35nd acs national meeting april 6-10, 2008 new orleans, louisiana organizers : umit s. ozkan...

35nd ACS National Meeting April 6-10, 2008 New Orleans, Louisiana

Organizers : Umit S. Ozkan Jingguang G Chen

Presiding: Thursday April 10, 2008, 11:45 am. -12:15 PM. Morial Convention Center, Room: Rm. 208

N.Galea, D.Knapp, E.Kadantsev, M.Shiskin, T.Ziegler Department of Chemistry University of Calgary,Alberta, Canada T2N 1N4

New Orleans National Meeting

Studying SOFC anode activity with DFT: Suggestions for cokereduction and the effects of hydrogen sulfide adsorption

Symposium on Roles of Catalysis in Fuel Cells

Division for Petrochemistry

Solid Oxide Fuel Cell – CH4

2O2-

O2 + 4 e-

O2 -

H2O + 2e-

H2 + O2-

*Most commonSOFC material

*Ni-YSZTemp.800 –

1000 oC

V +-

Anode CathodeElectrolyte

*YSZ

CH4 + 4O2- 2H2O + CO2 + 8e- (Direct Oxidation,coaking) CH4 + H2O CO + 3H2 (Steam Reforming Reaction) H2/CO + O2- H2O/CO2 + 2e- (Oxidation Reaction)

Molecular hydrogen or methane gas is typical anode fuel.CH4 adsorbs on Ni anode surface and decomposes, blocking adsorption sites with graphene, most stable form of carbon.

The problem of cokingThe problem of coking

Activation on Ni

H2 --> 2H*

CH4 --> xH*+CH4-x

Triple Phase Boundary (TPB) Reactions

Anode Electrolyte Cathode

2O2- 2O2-

2O2-

Nickel/YSZ YSZ

Nickel

YSZ

O2(g)

Oxygen rich YSZ

4e-

Pre-activation on Ni

Burning on oxygen rich YSZ

2H+ O2 ----> H2O +2e-

CH4-x + +(8-x)/2 O2- ---> CO2+(4-x)/2H2O+(8-x)e-

+C(Coke)

Surface Calculations – CH4

Two classes of active adsorption sites. Stepped surfaces more reactive than planar surfaces. Supercell; 3 layers, 2x2(planar) or 2x3(stepped) surface.

Planar (111) - *CStepped (211) - *C

Steps and TerracesSteps and Terraces

Calculations – CH4

Vienna Ab Initio Package (VASP). ADF BAND Projector augmented wave (PAW) method. Frozen core (BAND) Generalized gradient approximation (GGA) functional PBE96. Planar (111) Surfaces: 2x2 unit cell, with 3 layers. Stepped (211) Surfaces: 3x3 unit cell, with 3 layers. Theoretical equilibrium bulk lattice constants, aO(Ni) is 3.52Ǻ and aO(Cu) is 3.61Ǻ. 10Ǻ vacuum region between slabs. Cu(111): 5 x 5 x 1 Monkhorst-Pack k-point mesh. Other Surfaces: 4 x 4 x 1 Monkhorst-Pack k-point mesh. Kinetic energy (wave function) cutoff energy is 25Ry = 340eV. Charge density (augmentation) cutoff energy is 50Ry = 680eV. Energies converged to 10-3eV. TS and reaction barriers calculated using the nudged-elastic band (NEB) method.

MatLab mathematical software package.

Computational DetailsComputational Details

N.Galea,D.Knapp,T.Ziegler Journal of Catalysis 247 (2007) 20-33

Ni(111) and Ni(211) Surfaces :Adsorption and Decomposition of CH4

Theoretical literature – Nørskov. Planar surface implies that coking should not occur. Stepped surface energies illustrating final exothermic

dissociation reaction is driving force of coke formation.

-25

-20

-15

-10

-5

0

5

10

Relative Energy (kcal/mol)

Surface

Ni(211)

CH4(g)

(b)

(a)

Ni(111)

*CH3, *H *CH2, 2*H *CH, 3*H *C, 4*H

(a) (b)

Decomposition of CH4 on steps and terraces of NiDecomposition of CH4 on steps and terraces of Ni

Graphene

Ni(111) & Ni(211)

25

1317

24

11

41

24

31

2320

1011

23

4

-5

22

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

Relative Energy (kCalmol

-1)

Ni(111) : Planar SurfaceNi(211) : Stepped Surface

Graphene

CH4(g)+ Surface

*CH3,*H *CH2,2*H

*CH,3*H

*C,4*H

Bengaard et al. J. Catal. 2002, 209 , 365-384.

