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Université de SherbrookeUniversité de Sherbrooke
N. Abatzoglou, Kandaiyan Shanmuga Priya
S. Rakass, H. Oudghiri-Hassani and P. Rowntree
1
Surface nanometric sulphur and carbon moieties in Ni-catalyzed steam reforming of
hydrocarbons
Université de SherbrookeUniversité de Sherbrooke
Department of Chemical & Biotechnological Engineering
May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
Outline
Introduction Rationale Actual knowledge
Materials and methods
Results
Conclusions
Acknowledgments
2 May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeIntroduction
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
3May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeIntroduction
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
4May 17, 2011: NTUA
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5
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.
J.R. Rostrup-Nielsen, J. Catal. 85 (1984) 31
Scientific background (2)
May 17, 2011: NTUA
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6
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.
Scientific background (3)
May 17, 2011: NTUA
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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
Scientific background (4)
May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
Based on DFT calculationsA new S-Ni phase diagram
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.
J.H. Wang, M. Liu, Electrochem.Commun., 9 (2007) 2212-2217
8
Scientific background (5)
May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeMaterials and methods
The unsupported Ni powder
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
9 May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeMaterials and methods
SEM of the Ni Powder
Powder I (1-20µm)
Volume (%)
Number (%)
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May 17, 2011: NTUA11
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.
Université de SherbrookeUniversité de SherbrookeMaterials and methods
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
Université de SherbrookeUniversité de SherbrookeMaterials and methods
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
Université de SherbrookeUniversité de SherbrookeMaterials and methods
The differential reactor set-up
..... C atalyt ic C ells
1 -7T = 2 5 -1 1 0 0 C
M ass -FlowC ontroller s
C ar r ier
Fuel-1
Fuel-2
H 2 O
M isc
1 of 1 6S elector
Valve
...Q M G -4 2 0
M ass S pectrometer1 0 - 1 0 tor r
- 9 - 6
Vulcain Cat alyt ic M at er ialsT est ing S yst em
b
a:
a
cC:
b:Four
14 May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeMaterials and methods
The differential reactor set-up: details
15 May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeBasic 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 m, 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
Materials and methods
16 May 17, 2011: NTUA
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Experimental campaigns
Q1: What happens to the Ni ? Steam Reforming with pristine and
alkanethiols- impregnated NiQ2: What if the surfaces are thermally
pretreated?Steam reforming with thermally pretreated
pristine and alkanethiols impregnated NiQ3: Which is the source of the aromatic carbon?
CH4 vs Alkanethiols
Materials and methods
17 May 17, 2011: NTUA
Université de SherbrookeUniversité de SherbrookeResults 0: Analyses before steam reforming
DRIFTS spectra of the as-prepared thiol- contaminated Ni catalysts
2750 2800 2850 2900 2950 3000 3050
d+=sym
(CH2)
d-=antisym
(CH2)
r+=sym
(CH3)
r-=antisym
(CH3)
r-
r+
d-
d+
(*2)
Ni-C10
S
Ni-C6S
Ni-C4S
0.005
Ab
sorb
ance
(u
.a.)
Frequency (cm-1)
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XPS spectra of the as-prepared thiol- contaminated Ni
278 280 282 284 286 288 290 292 294
200
400
600
800
1000
1200
1400
C=O
Graphitica
Ni-C4S
Ni-C5S
Ni-C6S
Ni-C10
S
C(1s)
Inte
nsi
ty (
CP
S)
Binding Energy (eV)152 156 160 164 168 172 176 180
160
180
200
220
240
260Thiolates
Sulfonatesb
Ni-C10
S
Ni-C6S
Ni-C5S
Ni-C4S
S(2p)
Inte
nsit
y (
CP
S)
Bindin Energy (eV)
(a) carbon C(1s)(b) sulfur S(2p)
Results 0: Analyses before steam reforming
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20 May 17, 2011: NTUA
S/Ni Evaluation through XPS
Sample Stotal/Ni (%)
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.
