Kinetics & Catalysis of Kinetics & Catalysis of Methane Steam Reforming Methane Steam Reforming in SOFCs and Reformersin SOFCs and Reformers

Fuel Cell CenterChemical Engineering Department

Worcester Polytechnic InstituteWorcester, MA

Caitlin A. Callaghan (PhD), James Liu (MS candidate), Ilie Fishtik, and Ravindra Datta

Alan Burke, Maria Medeiros, and Louis Carreiro

Naval Undersea Warfare CenterDivision Newport

Newport, RI

Methane Steam ReformingMethane Steam Reforming•Consists of three reversible overall reactions (OR):

Rostrupnielsen J. R, Journal of Power Sources 105 (2002) 195-201

•Endothermic (reforming is favored by high temperature)

•Exothermic (favors low temperature while pressure is unaffected)

•Steam to Carbon ratio (P(H2O)/P(CH4) or S/C) around 3 are applied

Solid Oxide Fuel CellSolid Oxide Fuel Cell

Similar ORs and Chemistry

Microkinetic & Graph Theoretic Approach

• Develop Molecular Mechanisms

• Predict Kinetics of Elementary Reactions (UBI-QEP or Ab Initio)

• Draw Reaction Route (RR) Networks

• Microkinetic Analysis of Network

• Comparison with Experiment

• Design of better Catalysts

RR RR GraphsGraphs

A RR graph may be viewed as several hikes through a mountain range: Valleys are the energy levels of reactants and products Elementary reaction is a hike from one valley to adjacent valley Trek over a mountain pass represents overcoming the energy barrier

RRRR Graph Topology Graph Topology

A + B

C

s1 s2 s5

s3 s4

s5

s1 s2

s3 s4

s5

OR

s1: A + S A·Ss2: B + S B·Ss5: A·S + B·S C + 2SOR: A + B C

s3: A·S + B·S C·S + Ss4: C·S C + S

–s5: C + 2S A·S + B·S OR: 0 0

Full Route

s1: A + S A·Ss2: B + S B·Ss3: A·S + B·S C·S + Ss4: C·S C + Ss5: A·S + B·S C + 2S

Mechanism: A + B C

Empty Route

Rate, Affinity & ResistanceRate, Affinity & Resistance• DeDonder Relation:

• Reaction Affinity:

• Reaction Rate (Ohm’s Law):

1 1 expr

r r rr

A

!

1 1 1

ln ln ln lnqn n

i i o o k k i ii k i

AK P

RT

A

rR

A

(conventional)net reaction ratereaction affinity

RESISTANCE

ln1

rr

Rr r r

!

"!

forward reaction rate

Electrical AnalogyElectrical Analogy

Kirchhoff’s Current Law– Analogous to conservation of mass

Kirchhoff’s Voltage Law– Analogous to thermodynamic consistency

Ohm’s Law– Viewed in terms of the De Donder Relation

a b c d e 0r r r r r

ab

c

d

e

f g

i h

f g h i 0 A +A A A

Rr

A=

Example ofExample ofWGS ReactionWGS Reaction

E

Elementary Reaction

Steps E

!

!

s1 0 1.5 106 CO + S CO·S 12.0 1014

s2 0 106 H2O + S H2O·S 13.6 1014

s3 25.4 1013 H2O·S + S OH·S + H·S 1.6 1013

s4 10.7 1013 CO·S + O·S CO2·S + S 28.0 1013

s5 0 1013 CO·S + OH·S HCOO·S + S 20.4 1013

s6 15.5 1013 OH·S + S O·S + H·S 20.7 1013

s7 0 1013 CO·S + OH·S CO2·S + H·S 22.5 1013

s8 1.4 1013 HCOO·S + S CO2·S + H·S 3.5 1013

s9 4.0 1013 HCOO·S + O·S CO2·S + OH·S 0.9 1013

s10 29.0 1013 H2O·S + O·S 2OH·S 0 1013

s11 26.3 1013 H2O·S + H·S OH·S + H2·S 0 1013

s12 1.3 1013 OH·S + H·S O·S + H2·S 4.0 1013

s13 0.9 1013 HCOO·S + OH·S CO2·S + H2O·S 26.8 1013

s14 14.6 1013 HCOO·S + H·S CO2·S + H2·S 14.2 1013

s15 5.3 4 1012 CO2·S CO2 + S 0 106

s16 15.3 1013 H·S + H·S H2·S + S 12.8 1013

s17 5.5 6 1012 H2·S H2 + S 0 106

s18 15.3 6 1012 H·S + H·S H2 + S 7.3 106

Adsorptionand

DesorptionSteps

Surface Energetics for Cu(111) Catalyst:

Activation energies: kcal/mol

Pre-exponential factors:atm-1s-1 (ads/des) s-1 (surface)

Constructing the Constructing the RRRR Graph Graph

1. Select the shortest MINIMAL FR

OR = s1+s2+s3+s15+s7+s18

s1 s2 s3 s15 s7 s18

s18 s7 s15 s3 s2 s1

1

Constructing the Constructing the RRRR Graph Graph

2. Add the shortest MINIMAL ER to include all elementary reaction steps

s4 + s6 – s7 = 0s5 + s8 – s7 = 0s5 + s9 – s4 = 0s6 + s16 – s12 = 0s8 + s16 – s14 = 0s16 + s17 – s18 = 0

