra presented in Figure 4.18 because it is overlapped by bands due to phenyl group.
4.4 Hydroformylation of 1-Hexene with the Immobilized Rh Catalyst in CO2
4.4.1 Identification of the Species Formed Under Reaction Conditions
The aim of the in situ studies is to observe the species that might be present on the
surface of the immobilized catalyst, which in turn might give some insight into the
mechanism of hydroformylation reaction by the immobilized catalyst.
95
Cup of the DRIFTS cell was filled with 25 mg of the catalyst, corresponding to
1.2*10-5 moles of rhodium. The catalyst was exposed to a mixture of CO (0.01 mol), H2
(0.01mol), 1-hexene (9.6*10-4 mol) and CO2 at 100 °C and total pressure of 1250 psig.
Figure 4.20 represents the spectrum taken 5 minutes after the catalyst was exposed to
reaction mixture.
2.4
2.2
5 min
2
1.8
Absorbance
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
Wavenumber (1/cm)
Figure 4.20: IR spectrum of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
P=1250 psig.
Initially, bands due to 1-hexene at 3084, 1828, 1643, 1455, 1384, 993 and 914 cm1
as well as gas phase reactants and CO2 (2400-2000 cm-1) are present. Additionally, the
band at 1710 cm-1 is present. This is consistent with the previous observation that this
band is formed as soon as catalyst is exposed to reactants or CO2. The bands in range
2230-2450 cm-1 are due to gas phase CO2, while bands in range 2000-2230 are due to gas
96
phase CO. The reaction progress is evident from the disappearance of bands due to 1hexene in Figure 4.21.
2.4
2.4
2.4
2.4
2.2
2.2
2.2
2.2
2
2
2
2
1.8
1.8
1.8
1.8
1.6
1.6
1.6
1.6
1.4
1.4
1.4
1.4
285 min
1.2
1.2
1.2
1.2
165 min
1
1
1
1
0.8
0.8
0.8
0.8
0.6
0.6
0.6
30 min
0.6
0.4
0.4
0.4
0.4
15 min
0.2
0.2
0.2
1640 min
480 min
Absorbance
360 min
0
3100
3050
0
1850
60 min
0.2
5 min
0
0
1800
1650
1600
Wavenumber (1/cm)
105 100 950 900 850
0
0
Figure 4.21: IR spectra of the catalyst under CO, H2, C6H12 and CO2; T=100 °C, P=1250
psig; bands due to 1-hexene vibrations.
In conjunction with the disappearance of 1-hexene, the band at 1735 cm-1
increases in intensity with time of exposure and the intensity of the band at 1643 cm-1
(assigned to 1-hexene) decreases, as can be seen in Figure 4.22.
The band at 1735 cm-1 is assigned to C=O stretch of aldehyde, as previously
discussed. Aldehyde C=O stretch has been reported to be in the region 1740-1720 cm-1.
Moser et al. studied hydroformylation of 1-hexene at 70 °C and pressure of 200 psi
(CO:H2=1:1) using Rh4(CO)12 as a catalyst precursor and triphenylphosphine as a ligand
with dichloroethane as a solvent [13]. They reported that a band at 1723 cm-1 was present
in the IR spectrum and assigned it to aldehyde product. Liu and Garland reported that
97
propanal was formed in the ethylene hydroformylation, as evident from absorbance at
1730 cm-1 [43]. The reaction was carried out in n-hexane at 20 °C and partial pressures of
CO, H2 and ethylene were 43.5, 43.5, and 580 psi, respectively. The homogeneous Rh
catalyst was obtained starting with Rh4(CO)12 as a precursor.
1.8
1640 min
1.6
480 min
1.4
360 min
Absorbance
1.2
285 min
1
165 min
0.8
60 min
0.6
30 min
0.4
15 min
0.2
0
1800 1750 1700 1650 1600
5 min
Wavenumber (1/cm)
Figure 4.22: IR spectra of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
P=1250 psig; bands due to 1-hexene and aldehyde vibrations.
Haji and Erkey studied hydroformylation of ethylene at 14 °C and 942.5 psi in
liquid CO2 [11]. The catalyst used was RhH(CO)L3, (L=P(3,5-(CF3)2C6H3)3) and partial
pressures of CO, H2 and ethylene were 166.8, 166.8 and 21.8 psi, respectively. The
spectrum under the reaction conditions revealed the peak at 1741 cm-1 that was assigned
to the C=O stretch of propanal.
Park and Ekerdt studied hydroformylation of 1-hexene with RhH(CO)(PPh3)3
bound to phosphinated gel-form polystyrene-divinylbenzene beads at 264.5 psi total
98
pressure and ambient temperature [91]. They observed the band at 1730 cm-1, which was
assigned to heptanal. The band at 1733 cm-1 was also observed in a study by Chuang and
Pien [14]. The study involved heterogeneous Rh on SiO2 and was carried out at 100 °C
and 14.7 psi of CO, H2 and ethylene.
The literature reports for the C=O stretch of aldehyde in the region of 1730-1740
cm-1 form the strong basis that the peak at 1735 cm-1 is due to aldehyde formation. The
observation of aldehyde agrees also with Tadd et al. [7] who have observed aldehyde
formation with the same catalyst as used here.
As previously mentioned, Tadd et al. have studied hydroformylation of 1-hexene
with [RhCl(COD)]2 immobilized on phosphinated silica [8]. They observed heptanal, 2ethylpentanal, and 2-methylhexanal formation as well as isomerization of 1-hexene to 2hexene. Isomerization was also observed during hydroformylation in the IR cell as
evident from Figure 4.23.
The bands at 993 and 914 cm-1 are due to 1-hexene. The band at 970 cm-1 appears
at ~285th minute of reaction and the intensity of this band increases with time. In the C-H
stretch region it can be seen that the shoulder appears ~3025 cm-1. The band at 970 cm-1
is assigned to C-H deformation vibration of 2-hexenes. The band at 3020 cm-1 is assigned
to C-H stretch of 2-hexenes. The assignment of bands due to 2-hexene is supported by the
IR spectra of a standard mixture of cis- and trans-2-hexenes purchased from SigmaAldrich and depicted in Figure 4.24.
99
Absorbance
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
1640 min
1200 min
960 min
840 min
720 min
600 min
480 min
360 min
285 min
5 min
0
3050 3000
0
1050
1000
950
900
850
Wavenumber (1/cm)
Figure 4.23: IR spectra of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
Absorbance
P=1250 psig; bands due to 1-hexene and 2-hexenes vibrations.
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
2-hexene (in CO2)
0
3100 3000 2900 2800 2700 2600 2500
0
1570 1470 1370 1270 1170 1070
Wavenumber (1/cm)
Figure 4.24: IR spectrum of the 2-hexenes in the CO2.
100
970
870
At longer reaction times (1200-1640 minutes), bands at 1740, 1810, 970, 1460
and 1390 cm-1 are prominently observed. 1-Hexene is nearly completely converted at
these reaction times, as evident from the absence of peaks at 3084 and 1643 cm-1.
However, as shown in Figure 4.25, the bands at 1460 and 1390 cm-1 are still present. The
observation of these bands in spite of 1-hexene disappearance supports the finding that
Absorbance
aldehyde and 2-hexenes are present.
2.6
2.6
2.4
2.4
2.2
2.2
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
3100
1640 min
1200 min
1.2
3000
2900
2800
1750
1650
1550
1450
1350
Wavenumber (1/cm)
Figure 4.25: IR spectra of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
P=1250 psig; bands due to 2-hexene and/or aldehyde vibrations.
The acylrhodium complex formation has been reported by several groups [11, 35,
132]. For example, Haji and Erkey observed that 3 different acyl species were formed
when 2.73 mM (300 mg) of homogeneous catalyst, (RhH(CO)L3), was subjected to a
mixture of 63 mM of ethylene and 240 mM of each CO and H2 at 14 °C and 942.5 psi
101
total pressure in liquid CO2 [11]. The acyl bands were observed at 1645, 1672 and 1695
cm-1.
In this study, acyl peak presence can not be discerned from the spectra obtained.
This might stem from either low band intensity or interference from the broad band at
~1710 cm-1. Equally possible is that the acyl complex forms but the reaction step that
follows is fast so that this species is only present in very small quantities.
Figure 4.26 presents spectra taken upon removing gas phase mixture of reactants
and CO2. The bands present are positioned at 2074, 2013 with shoulder at ~1990, 1800,
and the broad band at ~1710 cm-1. The band at 2074 is assigned to a moiety of Rhdicarbonyl species, while the other two bands can be from moieties of rhodiumdicarbonyl
or rhodium monocarbonyl, or from Rh-H stretch. At present it can not be concluded
whether HRh(CO)yLx reverts back to ClRh(CO)yLx as bands due to Rh-Cl could not be
observed since Rh-Cl band is expected to be observed in the far-infrared spectrum (νRhCl=295
cm-1) [153]. Large scale reversion of the hydrido form to chloride would be highly
unlikely. Since the catalyst was active for hydroformylation, it is expected that
HRh(CO)2Lx and/or HRh(CO)Lx is present on the surface.
The silica-tethered rhodium thiolate complex catalysts Rh-S/SiO2 and Rh-SP/SiO2 were active for hydroformylation of 1-octene in the presence of phosphine donor
ligands at 60°C and 14.7 psi [101]. Catalysts exhibiting highest hydroformylation activity
had a Rh(SR)(CO)2(PR’3) type of complex as the major species on the surface. The
observation of the rhodium dicarbonyl complex after hydroformylation agrees with the
report of Gao and Angelici that dicarbonyl species is associated with catalyst activity.
102
2
Absorbance
1.8
post rxn
1.6
1.4
1.2
1
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.26: IR spectrum of the catalyst after hydroformylation mixture was removed by
nitrogen, T=100 °C, P=1250 psig.
4.4.2 Assignment of the Band at 1710-1730 cm-1
The spectra taken following hydroformylation catalyzed by Rh immobilized on
phosphinated silica reveals that a broad band was present in the range of 1712-1724 cm-1.
Sanger and Schallig studied the complexes formed under CO by catalyst prepared
from [RhCl(c-C8H12)]2 and poly(p-chlorostyrene) resin, where 83 percent of chlorine
atoms were replaced by PPh2 groups [59]. They observed that apart from dicarbonyl
rhodium complex (2096 and 2034 cm-1), a weaker band at 1714 cm-1 was also present in
the spectrum. A Rh moieties linked by CO were suggested as possible assignment for
band at 1714 cm-1 [59].
The band in the range of 1710-1730 cm-1 was not observed when phosphinated
silica support was exposed to a mixture of CO and CO2 or to a mixture of CO, H2, 1-
103
hexene and CO2, as evident from Figure 4.27. However, the band in the range 1720-1733
cm-1 was observed when Rh on phosphinated silica was exposed to pure H2 or H2 and
CO2 mixture, respectively. The band at 1716 cm-1 was observed when Rh on
phosphinated silica was exposed to a CO and CO2 mixture while under H2/CO and CO2
mixture the band is observed in the range 1726-1730 cm-1. Since this band appears to be
associated with CO and H2, its assignment to bridging carbonyls cannot be made.
1.8
Absorbance
1.6
1.4
post CO,H2,CO2, Rh on Silica
1.2
postCO/CO2, Rh on Silica
1
post H2/CO2, Rh on Silica
0.8
post H2, Rh on Silica
0.6
post CO, H2, 1-hexene, CO2, Silica
0.4
post CO/CO2, Silica
0.2
0
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.27: IR spectra of the catalysts and the support under different atmospheres,
region ~ 1720 cm-1.
In order to find the origin of this band, the spectra of the catalysts and the support
under nitrogen at both room temperature and 100 °C are compared. The spectra in Figure
4.28 shows that for both phosphinated silica support and Rh on phosphinated silica
(Rh:P=1:2), there is no band in the range 1710-1730 cm-1. The spectra shown in Figure
4.28 represent spectra where no subtraction is involved.
104
3.5
high T (phosphinated silica)
3
low T (phosphinated silica)
high T (Rh:p=1:1, light yellow)
2.5
Absorbance
low T (Rh:P=1:1, light yellow)
2
high T (Rh:P=1:1)
low T (Rh:P=1:1)
1.5
high T (Rh:P=1:2)
1
low T(Rh:P=1:2)
0.5
highT (Rh:P=1:3)
0
1850
lowT (Rh:P=1:3)
1750
1650
Wavenumber (1/cm)
Figure 4.28: IR spectra of the support and different catalysts at room temperature and at
100 °C.
However, the band around 1730-1710 cm-1 was observed for cases in which the
rhodium to phosphorus ratio was 1:1 or 1:3. Both of these catalysts were dark yellow in
color. It should be noted that these dark yellow catalysts were older samples and might
have been oxidized. The spectra of the catalyst Rh on phosphinated silica with Rh:P=1:1
and of light yellow color was also examined (spectra named Rh:P=1:1, light yellow), and
appeared similar to catalyst with Rh:P=1:2 and/or the spectra of phosphinated silica
without Rh attached, in that no band at 1730-1710 cm-1 was observed.
All catalysts were tested for hydroformylation activity in batch reactor
experiments and were found to be active [154, 155]. The spectra obtained after
hydroformylation using these materials is presented in Figure 4.29.
105
3
2.8
2.6
post Rxn, Rh:P=1:2, Prxn=1250 psig
2.4
2.2
post Rxn, Rh:P=1:1, light yellow, Prxn=1240 psig
Absorbance
2
1.8
1.6
post Rxn, Rh:P=1:1, light yellow, Prxn=1340 psig
1.4
1.2
post Rxn, Rh:P=1:1, dark yellow, Prxn=1240 psig
1
0.8
post Rxn, Rh:P=1:3, dark yellow, Prxn=1000 psig
0.6
0.4
0.2
0
2200 2100 2000 1900 1800 1700 1600
Wavenumber (1/cm)
Figure 4.29: IR spectra of the different catalysts after hydroformylation reaction was
completed.
Figure 4.29 shows that all used catalysts have a band in the range of 1710-1730
cm-1. The light yellow catalyst with Rh:P=1:1, however, has no band at 1800 cm-1 and
also the bands due to Rh dicarbonyl species have rather low intensity. The reason for this
is not known but might be due to Rh leaching as this catalyst was nearly white (as is the
phosphinated silica support) after reaction. Since the band at 1710-1730 cm-1 is observed,
even though the band due to bridging and terminal carbonyls are not present or have low
intensity, it is suspected that this band is not due to rhodium carbonyl species.
Figure 4.30 presents comparison of the spectra obtained under hydroformylation
conditions in the presence of bare phosphinated silica and in the presence of Rh
immobilized on phosphinated silica (Rh:P=1:2).
106
1.2
Absorbance
1
Rh on phosphinated silica (Syn/1-hexene/CO2-5 min)
0.8
0.6
Phosphinated silica (Syn/1-hexene/CO2-5 min)
0.4
0.2
1800
1700
1600
Wavenumber (1/cm)
Figure 4.30: IR spectra of the catalyst and the support under hydroformylation conditions.
The band in the 1710-1730 cm-1 is absent in the spectrum of the phosphinated
silica, suggesting that the band is due to species associated with metal precursor. Thus,
the band in the 1710-1730 cm-1 might be due to some reaction of Rh complex which does
not necessarily yield bridging carbonyls. It is also possible that the catalyst was oxidized
during the reaction by water present in the silica.
4.4.3 Assignment of the Band at 1800 cm-1
The spectrum taken after hydroformylation reaction shows a band at 1800 cm-1.
This band was observed to form shortly after the start of the reaction and increases in
intensity with time of exposure of the catalyst to CO, H2, 1-hexene and CO2, as seen in
Figure 4.31. This band is assigned to bridging carbonyls; i.e. two Rh atoms linked by a
CO molecule.
107
2
1.8
1.6
post Rxn
1.4
1640 min
Absorbance
1200 min
1.2
840 min
1
600 min
0.8
360 min
165 min
0.6
30 min
0.4
5 min
0.2
0
1950
1850
1750
Wavenumber (1/cm)
Figure 4.31: The spectra of the catalyst under CO, H2, C6H12 and CO2; T=100 °C,
P=1250 psig; bands in the bridging carbonyl region.
Luchetti et al. observed that prolonged treatment of catalyst with CO at 100 °C
led to appearance of band at 1804 cm-1 [148]. They proposed that the structure depicted
in Figure 4.32 produced the response. However, they also reported that the dimer was not
stable and the only species present after 10 days was rhodiumdicarbonyl complex.
Rh dimer, [Rh(CO)2(PPh3)2]2, formation was also reported for systems using
homogeneous catalyst [11, 36]. Formation of the dimer, depicted in Figure 4.33, was
observed by Haji and Erkey, who studied the interaction of a homogeneous Rh based
catalyst with CO in CO2 [11]. The reported IR bands were at 1827 and 1799 cm-1
.
108
Cl
O
Si CH2 CH2 PPh2
Rh
CO
CO
O
Si CH2 CH2 PPh2
CO
Rh
CO
Cl
Figure 4.32: Structure of dimer reported by Luchetti et al. [148].
O
C
L
Rh
L
CO
L
Rh
C
O
L
CO
Figure 4.33: Structure of Rh dimer reported by Haji and Erkey [11].
As evident from above, different structures are proposed for dimer formation.
Figure 4.34 compares spectra obtained after different pre-treatments of the catalyst. The
band at 1800 cm-1 as seen to form during hydroformylation was not seen to form under
either carbon monoxide or hydrogen alone, but it does form under the presence of both.
