Kinetics of Methanol Steam Reforming with a Pd-Zn-Y/CeO sub(2) Catalyst under Realistic Operating Conditions of a Portable Reformer in Fuel Cell Applications

Kinetics of methanol steam reforming (MSR) with a catalyst containing palladium and zinc on a cerium oxide support was investigated using a differential reactor approach. The goal of the study was to develop optimal process conditions for portable fuel reformers in fuel cell applications. Activation energies for the MSR reaction and for the overall methanol conversion, as well as pre-exponential factors and the reaction orders for CH sub(3)OH, H sub(2)O, H sub(2), CO sub(2), and CO were determined. The study covers the temperature range from 230 to 320 degree C, consistent with the operation of a reformer integrated to a portable power fuel cell device. All work was done with a mixture of CH sub(3)OH and H sub(2)O with a volume ratio 2:1 (molar ratio 0.88:1) at atmospheric pressure, which is representative of the process conditions of practical interest for this application. For the determination of reaction orders the concentration of each reactant under consideration was varied to mimic a broad range of CH sub(3)OH conversions. The following power law kinetic equations for methanol steam reforming reaction and for overall methanol conversion were established: (i) For methanol steam reforming CH sub(3)OH + H sub(2)O = 3H sub(2) + CO sub(2), R sub(MSR) = 34.476 e super(-54270/(RT)) p sub(CH3OH) super(0.54) p sub(H2O) super(0.10) p sub(H2) super(-0.40) p sub(CO2) super(-0.13) p sub(CO) super(-0.075). (ii) For overall methanol conversion (MSR plus CO formation), R sub(overall) = 53.309 e super(-55860/(RT)) p sub(CH3OH) super(0. 54) p sub(H2O) super(0.10) p sub(H2) super(-0.40) p sub(CO2) super(-0.13) p sub(CO) super(-0.075). In these equations, R sub(MSR) and R sub(overall) are the reaction rates (mol.s super(-1).g sub(Pd) super(-1)); 34.476 and 53.309 are the pre-exponential factors; 54270 and 55860 are the activation energies of MSR and of the overall methanol conversion, respectively (J.mol super(-1)); R is the molar gas constant (8.314472 J.mol super(-1).K super(-1)), T is the temperature (K), and p sub(i) is the partial pressure of the ith component (kPa).