kinetics & catalysis of the water-gas-shift...
TRANSCRIPT
Kinetics & Catalysis of theWater-Gas-Shift Reaction:
A Microkinetic and Graph Theoretic Approach
March 31, 2006
Caitlin A. Callaghan
A PhD Defense
Fuel Cell CenterDepartment of Chemical EngineeringWorcester Polytechnic InstituteWorcester, MA 01609
Research Objectives• Develop a predictive microkinetic model for LTS
and HTS water gas shift catalysts– Identify the slow steps– Develop reduced kinetic model
• Simulate the reaction for various metal catalysts
• Eventual goals:– detailed kinetic analysis– a priori design of WGS catalysts in fuel reformers for
fuel cells
That was thenThat was then……
• Catalyst design via trial and error• Mechanisms not comprehensive,
involving only a few elementary reaction steps
• Kinetic analysis of a mechanism based on arbitrary assumptions (i.e., RLS, QE, etc.)
This is nowThis is now……
• Comprehensive mechanism• Systematic methodology for mechanistic
analysis – RR Graph theory– Kirchhoff’s Laws
• Rational basis for catalyst design
AccomplishmentsAccomplishments
• Comprehensive mechanism• RR Graph Theory
– Graphical depiction of complete mechanism– Application of network theory (i.e., Kirchhoff’s
Laws)– Systematic simplification and reduction– QE reactions, RLSs identified
OutlineOutline
• Why study the WGSR?• Catalytic Kinetic Analysis
– LHHW Approach– Microkinetic Approach
• Reaction Route Graphs– RR Graph Theory– Network Reduction & Analysis
• Future Work
The Fuel CellThe Fuel CellImportance
• Environmental Issues:– Depletion of fossil fuels– Harmful by-products released during combustion
in power production
• Fuel Cells provide an alternative to traditional methods of obtaining power.
… Fuel Cells…a cleaner, more efficient alternative
Where does HWhere does H22 come from?come from?
Burner
FuelTank
AIR
EXHAUST
H2OFUEL CELL
FUEL
Reformer(ATR or SR)
HTSReactor
LTSReactor
PreferentialOxidation
(PrOx)
Generator+
-
Saturator
Radiator
Battery
Cathode Anode
Effect of CO on PEM Fuel Cell Effect of CO on PEM Fuel Cell PerformancePerformance
S. Gottesfeld, and J. Pafford, J. Electrochem. Soc., 135, 2651 (1988).
Why is the WGSR important?– Many industrial applications:
• Ammonia synthesis• Methanol synthesis• Hydrogen production
– WGSR is the greatest catalytic challenge in fuel processing– Recovers lost energy– The ideal catalyst must have sufficient activity and durability
start-up, shutdownair exposureover a wide temperature range
Why is the WGSR studied?– Detailed understanding of mechanism and kinetics is lacking– At present, development of catalyst is by trial and error and
substantial experimentation with limited success– Design of catalyst via simulation is attractive
The WaterThe Water--GasGas--Shift ReactionShift Reaction
H2O + CO H2 + CO2
The WGS Reaction:
LHHW Approach (1)LHHW Approach (1)
• Single RRmechanism
• Single RLS assumed
• Remaining steps at QE
s1: A + S A·S QEs2: A·S B·S RLSs3: B·S B + S QE
B2 A
AOR
A A
11
1
t
A B
PC k PK P
rK P K P
⎛ ⎞−⎜ ⎟
⎝ ⎠=+ +
LHHW Approach (2)LHHW Approach (2)
• Boudart (1984)– 2 RLS– Single RR
• Ovesen, et al. (1996)– 3 RLS– Single RR
CO·S + O·S CO2·S + S
OH·S + S O·S + H·S
H2O·S + S OH·S + H·S
Redox Reaction Mechanism
O·S + CO CO2 + S
H2O + S O·S + H2
Two-Step Redox Reaction Mechanism
Boudart, M.; Djega-Mariadassou, G. Kinetics of Heterogeneous Catalytic Reactions; Princeton University Press: Princeton, 1984.; Ovesen, C. V., et al., J. Catal. 1996, 158, 170.
