Supporting Information
Screening Lewis Pair Moieties for Catalytic Hydrogenation of CO2 in Functionalized UiO66
1
Jingyun Ye , J. Karl Johnson1,2,*
1
Department of Chemical & Petroleum Engineering, University of Pittsburgh, Pittsburgh,
Pennsylvania 15261, United States
2
Pittsburgh Quantum Institute, Pittsburgh, Pennsylvania 15261, United States
*E-mail: [email protected]
Solvent Effects
The free energies of solvation were estimated in single-point the integral equation formalism
model (IEFPCM) calculations using the UFF atomic radii and the M06-2X/6-311++g(d,p) method
for the gas-phase optimized geometries in Gaussian09 program.1 We have estimated the effect of
implicit solvent models on the hydride attachment energy by computing the free energy difference
between X with an attached hydride [XH] and the free energy of X, so that ∆G = G([XH]) - G(X).
This quantity is different from the hydride attachment energy only by a constant, G([H]), which
will not affect the trends. These energies are given in Table S1, along with the difference in the
energies. The energy differences are roughly constant, meaning that the trends are the same.
Table S1. Energy difference between [XH]- and X ∆G = G([XH]-) - G(X) where ∆G1 is the gas
phase value and ∆G2 is value computed using the IEFPCM implicit solvent model using toluene
as the solvent.
X
∆G1/eV
∆G2/eV
(∆G1-∆G2)/eV
(gas phase)
(toluene)
P-B(CH3)2
-17.015
-18.121
-1.106
P-BH2
-17.358
-18.673
-1.316
P-BF2
-17.618
-18.858
-1.241
P-BCl2
-18.301
-19.518
-1.217
P-BBr2
-18.630
-19.285
-0.655
P-B(CN)2
-19.186
-20.197
-1.011
P-B(CF3)2
-19.369
-20.320
-0.951
P-B(NO2)2
-19.992
-21.013
-1.021
S-1
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
Figure S1. Primitive cell structures of eight different UiO-66-X materials. The UiO-66
framework atoms are represented by lines and the X functional moieties are represented by balls
and sticks. Atom colors: Zr for cyan, gray for C, red for O, dark blue for N, pink for B, white for
H, light blue for F, light green for Cl, brown for Br.
S-2
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
Figure S2. Structures of H2 adsorbed in UiO-66-X. The color scheme is the same as in Figure S1.
S-3
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
Figure S3. Structures of CO2 adsorbed in UiO-66-X. The color scheme is the same as in Figure
S1.
S-4
Table S2. The structural details of CO2 and H2 adsorbed in UiO-66-X. (bond length: d/Å, angle:
∠/degree)
CO2
H2
d(C Oa ) d(C Ob )
H2(g)
CO2(g)
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
(Oa C Ob ) d(Oa  B ) d(C  N 2 )
d ( H a  Hb ) d ( H a  B ) d ( H b  N 2 )
0.732
1.176
1.302
1.313
1.313
1.321
1.326
1.323
1.321
1.336
1.176
1.215
1.209
1.214
1.208
1.207
1.205
1.204
1.202
180.000
131.217
130.313
131.180
130.413
130.236
129.879
129.359
129.557
1.568
1.526
1.540
1.518
1.499
1.516
1.501
1.465
1.462
1.466
1.462
1.458
1.456
1.458
1.465
1.460
2.210
2.249
2.399
2.987
2.996
2.487
2.187
2.339
1.220
1.219
1.215
1.199
1.195
1.210
1.208
1.197
1.016
1.018
1.016
1.020
1.022
1.017
1.017
1.017
Table S3. Relative energies for the potential energy profiles shown in Figure 3. The energies are
relative to gas phase H2 and CO2. The energy of gas phase (desorbed) trans-formic acid is -0.20
eV on this scale.
UiO-66-X
H2(vdW)
TS1
2H* CO2+2H*
TS2
HCOOH
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
-0.17
-0.08
-0.16
-0.17
-0.17
-0.15
-0.17
-0.16
0.92
0.40
0.43
0.61
0.60
0.69
0.36
0.66
-0.14
-0.59
-0.75
-0.82
-1.00
-1.19
-1.63
-1.72
S-5
-0.56
-0.99
-1.12
-1.08
-1.30
-1.56
-1.92
-2.00
-0.28
-0.32
-0.40
-0.09
-0.16
-0.17
-0.31
-0.21
-0.88
-0.67
-0.79
-0.73
-0.76
-0.62
-0.67
-0.61
UiO-66-P-B(CH3)2
(a)
(b)
(c)
(d)
Figure S4. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-B(CH3)2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2
reacting with dissociatively adsorbed H2 in UiO-66-P-B(CH3)2. The curves are drawn as a guide
to the eye.
