Kinetics

1
Kinetics Catalysis of Methane Steam Reforming
in SOFCs and Reformers
Caitlin A. Callaghan (PhD), James Liu (MS
candidate), Ilie Fishtik, and Ravindra Datta

• Fuel Cell Center
• Chemical Engineering Department
• Worcester Polytechnic Institute
• Worcester, MA

Alan Burke, Maria Medeiros, and Louis Carreiro
Naval Undersea Warfare Center Division
Newport Newport, RI
2
Methane Steam Reforming

• Consists of three reversible overall reactions
  (OR)

• 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

Rostrupnielsen J. R, Journal of Power Sources 105
(2002) 195-201
3
Solid Oxide Fuel Cell
Similar ORs and Chemistry
4
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

5
RR Graphs

• 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

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RR Graph Topology
Mechanism A B ? C
s1 A S ? AS s2 B S ? BS s3 AS BS ?
CS S s4 CS ? C S s5 AS BS ? C 2S
Full Route
A B
s1 A S ? AS s2 B S ? BS s5 AS BS ? C
2S OR A B ? C
s1
s2
s5
C
Empty Route
s3 AS BS ? CS S s4 CS ? C S s5 C
2S ? AS BS OR 0 ? 0
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Rate, Affinity Resistance

• DeDonder Relation
• Reaction Affinity
• Reaction Rate (Ohms Law)

(conventional)
RESISTANCE
8
Electrical Analogy
a

• Kirchhoffs Current Law
• Analogous to conservation of mass
• Kirchhoffs Voltage Law
• Analogous to thermodynamic consistency
• Ohms Law
• Viewed in terms of the De Donder Relation

b
e
c
d
f
g
i
h
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Example ofWGS Reaction
10
Surface Energetics for Cu(111) Catalyst
Adsorption and Desorption Steps
Activation energies kcal/mol Pre-exponential
factors atm-1s-1 (ads/des) s-1 (surface)
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Constructing the RR Graph

1. Select the shortest MINIMAL FR

1
s1
s2
s3
s15
s7
s18
s18
s7
s15
s3
s2
s1
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Constructing the RR Graph

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

2
s4 s6 s7 0
s5 s8 s7 0
s5 s9 s4 0
s6 s16 s12 0
s8 s16 s14 0
s16 s17 s18 0
s4
s6
s12
s1
s2
s3
s15
s7
s18
s9
s16
s5
s17
s8
s14
All but 3 steps included!
s14
s17
s5
s8
s16
s9
s18
s7
s15
s3
s2
s1
s12
s4
s6
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Constructing the RR Graph

1. Add remaining steps to fused RR graph

3
s3 s16 s11 0 s6 s10 s3 0 s3 s13
s8 0
?
?
s4
?
s6
s12
s1
s2
s3
s15
s7
s18
s11
s9
s16
s5
s17
s8
s14
s13
s10
s10
s14
s13
s5
s17
s8
s16
s9
s11
s7
s18
s15
s3
s2
s1
s12
s4
s6
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Constructing the RR Graph

1. Balance the terminal nodes with the OR

4
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RR Network
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RR enumeration
FR1 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
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(No Transcript)
18
Quasi Equilibrium RDS
Simulations based on energetics of Cu(111)
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Reduced Rate Expression

• rOR r8 r10 r15

where
(OHS is the QSS species.)
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Simulation of Microkinetic Model
Experimental Conditions Experimental Conditions
FEED COinlet 0.10 H2Oinlet 0.10 CO2 inlet 0.00 H2 inlet 0.00 Space time 1.80 s
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Other Catalysts
Pt
Pd
Rh
Ru
22
Example ofMSR Reaction
23
Theoretical Thermodynamic Equilibrium Calculations
Roine, A. HSC Chemistry Ver. 4.1 ed. Outokumpu
Research Oy, Pori, Finland.
24
S. Rakass, H. Oudghiri-Hassani, P. Rowntree and
N. Abatzoglou
Roine, A. HSC Chemistry Ver. 4.1 ed. Outokumpu
Research Oy, Pori, Finland.
Rakass, S. Journal of Power Sources xxx(2005)
xxx-xxx
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Froment et al. Mechanism forMethane Steam
Reforming
s1 CH4 S CH4.S s2 H2O S O.S H2
s3 CO.S CO S s4 CO2.S CO2 S s5
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.S s9 CH2.S O.S CH2O.S S s10
CH2O.S S CHO.S H.S s11 CHO.S S CO.S
H.S s12 CHO.S O.S CO2.S H.S s13
CO.S O.S CO2.S S
Xu, J. Froment, G. F. , AIChE Journal, 1989, 35,
88
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MSR RR Network
OR1 -CH4 - H2O CO 3H2 0 OR2 -CH4 - 2H2O
CO2 4H2 0 OR3 -H2O - CO CO2 H2
0 OR4 -CH4 - CO2 2CO 2H2 0
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Activities of Metals for Steam Reforming
Rostrupnielsen J. R , Journal of Catalysis 144,
38-49 (1993)
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Ni Catalyst
Ni ExperimentalResults
Theoretical Equilibrium Calculations of MSR
Roine, A. HSC Chemistry Ver. 4.1 ed. Outokumpu
Research Oy, Pori, Finland.
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Rhodium Catalyst
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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

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Benefits 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

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For more information.

• WPI Worcester, MA
• Caitlin Callaghan caitlin_at_alum.wpi.edu,
  http//alum.wpi.edu/caitlin
• James Liu jliu0928_at_wpi.edu
• Ilie Fishtik ifishtik_at_wpi.edu
• Ravindra Datta rdatta_at_wpi.edu
• NUWC Newport, RI
• Alan Burke - BurkeAA_at_Npt.NUWC.Navy.Mil