2

s1 s2 s3 s15 s7 s18

s18 s7 s15 s3 s2 s1s4

s5

s4

s5s9

s9

s6

s6

s12

s12

s8

s8

s14

s14

s17

s17 s16

s16

All but 3 steps included!

s11

s5

s16

Constructing the Constructing the RRRR Graph Graph

3. Add remaining steps to fused RR graph

s3 + s16 – s11 = 0s6 + s10 – s3 = 0s3 + s13 – s8 = 0

3

s1 s2 s3 s15 s7 s18

s18s7 s15 s3 s2 s1s4

s5

s4

s9

s9

s6

s6

s12

s12

s8

s8

s14

s14

s17

s17 s16 s11

s10 s10

s13

s13

Constructing the Constructing the RRRR Graph Graph

4. Balance the terminal nodes with the OR4

s18

s4

s5

s15 s17

s9

s7

s16

s14

s12

s6

s18

s4

s5

s15s17

s9

s7

s16

s12

s8s14

s8

s1

s1

OR

OR

s2 s3

s3 s2

s11s10

s10

s13

s13

s11

s6

RR RR NetworkNetwork

R1

OR

OR

R1

R2 R3

R13

R15 R4 R12 R17

R2R3R15R4R12R17

R18

R18 R16R16

R6

R6 R11

R11

R9

R9 R14

R14

R5

R5

R8

R8R13

R7

R7

R10

R10

RRRR enumeration enumerationFR1: s1 + s2 + s3 + s7 + s15 + s18 = OR

FR2: s1 + s2 + s7 + s11 + s15 + s17 = OR

FR3: s1 + s2 + s3 + s4 + s6 + s15 + s18 = OR

FR4: s1 + s2 + s3 + s5 + s8 + s15 + s18 = OR

FR5: s1 + s2 + s4 + s6 + s11 + s15 + s17 = OR

FR6: s1 + s2 + s3 + s4 + s12 + s15 + s17 = OR

FR7: s1 + s2 + s3 + s5 + s14 + s15 + s17 = OR

FR8: s1 + s2 + s3 + s7 + s15 + s16 + s17 = OR

FR9: s1 + s2 + s5 + s8 + s11 + s15 + s17 = OR

FR10: s1 + s2 + s7 + s8 – s13 + s15 + s18 = OR

FR250: s1 + s2 + s4 – s10 – 2s13 + 2s14 + s15 + 2s17 – s18 = OR

FR251: s1 + s2 + s5 + 2s10 + 2s12 + s13 + s15 – 2s16 + s18 = OR

FR252: s1 + s2 + s5 + 2s10 + 2s12 + s13 + s15 + 2s17 – s18 = OR

ER1: s4 + s6 – s7 = 0

ER2: s4 – s5 – s9 = 0

ER3: s5 – s7 + s8 = 0

ER4: s6 – s8 + s9 = 0

ER5: s3 – s6 – s10 = 0

ER6: s3 – s8 + s13 = 0

ER7: s3 – s11 + s16 = 0

ER8: s6 – s12 + s16 = 0

ER9: s8 – s14 + s16 = 0

ER10: s9 + s12 – s14 = 0

ER115: s5 – s7 + s9 – s10 + s11 + s17 – s18 = 0

ER116: s4 – s7 – s10 – s13 + s14 + s17 – s18 = 0

ER117: s5 – s7 + s10 + s12 + s13 + s17 – s18 = 0

Quasi Equilibrium & RDSQuasi Equilibrium & RDS

Simulations based on energetics of Cu(111)

R1 R2 R3

R5

R15 R17

R12

R8

R16 R7

R4

AOR

n1 n2 n3 n4

n5

n6

n7 n8

n9 n10

R3

R7

R12

R5R8

R4

AOR

273 373 473 573 673 773 87310

-4

10-2

100

102

104

106

108

1010

1012

Temperature (K)

Res

ista

nce

(ra

te(s

-1))

R7(R5+R8)

R7+R5+R8

R16

273 373 473 573 673 773 87310

-10

10-5

100

105

1010

1015

Temperature (K)

Res

ista

nce

(1/

rate

(s-1))

R3

R15, R17

R2

R1

Reduced Rate ExpressionReduced Rate Expression

rOR = r8 + r10 + r15

where

(OHS is the QSS species.)