The formation of the species with the band at 1800 cm-1 is also independent of the
presence of CO2, as it forms under CO/H2 with or without addition of CO2. Since the
band at 1800 cm-1 is not formed in the presence of CO alone, it is not likely that species
109
reported by Luchetti et al. [148] and depicted in Figure 4.32 is formed. Rather, the dimer,
structurally similar to dimer depicted in Figure 4.33, is the most likely structure. Based
on the analogy with this species, the structure for the dimer formed on phosphinated
silica support is proposed as depicted on Figure 4.35.
2.2
2
1.8
1.6
post CO/H2 in CO2
Absorbance
1.4
post CO/H2
1.2
1
post CO
0.8
post H2
0.6
0.4
0.2
0
2150
2050
1950
1850
1750
Wavenumber (1/cm)
Figure 4.34: IR spectra of the catalyst after different pretreatments, bridging carbonyl
region.
110
CO
CO
O
C
Rh
Ph
P
Rh
Ph
CH2
Ph
C
O
P
Ph
CH2
CH2
CH2
Si
Si
Figure 4.35: Structure of the dimer, [Rh(CO)2L]2, formed on the phosphinated silica
support.
Since it is also possible that each Rh is coordinated to two phosphorus atoms, the
structure as depicted in Figure 4.36 is also possible assignment for the band at 1800 cm-1.
CO
L
CO
O
C
Rh
L
Rh
C
O
L
L
L=PPh2 CH2 CH2 Si
Figure 4.36: Structure of the dimer, [Rh(CO)2L2]2, formed on the phosphinated silica
support.
111
4.5 Investigation of Reaction Intermediates
The catalyst used in this study involves Rh complex anchored to phosphinated
silica support. This implies that the mechanism for the immobilized transition metal
complex should be similar to the mechanism proposed for homogeneously catalyzed
hydroformylation. Based on mechanism proposed by Evans et al. [25], the following
mechanism is suggested for hydroformylation by immobilized catalyst as depicted by
Figure 4.37.
Rh(COD)ClLx
(1)
CO/H2
HRh(CO)yLx + HCl + COD
(2)
RCOH
CH2=CH-(CH2)3 CH3
H2 Rh(CO)yLxC(O)R
(5)
RhR(CO)yLx
(3)
H2
CO
Rh(CO)yLxC(O)R
(4)
R=CH2CH2 (CH2 )3 CH3
Figure 4.37: Mechanism proposed for hydroformylation by immobilized Rh catalyst.
The RhCl(COD) is anchored to the phosphinated silica support through a
phosphine ligand. Marteel characterized Rh immobilized on phosphinated silica with
CP/MAS
13
C NMR spectroscopy [4]. Comparison of the spectra of the catalyst before
112
and after being used in hydroformylation reaction revealed that COD moiety was absent
from the spectra of the used catalyst. It was suggested that COD was replaced by species
such as phosphine groups. It was further suggested that x was 2 or 3. The results obtained
with IR spectroscopy showed that two CO molecules are bound to Rh complex,
suggesting the presence of complexes (S1) and (S2), shown previously. It should be
noted that during hydroformylation reaction, these complexes would be converted to
hydrido complexes and therefore, chloride would be replaced with hydride. Other
possible complexes based on the requirement that Rh forms 16 or 18 electron complexes
are depicted in Figure 4.38.
CO
CO
H
Rh
H
L
L
L
(S3)
CO
OC
Rh
Rh
L
L
L
L
(S4)
L
H
L
Rh
(S5)
CO
H
(S6)
L=P(C6H5)2CH2CH2Si
Figure 4.38: Structures of possible Rh complexes immobilized on phosphinated silica
support during hydroformylation.
113
DRIFTS study suggests that y is 2 as dicarbonyl species was observed
immediately after hydroformylation. Evans et al. had proposed that hydridorhodium
dicarbonyl complex participated in hydroformylation cycle [25]. However, the system
used by Evans et al. was homogeneous Rh complex and the cycle proposed had some
steps involving ligand dissociation and/or association. There is no proof that this might be
occurring with the immobilized catalyst. Monocarbonyl Rh complex (S3) might have
been formed on the catalyst but the band due to this species was not observed since it was
overlapped by dicarbonyl and/or gas phase CO during the hydroformylation. As will be
shown later, the spectra of the catalyst taken after hydroformylation also shows the band
at 2015 cm-1. This band might be due to monocarbonyl species, HRh(CO)Lx. So, the
dicarbonyl Rh complex observed after hydroformylation experiments already described
might be the resting state of the catalyst and not the active catalytic species. The proposed
cycle would then be the same as the generally accepted mechanism for hydroformylation
described in literature where x is 2 [26].
Reaction of [RhCl(COD)]2 immobilized on phosphinated silica with CO/H2 led to
formation of RhH(CO)yLx. Even though the spectra obtained could not be unequivocally
identified as the hydridocarbonyl complex, the catalyst was active for hydroformylation,
therefore, it is expected that hydrogen was coordinated to Rh.
Upon reaction of [RhCl(COD)]2 immobilized on phosphinated silica with CO and
H2, COD and HCl are liberated. Coordination of alkene to rhodium complex leads to
formation of rhodium alkyl complex (3). Even though observation of alkyl complex has
been reported [35, 40], studies usually involved reactant or a catalyst that form stable
alkyl complexes. The next step in the proposed cycle is formation of the acylrhodium
114
complex (4). This species is formed by alkyl migration to CO. Observation of an acyl
complex by IR spectroscopy has also been reported [42, 95]. Formation of dihydrido acyl
species by reaction of acyl with H2 is the next step in the proposed cycle. The formation
of aldehyde and its liberation leads back to complex (2).
Either of proposed complexes HRhL3 (S5) and HRh(CO)2L (S2) would follow
this cycle. Both of these complexes could coordinate 1-hexene since they are 16 electron
species. It is generally accepted that Rh complexes with three ligands coordinated are in
their resting state when excess ligand is present, otherwise ligand dissociation occurs.
Therefore, Rh complexes that are active and selective are usually reported to have 2
ligands coordinated.
If complexes HRh(CO)L3 and/or HRh(CO)3L were to form then the cycle
depicted in Figure 4.38 would have to be modified since these are 18 electron species that
are coordinatively saturated. CO dissociation would have to occur to create an active
catalyst. The cycle would then resemble those for HRhL3 and HRh(CO)2L.
Concerning the complex (S1), Evans et al. suggested that it participates in
dissociative cycle by loosing PPh3 (or CO) and that formation of acylrhodium complex
(4) proceeds by alkyl migration to CO, and no additional CO is coordinated (from (3) to
(4), in case when PPh3 is dissociated in the first step), rather phosphine ligand is
coordinated [25]. Complex HRh(CO)2L2, (S1), is also an 18 electron species. While for
this species dissociation of CO ligand is envisioned, Evans et al. proposed the associative
mechanism based on this species as the active catalytic species [25]. The authors
proposed that formation of a 20 electron intermediate by coordination of alkene (Figure
115
2.8, 1C) was possible since the intermediate was short-lived. Nevertheless, the CO
coordination between (3) and (4) would then occur between (5) and (2).
4.5.1 Investigation of the Acylrhodium Complex Immobilized on Silica Support
Acylrhodium complex is one of the species formed during hydroformylation.
Several groups reported observing the acylrhodium complex, as summarized in Table 4.3,
which indicates the frequencies at which the acyl complex has been reported for different
substrates and catalysts.
Table 4.3: Reported C=O stretch for acyl metal complexes.
Catalyst
Substrate
RhH(CO)(PPh3)3
1-hexene
RhH(CO)(L)3,
L=P(3,5-
νCO
Solvent
1620-1660
Reference
35
1645-Rh(CO)L2(COEt)
Ethylene
1673- Rh(CO)2L2(COEt)
CO2
11
1695- Rh(CO)3L(COEt)
(CF3)2C6H3)3
IrH(CO)3P-i-Pr3
Ethylene
1671
Heptane
40
Rh4(CO)12
1-hexene
1702.9
n-hexane
42
RhNaY
Propylene 1660
solid
95
As can be seen from Table 4.3, the range of acyl complex absorption frequencies
is from 1620-1703 cm-1. Thus, this range was evaluated in the experiments performed.
The experiment where reaction was performed with 1-hexene, CO, H2 and CO2 at
100 °C and 1250 psig (explained previously) could not reveal whether acyl was formed
116
under reaction conditions. There was a small peak seen at ~1690 cm-1 which could not be
unequivocally assigned since the spectra of the solid samples reveals broad peaks in this
region. The experiment was performed where the catalyst was treated with CO/H2/CO2
mixture at the same conditions as the hydroformylation reaction. Figure 4.39 provides a
comparison of the spectra of the catalyst under an atmosphere of CO/H2 alone and that of
CO/H2 and 1-hexene in CO2.
2.8
2.6
2.4
2.2
1-hex/Syn/CO2-360 min
2
Absorbance
1.8
Syn/CO2-360 min
1.6
1-hex/Syn/CO2-60 min
1.4
Syn/CO2-60 min
1.2
1
1-hex/Syn/CO2-30 min
0.8
Syn/CO2-30 min
0.6
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 4.39: Comparison of IR spectra obtained under hydroformylation conditions and
under CO/H2/CO2, T=100 °C, P=1250 psig.
The band at 1643 cm-1 is band due to 1-hexene while the band at 1735 cm-1 is
band due to aldehyde. The spectra, however does not reveal whether the band is present
in the range of reported aldehyde frequencies (1620-1703 cm-1). Since the overlapping of
the spectra obtained in these two experiments could not reveal any difference, the
117
difference between the spectra obtained in the 5th minute of the corresponding reaction
and the spectra obtained at the specified time is presented in Figure 4.40.
2.8
2.6
2.4
2.2
1-hex/Syn/CO2-360 min
2
Absorbance
1.8
Syn/CO2-360 min
1.6
1-hex/Syn/CO2-60 min
1.4
1.2
Syn/CO2-60 min
1
0.8
1-hex/Syn/CO2-30 min
0.6
Syn/CO2-30 min
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 4.40: Comparison of the difference spectra obtained under hydroformylation
conditions and under CO/H2/CO2.
The difference spectra reveal that the absorption due to 1-hexene (1643 cm-1) is
disappearing as indicated by the negative band and that band due to aldehyde is
increasing as indicated by the positive band at 1735 cm-1. The spectra also indicate that
there is a small difference between the spectra taken under CO/H2 alone and the spectra
taken under CO/H2 and 1-hexene mixture at ~1690 cm-1.
It should be noted that most mechanistic studies, as explained in Chapter 2, were
done using homogeneous HRh(CO)L3 type catalyst. The catalyst is then in the form of
the active species.
118
In an attempt to obtain more conclusive results related to the acyl complex, the
experiment was also designed where the catalyst was first pre-treated with CO/H2 in CO2.
This was done in order to create RhH(CO)yLx anchored on silica support. The gas phase
mixture of CO and H2 and CO2 was then removed by flowing nitrogen for 10 minutes.
The catalyst was then exposed to mixture of 1-hexene and CO in CO2. This would be
expected to yield the acyl complex, since this complex is stable in CO. The spectra
obtained under CO, 1-hexene and CO2 as a function of time is presented in Figure 4.41.
These spectra are the result of difference between the spectrum taken at specified point of
time under CO, 1-hexene and CO2 and the spectrum taken after removal of CO, H2 and
CO2 mixture.
2.5
3.1
600 min
2.9
2.3
480 min
2.7
Absorbance
2.1
1.9
2.5
420 min
2.3
300 min
2.1
180 min
1.9
120 min
1.7
1.5
1.7
60 min
1.5
1.3
30 min
1.3
15 min
1.1
1.1
5 min
0.9
1800
0.9
1700
1600
950
850
Wavenumber (1/cm)
Figure 4.41 IR spectra of the pretreated catalyst under mixture of CO, 1-hexene and CO2,
T=100 °C, P=1160 psig.
The spectra reveal that peaks due to 1-hexene do not decrease appreciably and
that just at longer times (480 and 600th minute) the small peak at 980 cm-1 appear. No
119
distinctive peak is detectible in the region 1680-1750 cm-1, suggesting that acyl did not
form.
In the experiment above, it was assumed that RhH(CO)yLx was stable after gas
phase CO, H2 and CO2 were removed. However, if this were not so, i.e. if RhH(CO)yLx is
not stable and it reverts to RhCl(CO)2Lx, then the acyl would not be observed. That the
catalyst complex contains CO bonded to Rh can be inferred from spectra (not shown), but
due to inability to discern Rh-H band, it was not possible to say that hydrido complex
was stable under nitrogen.
An experiment was also performed where the CO/H2/CO2 mixture was not
removed by flowing, but rather the cell was only evacuated and then mixture of CO, 1hexene and CO2 introduced. The experiment done in this way would then assure that
HRh(CO)yLx is present. The spectra obtained under the atmosphere of CO, 1-hexene and
CO2 (not shown), however, did not indicate that any changes occurred in acyl complex
region.
Since the experiments did not reveal whether the acylrhodium complex was
formed, a different experiment was envisioned. The catalyst was pre-treated with CO/H2
in CO2 but the gas phase mixture was evacuated down to 200 psig after the catalyst was
treated with this mixture for 1 hour. It is expected that the catalyst would remain in the
form of HRh(CO)yLx. This assumption is supported by the observation that under
hydroformylation conditions with the catalyst some aldehyde was already formed after 1
hour in the experiment carried under atmosphere of syn gas, 1-hexene and CO2 (Figure
4.22).
120
The catalyst was then exposed to the mixture of 1.5*10-3 mol CO and 6.9*10-4
mol 1-hexene in CO2 and changes were monitored by IR. The spectra taken during this
process is presented in Figure 4.42.
1.8
1.6
1.4
600 min
Absorbance
1.2
480 min
1
360 min
0.8
15 min
0.6
5 min
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 4.42: IR spectra of the catalyst under mixture of CO, 1-hexene and CO2, T=100
°C, P=1120 psig.
The spectra shown in Figure 4.42 do not indicate that any band is present at
~1690 cm-1. When the difference of spectra between spectra at 5th minute and those taken
afterwards is taken, the band at 1690 cm-1 can be observed. This can be seen in Figure
4.43.
Bianchini et al. observed the formation of a very small amount of complex with
the structure analogous to structure 8 in Figure 2.10 (dicarbonyl acylrhodium complex)
when RhH(CO)(PPh3)3 was exposed to 290 psi of CO and 1-hexene (1-hexene: catalyst=
30:1) in absence of hydrogen [44]. The reason for small extent of dicarbonyl acyl
121
formation was the competitive formation of Rh dimers [44]. So, according to Bianchini et
al., even if acyl formed in above experiment, it would be in minute quantities, perhaps
unobservable, since formation of dimeric species would occur as was observed under
conditions studied and can be seen in the Figure 4.43 by the appearance of band at 1800
cm-1.
1.2
1
600 min
Absorbance
0.8
480 min
0.6
360 min
0.4
15 min
0.2
0
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.43: The difference of the spectra taken at 5th minute and the time indicated under
conditions as specified in Figure 4.42.
Literature reports include various conditions under which the acylrhodium
complex was formed and observed. One of those is the study by Haji and Erkey who used
RhH(CO)L3, (L=P(3,5-(CF3)2C6H3)3) to study intermediates formed in CO2 [11]. They
reported that three different acyl complexes were observed at 1.5 °C and up to 609 psi in
CO2. The mol ratio of CO to C2H4 was 1:1 and CO to Rh was 64:1. They also reported
122
that by changing CO to C2H4 ratio from 1:1 to 0.35 to 0.035 the intensities of the three
peaks due to acyl complexes changed.
In order to mimic studies by Haji and Erkey, the experiment was also done where
catalyst was first pre-treated with CO/H2 in CO2, after which mixture was evacuated to 0
psig. The catalyst was then exposed to 25 psig of 1-hexene followed by addition of CO
up to 40 psig. The CO2 was then added to the final pressure of 1260 psig. The spectra
were then periodically taken to monitor changes and are shown in Figure 4.44.
1.4
1-hexene/CO/CO2-120 min
1.2
Absorbance
1-hexene/CO/CO2-60 min
1
1-hexene/CO/CO2-30 min
1-hexene/CO/CO2-15 min
0.8
1-hexene/CO/CO2-5 min
0.6
1700
1600
Wavenumber (1/cm)
Figure 4.44: IR spectra of the catalyst under PCO=15 psig; PC6H12=25 psig, T=100 °C.
As evident from Figure 4.44 no appreciable changes can be seen in the range
expected for acyl complex, Rh(C(O)C6H13)Lx.
Haji and Erkey also carried out hydroformylation with the above mentioned
catalyst at 14 °C and 942.5 psi in liquid CO2 with a syn gas to ethylene ratio of 3.81 [11].
They reported that at these conditions three acyl complexes could be observed. A similar
123
experiment was also conducted in this study where synthesis gas to 1-hexene ratio was
~2.5 (1*10-2 mol each CO and H2 and 4*10-3 mol 1-hexene). The spectra taken during a
reaction is depicted in Figure 4.45.
2.4
2.2
Syn/1-hex/CO2-150 min after additional CO2
2
Syn/1-hex/CO2-120 min after additional CO2
1.8
Syn/1-hex/CO2-60 min after additional CO2
Absorbance
1.6
Syn/1-hex/CO2-30 min after additional CO2
1.4
Syn/1-hex/CO2-15 min after additional CO2
1.2
Syn/1-hex/CO2-5 min after additional CO2
Syn/1-hex/CO2-120 min
1
Syn/1-hex/CO2-60 min
0.8
Syn/1-hex/CO2-30 min
0.6
Syn/1-hex/CO2-15 min
0.4
Syn/1-hex/CO2-5 min
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 4.45: IR spectra of the catalyst under CO, H2, 1-hexene and CO2 (CO:H2:1Hexane = 2.5:2.5:1), T=100 °C.
