Université de Sherbrooke
Surface nanometric sulphur and carbon moieties in
Ni-catalyzed steam reforming of hydrocarbons
N. Abatzoglou, Kandaiyan Shanmuga Priya
S. Rakass, H. Oudghiri-Hassani
and P. Rowntree
Department of Chemical & Biotechnological Engineering
1
May 17, 2011: NTUA
Université de Sherbrooke
Outline
 Introduction
 Rationale
 Actual knowledge
 Materials and methods
 Results
 Conclusions
 Acknowledgments
2
May 17, 2011: NTUA
Introduction
Université de Sherbrooke
Rationale
 Previous published work by the authors proved the efficiency of
pristine micrometric Ni powders as steam reforming catalysts
 Sulfur contamination of the Ni surface is known to cause catalyst
partial or total deactivation
 Commercial natural gas is artificially contaminated with alkanethiols
and sulfides (i.e tert-butyl-mercaptan and di-methyl-sulfide)
This work tries to elucidate the role of the
sulfur at the surface of Ni-based catalysts
3
May 17, 2011: NTUA
Introduction
Université de Sherbrooke
Scientific background (1)
Conventional supported Ni catalysts are known to deactivate by
sintering, sulfur passivation and carbon deposition
 The sulfur compounds in gasoline and H2S produced from these
sulfur compounds in the hydrocarbon reforming process are
poisonous to the Reforming and WGS catalysts
 Deactivation of supported metal catalysts by carbon formation is
another serious problem in steam reforming due to:
 fouling of the metal surface
 blockage of catalyst pores
 loss of the structural integrity of the catalyst support material
4
May 17, 2011: NTUA
Université de Sherbrooke
Scientific background (2)
 Sulfur passivated reforming process (SPARG) : Trace amount (2ppm) of H2S with
the feed gas.
 S selectively poisons active sites of Ni catalyst - Small loss in the reforming
activity. Rationale: Trace amounts of S affect the deactivation rate much more than
the reforming rate.
 Adsorbed S deactivate the occupied Ni site, thus changing the “Number/Surface
unit” of the catalytically active ensembles.
 Size of these ensembles is critical in allowing SR with minimal formation of coke.
 SR is thought to involve ensembles of 3-4 Ni atoms, while C formation requires
6-7 Ni atoms.
 Complete coverage of catalyst with S results in total deactivation; however, at S
coverage of around 70% of saturation, C deposition could effectively be
eliminated while SR still proceeds.
5
J.R. Rostrup-Nielsen, J. Catal. 85 (1984) 31
May 17, 2011: NTUA
6
Université de Sherbrooke
Scientific background (3)
 Interfacial reactions between H2S and Ni surface leads to rapid
adsorption of monolayer of S atoms on Ni surface.
 These observations are consistent with predictions from first-
principles calculations : H2S dissociation on transition-metal surfaces
has small dissociation barriers (weak H-S bonds), and high
exothermicities (strong S-metal bonds).
 Self-assembled monolayers (SAM) are formed from adsorption of
organothiols on metal surfaces such as Au and Ni.
•G.A. Sargent, G.B. Freeman, J.L.Chao, Surf. Sci 100 (1980) 342.
•B. McAllister, P. Hu, J. Chem. Phys. 122 (2005) 84709.
•S. Rakass, H. Oudghiri-Hassani, N. Abatzoglou & P. Rowntree, J. Power Sources 162 (2006) 579.
May 17, 2011: NTUA
Université de Sherbrooke
Scientific background (4)
Conclusions based on TPD & XPS
 Adsorbed CH3S on Ga sites exhibits greater thermal
stability than CH3SH because surface hydrogen is absent.
 Comparison between the adsorptions of CH3SH and
CH3SSCH3: dialkyl disulfides can produce a thiolate
layer; the resulting monolayer survives to a greater
temperature than that obtained from alkanethiols
because surface hydrogen is not produced during
adsorption.