2

2

2 2 2

2

2

1/ 2H2 6 2 12 17 CO

3 2 H O 0 5 7 1 CO 12 1/216 17 4 2 12 17 CO 12 H CO H

1/ 2H3 4 2 12 17 CO

12 5 7 1 CO1/23 16 174 2 12 17 CO 12 H

( )( )

1

( )( )

OR

P k K K K Pk K P θ k k K P k

K K k K K K P k P P Pr

KPk k K K K Pk k k K P

K K Kk K K K P k P

2H O COP P

2

2

0 1/ 2H

1 H O 2 1/ 24 5

1

1 CO

PK P K P

K K

Simulation of Microkinetic Model Simulation of Microkinetic Model

Ni(111)

Fe(110)

Cu(111)Experimental Conditions

FEED:COinlet = 0.10H2Oinlet = 0.10CO2 inlet = 0.00H2 inlet = 0.00

Space time: 1.80 s

Other CatalystsOther Catalysts

PtPt PdPd

RhRh RuRu

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

600 650 700 750 800 850 900 950 1000

Temperature (K)

Co

nve

rsio

n o

f C

O, H

2

Feed 1, X(CO)

Feed 2, X(H2)

Feed 3, X(CO)

0

0.1

0.2

0.3

0.4

0.5

0.6

400 500 600 700 800 900 1000

Temperature (K)

Co

nve

rsio

n C

O, H

2

Feed 1, X(CO)

Feed 2, X(H2)

Feed 3 X(CO)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

400 500 600 700 800 900 1000

Temperature (K)

Co

nve

rsio

n o

f C

O, H

2

Feed 1, X(CO)

Feed 2, X(H2)

Feed 3, X(CO)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

600 650 700 750 800 850 900 950 1000

Temperature (K)

Co

nve

rsio

n o

f C

O,H

2

Feed 1, X(CO)

Feed 2, X(H2)

Feed 3, X(CO)

Example ofExample ofMSR ReactionMSR Reaction

Theoretical Thermodynamic Equilibrium Calculations

kmoles of species vs H2O/CH4 @ T=1000 K

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3

H2O/CH4

km

ol

H2

H2O

CH4

CO

CO2

O2

Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

S. Rakass, H. Oudghiri-Hassani, P. Rowntree and N. Abatzoglou Effects of Temperature and CH4:H2O molar ratio, on theoretical equilibrium values

0%10%20%30%40%50%60%70%80%90%

100%

300 350 400 450 500 550 600 650 700

Teemperature C

CH

4 c

on

vers

ion

(%

)

CH4:H2O = 1:2

CH4:H2O = 2:2

CH4:H2O = 3:2

CH4:H2O = 4:2

Rakass, S. Journal of Power Sources xxx(2005) xxx-xxxRoine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

Froment et al. Mechanism forFroment et al. Mechanism forMethane Steam ReformingMethane Steam Reforming

s1: CH4 + S = CH4.S

s2: H2O + S = O.S + H2 s3: CO.S = CO + S s4: CO2

.S = CO2 + Ss5: H.S + H.S = H2

.S + S s6: H2

.S = H2 + S s7: CH4

.S + S = CH3.S + H.S

s8: CH3.S + S = CH2

.S + H.Ss9: CH2

.S + O.S = CH2O.S + Ss10: CH2O.S + S = CHO.S + H.Ss11: CHO.S + S = CO.S + H.Ss12: CHO.S + O.S = CO2

.S + H.Ss13: CO.S + O.S = CO2

.S + S

Xu, J.; Froment, G. F. , AIChE Journal, 1989, 35, 88

MSR RR Network

s2

s3

s4

s12

s12

s13

s3

s2

OR3

OR3

OR1

OR1

IR

IRs4

s13

s11

s11

OR2

OR2

OR4OR4

OR1: -CH4 - H2O + CO + 3H2 = 0

OR2: -CH4 - 2H2O + CO2 + 4H2 = 0

OR3: -H2O - CO + CO2 + H2 = 0

OR4: -CH4 - CO2 + 2CO + 2H2 = 0

Rostrupnielsen J. R , Journal of Catalysis 144, 38-49 (1993)

Activities of Metals for Steam Reforming

Ni CatalystThermodynamic Steadystate 2:1 ratio of Steam to Methane

0

10

20

30

40

50

60

70

80

90

573 673 773 873 973 1073 1173

Temperature K

ml/m

in

H2

CO

CH4

CO2

Thermodynamic

0

1

2

3

4

5

6

7

573 673 773 873 973 1073 1173

Temperature K

km

ol

H2

H20

CH4

CO

CO2

Ni ExperimentalResults

Theoretical Equilibrium Calculations of MSR

Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

Rhodium Catalyst

Experimental Results

0

10

20

30

40

50

60

70

80

90

300 350 400 450 500 550 600 650

Temperature K

ml/m

in . H2

CO

CH4

CO2

Future Work

• Combine both WGSR and MSR Network together• Determine promising catalyst candidates for

reforming based upon RR graph theory.• Perform MSR and ATR studies

Benefits to the NavyBenefits to the Navy

Extend fundamental understanding of reaction mechanisms involved in logistics fuel reforming reactions

Gather data on air-independent autothermal fuel reformation with commercially available catalysts

Develop new catalytic solutions for undersea fuel processing

Develop relationship between ONR and WPI

For more information….

WPI – Worcester, MACaitlin Callaghan – caitlin@alum.wpi.edu, http://alum.wpi.edu/~caitlin

James Liu – jliu0928@wpi.edu

Ilie Fishtik – ifishtik@wpi.edu

Ravindra Datta – rdatta@wpi.edu

NUWC – Newport, RIAlan Burke - BurkeAA@Npt.NUWC.Navy.Mil