S-6
UiO-66-P-BH2
(a)
(b)
(d)
(c)
Figure S5. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-BH2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2 reacting
with dissociatively adsorbed H2 in UiO-66-P-BH2. The curves are drawn as a guide to the eye.
S-7
UiO-66-P-BCl2
(a)
(b)
(c)
(d)
Figure S6. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-BCl2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2 reacting
with dissociatively adsorbed H2 in UiO-66-P-BCl2. The curves are drawn as a guide to the eye.
S-8
UiO-66-P-BBr2
(a)
(b)
(c)
(d)
Figure S7. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-BBr2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2
reacting with dissociatively adsorbed H2 in UiO-66-P-BBr2. The curves are drawn as a guide to
the eye.
S-9
UiO-66-P-B(CN)2
(a)
(b)
(d)
(c)
Figure S8. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-B(CN)2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2
reacting with dissociatively adsorbed H2 in UiO-66-P-B(CN)2. The curves are drawn as a guide
to the eye.
S-10
UiO-66-P-B(CF3)2
(a)
(b)
(d)
(c)
Figure S9. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-B(CF3)2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2
reacting with dissociatively adsorbed H2 in UiO-66-P-B(CF3)2. The curves are drawn as a guide
to the eye.
S-11
UiO-66-P-B(NO2)2
(a)
(b)
(d)
(c)
Figure S10. (a) and (c) are the structures and reaction energy profile for H2 dissociation in UiO66-P-B(NO2)2; (b) and (d) are the structures and reaction energy profile for physisorbed CO2
reacting with dissociatively adsorbed H2 in UiO-66-P-B(NO2)2. The curves are drawn as a guide
to the eye.
Table S4. The structural details of transition states involved in H2 dissociation in UiO-66-X.
(bond length: d/Å, angle: ∠/degree)
S-12
d( H a Hb )
free H2
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
0.732
0.733
0.732
0.731
0.731
0.730
0.730
0.736
0.729
Complex
d ( H a  B ) d ( H b  Nb )
4.803
3.057
4.014
4.760
4.140
4.800
5.583
4.103
2.675
2.800
2.846
2.729
3.521
2.921
3.888
3.743
TS
d( H a Hb )
d( H a  B )
d ( H b  Nb )
0.975
0.927
0.912
0.897
0.912
0.908
0.945
0.898
1.414
1.489
1.461
1.519
1.568
1.566
1.734
1.615
1.384
1.455
1.440
1.567
1.639
1.696
1.789
1.574
Table S5. The structural details of transition states involved in CO2 attacking the dissociated H
atoms for HCOOH production in UiO-66-X. (bond length: d/Å, angle: ∠/degree)
Complex
d(C Oa ) d(C Ob ) (Oa C Ob ) d( H a C ) d( H a  B ) d( H b Ob ) d ( Hb  Nb )
free CO2
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
free CO2
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
1.176
1.171
1.183
1.172
1.175
1.172
1.182
1.170
1.170
1.176
1.182
1.169
1.183
1.179
1.179
1.169
1.183
1.183
180.000
177.557
178.152
176.556
179.231
179.284
179.671
179.787
179.688
1.223
1.214
1.215
1.201
1.196
1.210
1.201
1.194
2.057
1.999
2.093
2.645
2.438
2.076
2.035
1.995
1.020
1.021
1.020
1.020
1.021
1.021
1.023
1.022
d(C Oa ) d(C Ob )
2.712
2.554
2.703
2.751
2.800
2.743
2.487
2.504
TS
(Oa C Ob ) d( H a C )
d( H a  B )
d( H b Ob )
d ( H b  Nb )
1.176
1.221
1.280
1.219
1.217
1.216
1.166
1.208
1.204
180.000
133.670
133.83
131.352
133.867
133.673
132.384
129.316
130.773
1.658
1.632
1.726
1.663
1.717
1.680
1.699
1.606
1.368
1.296
1.243
1.323
1.299
1.166
1.193
1.178
1.171
1.210
1.256
1.194
1.215
1.343
1.384
1.359
1.176
1.280
1.214
1.289
1.278
1.283
1.208
1.314
1.301
S-13
1.202
1.217
1.200
1.222
1.216
1.215
1.307
1.303
Figure S11. Diffusion barrier for cis-formic acid diffusing from the octahedral to the tetrahedral
cage of UiO-66-P-BF2 as computed from NEB.
