Kinetic and bifurcation analysis of the cooxidation of CO and H2 in catalytic monolith reactors

Existing micro and global reaction kinetic models are not able to capture some of the key experimentally observed light-off trends of the CO-H-2-O-2 system in a monolithic reactor. We modify the literature microkinetic mechanisms to correctly predict the H-2 light-off at room temperature in the absence of CO, selectivity towards CO oxidation before the simultaneous light-off of CO and H-2, the enhancement effect of H-2, and the inhibiting effect of CO on light-off in a CO-H-2-O-2 system. To explain the effect of H-2 on light-off behavior of CO, we have proposed the formation and decomposition of a H-CO complex on Pt. This results in a decrease of CO desorption activation energy with an increase in the coverage of H species on Pt, thus assisting in the creation of more sites for oxygen adsorption. Based on the microkinetic studies and experimental results available in the literature, modifications have also been made to the global reaction kinetics, which currently do not distinguish between CO and H-2 oxidation kinetics, and also do not contain the effect of H-2 on CO oxidation kinetics. We propose global kinetics with composition dependent activation energies to explain the experimentally observed light-off behavior. A bifurcation analysis of a short monolith reactor model has been conducted to study the effect of inlet temperature, inlet concentrations and the exposed Pt surface area on the light-off and multiplicity behavior. A comparison of the light-off curves generated using the global model and microkinetic model is done and the effect of rate parameters on the region of multiplicity is investigated. (c) 2008 Elsevier Ltd. All rights reserved.