Kinetics & Catalysis of Methane Steam Reforming in SOFCs and Reformers Fuel Cell Center Chemical Engineering Department Worcester Polytechnic Institute Worcester, MA Caitlin A. Callaghan (PhD), James Liu (MS candidate), Ilie Fishtik, and Ravindra Datta Alan Burke, Maria Medeiros, and Louis Carreiro Naval Undersea Warfare Center Division Newport Newport, RI

Methane Steam Reforming Consists of three reversible overall reactions (OR): Rostrupnielsen J. R, Journal of Power Sources 105 (2002) 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 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 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

RR Graph Topology A + B C s1s1 s2s2 s5s5 s3s3 s4s4 s5s5 s1s1 s2s2 s3s3 s4s4 s5s5 OR s 1 :A + S  A·S s 2 :B + S  B·S s 5 :A·S + B·S  C + 2S OR:A + B  C s 3 :A·S + B·S  C·S + S s 4 :C·S  C + S – s 5 :C + 2S  A·S + B·S OR:0  0 Full Route s 1 :A + S  A·S s 2 :B + S  B·S s 3 :A·S + B·S  C·S + S s 4 :C·S  C + S s 5 :A·S + B·S  C + 2S Mechanism: A + B  C Empty Route

Rate, Affinity & Resistance DeDonder Relation: Reaction Affinity: Reaction Rate (Ohm’s Law): (conventional) net reaction rate reaction affinity RESISTANCE forward reaction rate

Electrical 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 fg ih

Example of WGS Reaction

Adsorption and Desorption Steps Surface Energetics for Cu(111) Catalyst: Activation energies: kcal/mol Pre-exponential factors: atm -1 s -1 (ads/des) s -1 (surface)

Constructing the RR Graph 1.Select the shortest MINIMAL FR s1s1 s2s2 s3s3 s 15 s7s7 s 18 s7s7 s 15 s3s3 s2s2 s1s1 1

Constructing the RR Graph 2.Add the shortest MINIMAL ER to include all elementary reaction steps s 4 + s 6 – s 7 = 0s 5 + s 8 – s 7 = 0s 5 + s 9 – s 4 = 0s 6 + s 16 – s 12 = 0s 8 + s 16 – s 14 = 0s 16 + s 17 – s 18 = 0 2 s1s1 s2s2 s3s3 s 15 s7s7 s 18 s7s7 s 15 s3s3 s2s2 s1s1 s4s4 s5s5 s4s4 s5s5 s9s9 s9s9 s6s6 s6s6 s 12 s8s8 s8s8 s 14 s 17 s 16 All but 3 steps included!

s 11 s5s5 s 16 Constructing the RR Graph 3.Add remaining steps to fused RR graph s 3 + s 16 – s 11 = 0 s 6 + s 10 – s 3 = 0 s 3 + s 13 – s 8 = 0 3 s1s1 s2s2 s3s3 s 15 s7s7 s 18 s7s7 s 15 s3s3 s2s2 s1s1 s4s4 s5s5 s4s4 s9s9 s9s9 s6s6 s6s6 s 12 s8s8 s8s8 s 14 s 17 s 16 s 11 s 10 s 13