S-14
Figure S12. (top) Rotation barrier for cis-formic acid rotation to trans-formic acid inside UiO66-P-BH2 as computed from NEB with CP2K. The rotation barrier is 0.77 eV and the energy
difference is about 0.2 eV. In comparison, gas phase calculations with CP2K favor the transformic acid confirmer by 0.18 eV, in good agreement with the experimental value of 0.17 eV.2
(bottom) Initial, transition and final states for the NEB pathway.
S-15
Table S6. The adsorption energy (eV) of H2 in UiO-66-X and X calculated using CP2K and
Gaussian09, respectively.
UiO-66-X
CP2K
X
CP2K
Gaussian
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
-0.14
-0.59
-0.75
-0.82
-1.00
-1.21
-1.63
-1.72
P-B(CH3)2
P-BF2
P-BH2
P-BCl2
P-BBr2
P-B(CN)2
P-B(CF3)2
P-B(NO2)2
-0.12
-0.34
-0.62
-0.69
-0.90
-1.20
-1.56
-1.74
0.03
-0.32
-0.36
-0.67
-0.84
-1.21
-1.53
-1.92
Table S7. The adsorption energy (eV) of CO2 in UiO-66-X and X calculated using CP2K and
Gaussian09, respectively.
UiO-66-X
CP2K
X
CP2K
Gaussian
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
-0.59
-0.93
-0.95
-0.65
-0.75
-0.84
-1.31
-1.38
P-B(CH3)2
P-BF2
P-BH2
P-BCl2
P-BBr2
P-B(CN)2
P-B(CF3)2
P-B(NO2)2
-0.51
-0.61
-0.75
-0.55
-0.65
-0.74
-1.19
-1.20
-0.50
-0.66
-0.66
-0.67
-0.74
-0.88
-1.42
-1.60
Table S8. The electronegativity, hardness and softness of Lewis pairs functional groups.
X
Electronegativity hardness
Softness
(χ/eV)
(η/eV)
(S/eV)
P-B(CH3)2
4.66
3.70
0.14
P-BF2
5.00
3.86
0.13
P-BH2
4.91
3.78
0.13
P-BCl2
5.08
3.73
0.13
P-BBr2
5.11
3.67
0.14
P-B(CN)2
5.75
3.61
0.14
P-B(CF3)2
5.63
3.74
0.13
P-B(NO2)2
5.93
3.71
0.13
S-16
Table S9. Structural details of UiO-66-X.
UiO-66-X
Nb···B
Nb-Na
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
2.485
2.477
2.469
2.469
2.469
2.452
2.462
2.435
1.391
1.385
1.396
1.393
1.396
1.400
1.407
1.402
Na-B
∠Nb-Na-B
1.462
1.444
1.427
1.442
1.438
1.420
1.412
1.402
121.17
122.22
121.96
121.14
121.19
120.79
121.60
120.56
Torsion
(Nb-Na-B-X)
8.36
22.84
0.54
8.04
7.19
0.61
20.04
7.39
Table S10. Structural details of UiO-66-X with dissociated H atoms.
UiO-66-X
Nb···B
Nb-Na Na-B ∠Nb-Na-B
Ha-Hb
UiO-66-P-B(CH3)2
UiO-66-P-BF2
UiO-66-P-BH2
UiO-66-P-BCl2
UiO-66-P-BBr2
UiO-66-P-B(CN)2
UiO-66-P-B(CF3)2
UiO-66-P-B(NO2)2
2.590
2.596
2.562
2.552
2.539
2.571
2.508
2.508
1.353
1.349
1.353
1.354
1.356
1.354
1.354
1.358
1.628
1.659
1.588
1.594
1.576
1.586
1.580
1.553
S-17
120.35
118.56
120.95
119.67
119.79
121.66
117.26
118.76
2.210
2.249
2.399
2.987
2.996
2.487
2.187
2.339
Torsion
(Hb-Nb-B-Ha)
0.34
15.48
24.97
79.44
79.38
30.91
18.79
21.77
Table S11. The DDEC charges3 of Lewis acid (B) and base (Nb) sites of functional group in
UiO-66-X2 and adsorbed CO2 or H2. The atom labels are defined in Figure S3.