Microkinetic Approach (1)Microkinetic Approach (1)
• More comprehensive mechanism
• Obtain kinetics, theoretically
• Assume a reactor type
CO(g)
+ H2O(g)
CO2(g)
+ H2(g)
H2O
OHCO H2
OCO2 H
Catalyst Surface
• Solve material balances for all species (including intermediates) using “black box” approach
Dumesic, J. A., et al. The Microkinetics of Heterogeneous Catalysis; ACS, 1993.Stoltze, P., Progress in Surface Science 2000, 65, 65.
Microkinetic Approach (2)Microkinetic Approach (2)
s 13: H2O·S + O·S 2OH·S
s 12: HCOO·S + O·S CO2·S + OH·S
s 11: HCOO·S + S CO2·S + H·S
s 10: CO·S + OH·S CO2·S + H·S
s 9: OH·S + S O·S + H·S
s 8: CO·S + OH·S HCOO·S + S
s 7: CO·S + O·S CO2·S + S
s 6: H2O·S + S OH·S + H·S
s 5: H2·S H2 + S
s 4: H·S + H·S H2·S + S
s 3: CO2·S CO2 + S
s 2: CO + S CO·S
s1: H2O + S H2O·S
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 3 6 9 12 15
Time (s)
Spec
ies
Cov
erag
eCO·S
H2O·S
H·S
Fishtik, I.; Datta, R., Surf. Sci. 2002, 512, 229.
RR RR GraphsGraphs
A RR graph may be viewed as several hikes through a mountain range:
Valleys are the energy levels of reactants and productsElementary reaction is a hike from one valley to adjacent valleyTrek over a mountain pass represents overcoming the energy barrier
Reaction Route Graph TheoryReaction Route Graph Theory
Powerful new tool in graphical and mathematical depiction of reaction mechanisms
New method for mechanistic and kinetic interpretation
“RR graph” differs from “Reaction Graphs”– Branches elementary reaction steps– Nodes multiple species, connectivity of elementary reaction
steps
Reaction Route Analysis, Reduction and Simplification – Enumeration of direct reaction routes– Dominant reaction routes via network analysis– RDS, QSSA, MARI assumptions based on a rigorous De Donder
affinity analysis– Derivation of explicit and accurate rate expressions for dominant
reaction routes
Ref. Fishtik, I., C. A. Callaghan, et al. (2004). J. Phys. Chem. B 108: 5671-5682. Fishtik, I., C. A. Callaghan, et al. (2004). J. Phys. Chem. B 108: 5683-5697. Fishtik, I., C. A. Callaghan, et al. (2005). J. Phys. Chem. B 109: 2710-2722.
RRRR Graph TopologyGraph Topology
A + B
C
s1 s2 s5
s3 s4
s5
s1 s2
s3 s4
s5OR
s1: A + S A·Ss2: B + S B·Ss3: A·S + B·S C·S + Ss4: C·S C + SOR: 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
Eρ ρΛ Elementary Reaction Steps
Eρ ρΛ
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)
Rate, Affinity & ResistanceRate, Affinity & Resistance• DeDonder Relation:
• Reaction Affinity:
• Reaction Rate (Ohm’s Law):
( )1 1 expr
r r rr
ρρ ρ ρ ρ
ρ
⎛ ⎞⎡ ⎤= − = − −⎜ ⎟ ⎣ ⎦⎜ ⎟
⎝ ⎠A
1 1 1
ln ln ln lnqn n
i i o o k k i ii k i
AK P
RTρ
ρ ρ ρ ρ ρ ρν µ α θ α θ β= = =
− = − = = − + + +∑ ∑ ∑A
rR
ρρ
ρ
=A
(conventional)
ln1
rr
Rr r r
ρ
ρρ
ρ ρ ρ
⎛ ⎞⎜ ⎟⎝ ⎠= =
−
RESISTANCE
net reaction rate
forward reaction rate
reaction affinity
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
Electrical AnalogyElectrical Analogya
b
cd
ea b c d e 0r r r r r− + − + =
f g h i 0− − =A +A A Af g
i h
Rr
ρρ
ρ
A=
Constructing the Constructing the RRRR GraphGraph
1. Select the shortest MINIMAL FROR = s1+s2+s3+s15+s7+s18
s1 s2 s3 s15 s7 s18
s18 s7 s15 s3 s2 s1
1
Constructing the Constructing the RRRR GraphGraph
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!