Results 0: Analyses before steam reforming
Université de SherbrookeUniversité de Sherbrooke
21 May 17, 2011: NTUA
Gas composition and T profile over time-on-stream for steam reforming with Pristine Ni catalyst
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
10
20
30
40
50
60
Pa
rtia
l p
res
su
re (
To
rr)
Te
mp
era
ture
(°C
)
Time (h)
T
Ni
H2
CH4
CO CO
2
Results 1: Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
22 May 17, 2011: NTUA
Methane Conversion for Ni and Ni-C5S
Results 1: Steam Reforming
350 400 450 500 550 600 650 7000
10
20
30
40
50
60
70
80
90
100
Meth
an
e C
on
vers
ion
(%
)
Temperature (°C)
Ni Ni-C
5S
Université de SherbrookeUniversité de Sherbrooke
23 May 17, 2011: NTUA
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
10
20
30
40
50
60
T
Par
tial
pre
ssu
re (
To
rr)
a
Time (h)
Tem
per
atu
re (
°C)
Ni-C4S
H2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 20
0
100
200
300
400
500
600
700
0
10
20
30
40
50
60
Par
tial
pre
ssu
re (
To
rr)
b
Tem
per
atu
re (
°C)
Time (h)
T
Ni-C5S
H2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
5
10
15
20
25
30
35
40
Par
tial
pre
ssu
re (
To
rr)
c Ni-C6S
Tem
per
atu
re (
°C)
Time (h)
T
H2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
5
10
15
20
Pa
rtia
l p
res
su
re (
To
rr)
Te
mp
era
ture
(°C
)
Time (h)
T
d Ni-C10
S
H2
CH4
CO CO
2
Gas composition and T profiles over time-on-stream for steam reforming with impregnated Ni
Results 1: Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
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
Observations (1)
Results 1: Steam Reforming
24 May 17, 2011: NTUA
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278 280 282 284 286 288 290 292 294
200
400
600
800
1000
Aromatic
C=O
Graphitic
Binding Energy (eV)
Inte
nsi
ty (
CP
S)
Ni-C4S
Ni-C5S
Ni-C6S
Ni-C10
S
a C(1s)
152 156 160 164 168 172 176 180
120
140
160
180
200
220
Binding Energy (eV)
Inte
nsi
ty (
CP
S)
Thiolatesb
S(2p)
Ni-C10
S
Ni-C6S
Ni-C5S
Ni-C4S
XPS spectra after steam reforming(a) carbon C(1s)(b) sulfur S(2p)
Results 1: Steam Reforming
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Université de SherbrookeUniversité de Sherbrooke
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
Carom/Ni and S/Ni after steam reforming
Results 1: Steam Reforming
May 17, 2011: NTUA26
Université de SherbrookeUniversité de Sherbrooke
SampleStotal/Ni (%)
BeforeStotal/Ni (%)
After
Ni-C4S 3.0 2.4
Ni-C5S 3.6 2.7
Ni-C6S 5.3 3.1
Ni-C10S 10.9 5.1
S/Ni before and after steam reforming
Results 1: Steam Reforming
May 17, 2011: NTUA27
Université de SherbrookeUniversité de Sherbrooke
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
Observations (2)
Results 1: Steam Reforming
28 May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
Gas composition and T profile over time-on-stream for steam reforming with thermally pretreated Ni at 700°C
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
10
20
30
40
50
Par
tial
pre
ssu
re (
To
rr)
Time (h)
Tem
per
atu
re (
°C)
Ni
T
H2
CH4
CO CO
2
Results 2: Thermal Pretreatment and Steam Reforming
29 May 17, 2011: NTUA
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0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
5
10
15
20
25
30
Pa
rtia
l p
res
su
re (
To
rr)
Te
mp
era
ture
(°C
)
Time (h)
a Ni-C4S
T
H2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
5
10
15
20
T
Pa
rtia
l p
res
su
re (
To
rr)
b
Te
mp
era
ture
(°C
)
Time (h)
Ni-C5S
H2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 200
100
200
300
400
500
600
700
0
5
10
15
20
Pa
rtia
l p
res
su
re (
To
rr)
cT
em
pera
ture
(°C
)
Time (h)
T
Ni-C6S H
2
CH4
CO CO
2
0 2 4 6 8 10 12 14 16 18 20
0
100
200
300
400
500
600
700
0
5
10
15
20
Pa
rtia
l p
res
su
re (
To
rr)
Te
mp
era
ture
(°C
)
Time (h)
Td
Ni-C10
S H2
CH4
CO CO
2
Gas composition and T profile over TOS for steam reforming with thermally pretreated at 700°C impregnated Ni
May 17, 2011: NTUA30
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
278 280 282 284 286 288 290 292 294
200
400
600
800Aromatic
Inte
nsi
ty (
CP
S)
Binding Energy (eV)
C=O
Graphitic
a
Ni-C5S
Ni-C10
S
Ni-C6S
Ni-C4S
C(1s)
152 156 160 164 168 172 176 180
120
140
160
180
200
Binding Energy (eV)
Thiolates
Inte
nsi
ty (
CP
S)
b
S(2p)
Ni-C10
S
Ni-C6S
Ni-C5S
Ni-C4S
XPS spectra(a) carbon C(1s)(b) sulfur S(2p)
31 May 17, 2011: NTUA
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
Carom/Ni and S/Ni
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: NTUA32
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
S/Ni without and with thermal pretreatment
SampleStotal/Ni (%)
withoutpretreatment
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: NTUA33
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
Car/Ni without and with thermal pretreatment
SampleCarom/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: NTUA34
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
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
Observations (2)
May 17, 2011: NTUA35
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
Despite the reduced S content, the Ni-C4S and Ni-C5S samples exhibit reduced catalytic activity following the Ar thermal pretreatment
Conclusion
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
May 17, 2011: NTUA36
Results 2: Thermal Pretreatment and Steam Reforming
Université de SherbrookeUniversité de Sherbrooke
Are the pre-adsorbed
alkanethiols or feed-gas CH4?