Lewis acid Lewis base
CO2
H2
B
Nb
C
Oa
Ob
Ha
Hb
UiO-66-P-B(CH3)2
+0.65
-0.32
w/CO2
+0.55
+0.03
+0.64 -0.41 -0.50
w/H2
+0.23
-0.15
-0.19 +0.75
UiO-66-P-BF2
+0.90
-0.29
w/CO2
+0.84
+0.03
+0.66 -0.47 -0.46
w/H2
+0.58
-0.13
-0.23 +0.32
UiO-66-P-BH2
+0.34
-0.32
w/CO2
+0.22
+0.03
+0.63 -0.36 -0.48
w/H2
-0.13
-0.16
-0.13 +0.33
UiO-66-P-BCl2
+0.41
-0.32
w/CO2
+0.47
+0.03
+0.65 -0.40 -0.45
w/H2
+0.25
-0.13
-0.13 +0.32
UiO-66-P-BBr2
+0.32
-0.31
w/CO2
+0.42
+0.03
+0.65 -0.39 -0.45
w/H2
+0.20
-0.13
-0.11 +0.31
UiO-66-P-B(CN)2
+0.35
-0.30
w/CO2
+0.33
+0.02
+0.64 -0.38 -0.43
w/H2
-0.01
-0.16
-0.07 +0.34
UiO-66-P-B(CF3)2
+0.18
-0.31
w/CO2
+0.02
+0.02
+0.62 -0.33 -0.41
w/H2
-0.31
-0.15
-0.06 +0.33
UiO-66-P-B(NO2)2
+0.40
-0.30
w/CO2
+0.34
+0.02
+0.64 -0.38 -0.41
w/H2
+0.04
-0.15
-0.08 +0.34
S-18
Figure S13. Calculated activation energies for H2 formation from the dissociated H atoms in
UiO-66-X plotted as a function of (a) the adsorption energies of H2 in UiO-66-X and (b) hydride
attachment energies of Lewis pair X.
Sabatier Activity Calculations
We present here details of a simple Sabatier rate analysis4-7 used to construct the Sabatier activity
contour plots in Figure 11 and Figures S14-S17. The following set of steps describe the overall
reaction:
H2 ( g )
H2 (vdW)
(1)
CO2 ( g )
CO2 (vdW)
H2 (vdW)  *
CO2 (vdW)  2H*
2H*
HCOOH(vdW) *
CO2 (vdW)  *
S-19
CO2*
(2)
(3)
(4)
(5)
HCOOH(vdW)  *
HCOOH(vdW)
HCOOH*
(6)
HCOOH( g )
(7)
The * symbol in the equations above denotes the Lewis pair (LP) acid and base sites, so that one
* can accommodate both dissociated H atoms in eq (3). We assume that adsorption of H2 and
CO2 from the gas phase is rapid and at equilibrium, so that the concentrations of H2(vdW) and
CO2(vdW) are given by an adsorption isotherm dependent only on the temperature, pressure, and
composition of the gas in contact with UiO-66-X. Therefore steps given by eqs (1) and (2) are
not considered in the simple Sabatier analysis. We ignore the competition between
chemisorption of CO2 and H2 by eliminating eq (5) from the model. In practice, this can be
accomplished by introducing H2 followed by CO2 sequentially or by modifying the structure and
properties of the LP such that they do not bind CO2 appreciably. Furthermore, we neglect
chemisorption of formic acid (FA) and assume that desorption of FA is fast and irreversible, thus
eliminating eqs (6) and (7) from the model. These simplifying assumptions allow for the
development of a model that gives the upper bound to the overall reaction rate as a function of
only two variables. These results than then be plotted as a 2-dimensional Sabatier activity
surface. The remaining steps, given by eqs (3) and (4), are used to construct the Sabatier activity
model, which is based on the upper bound to the overall reaction rate. We therefore consider
reaction rates for only the forward reactions in eqs (3) and (4) given by
   Ea 3  T Sa 3  
r3  CH2* exp 

kBT


(8)
and
Where CH2 and CCO2
   Ea 4  T Sa 4  
r4  CCO2 2H* exp 
(9)
,
kBT


are the concentrations of H2 and CO2 in the pores, respectively, given by
the adsorption isotherm and assumed to be equal molar for sake of simplicity in this work, *
and  2H* are the fraction of LP sites that are unoccupied and occupied by dissociated H atoms,
respectively,  is the frequency given by  kBT / h , where h is the Planck constant, Eai is the
forward barrier for reaction i, as computed from DFT, Sai is the entropy change in energy for
reaction i going from the initial state (vdW state) to the transition state, kB is the Boltzmann
constant and T is the absolute temperature. The fractional coverages can be computed by
assuming that eq (3) is in equilibrium with H2 in the gas phase (external to UiO-66-X) with an
equilibrium constant given by
   E3  T S3  
K3  exp 

kBT


where E3 is the reaction energy (at zero kelvin) for H2 dissociation given by
E3  E2H*  EH2 ( g )
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(10)
(11)
with E2H* and EH2 ( g ) given by the DFT total energies of chemisorbed H2 and gas phase H2,
respectively. The quantity S3 is the change in entropy for the combined adsorption and
dissociation process and is given by
S3  S2H*  SH2 ( g )  SH2 ( g )
(12)
The gas phase entropies of both H2 and CO2 (used below) were obtained from Yaws’ Handbook
of Thermodynamic Properties for Hydrocarbons and Chemicals.8 Values at 298 and 400 K are
given in Table S12.