 Stable thiolate self assembled monolayer is suggested to
be prepared by adsorption of diakyl disulfides, rather
than alkanethiols.
T.P Huang, T.H. Lin, T.F. Teng, Y.H. Lai, W.H.Hung, Surf. Sci.
603(2009)1244-1252.
7
May 17, 2011: NTUA
Université de Sherbrooke
Scientific background (5)
Based on DFT calculations
A new S-Ni phase diagram
J.H. Wang, M. Liu, Electrochem.Commun., 9 (2007) 2212-2217
 Existence of an intermediate state between
pure Ni and nickel sulfide Ni3S2-S atoms
adsorbed on Ni surfaces due to rapid reaction
of H2S with Ni(100) and Ni(111) surfaces.
 Clear distinction between Ni surfaces partially
covered with adsorbed S atoms and bulk Ni3S2.
 Accurate prediction of this adsorption phase is
vital to a fundamental understanding of the
sulfur poisoning mechanism of Ni-based
anodes.
8
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
The unsupported Ni powder





9
Inco Ni 255
BET Surface = 0.44 m2/g
Particle size distribution: 1-20µm
Open filamentary structure and irregular spiky surface
Produced by the thermal decomposition of Ni(CO)4
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
SEM of the Ni Powder
Powder I (1-20µm)
Volume (%)
Number (%)
10
May 17, 2011: NTUA
Université de Sherbrooke
Thiols/Disulfides as S-source
 Thiols : H-(CH2) n -SH, with n = 4, 5, 6 and 10
 All liquids at room temperature and used as received:
 n-decanethiol (Aldrich, 98%)
 n-hexanethiol (Aldrich, 98%)
 n-pentanethiol (Aldrich, 99%)
 n-butanethiol (Aldrich, 99%)
 Disulfides : All liquids at room temperature and used as received from Aldrich.
 Ethyl disulfide - C4H10S2
 Propyl disulfide - C6H14S2
 Iso pentyl disulfide – C10H22S2
 Hexyl disulfide – C12H26S2
 Methanol (Aldrich, 99%) used as solvent.
11
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
Ni Impregnation
 Pristine Ni powder in 10-3 M sol. of alkanethiols/methanol
 5g of Ni in 100 ml of solution: several orders of magnitude
excess thiol as compared to the monolayer quantities
 Immersion time under stirring: 20 h
 Rinsed thoroughly with fresh methanol
 Samples dried for 12 hours at ambient temperature
12
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
Experimental set-up
A multi-differential isothermal reactor set-up
equipped with a gas humidification system, a
programmable furnace and coupled to a
Quadrupole Mass Spectrometer
13
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
The differential reactor set-up
b:Four
a:
Mass-Flow
Controllers
.....
Fuel-1
Catalytic Cells
1-7
T = 25-1100 C
Fuel-2
b
a
H2O
Misc
Carrier
...
C: QMG-420
Mass Spectrometer
10 - 10 torr
-9
Vulcain Catalytic Materials
Testing System
14
1 of 16
Selector
Valve
c
-6
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
The differential reactor set-up: details
15
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
Basic experimental protocol
The reactant gas is composed of Ultra high purity CH4 and steam
Ar was used as inert diluent
The partial pressure of water in the gas is used to regulate the CH4/H2O
The gas compositions and flow rates are controlled by rotameters
The flow rate used was 25 ml/min per tube
0.25 g of catalyst packed into the quartz tubes and retained by quartz wool
 The inner tubes include porous fused quartz disks (coarse porosity of 40-90 mm,
1.5 cm diameter) supporting the Ni catalyst bed
 No entrainment of catalyst particles occurs downstream
 The reforming tests were conducted at a CH4/H2O molar ratio of 1:2 and at
sufficiently low GHSV






16
May 17, 2011: NTUA
Materials and methods
Université de Sherbrooke
Experimental campaigns
 Q1: What happens to the Ni ?
 Steam Reforming with pristine and alkanethiols- impregnated Ni
 Q2: What if the surfaces are thermally pretreated?