After 1-hexene, syn gas and CO2 were added, the pressure decreased in the first
120 minutes from 1230 to 1120 psig. After 120 minutes additional CO2 was introduced
into the cell to increase the pressure back to 1250 psig. The spectra do not reveal any new
species apart from small shoulders at 1690 cm-1, which again cannot be conclusively
assigned to acyl complex. The spectra also reveal that no appreciable amount of aldehyde
was formed. In some preliminary experiments carried by Tadd [156] with the same
catalyst used throughout this study, the rate of hydroformylation was slower when the
synthesis gas to 1-hexene ratio was lower. So, it is believed that the lack of a sharp
124
aldehyde peak at ~1740 cm-1 may be due to hydroformylation being too slow to produce
sufficient aldehyde at this reaction time.
The lack of observation of acyl complex on the phosphinated silica support even
though Haji and Erkey reported that acyl complex was formed, may be a result of the low
rhodium loading in the DRIFTS cell compared to the much higher loading used by Haji
and Erkey. The low rhodium loading will lead to formation of only small amounts of the
acylrhodium complex, generating a signal too low to be observed. However, the
conditions used in Haji and Erkey’s study could not exactly be replicated because the
amount of the catalyst used is limited by the design of the catalyst holder in the chamber.
Some of the literature reports include studies performed under low temperature
[11, 44, 132], and use gaseous ethylene rather than 1-hexene [11, 132]. These studies are
done at lower temperatures so that reaction would be slower, rendering more facile
observation of the acyl complex. However, such approach could not be taken with the
experimental setup used, since 1-hexene is liquid at room temperature. In order to slow
reaction, lower concentrations of reactants can be employed.
The catalyst was exposed to 5.5*10-4 mol of 1-hexene and 1*10-3 of each CO and
H2 in CO2. The spectra taken during the reaction at 100 °C and 1030 psig total pressure is
presented in Figure 4.46. Under the atmosphere of CO, H2, 1-hexene and CO2, the
dicarbonyl species is formed rapidly as evident from a peak at 2010 and 2100 cm-1. The
reaction proceeds rather slow, as evident from small decrease of peak at 1645 cm-1. The
shoulder appears at 975 cm-1, which can be, as previously discussed, due to formation of
2-hexene. However, only other change that occurs is increase of the band at ~1710 cm-1.
125
Absorbance
2.2
2.2
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1
1
0.8
0.8
30 min
0.6
0.6
5 min
0.4
0.4
0.2
0.2
500 min
480 min
360 min
0
2200 2100 2000 1900 1800 1700 1600
240 min
120 min
0
1050
950
850
Wavenumber (1/cm)
Figure 4.46: IR spectra of the catalyst under mixture of CO, H2, 1-hexene and CO2,
T=100 °C, P=1030 psig.
The experiments described above did not reveal any conclusion related to
presence of the acylrhodium complex. Yonker and Linehan reported observation of the
dicarbonyl acyl complex when Rh catalyst obtained from Rh(CO)2(acac) as the catalyst
precursor and tris(p-trifluoromethylphenyl)phosphine, (p-CF3C6H4)3P, as the ligand in
liquid CO2 [132]. The reported experimental conditions were 2001 psi (CO:H2=1:1), 43.5
psi of ethylene at a total pressure of 3001.5 psi at 50°C. This pressure was achieved by
adding CO2. However, the Rh complex precipitated and the NMR cell was evacuated to
290 psi and refilled with CO2, up to 3001.5 psi. The NMR spectrum obtained after this
procedure showed dicarbonyl acyl species formation. Similar experiment was also
performed with Rh complex anchored on phosphinated silica. The catalyst was exposed
to a mixture of CO and H2 (1.1*10-2 mol each) and 4.7*10-4 mol of 1-hexene. Therefore
126
the ratio of syn gas to 1-hexene was 24. The spectrum obtained during reaction at these
conditions is shown in Figure 4.47.
1.4
after evacuation of Syn/1-hex/CO2
1.2
Syn/1-hex/CO2-360 min
Absorbance
1
Syn/1-hex/CO2-300 min
Syn/1-hex/CO2-240 min
0.8
Syn/1-hex/CO2-180 min
Syn/1-hex/CO2-120 min
0.6
Syn/1-hex/CO2-60 min
Syn/1-hex/CO2-30 min
0.4
Syn/1-hex/CO2-15 min
0.2
0
1800
Syn/1-hex/CO2-5 min
1700
Wavenumber (1/cm)
1600
Figure 4.47: IR spectra of the catalyst taken under mixture of CO, H2, 1-hexene and CO2,
T=100 °C, P=1200 psig, CO:H2:C6H12=24:24:1.
Even at lower concentrations of 1-hexene, the reaction proceeds, as evident from
the disappearance of peak at 1643 cm-1. The spectra also reveal similarity with spectra in
Figure 4.22. The peak at 1735 cm-1, as in the case when syn gas to 1-hexene ratio was 10
to 1, is the most prominent feature in the region 1740-1710 cm-1. Even at these
conditions, the band due to the acylrhodium complex could not be observed.
Another reason for the failure to observe the rhodium acyl complex might stem
from the resting state of the catalyst. It is thought that resting state of the catalyst depends
on the amount of ligand present in the system. For example, in the presence of moderate
127
or high concentrations of phosphine, the resting state of the catalyst is HRh(CO)2(L)2 or
HRh(CO)(L)3, respectively [26].
The fact that dicarbonyl complex was observed after reaction indicates that the
likely resting state of the Rh immobilized on phosphinated silica is HRh(CO)2(L)x. The
catalyst used (Rh:P=1:2) corresponds to the homogeneous catalyst where ligand is
present in moderate to excess amounts. Therefore, in agreement with literature, the
acylrhodium complex was not observed during hydroformylation reaction because the
resting state of the catalyst is not the acylrhodium complex. The lack of observation of
the acylrhodium complex under conditions designed to detect it may also be due to dimer
formation that occurs during carbonylation reaction [44].
Literature reports imply that were the Rh to P ratio lower, 1 to 1, or if the catalyst
was not modified so that no phosphorus ligand was present, the acylrhodium complex
might have been observed. In order to test this possibility, the Rh complex anchored on
phosphinated silica with the Rh to P ratio of 1 was tested under hydroformylation
conditions. Figure 4.48 presents the spectra taken under hydroformylation in CO2 at 1240
psig and 100 °C with Rh immobilized on phosphinated silica where Rh to P ratio is 1 to1.
Disappearance of 1-hexene can be monitored by decreasing in the intensity of the
band at 1645 cm-1. The aldehyde formation is marked by appearance and increase of the
intensity of the band at 1740 cm-1. The spectra also show that 2-hexene is formed as
evident from appearance of the band at 970 cm-1. The band at 1690 cm-1 can also be seen
in Figure 4.48.
128
1.6
1.6
1.4
1.4
Absorbance
Syn/1-hex/CO2-260 min
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Syn/1-hex/CO2-240 min
Syn/1-hex/CO2-120 min
Syn/1-hex/CO2-30 min
Syn/1-hex/CO2-5 min
0
1800
1700
1600
0
1050
950
850
Wavenumber (1/cm)
Figure 4.48: IR spectra of the catalyst with Rh:P=1:1 under hydroformylation conditions;
1*10-2 mol of each CO and H2 and 1*10-3 mol of 1-hexene, T=100 °C,
P=1240 psig.
In order to discern whether the band at 1690 cm-1 is due to acyl complex the
catalyst (Rh:P=1:1) was also subjected to syn gas in CO2 at the same conditions at which
the reaction was completed. Figure 4.49 compares the spectra taken under CO/H2 in CO2
vs. spectra recorded under CO/H2 and 1-hexene mixture in CO2.
Spectra taken under atmosphere of 1-hexene and CO/H2 shows band at 1645 cm-1
(1-hexene) which is decreasing with time and also it shows appearance and increase in
intensity of band at 1740 cm-1 assigned to aldehyde. Comparison of spectra reveals that at
30th and 120th minute, there is a band at 1690 cm-1 present in the spectra taken under 1hexene and CO/H2 atmosphere which is not present under CO/H2 alone. However, it is to
129
be noted that this band was observed in the spectra taken under hydroformylation
conditions with the catalyst with Rh:P=1:2. Due to this fact, it can not be concluded that
this band is due to the acylrhodium complex. This does not negate the presence of the
acylrhodium complex as the band formed can be overlapped by the band at ~1720 cm-1.
This band is rather broad and starts at 1700 cm-1. If the band due to the acylrhodium
complex is at 1702.9 cm-1 as reported by Liu et al. [42] then this band could not be
discerned from the spectra obtained with the Rh immobilized on phosphinated silica.
Morris and Tinker also observed no acyl formation in hydroformylation of 1-hexene at 80
°C and 500 psig CO/H2 [12]. The catalyst used was RhH(CO)(PPh3)3. No acylrhodium
formation was also reported during hydroformylation of propene by RhCl(CO)(PPh3)2
anchored on polystyrene-divinylbenzene membrane [63].
5.5
5
4.5
Syn-240 min
1-hex/Syn-240 min
Syn-180 min
1-hex/Syn-180 min
Syn-120 min
1-hex/Syn-120 min
Syn-30 min
1-hex/Syn-30 min
Syn-5 min
1-hex/Syn-5 min
4
Absorbance
3.5
3
2.5
2
1.5
1
0.5
0
1800
1700
1600
Wavenumber (1/cm)
Figure 4.49: Comparison of the spectra of the catalyst with Rh:P=1:1 under
hydroformylation conditions and under CO/H2.
130
4.5.2 Hydroformylation of 1-Hexene with RhCl(PPh3)3
Since there is abundance of studies with Wilkinson catalyst [RhCl(PPh3)3], this
complex was tested for hydroformylation reaction in CO2. The catalyst precursor was
first pretreated with 500 psig CO/H2 (1:1) for 3 hours at 90 °C and then the reaction
mixture (CO, H2 and C6H12) and CO2 were added. The reaction was carried at 100 °C and
1250 psig. The spectra obtained under reaction conditions in the 2000-1600 cm-1 region is
presented in Figure 4.50.
Recalling that the band at 1643 cm-1 was observed for C=C stretch of 1-hexene, it
is expected that this band would also be present in the spectra of the system with
Wilkinson catalyst since gas phase band should be fairly independent of the catalyst.
Comparison of the spectra after pretreatment with CO/H2, i.e. before exposure to reaction
mixture with the spectra taken after exposure to reaction mixture, spectra “5 min”, it can
be seen that there is a band present at 1646 cm-1 in the spectra named 5 min. Therefore
this band is assigned to C=C stretch of 1-hexene. Other 1-hexene bands were also
observed but are not shown. This band decreases with time as can be seen from Figure
4.50. Aldehyde C=O stretch is expected to be observed at ~1735 cm-1 based on spectra
taken in CO2 in this study. Examination of the spectra in Figure 4.50 reveals that the band
appears at about 1740 cm-1. As discussed before, both dicarbonyl and the dimer species
are present under reaction conditions as the bands at 1917 and 1960 cm-1 are visible in the
spectra presented in Figure 4.50.
131
C=O
C=C
8
7.5
7
600 min
6.5
480 min
6
Absorbance
5.5
360 min
5
180 min
4.5
4
30 min
3.5
5 min
3
2.5
after pretreatment with Syn gas
2
1.5
1
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.50: IR spectra of Wilkinson catalyst under reaction conditions.
Apart from identification of HRh(CO)2L2 type species, the objective of studying
Wilkinson catalyst was to examine whether the acylrhodium species is formed in CO2.
Rh(C(O)R)L2 species was already discussed and as stated previously the range reported
was 1620-1703 cm-1. With immobilized catalyst this species was not detected but studies
in CO2 with Wilkinson type catalyst have shown that the acylrhodium species was
present under reaction conditions [11]. Examination of this region in the Figure 4.50 only
reveals band present at 1666 cm-1. However, this band is also observed after pretreatment
with CO/H2, therefore is not due to C=O stretch of the acylrhodium species. This
however does not indicate that the acylrhodium complex is not formed, as it might have
been overlapped by the band at 1666 cm-1. This indicate that the study of the mechanism
of the reaction by solid state method is rather difficult and in the absence of significant
132
amount of intermediate almost impossible since the bands have smaller intensities.
Additionally, the bands are less resolved i.e. broader than their counterparts in solution,
causing overlap with potential other bands.
4.5.3 Rate Determining Step
The nature of the rate determining step remains one of the controversial elements
of the hydroformylation cycle. Conducting reactions at different reaction conditions may
lead to identification of different steps as the rate limiting [157]. Evans et al. had
proposed that reaction of the acylrhodium complex with H2 was the rate determining step
[25]. The spectra obtained under hydroformylation conditions in CO2 with phosphinated
silica immobilized Rh as the catalyst (Rh:P=1:2) did not reveal any acylrhodium
formation. Based on this, it appears that addition of hydrogen is not rate limiting step.
Were this step rate limiting, the accumulation of the acylrhodium complex would have
been observed. This in turn suggests that the steps occurring earlier in the
hydroformylation cycle are slower. Therefore, rate determining step could be either
dissociation of CO from the dicarbonylrhodium complex or coordination of alkene.
Van der Veen et al. studied hydroformylation of 1-octene at 80 °C and pressure of
290 psi (CO/H2=1:1) with 1 mM of Rh based catalyst [30]. Throughout the reaction only
a (diphosphine)Rh(CO)2H complex was present. They noted that decreasing CO pressure
and increasing concentration of alkene led to increase of the reaction rate. Based on this it
was suggested that alkene coordination was the rate limiting step. Moser et al. studied 1hexene
hydroformylation
[13]
and
suggested
RhH(CO)2(PPh3)2 was the rate determining step.
133
that
CO
dissociation
from
Van der Veen et al. [158] studied the kinetics of
13
CO dissociation from
(diphosphine)Rh(13CO)2H complexes. They found that the rate of CO dissociation at 40
°C was higher than the rate of hydroformylation at 80 °C.
The two candidates for rate determining step are equally possible. But if the rate
of CO dissociation is as fast as reported by van der Veen et al. [158], then, the rate
limiting step is likely alkene coordination for the Rh immobilized on phosphinated silica
with Rh to P ratio 1 to 2. However, if the acylrhodium complex did not form in any of the
experiments designed to detect this complex, then CO dissociation is the rate determining
step.
In study with heterogeneous Rh on SiO2 catalyst, it was proposed that
hydrogenation of the acyl species was the rate determining [93]. This clearly is different
from the conclusion drawn from this study. Nevertheless, it does prove the assumption
that immobilization of the Rh through phosphorus ligand led to behavior of the
immobilized that is more similar to homogenous based phosphine modified Rh catalysts,
which retains advantages of heterogeneous catalyst such as facile recovery.
4.6 Hydroformylation of 1-Hexene with the Immobilized Rh Catalyst in the Absence
of CO2
The experimental results involving exposure to CO and H2 indicate that presence
of CO2 does not affect the corresponding complexes formed. In order to test whether
different Rh complexes would be formed if CO2 was absent from the system, the
hydroformylation was carried out in the presence of N2. The temperature and pressure
were maintained at 100 °C and 1220 psig.
134
The spectra presented in Figure 4.51 shows disappearance of 1-hexene, based on
the decreasing intensity of the bands at 3087, 1826, 1645, 993 and 912 cm-1 with time.
1.8
1.8
1.8
1.8
1.6
1.6
1.6
1.6
1.4
1.4
1.4
1.4
1.2
1.2
1.2
1.2
1
1
1
1
0.8
0.8
0.8
0.8
0.6
0.6
0.6
0.6
0.4
0.4
0.4
0.4
0.2
0.2
0.2
0.2
Absorbance
600 min
480 min
360 min
240 min
120 min
30 min
5 min
0
3100
3050
0
1850
0
1800
1600
Wavenumber (1/cm)
0
1050
950
850
Figure 4.51: IR spectra of the catalyst under 2*10-2 mol CO/H2 (1:1), 9.7*10-4 mol C6H12
and N2.
The aldehyde band was observed during hydroformylation in the presence of CO2
at 1735 cm-1. The spectra shown in Figure 4.52, however, do not indicate that the band at
1735 cm-1 is present. The only band observed is the band at 1715 cm-1, which was also
seen to form in the presence of CO2, and was discussed before.
135
1.8
600 min
1.6
480 min
1.4
1.2
Absorbance
360 min
1
240 min
0.8
120 min
0.6
0.4
30 min
0.2
5 min
0
1750
1700
Wavenumber (1/cm)
Figure 4.52: IR spectra of the catalyst under conditions reported in Figure 4.51,
1700-1750 cm-1 region.
Figure 4.53 presents spectra of the regions 3100-2990 and 1050-850 cm-1.
Concomitant with decrease of the intensity of the bands due to 1-hexene, the band at
3015 and 976 cm-1 appear and increase in intensity. This band was previously assigned to
C-H stretch and bending vibrations of 2-hexenes.Therefore, it can be concluded that in
the presence of nitrogen, 1-hexene is isomerized to 2-hexenes.
136
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
Absorbance
600 min
480 min
360 min
240 min
120 min
30 min
5 min
0
3090
3040
2990
Wavenumber (1/cm)
0
1050
1000
950
900
850
Figure 4.53: IR spectra of the catalyst under conditions reported in Figure 4.51,
2990-3100 and 850-1050 cm-1 regions.