The maximum fractional coverages, needed to obtain the upper bound to the reaction rates, are
given by
1
(13)
*max 
1  K3CH2
and
 2max
H* 
K3CH2
1  K3CH2
(14)
Equations (13) and (14) are substituted into eqs (8) and (9), respectively, to give the maximum
rates. The Sabatier rate is taken as the minimum of the two reaction rates,
(15)
rS  min{r3 , r4 }.
The Sabatier activity is given by
AS  kBT ln  rS /   .
(16)
The reaction barriers and energies required are given by the Brønsted-Evans-Polanyi (BEP)
relationships and scaling properties. In all cases we estimate the H2 dissociation barrier from the
hardness of the LP radicals, -X, as shown in Figure 8a,
Ea3  1.546  6.475.
(17)
The CO2 hydrogenation barrier is given by any of the following three relations:
Ea 4  0.954E2H*  0.139
X
Ea 4  0.881E2H*
 0.286
(18)
(19)
X
where E2H*
is the DFT energy for H2 dissociation on the gas phase functional group X, and
Ea 4  0.478Gha  0.849.
(20)
The reaction energy required in eq (10) can be computed directly if using eq (18) or from the
scaling relation
X
(21)
E2H*  0.852E2H*
 0.170
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if using eq (19). Similarly, using eq (20) requires the scaling property between the H2 adsorption
energy and the hydride attachment energy shown in Figure 7b given by
(22)
E2H*  0.479Gha  0.949.
The entropies required in eqs (8) and (9) are evaluated at two limits. First, assuming that the
entropy of the van der Waals adsorbed phase is much smaller than the gas phase and comparable
to the entropy of the transition state species we have
(23)
Sa 3  Sa 4  0.
In contrast, if we assume that the entropy of the adsorbed phase is identical to the entropy of the
gas phase we have
(24)
Sa3  SH2 (TS )  SH2 ( g )  SH2 ( g )
and
Sa 4  SCO2 (TS )  SCO2 ( g )  SCO2 ( g ) .
(25)
The Sabatier activity using eqs (17), (18) and (23) is plotted in Figure 9 for a temperature of 298
K and Figure S14 for 400 K. Contour plots using eqs (17), (19), (21) and (23) at 298 is given in
Figure S15. The Sabatier activities computed from eqs (17), (20), (22) and (23) are plotted in
Figure S16. Finally, Figure S17 gives results using eqs (17), (18), (24) and (25).
Table S12. Gas phase entropies for H2 and CO2 at 298 and 400 K in units of J mol-1 K-1 as taken
from Yaws’ Handbook of Thermodynamic Properties for Hydrocarbons and Chemicals8
400 K
298 K
H2(g)
130.68
139.73
CO2(g)
213.91
225.97
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Figure S14. Contour plot of the Sabatier activity for the overall reaction rate for CO2
hydrogenation at 400 K. The CO2 hydrogenation barrier is given by a BEP relationship with the
H2 adsorption energy and the H2 dissociation barrier is given by a relationship with the hardness
of the LP radicals -X. Specific LP groups are labeled on the figure.
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Figure S15. Contour plot of the Sabatier activity for the overall reaction rate for CO2
hydrogenation at 298 K. The CO2 hydrogenation barrier is given by a BEP relationship with the
H2 adsorption energy on the gas phase Lewis pair functional group X and the H2 dissociation
barrier is given by a relationship with the hardness of the LP radicals -X. Specific LP groups are
labeled on the figure.
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Figure S16. Contour plot of the Sabatier activity for the overall reaction rate for CO2
hydrogenation at 298 K. The CO2 hydrogenation barrier is given by a BEP relationship with the
hydride attachment energy ∆Gha to the gas phase Lewis pair X and the H2 dissociation barrier is
given by a relationship with the hardness of the LP radicals -X. Specific LP groups are labeled
on the figure.
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Figure S17. Contour plot of the Sabatier activity for the overall reaction rate for CO2
hydrogenation at 298 K assuming that the entropy of the physisorbed phase is equal to the gas
phase. The CO2 hydrogenation barrier is given by a BEP relationship with the H2 adsorption
energy and the H2 dissociation barrier is given by a relationship with the hardness of the LP
radicals -X. Specific LP groups are labeled on the figure.
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