 Steam reforming with thermally pretreated pristine and
alkanethiols impregnated Ni
 Q3: Which is the source of the aromatic carbon?
 CH4 vs Alkanethiols
17
May 17, 2011: NTUA
Results 0: Analyses before steam reforming
Université de Sherbrooke
DRIFTS spectra of the as-prepared thiolcontaminated Ni catalysts
-
d
Absorbance (u.a.)
d
+
+
d =sym(CH2)
r
-
d =antisym(CH2)
+
+
r
0.005
-
r =sym(CH3)
-
r =antisym(CH3)
Ni-C10S
Ni-C6S
(*2)
Ni-C4S
2750
18
2800
2850
2900
2950
-1
Frequency (cm )
3000
3050
May 17, 2011: NTUA
Results 0: Analyses before
steam reforming
Université de Sherbrooke
XPS spectra of the as-prepared
thiol- contaminated Ni
(a) carbon C(1s)
(b) sulfur S(2p)
1400
1200
a
Thiolates
Graphitic
260
C(1s)
1000
240
Ni-C10S
800
Ni-C6S
600
Ni-C5S
400
Intensity (CPS)
Intensity (CPS)
C=O
b
Sulfonates
S(2p)
Ni-C10S
220
Ni-C6S
200
Ni-C5S
180
200
Ni-C4S
278 280 282 284 286 288 290 292 294
Binding Energy (eV)
19
Ni-C4S
160
152 156 160 164 168 172 176 180
Bindin Energy (eV)
May 17, 2011: NTUA
Results 0: Analyses before
steam reforming
Université de Sherbrooke
S/Ni Evaluation through XPS
Sample Stotal/Ni (%)
20
Ni-C4S
3.0
Ni-C5S
3.6
Ni-C6S
5.3
Ni-C10S
10.9
• The coverage ratio of the
Ni by the sulfur increases
with the chain length of the
alkanethiol molecule
• The longer chain species
lead to a higher number
density of adsorbates
(alkanethiol molecules) on
the Ni powder surfaces.
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Gas composition and T profile over time-on-stream
for steam reforming with Pristine Ni catalyst
700
Ni
50
600
500
40
400
T
H2
CH4
CO
CO2
30
20
300
200
10
Temperature (°C)
Partial pressure (Torr)
60
100
0
0
2
4
6
8
10
12
14
16
18
0
20
Time (h)
21
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Methane Conversion for Ni and Ni-C5S
100
Methane Conversion (%)
90
Ni
Ni-C5S
80
70
60
50
40
30
20
10
0
350
400
450
500
550
600
650
700
Temperature (°C)
22
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Gas composition and T profiles over time-onstream for steam reforming with impregnated Ni
700
400
T
H2
CH4
CO
CO2
20
10
300
200
Partial pressure (Torr)
500
40
Temperature (°C)
0
2
4
6
8
10
12
14
16
18
b
50
500
400
T
H2
CH4
CO
CO2
30
20
300
200
100
0
0
20
600
40
10
100
0
Ni-C5S
0
2
4
6
8
10
12
14
16
18
0
20
Time (h)
Time (h)
20
25
20
600
500
400
300
15
200
10
Partial pressure (Torr)
Partial pressure (Torr)
T
H2
CH4
CO
CO2
30
Ni-C6S
Temperature (°C)
c
35
Ni-C10S
d
15
5
400
10
300
T
H2
CH4
CO
CO2
5
200
100
0
0
2
4
6
8
10
12
14
16
18
0
20
600
500
100
0
23
700
700
40
0
2
4
6
8
10
12
Temperature (°C)
Partial pressure (Torr)
600
50
30
700
60
Ni-C4S
a
Temperature (°C)
60
14
16
18
0
20
Time (h)
Time (h)
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Observations (1)
 The high catalytic activity and stability of Ni-C4S and
Ni-C5S catalysts were similar to that of pristine Ni
catalysts
 The activity of Ni-C6S catalysts decreased for
temperatures above 580oC
 No activity was obtained over the Ni-C10S at any
temperature
24
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
XPS spectra after steam reforming
(a) carbon C(1s)
(b) sulfur S(2p)
1000
Graphitic
a
C(1s)
220
Thiolates
b
C=O
600
Ni-C6S
400
Ni-C5S
S(2p)
200
Ni-C10S
Intensity (CPS)
Intensity (CPS)
800
Aromatic
180
Ni-C10S
160
Ni-C6S
Ni-C5S
140
200
Ni-C4S
278 280 282 284 286 288 290 292 294