s5
s16
Constructing the Constructing the RRRR GraphGraph
3. Add remaining steps to fused RR graphs3 + 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
s11
s10 s10
s13s13
RRRR enumerationenumerationFR1: 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
Parallel PathwaysParallel Pathways
100
1010
1020s4+s6-s7
R4 + R6R7
100
1010
1020s5-s7+s8
R5 + R8R7
100
1010
1020s4-s5-s9
R5 + R9R4
100
1015
1030s3-s6-s10
R6 + R10R3
100
1020s3-s8+s13
R3 + R13R8
100
1020s6-s8+s9
R6 + R9R8
100
1010
1020s3-s11+s16
R3 + R16R11
100
1010
1020
s6-s12+s16
R6 + R16R12
100
1010
1020s8-s14+s16
R8 + R16R14
10-3
10-2
10-1
100s16+s17-s18
R16 + R17R18
273 473 673 873100
1015
1030s10-s11+s12
R10 + R12R11
273 473 673 873100
1010
1020s11+s13-s14
R11 + R13R14
273 473 673 873100
1010
1020s9+s12-s14
R9 + R12R14
273 473 673 873100
1015
1030s9-s10-s13
Res
ista
nce
(1/ra
te(s
-1))
R10 + R13R9
Temperature (K)
Complete MechanismComplete Mechanismw/ and w/o s18
273 373 473 573 673 773 8730
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Con
vers
ion
of C
O
Temperature (K)
Overall MechanismEquilibriumw/o s18
Network Reduction (1)Network Reduction (1)
• Consider the effect of s18
• Similarly, s10 and s13 are not kinetically significant, as indicated in previous studies*.
• Thus far, mechanism reduced to 15 steps previously considered*.
• Now…
*Fishtik, et al., J. Phys Chem. B 108 (2004), 5683.
Network Reduction (2)Network Reduction (2)
CO2 inlet 0.00
H2 inlet 0.00
CO inlet 0.10
H2O inlet 0.10
Experimental ConditionsSpace time
1.80 s
Simulations based on energetics of Cu(111)
R1 R2 R3
R14 R5
R15 R17
R12
R8R16
R9R6
R11 R7
R4
AOR
(a)n1 n2 n3 n4
n5
n6
n7 n8
n9 n10
n3 to n6R3 + R16 vs. R11
n6 to n7R6 + R9 vs. R8
Parallel PathwaysParallel Pathways
100
1010
1020s4+s6-s7
R4 + R6R7
100
1010
1020s5-s7+s8
R5 + R8R7
100
1010
1020s4-s5-s9
R5 + R9R4
100
1015
1030s3-s6-s10
R6 + R10R3
100
1020s3-s8+s13
R3 + R13R8
100
1020s6-s8+s9
R6 + R9R8
100
1010
1020s3-s11+s16
R3 + R16R11
100
1010
1020
s6-s12+s16
R6 + R16R12
100
1010
1020s8-s14+s16
R8 + R16R14
10-3
10-2
10-1
100s16+s17-s18
R16 + R17R18
273 473 673 873100
1015
1030s10-s11+s12
R10 + R12R11
273 473 673 873100
1010
1020s11+s13-s14
R11 + R13R14
273 473 673 873100
1010
1020s9+s12-s14
R9 + R12R14
273 473 673 873100
1015
1030s9-s10-s13
Res
ista
nce
(1/ra
te(s
-1))
R10 + R13R9
Temperature (K)
Network Reduction (3)Network Reduction (3)
CO2 inlet 0.00
H2 inlet 0.00
CO inlet 0.10
H2Oinlet 0.10
Experimental ConditionsSpace time
1.80 s
Simulations based on energetics of Cu(111)
R1 R2 R3
R14 R5
R15 R17
R12
R8R16 R7
R4
AOR
(c)n1 n2 n3 n4
n5
n6
n7 n8
n9 n10
n4 to n7R8 + R16 vs. R14
COCO HH22OOs1 s2
s3
s5
s16
