Experiments and Modeling of Methane Autothermal Reforming over Structured Ni–Rh-Based Si-SiC Foam Catalysts

Novel silicon-infiltrated silicon carbide (Si-SiC) foams coated with a 100.3 wt % NiRh/MgAl2O4 catalyst were studied for the autothermal reforming of model biogas for the production of fuel cell hydrogen. Kinetic studies were performed by varying the inlet concentration of methane, water, and carbon dioxide as well as the temperature. Despite the very good heat conductivity of the SiC structured support, it was not possible to operate the reactor at isothermal conditions because of the succession of fast reactions that were, first, strongly exothermic and, second, strongly endothermic. The experimental data were compared to a reactor model taking explicitly the heat balance in the gas and solid phases into account. The reforming kinetics were based on the methane steam reforming model by Xu and Froment [Xu, J.; Froment, G.F. AIChE J., 1989, 35, 8896] complemented by a simple equation for methane oxidation. The kinetics were adapted by introducing an oxygen adsorption term to describe the consecutive complete methane oxidation and reforming reactions, in line with previous observations of two separate zones in the reactor. The model gives an adequate description of the data, giving the correct trends of the reaction orders of the reactants.