Binding Energy (eV)
25
Ni-C4S
120
152
156
160
164
168
172
176
180
Binding Energy (eV)
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Carom/Ni and S/Ni after steam reforming
26
Sample
Carom/Ni (%)
Stotal/Ni (%)
Ni-C4S
3.0
2.4
Ni-C5S
4.0
2.7
Ni-C6S
6.8
3.1
Ni-C10S
10.1
5.1
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
S/Ni before and after steam reforming
Stotal/Ni (%) Stotal/Ni (%)
Sample
Before
After
27
Ni-C4S
3.0
2.4
Ni-C5S
3.6
2.7
Ni-C6S
5.3
3.1
Ni-C10S
10.9
5.1
May 17, 2011: NTUA
Results 1: Steam Reforming
Université de Sherbrooke
Observations (2)
 In all cases, the total sulfur content (S/Ni) decreased following
use in steam reforming
 The quantity of aromatic carbon for the thiol contaminated Ni
catalysts measured after their use in steam reforming test
increased with the length of the alkyl chain.
 The observed deactivation of Ni-C6S and Ni-C10S during the
steam reforming of methane may be due to:
a) the deposition of aromatic carbon on the catalyst surface
b) a permanent poisoning of the surface caused by the high
level of chemisorbed sulfur species
28
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Gas composition and T profile over time-on-stream for
steam reforming with thermally pretreated Ni at 700°C
700
Ni
40
500
400
30
T
H2
CH4
CO
CO2
20
10
300
200
100
0
0
29
600
2
4
6
8
10
12
Time (h)
Temperature (°C)
Partial pressure (Torr)
50
14
16
18
0
20
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Gas composition and T profile over TOS for steam reforming
with thermally pretreated at 700°C impregnated Ni
700
700
Ni-C4S
T
H2
CH4
CO
CO2
15
500
400
300
10
200
5
15
0
500
400
10
300
200
5
100
2
4
6
8
10
12
14
16
18
0
0
20
0
2
4
6
8
20
500
400
10
300
200
5
100
0
0
2
4
6
8
10
12
Time (h)
14
16
18
0
20
14
16
18
700
0
20
T
H2
CH4
CO
CO2
d
600
Partial pressure (Torr)
Ni-C6S
Temperature (°C)
15
12
20
700
T
H2
CH4
CO
CO2
c
10
Time (h)
Time (h)
Partial pressure (Torr)
600
100
0
30
Ni-C5S
15
Ni-C10S
600
500
400
10
300
200
5
Temperature (°C)
20
Partial pressure (Torr)
600
Temperature (°C)
Partial pressure (Torr)
a
25
T
H2
CH4
CO
CO2
b
Temperature (°C)
20
30
100
0
0
2
4
6
8
10
12
14
16
18
0
20
Time (h)
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
XPS spectra
(a) carbon C(1s)
(b) sulfur S(2p)
200
Intensity (CPS)
800
600
400
a
Aromatic
C=O
C(1s)
Ni-C10S
Ni-C6S
Ni-C5S
200
Ni-C4S
278 280 282 284 286 288 290 292 294
Binding Energy (eV)
31
b
180
Intensity (CPS)
Graphitic
160
Thiolates
S(2p)
Ni-C10S
Ni-C6S
140
Ni-C5S
120
Ni-C4S
152 156 160 164 168 172 176 180
Binding Energy (eV)
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Carom/Ni and S/Ni
32
Sample
Caromatic/Ni (%)
Stotal/Ni (%)
Ni-C4S
5.0
2.1
Ni-C5S
6.1
2.5
Ni-C6S
7.5
2.6
Ni-C10S
11.0
4.0
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
S/Ni without and with thermal pretreatment
33
Sample
Stotal/Ni (%)
without
pretreatment
Stotal/Ni (%)
with
pretreatment
Ni-C4S
2.4
2.1
Ni-C5S
2.7
2.5
Ni-C6S
3.1
2.6
Ni-C10S
5.1
4.0
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Car/Ni without and with thermal pretreatment
34
Sample
Carom/Ni
without
pretreatment
Carom/Ni
with pretreatment
Ni-C4S
3.0
5.0
Ni-C5S
4.0
6.1
Ni-C6S
6.8
7.5
Ni-C10S
10.1
11.0
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Observations (2)
 The catalytic activity of the Ni contaminated by the