Figure 4.54 compares spectra obtained initially and after 600 minutes of exposure
of the catalyst to CO, H2, and 1-hexene in the presence of CO2 and N2. In both cases, both
the band at 1715 and the band at 1800 cm-1 are formed. The dimer with the bridging
carbonyls at 1803 cm-1 is slightly shifted to higher wave numbers, bur this is probably
due to the resolution of the instrument (4 cm-1). However, the band at 1735 cm-1 is absent
from the spectra taken under nitrogen. This can be taken as evidence that CO2 influences
the reaction, although it appears that similar species are formed regardless of the choice
of CO2 or N2. Although carbon dioxide and nitrogen are both supercritical fluids at the
conditions studied, the density of CO2 is much higher than that of N2.
137
2
1.8
1.6
Absorbance
1.4
in CO2-600 min
1.2
in N2-600 min
1
0.8
in CO2-5 min
0.6
in N2-5 min
0.4
0.2
0
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.54: Comparison of IR spectra of the catalyst under hydroformylation conditions
in the presence of CO2 and N2.
The spectrum obtained after hydroformylation reaction is carried out in the
presence of nitrogen is displayed in Figure 4.55. The bands present after
hydroformylation was attempted in N2, are at 1717, 1803, 2002 and 2076 cm-1.
Additionally there is shoulder present at ~ 2020 cm-1. The bands positioned at 2002 and
2076 cm-1 are due to dicarbonyl species, while the band at 1803 cm-1 is due to dimer. The
band at 1717 cm-1 was due to unknown species and was already discussed. The shoulder
at 2020 cm-1 might be due to additional carbonyl.
Figure 4.55 also gives bands present after hydroformylation in CO2. Since the
bands have similar appearance, it can be concluded that the same species are present on
the surface of the phosphinated silica independent of the choice of the additional gas.
138
3.2
3
Absorbance
2.8
post Rxn in CO2
2.6
post Rxn in N2
2.4
2.2
2
1.8
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 4.55: Comparison of IR spectra of the catalyst after hydroformylation reaction in
the presence of CO2 and N2.
During hydroformylation in the presence of nitrogen, side reactions also occur.
The spectra presented in figure 4.56 shows that the bands at 2360, 2340 and 670 cm-1
develop and their intensity increase with time. These bands are due to CO2. Therefore,
water gas shift reaction is catalyzed by Rh complex anchored on phosphinated silica.
139
Absorbance
4
3.8
3.6
3.4
3.2
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2400
4
3.8
3.6
3.4
3.2
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2350
2300
2250
600 min
360 min
120 min
60 min
30 min
15 min
700
650
600
Wavenumber (1/cm)
Figure 4.56: IR spectra of the catalyst under hydroformylation conditions in the presence
of N2, 2400-2250 and 700-600 cm-1 regions.
Figure 4.57 compares the bands attributed to CO2 when the catalyst was exposed
to different gases. The spectra is obtained by subtracting the spectra obtained at 5th
minute from the spectra obtained at 120 minute of the exposure to remove any CO2 that
might have been present initially during inadequate evacuation.
Carbon dioxide is formed on the catalyst independent of whether the catalyst is
exposed to CO/H2, CO/H2 and 1-hexene mixture, or carbon monoxide. Since large gas
phase bands are present under atmosphere of CO2, it can not be concluded whether CO2
forms during hydroformylation in the presence of CO2.
140
2.8
2.6
2.4
2.2
2
CO/H2/1-hexene/N2-120 min
Absorbance
1.8
1.6
CO/H2/1-hexene-120 min
1.4
1.2
CO/H2-120 min
1
0.8
CO-120 min
0.6
0.4
0.2
0
2450
2400
2350
2300
2250
Wavenumber (1/cm)
Figure 4.57: IR spectra of the catalyst under different environments; 2250-2450 region.
141
CHAPTER 5
EFFECT OF CO2
Utilization of a supercritical fluid (SCF) as a solvent in which to conduct
chemical reactions takes advantage of a unique combination of solvent properties that are
intermediate between a liquid and a gas. Several advantages are stated in Chapter 2.
A large body of research has been conducted and results reported related to
advantages of supercritical fluids. In many cases, reaction rates in supercritical fluid
solvents are found to be comparable to those in liquids [116], because of increased
solubility and/or improved mass transfer. In addition, in work with systems employing a
heterogeneous catalyst, SCFs have been found useful for extending catalyst life due to
dissolution of coke precursors in SCF [159].
Clustering is the term used to describe a phenomenon that occurs due to attraction
between solute and solvent molecules and leads to “nonuniform spatial distribution of
solvent molecules about a solute molecule” [106]. This phenomenon can lead to local
densities and local compositions to be different from the rest of the medium [105]. The
clustering phenomenon can affect the reaction rate in a positive or negative manner.
Formation of solute-solute clusters results in enhanced local density of the solute [106].
Solvent molecules can also form a cage around solute molecule and therefore prevent
interaction of solute molecules [106, 160].
142
A number of spectroscopic techniques can be used to study intermolecular
interactions between a solute and solvent molecules [161]. These techniques can,
therefore, provide a means to study the effect of SCFs on local density and local
composition.
Randolph and Carlier studied Heisenberg spin exchange reaction between
nitroxide free radical in near critical and supercritical ethane with electron paramagnetic
resonance spectroscopy [162]. They found that the rate constants in the region close to
critical point were larger than those predicted using equations for diffusion controlled
reactions. The finding was attributed to solvent cage or clustering. They also reported
collision duration was in the order of 0.01 picoseconds whereas the diffusion time was in
order of nanosecond. Influence of solute-solvent interactions was also reported [163].
Kim and Johnston studied molecular interactions in SCFs by UV-visible
spectroscopy [164]. Phenol blue, a dye, was used as a solvatochromic probe. They found
that clustering of supercritical solvent occurred. However, sometimes the effects such as
clustering and/or interaction of CO2 with reactants may be difficult to observe. Baiker
points out that using vibrational spectroscopy to in situ monitor reactions taking place on
the surface of the heterogeneous catalysts is challenging at elevated pressures because
“the high gas concentration together with the long beam path lengths give rise to intense
gas phase bands, making their subtraction from the in situ spectra unreliable” [106]. Such
was the case in this study as high concentrations of CO and H2 were used and large gas
phase absorptions were observed making detection of small changes impossible.
Additionally, 1-hexene is a non-polar molecule and interaction between non-polar
substances is not expected to produce any shift in IR wavelength.
143
5.1 Effect of Total Pressure by Addition of CO2
The effect of CO2 as an additional gas/solvent in the reacting system consisting of
the immobilized catalyst, CO, H2, 1-hexene and CO2 was studied by DRIFTS. For the
purpose of studying the effect of CO2, the procedure used in the first part of this study
was modified. Previously, the reactants and CO2 were mixed in a single cylinder and the
contents transferred to the reactor cell. However, preliminary results showed that the
amounts of reactants could not be kept constant using this procedure. So, in the second
part of the study, the reactants were mixed in the single cylinder and heated to 100 °C.
Upon reaching the desired temperature, the mixture of reactants was transferred to the
reactor cell to predetermined pressure. The CO2 was then added from another cylinder
held at 100 °C to the desired final pressure. This procedure ensured that the amounts
(number of moles) of CO, H2 and 1-hexene were not changing from one experiment to
another. Throughout experiments the amount of catalyst used was 25 mg. All reactions
were performed at 100 °C and for 600 minutes. The start of reaction was taken to be the
time CO2 was added to reactor. Table 5.1 gives the amount of each reactant used and the
final pressure of the reactor.
144
Table 5.1: The number of moles of reactants present initially at given total pressures and
100 °C in reactions carried out in the presence of CO2
Number of
moles/ P
500
840
1020
1250
CO
9.1*10-3
1.2*10-2
1.4*10-2
9.3*10-3
H2
9.1*10-3
1.2*10-2
1.4*10-2
9.3*10-3
1-hexene
9.2*10-4
1.5*10-3
1.4*10-3
9.1*10-4
(psig)
5.1.1 The Species Present Under Hydroformylation Conditions
Spectra taken 5 minutes after the onset of reaction at different total pressures in
CO2 are shown in Figure 5.1. The bands due to 1-hexene at 3086, 3000-2800, ~18201830, 1645, 995 and 914 cm-1 can be observed in each spectrum. Additionally band at ~
1720 cm-1 was observed. The assignment of this band was not made as discussed before.
The intensity of the band at 1645 cm-1 varies with pressure. Even though variation
of the concentration of the reactants can account for some of these changes, the
difference between amounts of 1-hexene initially present at the highest and the lowest
pressure was small yet the areas under these two bands are markedly different. The phase
behavior of the reaction mixture was calculated using ChemCAD, version 5.4.6. The
Soave-Redlich-Kwong and the Peng-Robinson equations of state are usually used to
calculate fugacity coefficients [165]. The Soave-Redlich-Kwong was used in this
simulation. At each pressure studied the mixture of reactants and CO2 was determined to
145
form a single phase. So, the variation of intensity and area with pressure can not be
Absorbance
attributed to formation of liquid phase 1-hexene.
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
3000
2800
0
2000
1250 psig in CO2,
5 min
1020 psig in CO2,
5 min
840 psig in CO2, 5
min
500 psig in CO2, 5
min
0
1800
1600
1000
800
Wavenumber (1/cm)
Figure 5.1: IR spectra of the catalyst 5 minutes upon the onset of hydroformylation
reaction at varying total pressures in the presence of CO2.
Phase behavior has important implications on the spectra taken. Any 1-hexene
and heptanal that condenses will not be present in the spectra since the IR beam only
samples vapor phase and the catalyst surface.
Tadd at al. have shown that 1-hexene can be hydroformylated to both 2methylhexanal and heptanal, and can also be isomerized to 2-hexenes [8]. 2-Hexenes are
also hydroformylated to branched aldehydes. Since the reactions that are occurring are
rather complex, simplifications are made, such as that 1-hexene is converted to heptanal
only. Physical properties of linear and branched aldehydes are similar [166], so it was
thought that this assumption would not affect phase behavior. Also, since 2-hexenes are
146
also hydroformylated, they were not included in simulation of phase behavior. According
to the simulation, phase separation occurs earlier in reaction, but 1-hexene stays in the
vapor phase up to 25 % conversion. Phase behavior simulations also showed that 1hexene is not present in the liquid phase when reaction is carried at 1020 or 1250 psig.
1-Hexene disappearance at all pressures can be seen in Figure 5.2. The spectra in
Figure 5.2 show that 1-hexene concentration decreases in all cases as evident from the
decrease of the band at 1645 cm-1. During reactions carried out at 500 and 840 psig, up to
about 25 % 1-hexene conversion, all 1-hexene was present in vapor phase, based on the
results of the ChemCAD analysis (detailed ChemCAD output is presented in Appendix
1). As a result, only spectra taken during the first 60 minutes, corresponding to less than
25 % change in area of band at 1645 cm-1, is shown.
840 psig
500 psig
1250 psig
1020 psig
1.4
1.4
1.4
1.4
1.2
1.2
1.2
1.2
1
1
1
1
600 min
Absorbance
360 min
0.8
0.8
0.8
0.8
0.6
0.6
0.6
0.6
60 min
30 min
15 min
0.4
0.4
0.4
0.4
0.2
0.2
0.2
0.2
0
1800
1700
1600
Wavenumber (1/cm)
0
1800
1700
1600
0
1800
5 min
0
1700
1600
1800
1700
1600
Figure 5.2: IR spectra of the catalyst under hydroformylation conditions at varying total
pressures in the presence of CO2; 1600-1800 cm-1 region.
147
The spectra in Figure 5.2 also show the presence of a band at 1720 cm-1 and a
shoulder at 1735 cm-1 in the case when reaction was conducted at 1020 and 1250 psig.
The shoulder at 1735 cm-1 is assigned to C=O stretch of the aldehyde as previously
discussed.
Spectra obtained after 600 minutes of reaction is presented in Figure 5.3. The
band at 1645 cm-1, indicative of 1-hexene concentration, is present at all pressures but has
significantly smaller intensity. The shoulder at 1735 cm-1 is clearly observed at 1250
psig, while smaller shoulders are also present from reactions performed at 840 and 1020
psig. However, no shoulder was observed for the reaction conducted at 500 psig. The
other spectral features appear similar. This indicates that aldehyde was formed at 840,
Absorbance
1020 and 1250 psig, but may not have been formed at 500 psig.
2.8
2.8
2.6
2.6
2.4
2.4
2.2
2.2
2
2
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
2.8
2.6
2.4
2
1.6
1.4
840 psig in CO2, 600 min
1.2
1
1
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
0
2800
1020 psig in CO2, 600 min
1.8
0.8
3000
1250 psig in CO2, 600 min
2.2
1
2000
1800
1600
Wavenumber (1/cm)
500 psig in CO2, 600 min
1000
800
Figure 5.3: IR spectra of the catalyst 600 minutes upon the onset of hydroformylation
reaction at varying total pressures in the presence of CO2.
148
Phase behavior simulations have also indicated that at corresponding reaction
conditions, all aldehyde formed will be in vapor phase at 10%, 20%, and 50% of 1hexene conversion at 500, 840 and 1020 psig, respectively. At 1250 psig one phase will
exist at all conversions. In order to discern whether aldehyde formation varied with
increase in total pressure, comparison of the spectra taken at 30th minute of reaction is
made and is presented in Figure 5.4. Spectra taken at 30 minute is selected since that
presents the percent change in the area of the band at 1645 cm-1, assigned to C=C stretch
of 1-hexene, that ensures that at that conversion all aldehyde produced is in vapor phase.
Figure 5.4 shows that the shoulder at 1735 cm-1 had the highest intensity when the
reaction was carried out at 1250 psig and that the intensity of this peak decreased as the
pressure was decreased. This suggests that aldehyde formation increased with increasing
pressure.
1.2
1
Absorbance
in CO2,1250 psig, 30 min
0.8
in CO2, 1020 psig, 30 min
0.6
in CO2, 500 psig, 30 min
0.4
0.2
1800
1700
1600
Wavenumber (1/cm)
Figure 5.4: Comparison of the spectra taken at varying total pressures in the presence of
CO2; 1600-1800 cm-1 region.
149
The effect of pressure on chemical reaction can be deduced from equation (1)
[165].
∗
∆V
 ∂ ln k 

 =−
RT
 ∂P  T
(1)
In a rigorous thermodynamic analysis of elementary reaction steps, ∆V* would be the
difference in the molar volume of activated complex and the molar volume of the
reactants. The magnitude and the direction of the change in the value of rate constant, k,
are affected by the magnitude and the sign of the ∆V*. So, according to this theory, the
reaction rate increases with pressure if ∆V* is negative. The volume changes due to both
intrinsic and due to solvation component contribute to overall ∆V* [168]. Volume
changes due to bond formation, breakage or some other mechanistic feature represent
intrinsic contribution.
There are no interactions in ideal solution and solvation
contribution to ∆V* is zero. The information regarding reaction mechanism can then be
obtained. Values for intrinsic contribution to ∆V* are typically in the range of -50 to 25
cm3/mol [169]. However, at high pressure, and therefore highly non-ideal situation,
molecules interact and ∆V* largely represent solvation effect and information about
reaction mechanism can not be obtained.
In order to determine the effect of pressure on the rate of reaction, the rate of 1hexene conversion was calculated from the area under the band at 1645 cm-1 at 5th, 15th,
30th and 60th minute of the reaction. Since all 1-hexene was present in the vapor phase at
these points in time, decrease in areas at 1645 cm-1 was taken as indication of 1-hexene
150
disappearance. This peak was chosen since it did not overlap any other band and also no
other species are expected to show vibration at this wave number.
Figure 5.5 area counts vs. time plot for 1-hexene disappearance. Even though area
counts vs. concentration or number of moles of 1-hexene in the DRIFTS cell were not
calibrated, it was thought that the rate of 1-hexene disappearance could be compared by
fitting the data to a kinetic model from which rate constants could be obtained. The
disappearance of 1-hexenes is well represented by the first order kinetics [170]:
−
dC1− hexene
= k1C1− hexene
dt
(2)
where k1 is the rate constant for 1-hexene disappearance. The points represent the
experimental data while the model prediction is represented by a solid line.
Estimated rate constants are summarized in Table 5.2. Both Tadd [154] and Tack
[155] studied hydroformylation of 1-hexene by immobilized rhodium catalyst in scCO2.
Rate constants obtained by Tadd and by Tack for disappearance of 1-hexene are also
given in Table 5.2. The value for the rate constant at 1250 psig is similar to the value
obtained by Tadd [154] at 2000 psig and 90 °C.
151
5
4.5
4
Area counts
3.5
CO2; 500 psig
3
CO2; 840 psig
2.5
CO2; 1020 psig
2
CO2; 1250 psig
1.5
1
0.5
0
0
100
200
300
400
500
600
Time (min)
Figure 5.5: Area counts vs. time for 1-hexene disappearance during reactions carried out
in the presence of CO2 at varying total pressures.
Table 5.2: Estimated rate constants for 1-hexene disappearance.
P (psig)
T ( °C)
Rate constant
Reference
500
100
353.02
This work
840
100
594.89
This work
1020
100
657.84
This work
1250
100
863.71
This work
2000
90
894.9
154
2700
100
623.19
155
152
Estimated rate constants were plotted as a function of pressure in Figure 5.6. The
value of ∆V* obtained is -526 ml/mol. The negative value of the volume of activation,
∆V*, indicates that the reaction rate is enhanced by increasing the pressure.