Which molecule is responsible for the formation of aromatic carbon ?
Results 3: CH4 vs Alkanethiols
37 May 17, 2011: NTUA
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XPS spectra after thermal treatment under Ar at 700°C for 2h
152 156 160 164 168 172 176 180
120
140
160
180
200
Binding Energy (eV)
Thiolates Sulfonates
Inte
nsi
ty (
CP
S)
Ni-C4S
Ni-C5S
Ni-C6S
Ni-C10
S
b
S(2p)
278 280 282 284 286 288 290 292 294
100
200
300
400
500
600
700
800
900
C=O
Aromatic
Graphitic
Inte
nsi
ty (
CP
S)
Binding Energy (eV)
Ni
a
Ni-C5S
Ni-C10
S
Ni-C6S
Ni-C4S
C(1s)
Results 3: CH4 vs Alkanethiols
(a) carbon C(1s)(b) sulfur S(2p)
38 May 17, 2011: NTUA
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Carom/Ni and S/Ni a) after thermal treatment and b) after steam reforming
a) Sample(thermal)
Carom/Ni
(%)
Stotal/Ni (%)
Ni-C4S 3.0 2.4
Ni-C5S 4.1 2.6
Ni-C6S 6.9 3.3
Ni-C10S 10.1 5.1
b) Sample(reform)
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
The area coverage by aromatic carbon and sulfur are similar to those reported for thiol contaminated Ni catalysts after their use in steam reforming test
Results 3: CH4 vs Alkanethiols
These results confirm that the formation of aromatic carbon is due to the degradation of the n-alkanethiols
pre-adsorbed on the nickel surfaces 39 May 17, 2011: NTUA
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0 10000 20000 30000 40000 50000 60000 700000
100
200
300
400
500
600
700
0
10
20
30
40
C6S
Tem
pera
ture
(°C
)
Par
tail
pres
sure
(Tor
r)
Time (s)
T
C
B
A
H2
CH4
CO CO
2
276 280 284 288 292 296
200
400
600
800
1000
Ni-C6S
ref-400°C
ref-580°C
ref-700°C
(%) of Carom
A 4.2B 4.6C 5.5
C=OAromatic
Graphitic
B
C
A
C(1s)
Inte
nsi
ty (
CP
S)
Binding Energy (eV)
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
Results 3: CH4 vs Alkanethiols
40 May 17, 2011: NTUA
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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%
Results 3: CH4 vs Alkanethiols
Observations (4)
Estimated threshold
for significant surface deactivation
41 May 17, 2011: NTUA
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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
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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
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44
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?
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45
Results & Discussion
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46
Results & Discussion
0
2
4
6
8
10
Ni-C6S2Ni-C4S2Ni-255
CO
/CO
2
Theoretical Ni-C10S2
TOS
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47
Results & Discussion
May 17, 2011: NTUA
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48
Results & Discussion
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49
TT-TOS-C4S2TT-TOS-Ni 255
TT-TOS-C6S2 TT-TOS-C6S
Results & Discussion
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50
Results & Discussion
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51
Results & Discussion
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52
Graphitic carbon
Results & Discussion
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Conclusion
53
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).
May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
54
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 Ni-S, the criteria factor responsible for the higher carbon tolerance in Ni-C4S2 (TPD & XPS)
May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
Acknowledgments
Funding OrganismsCFI (Canadian Foundation for Innovation)NSERC (National Science and Engineering
Research Council) Sonia Blais for her assistance in the XPS analysis
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Université de SherbrookeUniversité de Sherbrooke
Wilhelm Ostwald
56
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
May 17, 2011: NTUA
Université de SherbrookeUniversité de Sherbrooke
SampleCarom/Ni
(%)
Stotal/Ni (%)
Ni-C4S 3.0 2.4
Ni-C5S 4.1 2.6
Ni-C6S 6.9 3.3
Ni-C10S 10.1 5.1
Carom/Ni and S/Ni after thermal treatment under Ar at 700°C for 2 h
Results 3: CH4 vs Alkanethiols
May 17, 2011: NTUA57
Université de SherbrookeUniversité de SherbrookeArea 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