Ni

NiNi

NiNi

C

NiNi

Ni

Ni

NiNi

NiNi C

Ni

H

H

Ni

Ni

Ni

NiNi

H

Ni

HC

Ni

Ni

H

Ni

Ni

Ni

NiNi

NiNi

C

Ni

H

Ni

Ni

Ni

Ni

Ni

H

Ni

H

Ni

C

H

H

Ni

Ni

Ni

Ni

NiNi

NiNi

Ni

H

Ni

Ni

Ni

Ni

H

C

Ni

H

H

1-fold@edge

2-fold@edge

5 coordinate site

3-fold

Decomposition of CH4 on steps and terraces of NiDecomposition of CH4 on steps and terraces of Ni


Graphene

Carbon is adsorbed at step base, resulting in formation of graphene (coke) layer on (111) terrace. Ni and hexagonally structured carbon atoms lie parallel to one another.

Graphene island of finite size

is required for stability.

Blocking all step sites is

NOT needed to prevent formation.

Sparse covering of promoter atoms (e.g. gold, sulfur, alkali) or replacing Ni with Cu can hinder coke formation.

NiNiNi

NiNiNiNi

Ni

Ni

Ni

Ni

Ni

Ni

NiNi

NiNi

Ni

Ni

Ni

Ni

NiNi

NiNiNi

(Pictorialrepresentation

of surface)

Graphen formationGraphen formation

Cu(111) and Cu(211) Surfaces :Adsorption and Decomposition of CH4

Activity of copper in the dissociation of methane will be poor. Carbon cokes will not form on copper surfaces. Consistent with experimental SOFC observations.

0

10

20

30

40

50

60

70

80

90

100

110


Surface

Cu(211)

CH4(g)

Cu(111)

*CH3, *H *CH2, 2*H *CH, 3*H *C, 4*HTS TS TS TS

Galea et al. Journal of Catalysis 247 (2007) 20-33

Decomposition of CH4 on steps and terraces of CuDecomposition of CH4 on steps and terraces of Cu


Cu(111) and Cu(211) Surfaces :Adsorption and Decomposition of CH4

Activity of copper in the dissociation of methane will be poor. Carbon cokes will not form on copper surfaces. Consistent with experimental SOFC observations.


0

10

20

30

40

50

60

70

80

90

100

110


Surface

Cu(211)

CH4(g)

Cu(111)

*CH3, *H *CH2, 2*H *CH, 3*H *C, 4*HTS TS TS TS



Cu(111) & Cu(211)

86.79

105.35

56.09

70.50

44.70

23.33

70.69

44.54

27.11

40.10

7.75

33.24 30.49

48.19

72.03 72.30

0

10

20

30

40

50

60

70

80

90

100

110

Relative Energy (kCal/mol)

Cu(111)Cu(211)

CH4(g) + Surface *CH3 + *H *CH2 + 2*H *CH + 3*H *C + 4*H

*CH3 = 2-fold@Edge

*CH2 = 3-fold@edge2f

*CH = 5-coordination site

*C = 5-coordination site*H = 3-fold@edge2f

CH4(g) = 2-fold@Edge

Cu(111) & Cu(211)Supercell surface unit cells = (2x2) & (3x3).

Layers = 3 & 9.Lattice Constant, a = 3.615 Angstroms.

Lattice Vectors (Angstroms) :-x = 4.316 & 6.261.y = 4.984 & 7.668.

z = 14.069 & 16.588.GGA = PBE, utilizing PAW Method.

Cutoff Energies (Ry) :-Wavefunction = 37 & 25.

Charge Density = 74 & 50.k-points : Monkhorst-pack = 3x2x1 & 4x4x1.

Adsorption Energy(eV)

*CH3 : 1.30 & 1.78*CH2 : 3.91 & 3.33*CH : 4.69 & 5.47*C : 4.50 & 5.81*H : 2.42 & 2.58

Cu

Cu

Cu

Cu

Cu

HH

H

C

Cu

Cu

Cu

H

Cu

Cu

Cu

Cu

Cu

H

C

H

Cu

Cu

Cu

H

Cu

CuCu

H

Cu

C

Cu

H

Cu

CuCu

Cu

C

Cu H

CuCu

H

Cu

H

Cu




Step Edge - Cu-Ni(211) : Adsorption and Decomposition of CH4

Cu surface segregation occurs as Cu has a lower surface energy than Ni.