The rate of formation of aldehydes and 2-hexene could not be extracted as the
bands due to these substances, ~1735 and 3020 cm-1, respectively, were overlapped by
the bands of other species, so that correct area could not be calculated. In addition, the
band at 1735 cm-1, assigned to C=O stretch of aldehyde, could not be observed at 500
psig, therefore aldehyde, if formed, was formed in minute concentrations. Also bands at
1735 cm-1 of lower intensity were observed at intermediate pressures, while this band had
the highest intensity at the highest pressure confirming that the pressure effect might
exist.
7
y = 0.0172x + 5.3035
6.8
6.6
ln (k1)
6.4
6.2
6
5.8
5.6
30
40
50
60
70
Pressure (atm)
Figure 5.6: Effect of total pressure on rate of 1-hexene disappearance in
hydroformylation accomplished in the presence of CO2.
153
80
90
This is expected from previously reported results [7]. They found that
hydroformylation proceeded faster at 2703.4 psi than at 1998.2 psi and reported that ∆V*
was -357 cm3/mol for conversion of 1-hexene to internal alkenes, and -491 and -431
cm3/mol for conversion of 1-hexene to heptanal and 2-methylhexanal, respectively. The
negative values indicated that increasing pressure increased the rates of both
isomerization and hydroformylation, but enhanced the hydroformylation reaction more as
evident from the larger negative values for ∆V* for formation of aldehyde products.
Figure 5.7 shows spectra obtained in the 600th minute of reaction vs. pressure. For
comparison the spectra obtained in the 5th minute of reaction is also shown.
2
2
1.6
1.6
1.2
1020 psig, 5 min
840 psig, 5 min
Absorbance
Absorbance
1250 psig, 5 min
1250 psig, 600 min
1020 psig, 600 min
1.2
840 psig, 600 min
500 psig, 600 min
0.8
500 psig, 5 min
0.8
0.4
0
1000 950
900
850
Wavenumber (1/cm)
0.4
1000 950
900
850
Wavenumber (1/cm)
Figure 5.7: IR spectra of the catalyst at 5th and 600th minute of hydroformylation reaction
at varying total pressures in the presence of CO2, 100-850 cm-1 region.
154
The band at 920 cm-1 is due to 1-hexene. In the data from 600 min, it can be seen
that bands due to 1-hexene have decreased, and that new band appears at ~970 cm-1. This
band is due to 2-hexenes as previously discussed.
The only other feature that is different is the band at 1800 cm-1 that is attributed to
(Rh(CO)2Lx)2. Even though formation of this species starts earlier in the reaction, the
spectra depicted in Figure 5.8, show the increase in the intensity of the band at ~ 1800
cm-1. The spectra in Figure 5.8 are obtained by subtracting spectra at 5th minute from the
spectra at 600th minute of reaction.
1.8
1.6
1.4
1250 psig
Absorbance
1.2
1020 psig
1
0.8
840 psig
0.6
500 psig
0.4
0.2
0
1850
1750
Wavenumber (1/cm)
Figure 5.8: IR spectra of the catalyst during hydroformylation reaction at varying total
pressures in the presence of CO2, 1850-1750 cm-1 region.
The band at 1800 cm-1 is assigned to bridging carbonyls of (Rh(CO)2Lx)2 and is
observed at all pressures. The terminal CO bands due to this compound are overlapped by
gas phase CO bands. There is a shift of this band from 1801 cm-1 at 1250 psig to 1805
155
cm-1 at 500 psig. The shift in frequency of a given band usually is assigned to change in
the strength of the Rh-C bond. Even though such effect might be present here, it is
thought that rather this shift is due to resolution of the instrument (4 cm-1).
The intensity of the band at ~1800 cm-1 also changes with pressure. The plot of
the area under this band vs. pressure, Figure 5.9, shows that the intensity of this band
decreases with pressure. Even though the reason for this is obscure, it suggests that more
of the (Rh(CO)2Lx)2 is formed as pressure is decreased. It was previously reported that
formation of the dimer has detrimental effect on the hydroformylation activity [75]. This
is also observed in this study, as little to no aldehyde formation was observed at 500 psig,
with higher amounts at higher pressure, and the highest amount at 1250 psig.
Area under the band at ~1800 1/cm
5
4
3
2
30
40
50
60
70
80
90
Pressure (atm)
Figure 5.9: Pressure vs. integrated area under the band at 1800 cm-1 observed at 600th
minute of reactions carried out at different total pressures in the presence of
CO2.
156
5.1.2 The Species Present After Reaction/ Resting State of the Catalyst
The Rh complexes that are present under reaction conditions as well as the resting
state of the catalyst can be deduced from the spectra taken in the absence of the gas phase
CO, H2 and CO2, provided that this species are stable.
Figure 5.10 presents spectra taken after the gas phase was removed by flowing
nitrogen through the reaction cell for 10 minutes.
2.8
2.6
2.4
2.2
1250 psig in CO2, post Rxn
2
Absorbance
1.8
1020 psig in CO2, post Rxn
1.6
1.4
1.2
840 psig in CO2, post Rxn
1
0.8
0.6
500 psig in CO2, post Rxn
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 5.10: IR spectra of the catalyst after hydroformylation carried out in the presence
of CO2 at different total pressures.
At all pressures, bands at 2077 and 1997 with the shoulder at 2015 cm-1 are
present. This indicates that dicarbonyl species, RhH(CO)2Lx and monocarbonyl
RhH(CO)Lx complexes are formed. Yang and Garland studied heterogeneous Rh catalyst
and observed a band in the range 2045-2062 cm-1 and assigned it Rh-CO stretch of a
species that had one linear CO bonded to one Rh since it had frequency between the two
157
bands of Rh dicarbonyl species [146]. It is also possible that both of bands at 1997 and
2015 cm-1 are due to Rh dicarbonyl moiety since the surface of the catalyst is nonhomogeneous or that one of them may arise due to Rh-H stretch. The intensities of the
two bands appear to vary with pressure.
The ratio of intensities of the two carbonyl bands can be used to calculate the
angle between the two COs in the Rh complex. It is thought that this could give some
insight into whether the structure of Rh complex formed might have been distorted by
pressure. The angle between the two COs can be calculated by using equation (3) [171]
I ( sym )
I (asym )
θ 
= cot 2  
2
(3)
where I (sym) and I (asym) are intensities of the symmetric and asymmetric vibrations and θ
is the angle between the two COs. In rigorous analysis, integrated values of absorption
bands’ intensities are required [171], but due to overlap of the bands, the intensity at the
wavelength of maximum absorption is used.
Since it could not be discerned whether band at 1997 or at 2015 cm-1 is second
band that is associated with HRh(CO)2Lx the angle was calculated for both cases. The
angles as calculated from equation 3 are given in Table 5.3.
The angle between two CO molecules in dicarbonyl metal complex observed after
reactions in CO2 changes slightly with pressure. The angle increases with pressure
suggesting that there might be some effect of pressure. However, it should also be noted
that the angle is always close to 90°. This suggests that cis-HRh(CO)2Lx is formed at
each pressure.
158
Table 5.3: The calculated angles between two carbonyls in the possible dicarbonyl metal
complexes observed after hydroformylation carried out in the presence of CO2
at different total pressures.
Ө [°] between the carbonyl
Ө [°] between the carbonyl
ligands (bands at 2077 and
ligands (bands at 2077 and
1997 cm-1)
2015 cm-1)
1250
95
90.8
1020
96
91.6
840
93
89.2
500
88.4
86.4
Pressure (psig)
The band due to unidentified compound at ~1720 cm-1 is also present in the
spectra after hydroformylation. The presence of the dimer, (Rh(CO)2Lx)2 is evident from
the band at 1800 cm-1.
The spectrum of the catalyst was also taken one day after hydroformylation was
preformed and is presented in Figure 5.11. The sample was aged in air. The spectrum of
the aged sample reveals that two bands are present at 2008 and 2083 cm-1. Since the
bands are of approximately equal intensity, it can be concluded that cis-RhH(CO)2Lx is
present at the surface of the support. Comparison of the spectra taken 10 minutes after
hydroformylation reaction and the aged sample reveals that only two bands and no
shoulder is present on the aged sample. Thus, it is possible that monocarbonyl complex,
RhH(CO)Lx was present under hydroformylation conditions. Since the catalyst was aged
159
in the air, it is possible that RhH(CO)Lx was oxidized. This is supported by observation
of the presence of the bands due to CO2 in the spectra of the aged sample (not shown).
1.4
1.2
Absorbance
1
1250 psig in CO2, aged sample
0.8
0.6
1250 psig in CO2, post Rxn
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 5.11: Comparison of IR spectra obtained shortly after hydroformylation reaction
and aged catalyst (reaction carried in presence of CO2).
Luchetti et al. observed that under high pressures of CO, the band at 2078 and at
2024 cm-1 were of different intensities [148]. However, after left to age, only cisdicarbonyl was present. They reported that the rhodium carbonyl species formed at high
pressures were not stable and were thought to be the intermediates in hydroformylation
reaction. Therefore, the species present in the spectra taken few minutes after reaction is
performed, are likely intermediates in the reaction.
The spectra obtained from aged catalyst following reactions at different pressures
are presented in Figure 5.12.
160
2.8
2.6
2.4
2.2
1250 psig in CO2, post Rxn (1 day)
2
Absorbance
1.8
1020 psig in CO2, post Rxn (1 day)
1.6
1.4
1.2
840 psig in CO2, post Rxn (1 day)
1
0.8
510 psig in CO2, post Rxn (1 day)
0.6
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 5.12: IR spectra of the catalyst one day after hydroformylations carried out in the
presence of CO2 at different total pressures.
In all cases bands at 2080 and 2010 cm-1 appear and they are of approximately
equal intensity. This suggest that cis-RhH(CO)2Lx is present irrespective of the conditions
at which hydroformylation is carried out.
The band at 1800 cm-1 was also present in the spectra of the aged sample,
suggesting that this complex is at least slightly stable. The area under the band at 1800
cm-1 is calculated from the spectra obtained shortly after hydroformylation and the
spectra of the aged sample in order to discern whether the dimer is stable. It can be seen
from Figure 5.13 that the area does not change as the data points overlap, suggesting that
the dimer is a stable species.
161
10
9
8
Area under the bands
7
6
1710, 10 min after Rxn
5
1710, 1 day after Rxn
4
1800, 10 min after Rxn
3
1800, 1 day after Rxn
2
1
0
30
40
50
60
70
80
90
Pressure (atm)
Figure 5.13: Area counts vs. total pressure for bands at 1800 and 1710 cm-1 observed
after reaction accomplished in the presence of CO2.
Luchetti et al. [148], who also observed the formation of dimer based on the
presence of a peak at 1804 cm-1, reported however, that the dimer was lost after the
catalyst was allowed to age for 10 days. Even though the results obtained in this study do
not agree with observation of Luchetti et al., longer aging could have resulted in the
disappearance of the band due to dimer.
The compound with the unassigned band at ~1720 cm-1 is also present after 1 day
as evident from the spectra in Figure 5.12. The intensity of this band decreases on aging,
but compared to the spectra of the sample 10 minutes after hydroformylation, there is no
correlation, or uniform decrease of this band after aging process.
162
The results show that the pressure of the reaction leads to increase of the rate of
reaction. It was also seen that similar Rh complexes are formed independent of the
pressure at which the reaction is conducted.
5.2 The Effect of Total Pressure by Addition of N2
5.2.1 The Species Present Under Hydroformylation Conditions
In order to investigate whether the increased hydroformylation rate is solely due
to pressure and not due to some special properties of CO2, the reaction was also carried
out in N2 at different total pressures. In order to keep the numbers of moles of reactants
constant, the total pressure was achieved by adding varying amounts of N2. The
experiments carried out in this part are analogous to the experiments performed in CO2.
The number of moles of reactants in the reactor cell is given in Table 5.4.
Table 5.4: The number of moles of reactants present initially at given total pressures and
100 °C in reactions carried out in the presence of N2
Number of
510
810
1060
1250
CO
9.3*10-3
8.5*10-3
1.2*10-2
1.0*10-2
H2
9.3*10-3
8.5*10-3
1.2*10-2
1.0*10-2
1-hexene
9.1*10-4
8.4*10-4
1.2*10-3
1.0*10-3
moles/ P (psig)
The spectra obtained 5 minutes after introduction of reactants and N2 at different
pressures is presented in Figure 5.14.
163
Absorbance
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
3000
2800
0
2000
1800
1600
Wavenumber (1/cm)
1250psig in N2, 5 min
1060 psig in N2, 5 min
1.2
810 psig in N2, 5 min
1
0.8
0.6
510 psig in N2, 5 min
0.4
0.2
0
1000
800
Figure 5.14: IR spectra of the catalyst 5 minutes upon the onset of hydroformylation
reaction at varying total pressures in the presence of N2.
The bands at 914, 995, 1645, 1820-1830, 2880- 2970 and 3086 cm-1 due to 1hexene (as well as gas phase CO (2040-2250 cm-1), not shown) can be observed. Apart
from reactants peak, the band at 1710 cm-1 is also observed and is due to unknown
species. That the band at 1645 cm-1 appears the smallest at the lowest pressure was also
seen in the case of CO2.
1-hexene is converted to another species as evident from decrease in the intensity
of the band at 1645 cm-1 in Figure 5.15. As in the case of reactions carried in presence of
CO2, phase separation occurs, so only spectra taken at points in time when all 1-hexene is
in vapor phase is presented. Appendix 2 contains the output of the ChemCAD program
describing the phase behavior of this system in N2.
164
510 psig
810 psig
1060 psig
1250 psig
1.2
1.2
1.2
1
1
1
1
0.8
0.8
0.8
0.8
0.6
0.6
0.6
0.6
60 min
0.4
0.4
0.4
0.4
15 min
0.2
0.2
0.2
0.2
5 min
Absorbance
1.2
0
1800
1700
1600
Wavenumber (1/cm)
0
1800
1700
1600
0
1800
1700
1600
0
1800
600 min
300 min
1700
1600
Figure 5.15: IR spectra of the catalyst under hydroformylation conditions at varying total
pressures in the presence of N2, region 1800-1600 cm-1.
Spectra obtained after 600 minutes of reaction is presented in Figure 5.16.
Examination of the broad band in the region 1740-1710 cm-1, reveals that no marked
shoulder is present at 1735 cm-1 in spectra obtained at different pressures. In order to
discern whether some aldehyde might have formed the spectrum obtained at 5th minute
was subtracted from the spectrum obtained at 600 minutes. The Figure 5.17 presents the
spectra obtained after performing the subtraction.
165
Absorbance
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
0.8
0.8
1
0.8
0.6
3000
2800
510 psig in N2, 600 min
0.2
0.2
0
810 psig in N2, 600 min
0.4
0.4
0.2
1060 psig in N2, 600 min
0.6
0.6
0.4
1250 psig in N2, 600 min
0
0
2000
1800
1600
Wavenumber (1/cm)
1000
800
Figure 5.16: IR spectra of the catalyst 600 minutes upon the onset of hydroformylation
reaction at varying total pressures in the presence of N2.
1.7
1.6
1.5
1.4
N2-1250 psig-(600-5)
Absorbance
1.3
1.2
N2-1060 psig-(600-5)
1.1
N2-810 psig-(600-5)
1
0.9
N2-510 psig-(600-5)
0.8
0.7
0.6
1800
1700
1600
Wavenumber (1/cm)
Figure 5.17: The difference of the spectra obtained under hydroformylation conditions in
the presence of N2.
166
The band in the range 1710-1740 cm-1 is broad and does not yield whether the
aldehyde is truly present or whether it is due to the tails of the band at 1720 cm-1.
Therefore, if any aldehyde was formed it must be in a vapor phase in such a small amount
that it can not be differentiated from the overlapping band at 1720 cm-1.
Since ChemCAD simulations have indicated that all aldehyde that is formed will
be present in vapor phase only initially, the spectra obtained at 15th minute is shown in
Figure 5.18 for the purpose of finding whether there is any pressure influence on the
intensity of C=O band of aldehyde formed.
1.4
1.2
CO2-1250 psig-15 min
Absorbance
1
N2-1250 psig-15 min
N2-1060 psig-15 min
0.8
N2-810 psig-15 min
0.6
N2-510 psig-15 min
0.4
0.2
1800
1700
1600
Wavenumber (1/cm)
Figure 5.18: Comparison of the spectra taken at varying total pressures in the presence of
N2 in the 1600-1800 cm-1 region.
Figure 5.18 shows band at 1645 cm-1 due to 1-hexene, and it also shows band at
~1720 cm-1. The presence of shoulder is hard to discern and spectra appear similar,
therefore it can not be concluded whether aldehyde rate of formation varies with pressure.
167
The presence of shoulder and the intensity in case when reaction is carried in CO2 can
also be seen in Figure 5.18. Therefore, it appears that even if aldehyde was formed, the
rate of formation in the presence of nitrogen is much slower.
Figure 5.19 shows plot of area counts vs. time for 1-hexene disappearance during
reactions carried in the presence of N2 at different total pressures. The experimental vales
are represented by points, while solid lines represent the model prediction.
3.5
3
Area counts
2.5
2
N2; 510 psig
N2; 810 psig
1.5
N2; 1060 psig
N2; 1250 psig
1
0.5
0
0
100
200
300
400
500
600
Time (min)
Figure 5.19: Area counts vs. time for 1-hexene disappearance during reactions carried out
in the presence of N2 at varying total pressures.
Rate of 1-hexene disappearance was calculated by integrating the area under the
peak at 1650 cm-1 taking points at 5, 15, 30 and 60 minutes of reaction. The rate constants
were calculated by fitting the data according to the first order disappearance of 1-hexene
as given by equation (2). Since at 510 and 1060 psig the phase separation occurred early
168
in reaction, the rate constants could not be calculated for these two cases. The effect of
pressure on the rate of 1-hexene disappearance can then be deduced from equation (1).