short chain thiols decreases over time following the Ar
thermal pretreatment at 700oC
 For Ni-C6S and Ni-C10S, no catalytic activity was
observed
 The S/Ni is lower in the case of the thermal
pretreatment; but, the catalytic activity is worse !
 The Carom/Ni is higher in the case of the thermal
pretreatment
35
May 17, 2011: NTUA
Results 2: Thermal Pretreatment
and Steam Reforming
Université de Sherbrooke
Conclusion
Despite the reduced S content, the Ni-C4S and Ni-C5S
samples exhibit reduced catalytic activity following the Ar
thermal pretreatment
These findings suggest that the loss of catalytic
activity observed for the thiol-contaminated Ni
samples is due to the accumulation of aromatic
carbon on the Ni surface
36
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
Which molecule is responsible for the
formation of aromatic carbon ?
Are the pre-adsorbed
alkanethiols or feed-gas CH4?
37
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
XPS spectra after thermal treatment under Ar
at 700°C for 2h
(a) carbon C(1s)
(b) sulfur S(2p)
900
Graphitic
800
Thiolates
200
Aromatic
C=O
Ni-C10S
500
400
Ni-C6S
Ni-C5S
200
160
140
Ni-C4S
Ni
278 280 282 284 286 288 290 292 294
Binding Energy (eV)
38
S(2p)
Sulfonates
180
300
100
b
Ni-C10S
600
Intensity (CPS)
Intensity (CPS)
700
a
C(1s)
120
Ni-C6S
Ni-C5S
Ni-C4S
152 156 160 164 168 172 176 180
Binding Energy (eV)
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
Carom/Ni and S/Ni
a) after thermal treatment and
b) after steam reforming
a) Sample
(thermal)
Carom/Ni
(%)
Stotal/Ni
(%)
b) Sample
(reform)
Carom/Ni
(%)
Stotal/Ni
(%)
The area coverage by aromatic carbon and sulfur are
Ni-Cto
3.0
2.4
4S those3.0
similar
reported2.4for thiolNi-C
contaminated
Ni catalysts
4S
4.1steam reforming
2.6
afterNi-C
their
test
Ni-C
4.0
2.7
5S use in
5S
39
Ni-C6S
6.9
3.3
Ni-C6S
6.8
3.1
Ni-C10S
10.1
5.1
Ni-C10S
10.1
5.1
These results confirm that the formation of aromatic
carbon is due to the degradation of the n-alkanethiols
pre-adsorbed on the nickel surfaces
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
XPS C(1s) spectra of Ni-C6S catalyst obtained after its
use in steam reforming up to a temperature of (A) 400°C,
(B) 580°C and (C) 700°C
1000
40
C(1s)
C6S
B
30
20
500
400
300
A
200
10
800
600
Intensity (CPS)
T
H2
CH4
CO
CO2
Temperature (°C)
Partail pressure (Torr)
Graphitic
700
Ni-C6S
600
400
A
B
C
(%) of Carom
4.2
4.6
5.5
Aromatic
C=O
ref-700°C
C
ref-580°C
B
100
200
C
0
0
0
ref-400°C
A
10000 20000 30000 40000 50000 60000 70000
Time (s)
276
280
284
288
292
296
Binding Energy (eV)
40
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
Observations (4)
The Ni-C6S catalyst was deactivated as the
temperature exceeded ~580oC and at this
temperature the area coverage percentage of
aromatic carbon was 4.6%
Estimated threshold
for significant surface deactivation
41
May 17, 2011: NTUA
Université de Sherbrooke
Conclusions
 The longer alkyl chain species lead to increased
surface coverage on the catalyst
 The catalytic activity of the Ni-C4S, Ni-C5S, Ni-C6S
and Ni-C10S catalysts depends on the alkyl chain
lengths
 The deactivation of the unsupported Ni catalysts is
mainly due to the coverage of the catalyst surface by
aromatic-aliphatic carbon
42
May 17, 2011: NTUA
Université de Sherbrooke
Conclusions (cont.)