Likely that Ni steps that nucleate *C formation are blocked by Cu atoms, exposed terrace Ni sites contribute to activity.

Endothermic *C production on alloy, with reasonable activity.

(a)

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0

10

20

30

40

50


Surface

Ni(211)

CH4(g)

Cu(211)

*CH3, *H *CH2, 2*H *CH, 3*H *C, 4*H

Cu-Ni(211)

(a)

Copper


Decomposition of CH4 on Cu-steps and Ni-terraces Decomposition of CH4 on Cu-steps and Ni-terraces

S-Ni(211)

4.05

17.78

38.85

22.52

10.05

28.81

14.35

25.66

0

5

10

15

20

25

30

35

40

Relative Energy (kCal/mol)

CH4(g) + Surface *CH3 + *H *CH2 + 2*H *CH + 3*H *C + 4*H

NiS(211)Supercell surface unit cells = (2x3).

Layers = 9.Lattice Constant, a = 3.615

Angstroms.Lattice Vectors (Angstroms) :-

x = 6.1005, y = 4.9796, z = 16.000.GGA = PBE, utilizing PAW Method.

Cutoff Energies (Ry) :-Wavefunction = 25.

Charge Density = 50.k-points : Monkhorst-pack = 4x4x1.

*CH = 3-fold@edge2f

*C = 3-fold@edge2f

*H = 3-fold@edge2f



*Ni(111) = 24*Ni(211) = 20

*Ni(111) = 18*Ni(211) = 12

*Ni(111) = 7*Ni(211) = 12

*Ni(111) = 30*Ni(211) = 19

(26)

(19) (8)

(35)

*Bengaard et al. J. Catal. 2002, 209 , 365-384.

Ni

H

NiNi

S

NiNi

H

H

C

Ni

S

Ni

H

Ni

Ni

H

NiNi

S

NiNi

H

C

H

Ni

S

NiNi

Ni

H

NiNi

S

C

Ni

H

Ni

Ni

S

NiNi

Ni

Ni

H

Ni

S

Ni

C

Ni

H

Ni

S

NiNi


Decomposition of CH4 on S-steps and Ni-terraces Decomposition of CH4 on S-steps and Ni-terraces


100% Step – Au/S-Ni(211) : Adsorption and Decomposition of CH4

Small amounts of sulfur / gold can discourage the adsorption of carbon at the step by blocking edge sites, mimicking the nature of the planar nickel surface.

(a)-30

-20

-10

0

10

20

30


Surface

Ni(211)

CH4(g)

*CH3, *H *CH2, 2*H *CH, 3*H *C, 4*H

S100%-Ni(211)

*C", 4*H

(a)Ni(111)

Au100%-Ni(211)Sulfur or Gold


Decomposition of CH4 on (S,Au,S) steps and Ni-terraces Decomposition of CH4 on (S,Au,S) steps and Ni-terraces


A. Conclusions – CH4

Our research theoretically studies methods used experimentally to block step sites and reduce graphitic carbon formation.

Propensity to coking of Ni surface explained by strong adsorption of *C atoms at step edge, followed by graphene growth over terrace sites.

Thermodynamic energies and kinetic barriers of methane ads.n and dis.n on Cu surfaces are high, explaining poor activity and lack of coke.

Cu-Ni alloys, where Cu blocks step sites, the catalyst retains activity due to Ni, while *C formation remains endothermic due to Cu.

S-Ni stepped surface (and Au) demonstrates that step blocking renders step sites inactive to methane dis.n and forces ads.n onto terrace sites.

Galea, N.M.; Knapp, D.; Ziegler, T. J. Catal. 2007, 247, 20.