The plot of ln k vs. pressure (Figure 5.20) reveals that ∆V* is 278 ml/mol. The
positive value indicates that the rate of 1-hexene disappearance is inhibited by increasing
pressure with N2. Even though the system behavior should not be judged on the base of
two points the rate of 1-hexene disappearance does appear to decrease with increase in
pressure.
7
6.8
y = -0.0091x + 7.0922
6.6
ln(k1)
6.4
6.2
6
5.8
5.6
30
40
50
60
70
80
90
Pressure (atm)
Figure 5.20: Effect of total pressure on rate of 1-hexene disappearance in
hydroformylation carried out in the presence of N2.
The influence of nitrogen on the hydroformylation reaction has been previously
studied [172, 173, 174]. Bianchi et al. observed that the initial rate of cyclohexene
hydroformylation decreased by 28.4 % as the pressure of N2 was increased from 0 to
169
7250 psi at 100°C with Co2(CO)8 as the catalyst [174]. Formation of a cobalt complex
that contains nitrogen was thought to be responsible for observed behavior. A decrease in
concentration of a catalytically active species through which aldehyde would be formed,
led to a decrease in the rate of reaction.
Caporali et al. studied the effect of nitrogen on the RhH(CO)(PPh3)3 catalyzed
hydroformylation of 1-hexene [175]. The authors observed the linear increase of the
reaction rate in the range of 0-3625 psi, but further increase in nitrogen pressure (3625 to
20300 psi) led to no change in the initial rate. The same group also studied the influence
of additional gas on isomerization of 1-hexene in the presence of Ru(CO)3(PPh3)2 [176].
The conversion of 1-hexene decreased from 55.9 to 44.1 % as the pressure of nitrogen
was increased from 0 to 3538 psi. Formation of the nitrogen containing ruthenium
complex to which 1-hexene could not coordinate was thought to be the cause for reduced
rate of isomerization. Caporali et al. suggested that even though dinitrogen and alkene
competed for the coordination to unsaturated Rh complex, the rate determining step was
not the formation of the π-complex between the catalyst and the alkene, but rather was
activation of the dihydrogen or an acyl formation [175].
The results obtained suggest that 1-hexene disappearance probably decreased with
an increase in the total reaction pressure. This result would be in agreement with Salvini
et al. [176], who reported that 1-hexene conversion from isomerization decreased with an
increase in nitrogen pressure. However, the same group also reported that rate of
hydroformylation increased by about 6 % when the pressure of nitrogen was increased
from 0 (no nitrogen present) to 1812.5 psi [175]. The spectra reported in Figure 5.18,
however, did not reveal whether the aldehyde formation also increased with pressure, as
170
the small band due to C=O stretch of the aldehyde at ~1735 cm-1 was obscured by the
broad band at 1720 cm-1.
Previous analysis was based on the decrease of 1-hexene concentration over time
as evident from the decrease in the intensity of the band at 1645 cm-1. 1-hexene was
expected to be isomerized and/or hydroformylated. That isomerization is occurring can
be discerned from the spectra obtained by subtracting spectra obtained at 5th minute from
the spectra obtained at 600th minute. Figure 5.21 shows negative bands due to 1-hexene
(3090, 990 and 915 cm-1) and a positive bands at 976 and ~3030 cm-1. These two bands
are assigned to C-H stretch and C-H out-of-plane bending vibrations of 2-hexenes as
previously discussed.
1.6
1.6
1.4
1.4
Absorbance
N2-1250 psig-(600-5)
1.2
1.2
1
1
N2-1060 psig-(600-5)
N2-810 psig (600-5)
N2-510 psig-(600-5)
0.8
0.8
0.6
3100
3000
Wavenumber (1/cm)
0.6
950
850
Figure 5.21: The difference of the spectra obtained under hydroformylation conditions in
the presence of N2, 3100-300- and 1000-850 cm-1 regions.
171
The formation of (Rh(CO)2Lx)2 can be deduced from Figure 5.16, since the band
due to bridging carbonyls of this complex appear at ~1800 cm-1. Figure 5.22 represents
spectra obtained by subtracting spectrum obtained at 5th minute from the spectrum
obtained at 600th minute of reaction. The band due to dimer appears the smallest at the
highest pressure, as was also observed in reactions carried out in the presence of CO2.
The plot of intensity of the area under the band observed at ~1800 cm-1 at 600
minutes of reaction vs. pressure, Figure 5.23, shows that the intensity of this band
decreases with the pressure. Thus, the dimer formation is suppressed by increasing the
total pressure.
1.8
1.6
N2-1250 psig
Absorbance
1.4
N2-1060 psig
1.2
N2-810 psig
1
N2-510 psig
0.8
0.6
1850
1750
Wavenumber (1/cm)
Figure 5.22: The difference of the spectra obtained under hydroformylation conditions in
the presence of N2, 1850-1750 cm-1 region.
172
Area under the band at ~1800 1/cm
5
4
3
2
30
40
50
60
70
80
90
Pressure (atm)
Figure 5.23: Pressure vs. integrated area under the band at 1800 cm-1 observed at 600th
minute of reactions carried out in the presence of N2 at varying total
pressures.
5.2.2 Species Present After reaction/Resting state of the catalyst
The spectra of the catalyst was taken after the gas phase mixture was removed by
flowing nitrogen for 10 minutes in order to deduce the species that are present on the
catalyst surface. Figure 5.24 shows spectra taken after reaction has been accomplished at
different total pressures.
At all pressures bands at ~2077 and 2000 with the shoulder at 2015 cm-1 are
observed. The bands shift slightly but it is thought that this is due to the resolution of the
instrument and not the strength of the Rh-C bond. The band at 2077 cm-1 is due to
Rh(CO)2Lx moiety. The other CO band of the HRh(CO)2Lx moiety is either found at
173
2.8
2.6
2.4
2.2
1250 psig in N2, post Rxn
2
Absorbance
1.8
1060 psig in N2, post Rxn
1.6
1.4
810 psig in N2, post Rxn
1.2
1
510 psig in N2, post Rxn
0.8
0.6
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 5.24: IR spectra of the catalyst shortly after being used for hydroformylation of 1hexene in the presence of N2 at different total pressures.
2015 or 2000 cm-1. As discussed before, the presence of monocarbonyl species can not be
excluded.
The angles between the two CO ligands that give vibrations at 2077 and 2000 cm1
, as well as 2077 and 2015 cm-1 were calculated using equation (3) and are given in
Table 5.5. The angle between the two CO ligands in Rh complex does change slightly but
is close to 90 °, therefore, it can be concluded that cis-HRh(CO)2Lx complex is present
after hydroformylation on the surface of phosphinated silica support. The same behavior
was observed after the reactions accomplished in the presence of CO2, therefore, it
appears that slight distortion of the structure of the Rh complex is due to pressure.
174
Table 5.5: The calculated angles between the two carbonyls for possible dicarbonyl metal
complexes observed after hydroformylation carried out in the presence of N2 at
different total pressures.
Ө [°] between the carbonyl
Ө [°] between the carbonyl
ligands (bands at 2077 and
ligands (bands at 2080 and
2000 cm-1)
2015 cm-1)
1250
93.4
89.6
1060
90
87.2
810
89
88.2
510
86.4
84.6
Pressure (psig)
In the Figure 5.24 it can also be seen that band at 1800 cm-1 (assigned to
(Rh(CO)2Lx)2) and the band due to unknown complex at 1720 cm-1 are present.
The spectra of the catalyst after it was left in the air for 1 day is presented in
Figure 5.25 for the reaction carried out at 1250 psig. The spectrum of the aged sample
reveals that two bands at 2082 and 2005 cm-1 are present in the terminal carbonyl region.
Comparison of the spectra taken after reaction and the aged sample reveals that no
shoulder is present. Therefore it is likely that RhH(CO)2Lx was present during
hydroformylation reaction.
175
1.4
1.2
Absorbance
1
1250 psig in N2, aged sample
0.8
0.6
1250 psig in N2, post Rxn
0.4
0.2
0
2200
2100
2000
1900
1800
1700
1600
Wavenumber (1/cm)
Figure 5.25: Comparison of IR spectra obtained shortly after reaction is carried in the
presence of N2 and of aged sample.
The spectra taken for aged catalyst used at different pressures is presented in
Figure 5.26. The spectra appear similar independent of the reaction pressure. Comparison
of the spectra of the aged samples suggests that RhH(CO)2Lx is the active catalytic
species present on the catalyst. The bands appear of almost equal intensity suggesting that
two CO molecules are cis to each other.
Rh dimer (νCO=1800 cm-1) as well as the complex with the band at 1720 cm-1 are
also present on the aged sample suggesting that these species are stable. The plot of area
under these two bands (Figure 5.27) suggests that these complexes do not change when
left in air, thus confirming their stability.
176
2.8
2.6
2.4
2.2
1250 psig in N2, 1 day
2
Absorbance
1.8
1060 psig in N2, 1 day
1.6
1.4
810 psig in N2, 1 day
1.2
1
0.8
510 psig in N2, 1 day
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 5.26: IR spectra of the catalyst 1 day after being used for hydroformylation of 1hexene in the presence of N2 at different total pressures.
10
9
8
Area under the bands
7
6
1710, 10 min afterRxn
5
1710, 1 day after Rxn
1800, 1 day after Rxn
4
1800, 10 min after Rxn
3
2
1
0
30
40
50
60
70
80
90
Pressure (atm)
Figure 5.27: Area counts vs. pressure plot for bridged carbonyls observed after reaction
carried out in the presence of N2.
177
It was observed that CO2 formation occurs in reactions run in the presence of N2,
regardless of total pressure. This was evident from appearance of band at 2362 and ~2332
cm-1. So, the Rh complex catalyzes formation of carbon dioxide. Figure 5.28 presents the
difference of the spectra taken at 5 and 15 minutes of reaction.
1.2
1
N2-1250psi; 15 min
Absorbance
0.8
N2-1060psi; 15 min
0.6
N2-810psig; 15 min
0.4
N2-510psig; 15 min
0.2
0
2450
2400
2350
2300
2250
Wavenumber (1/cm)
Figure 5.28: The difference of the spectra obtained under hydroformylation conditions in
the presence of N2, 2450-2250 cm-1 region.
5.3 Effect of additional gas on Hydroformylation Reaction
5.3.1 Species Formed at 500 psig in the Presence of Different Additional Gas
Spectra taken at 5th and 600th minute after onset of the reaction with CO2 and N2
as additional gases are presented in Figures 5.29 and 5.30, respectively.
178
Absorbance
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
3000
2800
0
2000
CO2, 500 psig, 5 min
N2, 510 psig, 5 min
0
1800
1600
Wavenumber (1/cm)
1000
800
Figure 5.29: IR spectra of the catalyst 5 minutes after the onset of hydroformylation
Absorbance
reaction at ~ 500 psig in CO2 and N2.
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
CO2, 500 psig, 600 min
0
3000
2800
0
2000
N2, 510 psig, 600 min
0
1000
1800
1600
Wavenumber (1/cm)
800
Figure 5.30: IR spectra of the catalyst 600 minutes after the onset of hydroformylation
reaction at ~ 500 psig in CO2 and N2.
179
The spectra appear similar, indicating that similar species might have formed
whether carbon dioxide or nitrogen is added to the system.
Figure 5.31 compares the spectra at 15 minutes of reaction. No differences exist
between the two cases and the presence of aldehyde can not be discerned.
1.4
1.2
Absorbance
1
CO2, 500 psig, 15 min
0.8
0.6
N2, 510 psig, 15 min
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 5.31: IR spectra of the catalyst under hydroformylation conditions in the presence
of N2 and CO2, 1800-1600 cm-1 region.
The spectra taken after removal of gas phase mixture of reactants and additional
gas reveal presence of HRh(CO)2Lx and possibly HRh(CO)Lx. The spectra appear similar
with the bands at ~2076, 2015 and 2001 cm-1. The band at 1800 cm-1 due to
(Rh(CO)2Lx)2 as well as band at 1720 cm-1 is also present.
180
2.8
2.6
2.4
2.2
2
Absorbance
1.8
CO2, 500 psig, post Rxn
1.6
1.4
1.2
N2, 510 psig, post Rxn
1
0.8
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 5.32: IR spectra of the catalyst after hydroformylation reaction carried at ~500
psig in the presence of CO2 and N2.
5.3.2 Species Formed at 840 psig in the Presence of Different Additional Gas
The spectra obtained during reaction carried out at 840 psig total pressure and
100°C with CO2 and N2 as additional gases is presented in Figures 5.33 and 5.34 for 5th
and 600th minute of reaction, respectively.
In all case bands at 1800 and 1710 cm-1 are formed. However, as evident from
Figures 5.34, the small shoulder at 1735 cm-1 is formed only in CO2. This suggests that
some aldehyde was formed when the reaction was performed in carbon dioxide.
181
Absorbance
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
3000
2800
CO2, 840 psig, 5 min
N2, 810 psig, 5 min
0
0
2000
1800
1000
1600
800
Wavenumber (1/cm)
Figure 5.33: IR spectra of the catalyst 5 minutes after the onset of hydroformylation
Absorbance
reaction at ~ 840 psig in CO2 and N2.
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.2
0.2
0.4
0.2
0
3000
2800
0
2000
CO2, 840 psig, 600 min
N2, 810 psig, 600 min
0
1800
1600
1000
800
Wavenumber (1/cm)
Figure 5.34: IR spectra of the catalyst 600 minutes after the onset of hydroformylation
reaction at ~ 840 psig in CO2 and N2.
182
The spectra taken after removal of gas phase mixture appear similar with the
bands at ~2075, ~2015, ~1999, 1800 and 1710 cm-1 (Figure 5.35). The resting state of the
catalyst is cis-RhH(CO)2Lx irrespective of additional gas.
2.8
2.6
2.4
2.2
2
Absorbance
1.8
1.6
CO2, 840 psig, post Rxn
1.4
1.2
N2, 810 psig, post Rxn
1
0.8
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 5.35: IR spectra of the catalyst after hydroformylation reaction carried at ~ 840
psig in the presence of CO2 and N2.
5.3.3 Species Formed at ~ 1040 psig in the Presence of Different Additional Gas
The spectra of the catalyst and the reaction mixture at 5th and 600th minute for
hydroformylation reactions performed in CO2 and N2 as additional gas at ~ 1040 psig is
presented in Figures 5.36 and 5.37, respectively.
Initially the bands due to 1-hexene are present as well as band at 1720 cm-1.
However, as evident from Figure 5.37, the shoulder appears at 1735 cm-1 when reaction
is performed in CO2. This indicates that aldehyde is formed in carbon dioxide but its
presence in nitrogen can not be discerned.
183
Absorbance
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
2000
0
3000
2800
CO2, 1020 psig, 5min
N2, 1060 psig, 5min
0
1800
1000
1600
800
Wavenumber (1/cm)
Figure 5.36: IR spectra of the catalyst 5 minutes after the onset of hydroformylation
Absorbance
reaction at ~ 1040 psig in CO2 and N2.
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0
3000
2800
0
2000
CO2,1020 psig, 600 min
N2, 1060 psig, 600 min
0.2
0
1800
1600
1000
800
Wavenumber (1/cm)
Figure 5.37: IR spectra of the catalyst 600 minutes after the onset of hydroformylation
reaction at ~ 1040 psig in CO2 and N2.
184
Figure 5.38 compares the spectra taken in the presence of CO2 and N2 at 15th
minute of reaction. The slight shoulder appears when reaction is performed in CO2
suggesting that indeed more aldehyde might be present in this case.
Absorbance
0.4
CO2, 1020 psig, 15 min
0.2
N2, 1060 psig, 15 min
0
1800
1700
1600
Wavenumber (1/cm)
Figure 5.38: IR spectra of the catalyst under hydroformylation conditions in the presence
of N2 and CO2 at ~1040 psig, 1800-1600 cm-1 region.
The spectra taken after removal of gas phase mixture reveal bands at ~2077, 2015
and ~1998 in both cases (Figure 5.39). The resting state of the catalyst is irrespective of
pressure as well as of additional gas and is cis-RhH(CO)yLx,
185
2.8
2.6
2.4
2.2
2
Absorbance
1.8
CO2,1020 psig, post Rxn
1.6
1.4
1.2
N2, 1060 psig , post Rxn
1
0.8
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 5.39: IR spectra of the catalyst after hydroformylation reaction carried at ~1040
psig in the presence of CO2 and N2.
5.3.4 Species Formed at 1250 psig in the Presence of Different Additional Gas
Even larger differences are observed in the intensity of the bands in 1740-1710
cm-1 region between cases where CO2 and N2 are used as additional gas are evident from
spectra taken at 5th and 600th minute of hydroformylation carried out at total pressure of
1250 psig and 100°C. Theses spectra are presented in Figures 5.40 and 5.41, respectively.
186
Absorbance
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
2000
0
3000
2800
CO2, 1250 psig, 5 min
N2, 1250 psig, 5 min
0
1800
1000
1600
800
Wavenumber (1/cm)
Figure 5.40: IR spectra of the catalyst 5 minutes after the onset of hydroformylation
Absorbance
reaction at 1250 psig in CO2 and N2.
2.8
2.8
2.8
2.6
2.6
2.6
2.4
2.4
2.4
2.2
2.2
2.2
2
2
2
1.8
1.8
1.8
1.6
1.6
1.6
1.4
1.4
1.4
1.2
1.2
1.2
1
1
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
3000
2800
0
2000
CO2, 1250 psig, 600 min
N2, 1250 psig, 600 min
0
1800
1600
1000
800
Wavenumber (1/cm)
Figure 5.41: IR spectra of the catalyst 600 minutes after the onset of hydroformylation
reaction at 1250 psig in CO2 and N2.