 The formation of aromatic-aliphatic carbon during
steam reforming was found to be due to the pyrolysis
of carbon from n-alkanethiols preadsorbed on the
catalyst surface and not from the methane feed gas
 A Ni surface area coverage by aromatic carbon of
over 4.6% leads to complete deactivation of Ni
catalyst surface
43
May 17, 2011: NTUA
Université de Sherbrooke
Recent Experimental campaigns
•Q1 :
Compare Ni-255 disulfide vs thiol impregnation
•Q2 :
What happens if the disulfide impregnated catalysts were thermally
treated (TT) followed by SR?
•Q3 :
Is there any change in the ratio of reforming to WGS reaction due to
the different chain length of disulfides?
•Q4:
What is the reason for the catalyst deactivation as chain length of
disulfide increases; surface C or S species?
44
May 17, 2011: NTUA
Université de Sherbrooke
Results & Discussion
2.0
400
1.8
TOS
1.6
350
Ni-255
1.0
C10S2
0.8
C6S2
0.6
C4S2
Theoretical
0.2
0.0
H2 Yield (%)
Cout/Cin
1.2
0.4
250
Ni-255
200
C10S2
150
C6S2
100
C4S2
50
Th.
0
350
45
TOS
300
1.4
400
450
500
550
600
Temperature °C
650
700
300
350
400
450
500
550
Temperature °C
600
650
700
May 17, 2011: NTUA
Results & Discussion
Université de Sherbrooke
10
CO/CO2
8
6
4
2
0
Theoretical
Ni-C10S2
Ni-255
Ni-C4S2
Ni-C6S2
TOS
46
May 17, 2011: NTUA
Université de Sherbrooke
Results & Discussion
CH4 conversion
Reforming
WGS
100
90
80
70
%
60
50
40
30
20
10
0
Ni-255
Ni-C10S2
Ni-C6S2
Ni-C4S2
Th.
Catalysts
47
May 17, 2011: NTUA
Results & Discussion
48
Université de Sherbrooke
May 17, 2011: NTUA
Results & Discussion
TT-TOS-Ni 255
TT-TOS-C6S2
49
Université de Sherbrooke
TT-TOS-C4S2
TT-TOS-C6S
May 17, 2011: NTUA
Results & Discussion XPS
Université de Sherbrooke
C 1s
C4S2
TOS-C4S2
Carbidic C 1
Carbidic C 2
sp2
sp3
Graphitic C=C
C aromatic
C-O
Graphitic C=C
C 1s
C=O
O-C=O
O-C=O
275
280
285
290
295
300
305
275
280
TT-TOS-C4S2
285
290
295
300
305
C4S2-Quenching
Aromatic C
Aromatic C
50
275
280
285
290
295
300
305
275
280
285
290
May 17, 2011: NTUA
295
300
305
Results & Discussion
2.5
Université de Sherbrooke
Area ratio of S, C and O with respect to Ni
2
1.5
S/Ni
1
C/Ni
O/Ni
0.5
0
51
May 17, 2011: NTUA
Results & Discussion
1.2
Université de Sherbrooke
Area ratio of C species with respect to Ni
1
Graphitic carbon
0.8
0.6
Aromatic C/Ni
Graphitic C=C/Ni
0.4
Aliphatic C-C/Ni
0.2
0
52
May 17, 2011: NTUA
Université de Sherbrooke
Conclusion
 Short chain DADS impregnated Ni-255 catalysts were the most stable impregnated
catalysts with respect to deactivation during SRM.