Activation on Ni

H2 --> 2H*

CH4 --> xH*+CH4-x



2O2- 2O2-

2O2-

Nickel/YSZ YSZ

Nickel

YSZ

O2(g)

Oxygen rich YSZ

4e-

Pre-activation on Ni


2H+ O2 ----> H2O +2e-

CH4-x + +(8-x)/2 O2- ---> CO2+(4-x)/2H2O+(8-x)e-

M.Shishkin N.Galea,D.Knapp,T.Ziegler, work in progress



2O2- 2O2-

2O2-

Nickel/YSZ YSZ

Nickel

YSZ

O2(g)

Oxygen rich YSZ

4e-

Activation on YSZ

Activation and burning on oxygen rich YSZ

H2+O2- ----> H2O +2e-

CH4 +4 O2- ---> CO2+2H2O+8e-




2O2- 2O2-

2O2-

Nickel/YSZ YSZ

Nickel

YSZ

O2(g)

Oxygen rich YSZ

4e-

Activation on YSZ

9%-YSZ

Zr

O

Y


Molecular Hydrogen Adsorption onOxygen Rich YSZ

-140

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-40

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0


O"-Surface 2*OH *OH2 O'-Surface

H2(g)

H2O(g)

Initial adsorption of H2(g) on 9%-YSZ is energetically more favourable than on nickel.

TS energy barriers all < +5 kcal/mol.


Methane adsorption on Oxygen rich YSZ: initial stage.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

€

↑CH4



€

*CH4



€

↑CH3OH + V



€

*CH3 + *H-100

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E (kcal/mol)



are needed to see this picture.€

↑CH2O+↑ H2 + V



€

*CH3 + *H



€

*CH + *H+↑ H2

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10

E (kcal/mol)



€

*CH2+↑ H2

Methane adsorption on Oxygen rich YSZ: Second stage.

Third stage: formaldehyde decomposition on oxygen enriched YSZ surface.



€

↑CH2O



€

*CH2O



*CHO + *H

-140

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0

Energy (kcal/mol)



€

*CHO+↑ H2

Methane adsorption on oxygen deficient YSZ surface.

0

20

40

60

80

100

120

E (kcal/mol)



€

↑CH4



€

*CH4



↑CH3OH + V



€

*CH3 + *H

B. Conclusions – CH4

It might be possible to construct anodes of inactive conductors and electrolytes that can oxydize fuels

.


Activation on Ni

H2 --> 2H*

CH4 --> xH*+CH4-x

Solid Oxide Fuel Cell – H2S


2O2- 2O2-

2O2-

Nickel/YSZ YSZ

Nickel

YSZ

O2(g)

Oxygen rich YSZ

4e-

Pre-activation on Ni with sulfur deposition


2H+ O2 ----> H2O +2e-

CH4-x + +(8-x)/2 O2- ---> CO2+(4-x)/2H2O+(8-x)e- H2S --> S*+H2(g)

Calculations – H2S

Vienna Ab Initio Package (VASP). Projector augmented wave (PAW) method. Generalized gradient approximation (GGA) functional PBE96. Orthorhombic 2x2 unit cell, with 3 layers. Theoretical equilibrium bulk lattice constant, aO, is 3.52Ǻ. 10Ǻ vacuum region between slabs. 5 x 5 x 1 Monkhorst-Pack k-point mesh. Kinetic energy (wave function) cutoff energy is 400eV. Charge density (augmentation) cutoff energy is 800eV. Energies converged to 10-3eV. TS and reaction barriers calculated using the nudged-elastic band (NEB) method.

MatLab mathematical software package.

Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C 2007, 111, 14457.Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C 2007, 111, 14457.

Surface Calculations – H2S

Hydrogen (pairs) Surface Coverage, 2H , is ratio between number of adsorbed hydrogen atom pairs and number of Ni surface atoms.

i.e. 2H:Ni = 1:4, 2H = 0.25ML.

Repeated supercell; 3 layers, 2x2 surface.

Sulfur Surface Coverage, S , is ratio between number of adsorbed sulfur atoms and number of Ni surface atoms.

i.e. S:Ni = 1:4, S = 0.25ML.

Steps and TerracesSteps and Terraces

-60

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0

20

40

60


"S",

S = 0.25ML

"CleanSurface",

S = 0ML

"S__S",

S = 0.50ML

"S_S_S",

S = 0.75ML

"S_S_S_S",

S =1ML

H2S(g)

H2(g)

H2S(g)

H2(g)

H2S(g)

H2(g)

H2S(g)

H2(g)

Maximum Adsorption of H2S(g)

On the basis of thermodynamic energy, the most stable sulfur surface coverage is S = 0.50ML.

Concurs with experimental coverage of 0.50-0.60 ML. Natural S ads.n cutoff point explains decreased exp. activity.