187
The band at 1735 cm-1 appear in case of CO2 and is completely absent in N2. The
other bands, at 1720 and 1800 cm-1 are present in both cases. Since presence of two
phases might mask the presence of total amount of aldehyde present, the spectra taken at
15th minute of reaction where single phase behavior is expected is presented in Figure
5.42. The shoulder at 1735 cm-1 is clearly present when the reaction is carried out in CO2,
thus confirming that aldehyde formation is enhanced by the presence of CO2.
1.4
1.2
1
Absorbance
CO2, 1250 psig, 15 min
0.8
0.6
N2, 1250 psig, 15min
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 5.42: IR spectra of the catalyst under hydroformylation conditions in the presence
of N2 and CO2 at 1250 psig, 1800-1600 cm-1 region.
After removal of gas phase reaction mixture and additional gas, CO2 and N2,
bands at ~2078 and ~2000 cm-1 with a shoulder at 2015 cm-1 are present. As argued
before, the peaks at 2078 and 2000 cm-1 might be due to dicarbonyl Rh complex. Then
the band at 2015 cm-1 could be due to monocarbonyl or even due to Rh-H vibration.
188
2.8
2.6
2.4
2.2
2
Absorbance
1.8
CO2, 1250 psig, post Rxn
1.6
1.4
N2, 1250 psig, post Rxn
1.2
1
0.8
0.6
0.4
0.2
0
2200
2000
1800
1600
Wavenumber (1/cm)
Figure 5.43: IR spectra of the catalyst after hydroformylation reaction carried at 1250
psig in the presence of CO2 and N2.
The most notable difference in the appearance of the spectra is the presence of
shoulder at 1735 cm-1 in CO2 at 840 and 1050 psig but most significantly at 1250 psig. It
can not be argued that no aldehyde was formed in N2, since the band due to aldehyde
C=O stretch might be below the detection limit. The results show that aldehyde formation
is enhanced when reaction was accomplished in the presence of CO2.
Catalysts such as RhH(CO)(PPh3)3 catalyze isomerization of 1-alkenes [177].
Hydroformylation of branched alkenes is expected to be slower compared to linear
alkene. Slower hydroformylation of 2-hexene can be the reason for the absence of the
band at 1735 cm-1 in nitrogen.
Salvini et al. studied the influence of nitrogen and helium on isomerization of 1hexene in the presence of Ru(CO)3(PPh3)2 [176]. They reported that nitrogen has a
189
negative effect on conversion of 1-hexene and ascribed that to formation of a ruthenium
complex containing nitrogen. However, in the presence of helium, the conversion of 1hexene slightly increased from 55.9 to 61 % when the pressure of helium increased from
72.5-3726.5 psi. Caporali et al. reported that presence of helium had no influence on
initial rate of 1-hexene hydroformylation as the increase of helium from 0 (no helium
present) to 3625 psi decreased the initial rate from 0.67 to 0.63 mmol per hour [175].
However, the addition of nitrogen increased the rate from 0.67 to 1.11 mmol per hour
when 3625 psi of nitrogen was added to the system. In the literature there are some
indications that metal complexes containing nitrogen might form and since the results
indicate that aldehyde formation in the presence of N2 is suppressed, the reaction was
also accomplished in helium at 1250 psig.
Figure 5.44 shows comparison of the 1800-1600 cm-1 region for the
hydroformylation reaction in helium, nitrogen and CO2 at 100 °C and 1250 psig. The
band at ~1645 cm-1 is due to C=C stretch of 1-hexene. In both nitrogen and helium, a
band at 1714 and 1719 cm-1, respectively, due to unknown complex is present. Even
though this complex is present in CO2 also, the shoulder at 1735 cm-1 is only observed in
the presence of CO2. Therefore, it can be concluded that the major reason for suppressed
aldehyde formation in N2 is not formation of Rh complexes containing nitrogen.
190
1.6
1.4
1.2
CO2, 1250 psig, 15 min
Absorbance
1
0.8
N2, 1250 psig, 15 min
0.6
He, 1250 psig, 15 min
0.4
0.2
0
1800
1700
1600
Wavenumber (1/cm)
Figure 5.44: IR spectra of the catalyst under hydroformylation conditions in the presence
of He, N2 and CO2, 1800-1600 cm-1 region.
The results show that increasing pressure increases the rate of aldehyde formation
in the presence of CO2. However, the intermediate complexes formed are independent of
pressure and the presence of additional gas. Therefore, it appears that there are some
other phenomena that occur in CO2 which leads to enhanced hydroformylation. The
pressure increase was achieved by addition of carbon dioxide. The increase in pressure of
CO2 leads to increase of density. Therefore, the effect of pressure observed might
actually be due to a change in mixture density. With increase of the density the transport
properties will change. Additionally, literature reports have suggested that SCF can affect
the outcome of reaction by increasing local concentration of reactants through the
phenomena called clustering. Even though the evidence of this phenomenon could not be
obtained directly from this study, this effect can be operating in the system as increase in
191
local concentration of the reactants around the catalyst would accelerate the reaction.
Additionally, the partial molar volume of aldehyde was found to be larger and more
negative than the partial molar volume for 2-hexene formation [7], which implies that as
pressure is increased, the aldehyde formation is favored over 2-hexene formation.
192
CHAPTER 6
CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
The behavior of the rhodium complex immobilized on phosphinated silica under
hydroformylation conditions in supercritical CO2 was studied by Diffuse Reflectance
Infrared Fourier Transform Spectroscopy. 1-Hexene was used as a model substrate.
•
The rhodium complex immobilized on phosphinated silica support reacts with carbon
monoxide to create cis-RhCl(CO)2Lx. The presence of carbon dioxide does not affect
the catalytic species that are developed through interaction with CO.
•
Carbon dioxide dissociates in the presence of rhodium immobilized on phosphinated
silica to produce RhCl(CO)yLx.
•
Under an atmosphere of hydrogen, a band at 1990 cm-1 was developed but could not
be conclusively assigned to a Rh-H stretch.
•
Hydroformylation reaction was carried out at 100 °C and 1250 psig, CO:H2:1hexene=10:10:1 in CO2. Aldehyde and 2-hexenes were observed to form. The
acylrhodium complex that is proposed as an active intermediate could not be
identified under reaction conditions.
•
The resting state of the catalyst was determined to be HRh(CO)2Lx. The resting state
of the catalyst is independent of pressure and the presence of an additional gas. This
193
also suggests that the rate limiting step is either CO dissociation or alkene
coordination when the reaction is carried out in CO2 at 1250 psig.
•
A rhodium dimer, [Rh(CO)2Lx]2, where x is 2 or 4, was also formed under
hydroformylation conditions. The Rh dimer formation is observed at all pressure
studied independent whether reaction is carried in the presence of CO2 or N2. The
formation of the Rh dimer decreases as the reaction pressure increases
•
The hydroformylation reaction was studied at 100 °C at different total pressures,
achieved by adding CO2. It was observed that rate of 1-hexene disappearance
increases as the reaction pressure increase. Based on the intensity of the C=O stretch
of aldehyde, it was concluded that aldehyde formation also increase as the reaction
pressure is increased.
•
The hydroformylation reaction was also studied at different total pressures, achieved
by adding N2, at 100 °C. The effect of pressure on hydroformylation activity could
not be determined as the C=O stretch of aldehyde was overlapped by unidentified
band at ~1720 cm-1.
6.2 Recommendations
Within the current research, it was found that increasing reaction pressure by
adding CO2 could have an impact on the reaction rate that could not be explained based
on the pressure effect. The following studies will be useful and interesting to perform to
clarify and complement the results of the current research:
•
The reactions at varying total pressures achieved by adding CO2 or N2 should be
studied in a batch reactor to determine the kinetics of the reaction.
194
•
There are reports in the literature that nitrogen can interact with the catalyst but that
helium is truly inert. Therefore, kinetics of the reactions at varying total pressures
achieved by adding helium should also be studied and compared with reactions in the
presence of CO2 and/or N2.
•
The current study did not show that pressure had any effect on the formation of
reaction intermediates. It would be beneficial to study the pressure effect employing
homogeneous rhodium-based catalyst by FTIR. Studies employing solid catalysts
involve broad bands and low signals making identification of the complexes difficult.
•
Rh-H stretch could not be identified with certainty. This is because the Rh-H stretch
overlapped the Rh-CO stretch. Hydrogen containing species could, however, be
identified by H/D substitution. Since the mass of deuterium is larger, the frequency of
Rh-H stretch would decrease by few hundreds of wavenumbers. This could be used
to confirm the presence of HRh(CO)yLx. Alternatively, 13CO could be used, except in
this case bands due to Rh-CO stretch would be shifted, so the region between 2100
and 1900 cm-1 would be clear of carbonyl species.
•
Preliminary studies carried out in the high pressure flow system have shown that the
rhodium complex immobilized on phosphinated silica is stable for 125 hours and that
rhodium complex immobilized on MCM-41 deactivates slowly over time. The results
suggest that deactivation of immobilized rhodium catalyst is due to rhodium leaching
and not due to oxidation of ligand as suggested by literature. This could be more
clearly evaluated by DRIFTS studies during reaction in a continuous system.
195
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217
APPENDIX
218
APPENDIX 1
CHEMCAD OUTPUT FOR THE PHASE BEHAVIOR IN
THE PRESENCE OF CO2
CO2, P=500 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
1.0000
0.0091
0.0091
0.0009
0.0000
0.0029
Time: 13:20:55
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0091
0.0091
0.0009
0.0000
0.0029
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
1.0000
0.0090
0.0090
0.0008
0.0001
0.0029
219
Time: 13:26:26
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0090
0.0090
0.0008
0.0001
0.0029
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.99504
0.0089
0.0089
0.0007
0.0002
0.0029
Time: 13:28:56
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0089
0.0089
0.0007
0.0001
0.0029
0.0000
0.0000
0.0000
0.0001
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.98935
0.0088
0.0088
0.0006
0.0003
0.0029
Time: 13:31:20
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0088
0.0088
0.0006
0.0001
0.0029
0.0000
0.0000
0.0001
0.0002
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.98411
0.0087
0.0087
0.0006
0.0004
0.0029
220
Time: 13:35:19
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0087
0.0087
0.0005
0.0001
0.0029
0.0000
0.0000
0.0001
0.0002
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.97917
0.0086
0.0086
0.0005
0.0005
0.0029
Time: 13:39:44
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0086
0.0086
0.0004
0.0001
0.0029
0.0000
0.0000
0.0001
0.0003
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.97449
0.0085
0.0085
0.0004
0.0006
0.0029
Time: 13:41:44
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0085
0.0085
0.0003
0.0001
0.0029
0.0000
0.0000
0.0001
0.0004
0.0000
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.97001
0.0085
0.0085
0.0003
0.0006
0.0029
221
Time: 13:44:09
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0084
0.0084
0.0002
0.0001
0.0029
0.0000
0.0000
0.0001
0.0005
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.96569
0.0084
0.0084
0.0002
0.0007
0.0029
Time: 13:45:57
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0084
0.0083
0.0001
0.0001
0.0029
0.0000
0.0000
0.0000
0.0006
0.0000
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.96150
0.0083
0.0083
0.0001
0.0008
0.0029
Time: 13:47:55
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0083
0.0082
0.0001
0.0001
0.0029
0.0000
0.0000
0.0000
0.0007
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
500.0000*
0.95742
0.0082
0.0082
0.0000
0.0009
0.0029
222
Time: 13:49:57
2
Vapor
98.0000
500.0000
1.0000
3
Liquid
98.0000
500.0000
0.00000
0.0082
0.0081
0.0000
0.0001
0.0029
0.0000
0.0000
0.0000
0.0008
0.0000
CO2, P=840 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
1.0000
0.0120
0.0120
0.0015
0.0000
0.0246
Time: 16:27:31
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0120
0.0120
0.0015
0.0000
0.0246
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
1.0000
0.0118
0.0118
0.0014
0.0002
0.0246
Time: 16:29:51
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0118
0.0118
0.0014
0.0002
0.0246
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.99880
0.0117
0.0117
0.0012
0.0003
223
Time: 16:32:13
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0117
0.0117
0.0012
0.0003
0.0000
0.0000
0.0000
0.0000
Carbon Dioxide
0.0246
0.0246
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.99390
0.0116
0.0116
0.0010
0.0005
0.0246
Time: 16:34:28
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0115
0.0115
0.0010
0.0003
0.0245
0.0000
0.0000
0.0001
0.0002
0.0001
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.98938
0.0114
0.0114
0.0009
0.0006
0.0246
Time: 16:37:02
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0114
0.0114
0.0008
0.0003
0.0245
0.0000
0.0000
0.0001
0.0003
0.0001
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.98515
0.0113
0.0113
0.0008
0.0008
0.0246
224
Time: 16:39:52
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0112
0.0112
0.0007
0.0003
0.0245
0.0000
0.0000
0.0001
0.0005
0.0001
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.98115
0.0111
0.0111
0.0006
0.0009
0.0246
Time: 16:42:11
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0111
0.0111
0.0005
0.0003
0.0244
0.0000
0.0000
0.0001
0.0006
0.0002
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.97732
0.0110
0.0110
0.0005
0.0010
0.0246
Time: 16:44:35
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0109
0.0109
0.0004
0.0003
0.0244
0.0000
0.0000
0.0001
0.0007
0.0002
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.97365
0.0108
0.0108
0.0003
0.0012
0.0246
225
Time: 16:46:24
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0108
0.0108
0.0002
0.0003
0.0244
0.0000
0.0000
0.0001
0.0009
0.0002
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.97010
0.0106
0.0106
0.0002
0.0014
0.0246
Time: 16:48:14
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0106
0.0106
0.0001
0.0003
0.0243
0.0000
0.0001
0.0000
0.0010
0.0003
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
840.0000*
0.96665
0.0105
0.0105
0.0000
0.0015
0.0246
Time: 16:50:24
2
Vapor
98.0000
840.0000
1.0000
3
Liquid
98.0000
840.0000
0.00000
0.0105
0.0104
0.0000
0.0003
0.0243
0.0000
0.0001
0.0000
0.0012
0.0003
CO2, 1020 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
1.0000
0.0140
0.0140
0.0014
0.0000
226
Time: 16:53:05
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0140
0.0140
0.0014
0.0000
0.0000
0.0000
0.0000
0.0000
Carbon Dioxide
0.0680
0.0680
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
1.0000
0.0139
0.0139
0.0013
0.0001
0.0680
Time: 16:54:58
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0139
0.0139
0.0013
0.0001
0.0680
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
1.0000
0.0136
0.0136
0.0010
0.0004
0.0680
Time: 16:56:56
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0136
0.0136
0.0010
0.0004
0.0680
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
1.0000
0.0133
0.0133
0.0007
0.0007
0.0680
227
Time: 16:58:48
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0133
0.0133
0.0007
0.0007
0.0680
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
0.99787
0.0132
0.0132
0.0006
0.0008
0.0680
Time: 17:02:43
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0132
0.0132
0.0006
0.0007
0.0679
0.0000
0.0000
0.0000
0.0001
0.0001
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
0.99561
0.0130
0.0130
0.0004
0.0010
0.0680
Time: 17:00:33
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0130
0.0130
0.0004
0.0007
0.0679
0.0000
0.0000
0.0000
0.0003
0.0001
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
0.99341
0.0129
0.0129
0.0003
0.0011
0.0680
228
Time: 17:05:16
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0129
0.0129
0.0003
0.0007
0.0678
0.0000
0.0000
0.0000
0.0004
0.0002
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
0.99127
0.0127
0.0127
0.0001
0.0013
0.0680
Time: 17:07:13
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0127
0.0127
0.0001
0.0007
0.0677
0.0000
0.0000
0.0000
0.0005
0.0003
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1020.0000*
0.98918
0.0126
0.0126
0.0000
0.0014
0.0680
Time: 17:09:16
2
Vapor
98.0000
1020.0000
1.0000
3
Liquid
98.0000
1020.0000
0.00000
0.0126
0.0126
0.0000
0.0007
0.0677
0.0000
0.0000
0.0000
0.0007
0.0003
CO2, 1250 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0093
0.0093
0.0009
0.0000
0.0840
229
Time: 17:11:58
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0093
0.0093
0.0009
0.0000
0.0840
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0091
0.0091
0.0007
0.0002
0.0840
Time: 17:13:53
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0091
0.0091
0.0007
0.0002
0.0840
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0089
0.0089
0.0005
0.0004
0.0840
Time: 17:17:07
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0089
0.0089
0.0005
0.0004
0.0840
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0086
0.0086
0.0002
0.0007
0.0840
230
Time: 17:19:03
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0086
0.0086
0.0002
0.0007
0.0840
0.0000
0.0000
0.0000
0.0000
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005b
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Carbon Dioxide
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0084
0.0084
0.0000
0.0009
0.0840
231
Time: 17:20:44
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0084
0.0084
0.0000
0.0009
0.0840
0.0000
0.0000
0.0000
0.0000
0.0000
APPENDIX 2
CHEMCAD OUTPUT FOR THE PHASE BEHAVIOR IN