 The main proven advantage of modifying the catalyst is the decrease of graphitic-like
carbon formation / deposition at the surface of the catalyst during SRM.
 There is a gradual increase in the aromatic carbon peak with increase in the chain
length of DADS molecule during TOS.
 Relatively small amounts of sulfur moieties (S/Ni≤0.03) present on the surface of the
modified catalysts highly determine the carbon content and is found responsible for
the formation of different species of carbon on the surface of the catalyst.
 Surface chemistry of the catalysts tested is highly complex. Ni, S and C
species/moieties, affecting differently the chemisorption and adsorbed C, H and O
bearing chemical groups, must be studied throughly using advanced surface analysis
techniques (ie., TOF-SIMS and nano-SIMS).
53
May 17, 2011: NTUA
Université de Sherbrooke
Ongoing Work
1. Identify (and quantify?) the factors responsible for the catalyst deactivation; S and/or C
moieties
2. Use catalysts impregnated with molarity ratios ranging from 0.2M to 0.3M
3. Estimate the amount of C and S by XPS and relate to catalytic activity.
4. Find out the mechanism of adsorption of disulfides on Ni surface and adsorption phase of NiS, the criteria factor responsible for the higher carbon tolerance in Ni-C4S2 (TPD & XPS)
54
May 17, 2011: NTUA
Université de Sherbrooke
Acknowledgments
 Funding Organisms
CFI (Canadian Foundation for Innovation)
NSERC (National Science and Engineering Research Council)
 Sonia Blais for her assistance in the XPS analysis
55
May 17, 2011: NTUA
Université de Sherbrooke
It has pleased no less than surprised me that of the many studies whereby
I have sought to extend the field of general chemistry, the highest scientific
distinction has been awarded for those on Catalysis
Wilhelm Ostwald
56
May 17, 2011: NTUA
Results 3: CH4 vs Alkanethiols
Université de Sherbrooke
Carom/Ni and S/Ni after thermal
treatment under Ar at 700°C for 2 h
Sample
Ni-C4S
Ni-C5S
Ni-C6S
Ni-C10S
57
Carom/Ni
(%)
3.0
4.1
6.9
10.1
Stotal/Ni
(%)
2.4
2.6
3.3
5.1
May 17, 2011: NTUA
Université de Sherbrooke
Area ratio of aromatic carbon and the total sulfur on Ni calculated for the
thiol contaminated Ni catalysts Ni-C4S, Ni-C5S, Ni-C6S and Ni-C10S
measured after: a) the as-prepared thiol contaminated Ni catalysts, b)
their use in the steam reforming tests, c) their use in the steam reforming
test preceded by thermal treatment under Ar carrier gas at 700°C
Ni-C4S
Car/Ni
(%)
Ni-C5S
Car/Ni
(%)
Ni-C6S
Car/Ni
(%)
Ni-C10S
Car/Ni
(%)
Ni-C4S
S/Ni
(%)
Ni-C5S
S/Ni
(%)
Ni-C6S
S/Ni
(%)
Ni-C10S
S/Ni
(%)
(a)
-
-
-
-
3.0
3.6
5.3
10.9
(b)
3.0
4.0
6.8
10.1
2.4
2.7
3.1
5.1
(c)
5.0
6.1
7.5
11
2.1
2.5
2.6
4.0
58
May 17, 2011: NTUA