Formate RR
COCO22
s15
HH22
s17
s7
s12
ModifiedRedox RR
AssociativeRR
s8s4
C
C
O
H
H OH
C
O
OH
H
H
H H
H H
O O
C
O
O
C
O
O
CO O
H H C
O
O
s6
Redox RR
s4
H H
COCO HH22OOs1 s2
s3
s5
s16
Formate RR
COCO22
s15
HH22
s17
s7
s12
ModifiedRedox RR
AssociativeRR
s8s4
C
C
O
C
O
H
H OH
H OH
C
O
C
O
OH
HH
HH
HH HH
HH H
O OO O
C
O
C
O
C
O
O
C
O
OC
O
C
O
C
O
OO
CO O
CO OO O
HH HH C
O
C
O
C
O
O
s6
Redox RR
s4
H HHH H
WGSR Energy DiagramWGSR Energy Diagram
Based on energetics of Cu(111)
n1
Pote
ntia
l Ene
rgy
(kca
l/ mol
)
0
10
20
30
40
50
-10
-20
-30
-40
-50
Reaction Coordinate
s17s15
s12
s16
s4
s3s1
s2s5
s8
s7
n2
n3
n4 n7
n5 n6
n8
n9
n10
from the reduced RR network
Quasi Equilibrium & RDSQuasi Equilibrium & RDS
Simulations based on energetics of Cu(111)
273 373 473 573 673 773 87310
-10
10-5
100
105
1010
1015
Temperature (K)
Res
ista
nce
(1/ra
te(s
-1))
R3
R15, R17
R2
R1
273 373 473 573 673 773 87310
-4
10-2
100
102
104
106
108
1010
1012
Temperature (K)
Res
ista
nce
(rat
e(s
-1))
R7(R5+R8)
R7+R5+R8
R16
Reduced Rate ExpressionReduced Rate Expression
rOR = r8 + r10 + r15
where
( )2
2
0 1/ 2H
1 H O 2 1/ 24 5
1
1 COP
K P K PK K
θ =
+ + +
(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⎛ ⎞⎜ ⎟⎜ ⎟⎝ ⎠
Experimental ValidationExperimental Validation
Data Acquisition
Vent to Hood
ArAr
digital signaldigital signalmaterial flowmaterial flow
CO
MFC
CO
MFC
H2
MFC
H2
MFC
N2
MFC
N2
MFC
MFC Readout
Furnace
Packed Bed Reactor Condenser
Bypass
Data Acquisition
Gas Chromatograph
DI H2O
MFC
CO2
MFC
MFC
CO2
Syringe Pump
Vaporizing Section
Simulation of Microkinetic Model Simulation of Microkinetic Model for Cu(111)for Cu(111)
Experimental Conditions
Space time:
1.80 s
FEED:
COinlet = 0.10
H2Oinlet = 0.10
CO2 inlet = 0.00
H2 inlet = 0.00
0
0.2
0.4
0.6
0.8
1
0 100 200 300 400 500 600
Temperature (oC)
Con
vers
ion
of C
O
Experiment
Equilibrium
Simplified Model
Simulation of Microkinetic Model Simulation of Microkinetic Model for Fe(110)for Fe(110)
0
0.2
0.4
0.6
0.8
1
0 100 200 300 400 500 600Temperature (oC)
Con
vers
ion
of C
O
ExperimentFe15modelEquilibrium
FeExperimental Conditions
Space time:
1.34 s
FEED:
COinlet = 0.10
H2Oinlet = 0.10
CO2 inlet = 0.00
H2 inlet = 0.00
Simulation of Microkinetic Model Simulation of Microkinetic Model for Ni(111)for Ni(111)
0
0.2
0.4
0.6
0.8
1
0 100 200 300 400 500 600
Temperature (oC)
Con
vers
ion
of C
O
Experiment
EquilibriumMicrokinetic Model
NiExperimental Conditions
Space time:
1.80 s
FEED:
COinlet = 0.11
H2Oinlet = 0.256
CO2 inlet = 0.068
H2 inlet = 0.256
ConclusionsConclusions• Reaction network analysis is a useful tool for
reduction, simplification and rationalization of the microkinetic model.