THE PRESENCE OF N2
N2, 510 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
1.0000
0.0093
0.0093
0.0009
0.0000
0.0030
Time: 19:04:47
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0093
0.0093
0.0009
0.0000
0.0030
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
1.0000
0.0092
0.0092
0.0008
0.0001
0.0030
232
Time: 19:07:03
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0092
0.0092
0.0008
0.0001
0.0030
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.99516
0.0091
0.0091
0.0007
0.0002
0.0030
Time: 19:08:40
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0091
0.0091
0.0007
0.0001
0.0030
0.0000
0.0000
0.0000
0.0001
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.98984
0.0090
0.0090
0.0006
0.0003
0.0030
Time: 19:10:45
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0090
0.0090
0.0006
0.0001
0.0030
0.0000
0.0000
0.0001
0.0002
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.98493
0.0089
0.0089
0.0005
0.0004
0.0030
233
Time: 19:12:23
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0089
0.0089
0.0005
0.0001
0.0030
0.0000
0.0000
0.0001
0.0002
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.98046
0.0089
0.0088
0.0005
0.0005
0.0030
Time: 19:13:57
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0089
0.0088
0.0004
0.0001
0.0030
0.0000
0.0000
0.0001
0.0003
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.97597
0.0088
0.0088
0.0004
0.0005
0.0030
Time: 19:15:39
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0087
0.0087
0.0003
0.0001
0.0030
0.0000
0.0000
0.0001
0.0004
0.0000
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.97179
0.0087
0.0087
0.0003
0.0006
0.0030
234
Time: 19:17:33
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0087
0.0086
0.0002
0.0001
0.0030
0.0000
0.0000
0.0001
0.0005
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.96777
0.0086
0.0086
0.0002
0.0007
0.0030
Time: 19:20:35
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0086
0.0085
0.0001
0.0001
0.0030
0.0000
0.0000
0.0000
0.0006
0.0000
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.96387
0.0085
0.0085
0.0001
0.0008
0.0030
Time: 19:22:31
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0085
0.0085
0.0001
0.0001
0.0030
0.0000
0.0000
0.0000
0.0007
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
510.0000*
0.96007
0.0084
0.0084
0.0000
0.0009
0.0030
235
Time: 19:24:24
2
Vapor
98.0000
510.0000
1.0000
3
Liquid
98.0000
510.0000
0.00000
0.0084
0.0084
0.0000
0.0001
0.0030
0.0000
0.0000
0.0000
0.0008
0.0000
N2, 810 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
1.0000
0.0085
0.0085
0.0008
0.0000
0.0150
Time: 19:26:18
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0085
0.0085
0.0008
0.0000
0.0150
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
1.0000
0.0084
0.0084
0.0008
0.0001
0.0150
Time: 19:27:50
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0084
0.0084
0.0008
0.0001
0.0150
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.99841
0.0083
0.0083
0.0007
0.0002
0.0150
236
Time: 19:29:24
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0083
0.0083
0.0007
0.0001
0.0150
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.99509
0.0082
0.0082
0.0006
0.0003
0.0150
Time: 19:31:21
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0082
0.0082
0.0006
0.0001
0.0150
0.0000
0.0000
0.0000
0.0001
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.99200
0.0082
0.0082
0.0005
0.0003
0.0150
Time: 19:33:15
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0082
0.0082
0.0005
0.0001
0.0150
0.0000
0.0000
0.0000
0.0002
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.98909
0.0081
0.0081
0.0004
0.0004
0.0150
237
Time: 19:35:04
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0081
0.0081
0.0004
0.0001
0.0150
0.0000
0.0000
0.0000
0.0003
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.98634
0.0080
0.0080
0.0003
0.0005
0.0150
Time: 19:36:44
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0080
0.0080
0.0003
0.0001
0.0150
0.0000
0.0000
0.0000
0.0004
0.0000
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.98370
0.0079
0.0079
0.0003
0.0006
0.0150
Time: 19:38:20
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0079
0.0079
0.0002
0.0001
0.0150
0.0000
0.0000
0.0000
0.0004
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.98117
0.0078
0.0078
0.0002
0.0007
0.0150
238
Time: 19:39:50
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0078
0.0078
0.0001
0.0001
0.0150
0.0000
0.0000
0.0000
0.0005
0.0000
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.97872
0.0077
0.0077
0.0001
0.0008
0.0150
Time: 19:41:46
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0077
0.0077
0.0001
0.0001
0.0150
0.0000
0.0000
0.0000
0.0006
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
810.0000*
0.97636
0.0077
0.0077
0.0000
0.0008
0.0150
Time: 19:43:25
2
Vapor
98.0000
810.0000
1.0000
3
Liquid
98.0000
810.0000
0.00000
0.0077
0.0076
0.0000
0.0002
0.0150
0.0000
0.0000
0.0000
0.0007
0.0000
N2, 1060 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
1.0000
0.0120
0.0120
0.0012
0.0000
0.0229
239
Time: 19:53:02
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0120
0.0120
0.0012
0.0000
0.0229
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
1.0000
0.0119
0.0119
0.0011
0.0001
0.0229
Time: 19:54:41
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0119
0.0119
0.0011
0.0001
0.0229
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.99767
0.0118
0.0118
0.0010
0.0002
0.0229
Time: 19:56:19
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0118
0.0118
0.0009
0.0002
0.0229
0.0000
0.0000
0.0000
0.0001
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.99431
0.0116
0.0116
0.0008
0.0004
0.0229
240
Time: 19:57:51
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0116
0.0116
0.0008
0.0002
0.0229
0.0000
0.0000
0.0001
0.0002
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.99124
0.0115
0.0115
0.0007
0.0005
0.0229
Time: 19:59:21
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0115
0.0115
0.0006
0.0002
0.0229
0.0000
0.0000
0.0001
0.0003
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.98838
0.0114
0.0114
0.0006
0.0006
0.0229
Time: 20:00:51
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0114
0.0114
0.0005
0.0002
0.0229
0.0000
0.0000
0.0001
0.0004
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.98569
0.0113
0.0113
0.0005
0.0007
0.0229
241
Time: 20:02:20
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0113
0.0113
0.0004
0.0002
0.0229
0.0000
0.0000
0.0001
0.0005
0.0000
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.98314
0.0112
0.0112
0.0004
0.0008
0.0229
Time: 20:03:59
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0111
0.0111
0.0003
0.0002
0.0229
0.0000
0.0000
0.0001
0.0007
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.98070
0.0110
0.0110
0.0002
0.0010
0.0229
Time: 20:05:36
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0110
0.0110
0.0002
0.0002
0.0229
0.0000
0.0000
0.0000
0.0008
0.0000
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.97835
0.0109
0.0109
0.0001
0.0011
0.0229
242
Time: 20:07:06
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0109
0.0109
0.0001
0.0002
0.0229
0.0000
0.0000
0.0000
0.0009
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1060.0000*
0.97608
0.0108
0.0108
0.0000
0.0012
0.0229
Time: 20:08:33
2
Vapor
98.0000
1060.0000
1.0000
3
Liquid
98.0000
1060.0000
0.00000
0.0108
0.0108
0.0000
0.0002
0.0229
0.0000
0.0000
0.0000
0.0010
0.0000
N2, 1250 psig
X=0
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0100
0.0100
0.0010
0.0000
0.0350
Time: 20:10:26
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0100
0.0100
0.0010
0.0000
0.0350
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
1.0000
0.0099
0.0099
0.0009
0.0001
0.0350
243
Time: 20:11:54
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0099
0.0099
0.0009
0.0001
0.0350
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.2
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.99982
0.0098
0.0098
0.0008
0.0002
0.0350
Time: 20:13:26
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0098
0.0098
0.0008
0.0002
0.0350
0.0000
0.0000
0.0000
0.0000
0.0000
X=0.3
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.99747
0.0097
0.0097
0.0007
0.0003
0.0350
Time: 20:15:04
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0097
0.0097
0.0007
0.0002
0.0350
0.0000
0.0000
0.0000
0.0001
0.0000
X=0.4
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.99527
0.0096
0.0096
0.0006
0.0004
0.0350
244
Time: 20:16:30
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0096
0.0096
0.0006
0.0002
0.0350
0.0000
0.0000
0.0000
0.0002
0.0000
X=0.5
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.99321
0.0095
0.0095
0.0005
0.0005
0.0350
Time: 20:18:12
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0095
0.0095
0.0005
0.0002
0.0350
0.0000
0.0000
0.0000
0.0003
0.0000
X=0.6
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.99124
0.0094
0.0094
0.0004
0.0006
0.0350
Time: 20:20:01
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0094
0.0094
0.0004
0.0002
0.0350
0.0000
0.0000
0.0000
0.0004
0.0000
X=0.7
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.98937
0.0093
0.0093
0.0003
0.0007
0.0350
245
Time: 20:21:55
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0093
0.0093
0.0003
0.0002
0.0350
0.0000
0.0000
0.0000
0.0005
0.0000
X=0.8
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.98757
0.0092
0.0092
0.0002
0.0008
0.0350
Time: 20:23:44
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0092
0.0092
0.0002
0.0002
0.0350
0.0000
0.0000
0.0000
0.0006
0.0000
X=0.9
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.98584
0.0091
0.0091
0.0001
0.0009
0.0350
Time: 20:25:18
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0091
0.0091
0.0001
0.0002
0.0350
0.0000
0.0000
0.0000
0.0007
0.0000
X=1
CHEMCAD 5.3.8
Page 1
Job Name: chemcad8042005c
Stream No.
Stream Name
Temp C
Pres psig
Vapor mole fraction
Flowrates in gmol/sec
Hydrogen
Carbon Monoxide
1-Hexene
1-Heptanal
Nitrogen
Date: 04/08/2005
1
Feed
98.0000*
1250.0000*
0.98416
0.0090
0.0090
0.0000
0.0010
0.0350
246
Time: 20:27:11
2
Vapor
98.0000
1250.0000
1.0000
3
Liquid
98.0000
1250.0000
0.00000
0.0090
0.0090
0.0000
0.0002
0.0350
0.0000
0.0000
0.0000
0.0008
0.0000
APPENDIX 3
STABILITY OF Rh IMMOBILIZED ON PHOSPHINATED
SILICA AND MCM-41 SUPPORTS
A.3.1 Introduction
Previous studies of hydroformylation catalyzed by Rh anchored on phosphinated
silica and on MCM-41 revealed that both phosphorus and rhodium loss occurred [9].
Table A.3.1 gives the weight precent loss of Rh and phosphorus.
TableA.3.1: Elemental analysis of fresh and used catalysts.
Fresh
Catalyst
Used
Phosphorus
Rhodium
Phosphorus
Rhodium
(wt%)
(wt%)
(wt%)
(wt%)
2.91; 2.88
3.78; 4.59
2.72; 2.77
3.40; 3.40
0.95; 0.91
1.84; 1.81
0.76; *
0.6; *
Rh on
phosphinated
Silica
Rh on
phosphinated
MCM-41
* indicate that there was not enough sample to perform multiple analyses
247
Rh anchored on phosphinated silica lost about 5.18% of phosphorus and ~19% of
rhodium. Loss of phosphorus and rhodium for MCM-41 after hydroformylation was 18%
and 67%, respectively. These results were obtained after catalysts were used once in a
batch reactor in a reaction that lasted approximately 400 minutes.
A.3.2 Experimental Equipment
In order to study the stability of heterogeneous catalysis under supercritical
conditions, a continuous system was designed and built. The scheme of the system is
presented in Figure A.3.1. The reactor was purchased from Applied Separation and has a
volume of 24 ml and is rated to 10000 psi and a temperature of 150 ˚C. CO2 was
purchased from O. E. Mayer and had a dip tube so that liquid CO2 could be drawn. It was
pumped by a Haskel liquid pump and the flow rate at STP conditions was approximately
1200 ml/min. Pumped gas was transferred to a storage cylinder (Hoke) from where it was
further regulated to the reaction pressure. A mixture of 50% CO in balance H2 was
purchased from O. E. Mayer and the pressure was increased to 500 psi above reaction
pressure by Haskel gas booster. The gas was boosted into the storage cylinder (Hoke)
from which the pressure was decreased by a regulator to the reaction pressure. A liquid
substrate and standard were pumped from the cylinder by a liquid metering pump (Eldex)
at a rate of approximately 0.05 ml/min. Reactants and solvent were brought together into
a T element and into a reactor. The reactor was placed into a furnace (Applied
Separation) which was kept at a desired temperature. The pressure of the effluent of the
reactor was decreased by a metering valve, and the effluent was directed to a vial with 2-
248
propanol where organics were dissolved while gases were sent to the online gas
chromatograph for analysis.
CO2
cylinder
Chiller
1-hexene
CO/H2
cylinder
To
GC
Furnace
Figure A.3.1: Experimental setup for stability studies.
A.3.3 Experimental Procedure
In each experiment 0.1 g of Rh on support was mixed with 15 g of silicon oxide
(100 mesh) and placed in the reactor. CO/H2 and CO2 each were pumped to
249
approximately 500 psi above the reaction pressure. CO2 was introduced into the reactor
and it was flushed for 5-10 minutes so that air could be displaced. After that, valves were
closed and the pressure set to approximately 800-900 psi. Heating the reactor brought the
pressure to approximately 2400 psi. After setting the desired pressure, the metering valve
was opened and the outlet flow rate set to approximately 1200 ml/min. As the flow rate
stabilized, CO/H2 mixture was introduced. When GC analysis showed that desired ratio
of CO/H2 gas to CO2 was attained, the substrate pump was started and this marked as the
start of the reaction. Gas samples were taken every 40-60 minutes as to make sure that
the ratio was constant. Liquid samples were taken by dissolving the reactor effluent in 18
ml of IPA for 10 minutes. These samples were analyzed by GC equipped with FID
detector.
A.3.4 Results and Discussion
Yield and selectivity were measured during stability studies as they are important
reaction metrics. Yield is defined as mols of aldehydes produced per initial moles of 1hexene. Figure A.3.2 shows yield and selectivity of Rh anchored on phosphinated silica,
respectively. This experiment consisted of two parts; in the first part, up to 60 hours, the
experiment was carried at 75 °C. In the second part, the temperature was increased to 100
°C, and the experiment continued without stopping the reaction. Yield varied with time,
due to variation of total flow rate, comprised mostly of CO2.
250
0.10
3
Yield
Selectivity
0.09
3
0.07
2
0.06
0.05
2
0.04
Selectivity
(L:B)
Yield (Faldehydes/F1-h0)
0.08
1
0.03
0.02
1
0.01
0.00
0
25
50
75
100
125
0
150
Run time (hours)
Figure A.3.2: Aldehyde yield and selectivity during hydroformylation of 1-hexene on
rhodium anchored on phosphinated silica
Small changes in flow rate produced large variation in residence times. The yield
increased as temperature was increased which was expected since it is known that rate of
reaction will increase with increase in temperature. Even though a large scattering of data
was present, the catalyst was active during a period of approximately 125 hours.
Selectivity (L:B) vs. time graph is also shown in Figure A.3.2. It can be seen that
increasing the temperature (around 60 hours) did increase selectivity, but only slightly.
Selectivity was approximately 2.26 throughout the entire run.
Figure A.3.3 shows yield and selectivity of a rhodium catalyst anchored on
MCM-41. Despite the large scattering of data, it can be seen that the catalyst deactivated
with time. Deactivation of Rh on MCM-41 was modeled according to the first order
decay and the solid line shows the model. Deactivation was independent of concentration,
which is consistent with metal leaching. Comparison of yields obtained with Rh anchored
251
on silica and MCM-41 supports revealed that the yield of MCM-41 was nearly a
magnitude order higher. However, this was not observed when the reaction was carried in
the batch reactor. In the batch reactor, even though yield obtained during reaction
catalyzed by MCM-41 was higher, the difference was not as high as 10 fold. Referring
back to Table A.3.1, it can be seen that actually a higher loss of both rhodium and
phosphorus occurred during the reaction carried in the batch reactor. Moreover, 67 % of
Rh anchored on MCM-41 was lost just during the run which lasted 400 minutes. This
further proved that the catalyst anchored on MCM-41 deactivated fast due to leaching of
rhodium. Selectivity vs. time data for Rh anchored on MCM-41 is also shown in Figure
A.3.3. Selectivity is constant at 2.45 for approximately 100 hours. Selectivity for Rh
anchored on MCM-41 is slightly higher than selectivity calculated for the catalyst
anchored on silica. This was actually expected since previous studies [9] showed higher
selectivities for MCM-41 than for the catalyst anchored on silica. Marteel et al. [9]
offered the explanation that this might be due to pore size effect. Constant selectivity
despite the deactivation implies that actually the reaction pathway proposed by Tack
might be operable [153]. According to this pathway, depicted in Figure A.3.4, both
heptanal and 2-methylhexanal are formed by hydroformylation of 1-hexene. 2-ethyl
pentanal can be formed only by hydroformylation of 2-hexenes. During the experiment
performed in the flow reactor no ethyl pentanal was observed, suggesting that 2-hexenes
are not hydroformylated unless 1-hexene was depleted. Due to the fact that this was a
continuous flow reactor so that 1-hexene concentration was constant at any given time,
no hydroformylation of isomerization products occurred. So, no matter how much
252
catalyst was lost, ratio of linear to branched aldehyde was constant, even though the
amount of each varied.
3.5
1.0
Yield
0.9
Selectivity
3.0
2.5
0.7
0.6
2.0
0.5
1.5
0.4
0.3
Selectivity
(L/B)
Yield (Faldehydes/F1-h0)
0.8
1.0
0.2
0.5
0.1
0.0
0
25
50
75
0.0
100
Run time (hours)
Figure A.3.3: Yield and selectivity of rhodium anchored on phosphinated MCM-41.
Figure A.3.4: Reaction pathway for 1-hexene hydroformylation and isomerization.
253