Electronic Supplementary Material (ESI) for RSC Advances.
This journal is © The Royal Society of Chemistry 2014
Supporting Information
Effect of pretreatment on ceria-supported cobalt
catalyst for ammonia synthesis
Bingyu Lin*, Yanchao Qi, Kemei Wei, Jianxin Lin
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1. The main species detected
When CeO2 or Co catalysts prepared from Ce(NO3)2 and Co(NO3)3 was reduced in hydrogen,
different species such as HxO (x=0, 1, 2), NO2, NO, NH3 (x=0, 1, 2, 3) would be produced. The
amount of some species such as hydrogen or oxygen may also change. Consequently, the signal
measured at an m/z value may be mixed with two contributions. One is due to the direct ionization
of a specie, and the other is due to the dissociative ionization of larger species in the ionization
chamber. Table S1 gives some m/z values in mass spectra and their corresponding species during
the heating treatment process of CeO2 or Co catalysts.
Table S1 Different m/z values detected by means of mass spectrometer and their corresponding
species
m/z
species
2
H2
15
NH
16
NH2, O
17
NH3, HO
18
H2O
30
NO, N2H2
32
O2, N2H4
46
NO2
Fig. S1 showed the mass signal for blank tube with 5 vol% NH3/He pulse chemisorption at
50 °C and the ratios of relative signal intensity at 50 and 430 °C. These signals measured for m/z
=15, 16 and 17 results all were from the dissociative ionization of ammonia. The ratios of
2
NH/NH3 and NH2/NH3 ranged from 0.34-0.50 and 7.4-10.1, respectively. The ratios of O/H2O and
HO/H2O, which obtained by heating of silica gel pre-adsorbed water in Ar gas, were in the range
of 0.11-0.12 and 0.16-0.17, respectively (Fig. S2).
3.0E-9
50 oC
(A)
(B)
10
2.5E-9
NH2/NH3
o
430 C
NHx/NH3
Intensity (a.u.)
2.0E-9
1.5E-9
50 oC
1
1.0E-9
m/z=16
NH/NH3
5.0E-10
430 oC
m/z=17
m/z=15
0.0
0
5
10
15
20
25
30
35
0.1
0
40
1
2
3
4
5
6
7
8
9
10
11
NH3 pulse number
Time (min)
Fig. S1 (A) 5 vol% NH3/He pulse chemisorption results at 50 °C measured by mass spectrometer
and (B) The ratios of relative mass signal intensity: NH/NH3 and NH2/NH3 versus NH3 pulse
number.
0.18
110
1.0E-7
(B)
(A)
100
8.0E-8
HO/H2O
0.15
m/z=18
90
70
4.0E-8
60
2.0E-8
m/z=17
50
HxO/H2O
80
Temperature (oC)
Intensity (a.u.)
0.12
6.0E-8
O/H2O
0.09
0.06
0.03
m/z=16
0.0
40
0
5
10
15
20
25
30
35
40
45
50
0.00
10
15
20
25
30
35
40
45
50
Time (min)
Time (min)
Fig. S2 (A) Temperature programmed desorption results for silica gel pre-adsorbed water and (B)
The ratios of relative signal intensity measured by mass spectrometer: O/H2O and HO/H2O as a
function of the heating time.
Obviously, different species with same m/z values would be distinguished by comparing the
shape and the intensity ratio of the mass spectra with different m/z values.
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2. Surface area and pore size distributions
Table S2 BET surface area, micropore surface area and pore size of CeO2 and Co catalysts
Sample
SBET (m2/g)
Micropore surface area (m2/g)
Pore size (nm)
CeO2
121.2
16.4
8.7
Co/CeO2
111.6
15.8
8.9
Co/CeO2-H
87.3
13.3
10.6
Co/CeO2-O
56.0
10.1
14.3
0.007
Co/CeO2-O
0.006
Co/CeO2-H
dV/dD cm3 g-1 nm-1
0.005
0.004
0.003
0.002
0.001
0.000
1
4
7
10
40
70 100
400
Pore Diameter (nm)
Fig. S3 pore size distributions of Co catalysts.