• A direct analogy between a reaction network and electrical network exists.
• This analogy allows the application of Kirchhoff’s Laws and mechanism reduction
• Application of the formalism to the WGS reaction confirmed the reduced model developed earlier based solely on a numerical RR analysis
• Reasonable comparison with experimental results
The next stepsThe next steps……
• Elementary Reaction Kinetics– How can we improve the model?
• Reaction Route Graphs/Network Analysis– Where else can we apply the methodology?
• Experimental– What about methane production?
Elementary Reaction KineticsElementary Reaction KineticsReaction Energetics
• Transition State Complex identification• Activation Energies
– Ab Initio, semi-empirical methods• Pre-exponential factors
– Statistical Mechanics– Lund’s Methodology– Ab Initio
Elementary Reaction KineticsElementary Reaction KineticsStatistical Mechanics
Partition Function Parameters and Calculation Results (T = 190oC) [12,16]
Species H2 H·S H2O H2O·S O·S OH·S CO CO·S CO2 CO2·S HCOO·S m kg 3.32E-27 2.99E-26 4.65E-26 7.31E-26
ω? cm-1 1121 460 391 280 343 410 340
ω|| cm-1 928 48 508 49 24 31 36
ω cm-1 4405.3 1594.6 1600 670 2170 2089 1343 1343 760
3657.1 3370 667 667 1330
3755.8 745 2349 2349 1640
2910
1043
1377
1377
σ 2 2 1 2
B cm-1 60.8 1.93 0.39
IAIBIC kg3m6 5.77E-141
Ee kJ/mol -35 -40.7 -306 -359 -243 309.6 -132.2 -186.1 -359 -431 554
zt 3.34E+05 1.13E-02 9.03E+06 2.88E+01 2.53E-01 4.79E+01 1.75E+07 1.61E+02 3.45E+07 7.90E+01 7.21E+01 zv 1.06E-03 1.00E+00 8.37E-07 1.55E-04 1.00E+00 4.03E-01 3.43E-02 3.90E-02 1.33E-03 1.33E-03 1.09E-07 zr 2.65E+00 1.00E+00 8.30E+01 1.00E+00 1.00E+00 1.00E+00 1.67E+02 1.00E+00 4.12E+02 1.00E+00 1.00E+00 ze 8.86E+03 3.89E+04 3.25E+34 3.09E+40 2.55E+27 1.21E-35 8.13E+14 9.76E+20 4.08E+48 3.09E+40 3.29E-63 z 8.33E+06 4.41E+02 2.04E+37 1.38E+38 6.46E+26 2.33E-34 8.15E+22 6.11E+21 7.71E+55 3.24E+39 2.58E-68
Ref. Ovesen, et al. J. Catal. 1992, 134, 445; Ovesen, et al. J. Catal. 1996, 158, 170.
0AB
ABA S B S
expB B
B
zk T k T Sh z z h k⋅ ⋅
′′ ⎛ ⎞∆Λ = = ⎜ ⎟′′ ′′ ⎝ ⎠
‡‡
Elementary Reaction KineticsElementary Reaction KineticsLund’s Methodology
Lund, C., Ind. Eng. Chem. Res. 1996, 35, 2531.
