Surface nanometric sulphur and carbon moieties in Ni-catalyzed steam reforming of hydrocarbons

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


Department of Chemical & Biotechnological Engineering

May 17, 2011: NTUA


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


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


May 17, 2011: NTUA


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.


May 17, 2011: NTUA


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


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


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


SEM of the Ni Powder

Powder I (1-20µm)

Volume (%)

Number (%)

10 May 17, 2011: NTUA


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.


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


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


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


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


16 May 17, 2011: NTUA


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


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)

18 May 17, 2011: NTUA


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

19 May 17, 2011: NTUA


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


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


22 May 17, 2011: NTUA

Methane Conversion for Ni and Ni-C5S


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


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



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)


24 May 17, 2011: NTUA


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)


25 May 17, 2011: NTUA


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


May 17, 2011: NTUA26


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


May 17, 2011: NTUA27


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)


28 May 17, 2011: NTUA


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


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



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



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



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



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



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



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



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


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)


(a) carbon C(1s)(b) sulfur S(2p)

38 May 17, 2011: NTUA


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


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


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


40 May 17, 2011: NTUA


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%


Observations (4)

Estimated threshold

for significant surface deactivation

41 May 17, 2011: NTUA


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


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


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?

May 17, 2011: NTUA


45

Results & Discussion

May 17, 2011: NTUA


46


0

2

4

6

8

10

Ni-C6S2Ni-C4S2Ni-255

CO

/CO

2

Theoretical Ni-C10S2

TOS

May 17, 2011: NTUA


47


May 17, 2011: NTUA


48


May 17, 2011: NTUA


49

TT-TOS-C4S2TT-TOS-Ni 255

TT-TOS-C6S2 TT-TOS-C6S


May 17, 2011: NTUA

Université de SherbrookeUniversité de SherbrookeXPS

50


May 17, 2011: NTUA


51


May 17, 2011: NTUA


52

Graphitic carbon


May 17, 2011: NTUA


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


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


Acknowledgments

Funding OrganismsCFI (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


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


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


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

Date post:	14-Jan-2016
Category:	Documents
Upload:	usoa
View:	30 times
Download:	2 times

Surface nanometric sulphur and carbon moieties in Ni-catalyzed steam reforming of hydrocarbons

Documents