Surface + 4H2S(g) 4*S-Surface + 4H2(g)

“S”

“S__S” “S_S_S”

“S_S_S_S”

Surface+4H2S(g) <--> 4S*-surface+ 4H2S(g)Surface+4H2S(g) <--> 4S*-surface+ 4H2S(g)

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0

10

20

30


n*S-Surfacen*S-*SH2

n*S-*S-*H-*H

S = 0.25 - 0.50 ML, n = 1]

S = 0 - 0.25 ML, n = 0]

n*S-*Sn*S-

*SH-*Hn*S-

*SH-*H'n*S-

*S-*H*Hn*S-

*S-*H*H' *S--*S

TSTSTSTSTSTSTS

H2S(g)H2(g)

(b)

(a)

(c)

(d)

Hydrogen Sulfide Adsorption

S = 0-0.25 ML : H2S adsorption is an exothermic reaction. S = 0.25-0.50 ML : H2S adsorption is endothermic. Overall difference in energy is due to steric interactions on the

surface.

n*S-Surface + H2S(g) (n+1)*S-Surface + H2(g)

(c)

(a)

(d)

(b)

nS*-Surface+H2S(g) <--> (n+1)S*-surface+ H2(g)nS*-Surface+H2S(g) <--> (n+1)S*-surface+ H2(g)


Adsorption Energies

Adsorbed *S-Surface, Adsorption Ni-S Bond

Species Final S. Energy, EAds. Distance (Ǻ)

*SH2 10 2.18

*SH 0.25ML 77 2.18(x2)

*S 116 2.15(x3)

(*H) (64)

*SH2 7 2.30

*SH 0.50ML 53 2.24(x2)

*S 90 2.22, 2.19(x2)

(*H) (61) -

EAds (kcal/mol) = ESurface + EGas - EAdsorbedSpecies


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n*S-*H*H'

n*S-*H*H

n*S-*H-*H *H --*Hn*S-Surface*S --*S

S = 0.25ML, n = 1]

S = 0.50ML, n = 2]

2H = 0 - 0.25 ML)

TS TS TS TS TS TS

*H -*H

TS*H -*H-*H*H 4*H

2H = 0.25- 0.50 ML)

S = 0ML, n = 0]

H2(g)

H2(g)

Molecular Hydrogen Adsorption

0S : S = 0.00ML, max. 2H = 0.50ML : Ads.n strongly exothermic. 1S : S = 0.25ML, max. 2H = 0.25ML : Adsorption exothermic. 2S : S = 0.50ML, max. 2H = 0.25ML : Adsorption endothermic. Presence of surface sulfur reduces hydrogen adsorption by half.

n*S-Surface + xH2(g) 2x*H-n*S-SurfacenS*-Surface+xH2(g) <--> 2xH*-nS*-SurfacenS*-Surface+xH2(g) <--> 2xH*-nS*-Surface

-70

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10

30

50

70


"CleanSurface" "S__S"

"S" "S_S"

S = 0.25ML] S = 0.50ML]H2S(g)

H2S(g)

H2(g)

H2(g)

"S_H_H"

"S_S_H_H"

Multiple H2S(g) Adsorptions at 800oC

Surface + 2H2S(g) 2*S-Surface + 2H2(g)

Point A : Despite large TS barriers, exothermic/exergonic nature of overall reaction produces a S = 0.50ML surface.

Point B : Removal of H2S from the anode fuel feed allows the partial removal of surface sulfur, due to small difference in energy between species “S__S” and “S”.

Surface+2H2S(g) <--> 2S*-Surface+ 2H2(g) Surface+2H2S(g) <--> 2S*-Surface+ 2H2(g)

CSTR Kinetic Model

Continually Stirred Tank Reactor (CSTR) model. Reactor described by a ‘box’ (mimicking the anode), with a specific

volume and maintained at a particular temperature. The ‘surface’ within the box (mimicking the anode surface) has a specific

reactive surface and vacant adsorption site concentration. Gaseous fuel continually flows into CSTR (anode fuel feed) and gaseous

products or unused fuel continually flow out with a specific flowrate. Gaseous species can adsorb/desorb on the surface, and adsorbed species can

react with each other. Sulfur surface coverage and surface steric interactions are considered by

dissecting the surface into equally sized sections (2x2) and considering each section as a vacant site.

Determining Rate of Reactions : TS = T.S(translational/rotational).