( ) ( ), · , ,g gf i S f i trans iS S S∆ = ∆ −
( )
( )32
, 3
25 ln2g
gasi Btrans i gas
R Tm k TS R
h Pπ⎡ ⎤⎛ ⎞
⎢ ⎥⎜ ⎟= + ×⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦
exp jj j
SR
⎛ ⎞∆Λ = Λ −⎜ ⎟⎜ ⎟
⎝ ⎠
Lund Dumesic Forward Reverse Forward Reverse
s1 1.00E+06 8.01E+16 1.50E+06 1.00E+14s2 1.00E+06 2.02E+14 1.00E+06 1.00E+14s3 1.00E+13 8.25E+12 1.00E+13 1.00E+13s4 1.00E+13 2.38E+13 1.00E+13 1.00E+13s5 1.00E+13 2.90E+12 1.00E+13 1.00E+13s6 1.00E+13 6.80E+13 1.00E+13 1.00E+13s7 1.00E+13 1.62E+14 1.00E+13 1.00E+13s8 1.00E+13 5.59E+14 1.00E+13 1.00E+13s9 1.00E+13 8.23E+13 1.00E+13 1.00E+13s10 1.00E+13 1.21E+12 1.00E+13 1.00E+13s11 1.00E+13 7.05E+12 1.00E+13 1.00E+13s12 1.00E+13 5.81E+13 1.00E+13 1.00E+13s13 1.00E+13 6.78E+14 1.00E+13 1.00E+13s14 1.00E+13 4.78E+14 1.00E+13 1.00E+13s15 1.00E+13 7.59E+03 4.00E+12 1.00E+06s16 1.00E+13 8.54E+12 1.00E+13 1.00E+13s17 1.00E+13 1.81E+04 6.00E+12 1.00E+06s18 1.00E+13 1.55E+04 6.00E+12 1.00E+06
ExperimentalExperimentalPrecious Metal 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)
Con
vers
ion
of 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)
Con
vers
ion
CO
, H2
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 1000Temperature (K)
Con
vers
ion
of 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)
Con
vers
ion
of C
O,H
2
Feed 1, X(CO)
Feed 2, X(H2)
Feed 3, X(CO)
ExperimentalExperimentalMethanation
• The precious metal catalysts produced methane as a by-product of the WGS reaction…– Where did it come from?– How can we correct for
it?– Will a multiple OR RR
graph yield a model that will account for the production of CH4?
C + 2H2 CH4
CO2 + 4H2 CH4 + 2H2O
CO + 3H2 CH4 + H2O
2CO + 2H2 CO2 + CH4
CO2 + 2H2 C + 2H2O
CO + H2 C + H2O
2CO C + CO2
Possible Side Reactions of the WGS Reaction
Xue, E.; O'Keeffe, M. O.; Ross, J. R. H., Catal. Today 1996, 30, 107.
Reaction Route GraphsReaction Route GraphsMultiple OR Graphs
• Extension of RR graph theory to reaction mechanisms comprising multiple OR reactions– Steam Reforming Process:
CH4 + H2O CO + 3H2 (MSR)
CH4 + ½ O2 CO + 2 H2 (CPOX)
CO + H2O CO2 + H2 (WGS)
• How are the individual OR linked via their RRgraphs?
AcknowledgementsAcknowledgements
• Prof. Ravindra Datta, Advisor• Prof. Ilie Fishtik, Co-Advisor• Prof. Nikolas K. Kazantzis• Prof. Joseph D. Fehribach• Prof. Jennifer L. Wilcox• Dr. A. Alan Burke• Dr. Nikhil Jalani, Saurabh Vilekar, James Liu, Katherine Fay• Dr. Pyoungho Choi, Dr. Jingxin Zhang, Dr. Tony Thampan• Joe Kaupu, Sandy Natale, Jack Ferraro and Doug White• Students, Faculty and Staff of the Chemical Engineering Department• My family• …and everyone else I’ve met along the way!
• General Motors’ GM Fellowship• Office of Naval Research/University Laboratory Initiative Program
I would like to thank the following individuals for their assistance, support, guidance and inspiration during the time I have worked on this research.