3. Pulse chemisorption measurement with pure hydrogen
1.4E-8
N2
Ar
1.2E-8
×100
m/z=30
Intensity (a.u.)
1.0E-8
m/z=16
8.0E-9
6.0E-9
×100 m/z=32
4.0E-9
m/z=16
m/z=17
2.0E-9
m/z=18 ×0.1
m/z=2
H2
0.0
0
10
20
30
40
50
70 80 90 100 110 120 130 140 150
Time (min)
Fig. S4 Hydrogen pulse chemisorption results for Co/CeO2-H.
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4. N2-TPD profiles of Co/CeO2-H
4.0E-10
Intensity (a.u.)
3.5E-10
m/z=14
3.0E-10
2.5E-10
2.0E-10
m/z=28
1.5E-10
50
100
150
200
250
300
350
400
450
500
550
600
Temperature ( oC )
Fig. S5 Nitrogen temperature programmed desorption results of Co/CeO2-H.
5. Elimination of Heat- and Mass-Transfer Artifacts in ammonia synthesis test
The exothermic nature of ammonia synthesis can cause temperature and concentration gradients
that corrupt the kinetic origins and chemical significance of rates. These artifacts can be
eliminated by decreasing the size of catalyst or by volumetric dilution within the catalyst bed [1].
Co/CeO2-H with different pellet sizes (0.30-0.56 mm and 0.56-0.80 mm) and different dilution
ratios (quartz sand : catalyst 15:1-60:1) were used to measure the ammonia synthesis rates. The
space velocities changed from 0.8 to 2.6 cm3 gcat-1 h-1) at 430 °C. The results are shown in Fig. S6.
Neither pellet size and the nor dilution ratio affected the measured ammonia synthesis rates. The
catalyst showed high ammonia synthesis rate with space velocity at above 1.8 m3 gcat-1 h-1, and the
rate did not increase by further increasing space velocity. These results confirmed the absence of
transport artifacts during the activity measurement process.
5
0.06
rate (molNH3 g-1
h-1)
cat
0.05
0.04
0.03
0.02
0.01
0.00
Dilution Ratio
30
h-1 0.8
GHSV 105 cm3 g-1
cat
Pellet Diameter (mm)
30
1.4
30
1.8
30
2.4
0.30-0.56
15
2.6
60
2.3
30
2.5
0.56-0.80
Fig. S6 Ammonia synthesis rates for Co/CeO2-H (pellet diameters, 0.30-0.56 mm and 0.56-0.80
mm; quartz sand:catalyst 15:1-60:1) at 430 °C (0.8-2.6 cm3 gcat-1 h-1 space velocities).
6. Pulse chemisorption
Co/CeO2-H was reduced in hydrogen at 500 °C for 6 h, then flushed in Ar and cooled down to
430 °C. A single pulse of known volume (0.3541 mL) of hydrogen and nitrogen was introduced
into Co/CeO2-H with Ar as carrier gas, the pulse sequence used was H2→N2→H2. Fig. S7 shows
the MS signal response for pulse scheme H2→N2→H2. For H2 pulse 1, only the H2 peak can be
observed. During N2 pulse 2, the MS signal showed the peaks of nitrogen and hydrogen
suggesting the addition of nitrogen led to hydrogen desorbed from the catalyst. The concurrence
of nitrogen and hydrogen peaks can also be found in the MS signal obtained from the subsequent
H2 pulse 3. This result further confirmed hydrogen and nitrogen competitively adsorb on same
active sites for Co catalysts.
6
H2 pulse 3
Intensity (a.u.)
N2 pulse 2
H2 pulse 1
m/z=28
m/z=2
3
6
9
12
15
18
21
24
Time (min)
Fig. S7 MS signal response for pulse scheme H2→N2→H2 for Co/CeO2-H
Reference:
[1] R. M. Koros and E. J. Nowak, Chem. Eng. Sci., 1967, 22, 470.
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