H2S(g)/800oC, TS = 53 kcal/mol,

H2(g)/800oC, TS = 34 kcal/mol.

€

G = Δ H − TΔ S

k =kBT

hexp −

ΔG

RT

⎛

⎝ ⎜

⎞

⎠ ⎟


Rate of Formation of Individual Species

Individual rate constants, k, used to determine time-dependant rate of formation of each species in reaction scheme.

Example reaction mechanism :

Integration over time :

€

A + Bk−1

k1↔ C

k−2

k2↔ D

€

d

dtC[ ] = k1 A[ ] B[ ] − k−1 C[ ] − k2 C[ ] + k−2 D[ ]

d

dtD[ ] = k2 C[ ] − k−2 D[ ]

€

d

dtA[ ] = −k1 A[ ] B[ ] + k−1 C[ ]

d

dtB[ ] = −k1 A[ ] B[ ] + k−1 C[ ]


Point A – Surface Sulfur Formation : Initial Adsorption on S = 0ML Surface

A S=0.25ML surface (a 100% CSTR surface coverage of *S) is initially formed via H2S(g) adsorption and H2(g) desorption.

Anode Fuel at 800oC

pH2 = ~1atm,

pH2S = 1x10-5atm = 10ppm.

Initial Surface, S = 0.00ML.

Surface + H2S(g) *S-*H-*H

*S-*H-*H *S + H2(g)

*S + H2S(g) *S-*S-*H-*H

*S-*S-*H-*H *S--*S + H2(g)

Surface + 2H2(g) 4*H

Further H2S(g)/H2(g) adsorption/desorption results in a 100% CSTR surface coverage of 2*S, a S=0.50ML surface .

Point B - Surface Sulfur Removal :Initial Adsorption on S = 0.50ML Surface

Equilibrium is reached upon the production of a S=0.25ML surface (a 100% CSTR surface coverage of *S).

Anode Fuel at 800oC

pH2 = 1atm,

(No H2S(g) in fuel).

Initial Surface, S = 0.50ML.

*S--*S + H2(g) *S-*S-*H-*H

*S-*S-*H-*H *S + H2S(g)

*S + H2(g) *S-*H-*H

*S-*H-*H Surface + H2S(g)

Surface + 2H2(g) 4*H Model mimics experimental attempts to purge sulfur

from surface by eliminating H2S from anode fuel feed.

A. Conclusions – H2S

Our research studies the affects of consecutive adsorption and dissociation of H2S and subsequent desorption of H2 on Ni surfaces.

Failure of S-based pollutants in anode fuel to cause completely inoperable conditions within SOFC anode is due to inability of planar Ni to favourably adsorb H2S at a S coverage greater than 50%. The endergonic nature of H2S ads.n at S >0.50ML causes cutoff point.

Complete irreversibility of H2S ads.n caused by large endothermic/ endergonic energy difference between S = 0 and 0.25 (*S) ML.

A 2H = 0.50ML is achieved without the presence of surface sulfur. At S = 0.25 and 0.50 ML, only a 2H = 0.25ML coverage is formed.

Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C

2007, 111, 14457.

Removal of Remaining Sulfur by O2 Treatment

1S*-Surface+O2(g) --> “Clean surface +SO2(g)1S*-Surface+O2(g) --> “Clean surface +SO2(g)

Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C , accepted.Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C , accepted.

Removal of Sulfur by O2 Treatment

1S*-Surface+O2(g) --> “Clean surface +SO2(g)1S*-Surface+O2(g) --> “Clean surface +SO2(g)



2S*-Surface+O2(g) --> “1S* surface +SO2(g)2S*-Surface+O2(g) --> “1S* surface +SO2(g)



Surface coverage of selected species determined by kineticCSTR model at 8000 C of O2 exposure to S = 0.50ML surface.


B Conclusions – H2S

Sulfur with coverage S = 0.25 ML can be removed by O2

Galea, N.M.; Kadantsev, E.S.; Ziegler, T. J. Phys. Chem. C

accepted.

Acknowledgements Thank You!

Financial support was provided by the Alberta Energy Research Institute and the Western Economic Diversification Department.

Calculations were carried out on WestGrid computing resources, funded in part by the Canadian Foundation for Innovation, Alberta Innovation and Science, BC Advanced Education, and the participating research institutions.

35nd acs national meeting april 6-10, 2008 new orleans, louisiana organizers : umit s. ozkan...

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