Constructing the RR Graph 4.Balance the terminal nodes with the OR 4

RR Network

RR enumeration FR 1 :s 1 + s 2 + s 3 + s 7 + s 15 + s 18 = OR FR 2 :s 1 + s 2 + s 7 + s 11 + s 15 + s 17 = OR FR 3 :s 1 + s 2 + s 3 + s 4 + s 6 + s 15 + s 18 = OR FR 4 :s 1 + s 2 + s 3 + s 5 + s 8 + s 15 + s 18 = OR FR 5 :s 1 + s 2 + s 4 + s 6 + s 11 + s 15 + s 17 = OR FR 6 :s 1 + s 2 + s 3 + s 4 + s 12 + s 15 + s 17 = OR FR 7 :s 1 + s 2 + s 3 + s 5 + s 14 + s 15 + s 17 = OR FR 8 :s 1 + s 2 + s 3 + s 7 + s 15 + s 16 + s 17 = OR FR 9 :s 1 + s 2 + s 5 + s 8 + s 11 + s 15 + s 17 = OR FR 10 :s 1 + s 2 + s 7 + s 8 – s 13 + s 15 + s 18 = OR  FR 250 :s 1 + s 2 + s 4 – s 10 – 2s s 14 + s s 17 – s 18 = OR FR 251 :s 1 + s 2 + s 5 + 2s s 12 + s 13 + s 15 – 2s 16 + s 18 = OR FR 252 :s 1 + s 2 + s 5 + 2s s 12 + s 13 + s s 17 – s 18 = OR ER 1 :s 4 + s 6 – s 7 = 0 ER 2 :s 4 – s 5 – s 9 = 0 ER 3 :s 5 – s 7 + s 8 = 0 ER 4 :s 6 – s 8 + s 9 = 0 ER 5 :s 3 – s 6 – s 10 = 0 ER 6 :s 3 – s 8 + s 13 = 0 ER 7 :s 3 – s 11 + s 16 = 0 ER 8 :s 6 – s 12 + s 16 = 0 ER 9 :s 8 – s 14 + s 16 = 0 ER 10 :s 9 + s 12 – s 14 = 0  ER 115 :s 5 – s 7 + s 9 – s 10 + s 11 + s 17 – s 18 = 0 ER 116 :s 4 – s 7 – s 10 – s 13 + s 14 + s 17 – s 18 = 0 ER 117 :s 5 – s 7 + s 10 + s 12 + s 13 + s 17 – s 18 = 0

Quasi Equilibrium & RDS Simulations based on energetics of Cu(111) Temperature (K) Resistance (1/rate(s - 1 )) R 3 R 15,R 17 R 2 R 1

Reduced Rate Expression r OR = r 8 + r 10 + r 15 where (OHS is the QSS species.)

Simulation of Microkinetic Model Ni(111) Fe(110) Cu(111) Experimental Conditions FEED: CO inlet = 0.10 H 2 O inlet = 0.10 CO 2 inlet = 0.00 H 2 inlet = 0.00 Space time: 1.80 s

Other Catalysts PtPd RhRu

Example of MSR Reaction

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

S. Rakass, H. Oudghiri-Hassani, P. Rowntree and N. Abatzoglou Rakass, S. Journal of Power Sources xxx(2005) xxx-xxx Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

Froment et al. Mechanism for Methane Steam Reforming s1: CH 4 + S = CH 4. S s2: H 2 O + S = O. S + H 2 s3: CO. S = CO + S s4: CO 2. S = CO 2 + S s5: H. S + H. S = H 2. S + S s6: H 2. S = H 2 + S s7: CH 4. S + S = CH 3. S + H. S s8: CH 3. S + S = CH 2. S + H. S s9: CH 2. S + O. S = CH 2 O. S + S s10: CH 2 O. S + S = CHO. S + H. S s11: CHO. S + S = CO. S + H. S s12: CHO. S + O. S = CO 2. S + H. S s13: CO. S + O. S = CO 2. S + S Xu, J.; Froment, G. F., AIChE Journal, 1989, 35, 88

MSR RR Network OR 1 : -CH 4 - H 2 O + CO + 3H 2 = 0 OR 2 : -CH 4 - 2H 2 O + CO 2 + 4H 2 = 0 OR 3 : -H 2 O - CO + CO 2 + H 2 = 0 OR 4 : -CH 4 - CO 2 + 2CO + 2H 2 = 0

Rostrupnielsen J. R, Journal of Catalysis 144, (1993) Activities of Metals for Steam Reforming

Ni Catalyst Ni Experimental Results Theoretical Equilibrium Calculations of MSR Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

Rhodium Catalyst

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 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, MA Caitlin Callaghan – James Liu – Ilie Fishtik – Ravindra Datta – NUWC – Newport, RI Alan Burke -