Low temperature catalytic methane steam reforming over ceria-zirconia supported rhodium

This paper presents an experimental study of the catalytic steam reforming of methane over newly developed ceria-zirconia supported rhodium as an active candidate catalyst for low temperature sorption enhanced hydrogen production from methane. The kinetic experiments are performed in a tubular fixed bed reactor over a temperature range of 475-725 degrees C and a total pressure of 1.5 bar in the absence of mass transport limitations. The over all reaction orders in methane and steam are determined to be less than 1 from 475 to 625 degrees C. At low temperature, most of the gas product is composed of CO2 and H-2 due to the pronounced influence of the water-gas shift reaction. At higher temperature and low steam/carbon ratio (S/C), this influence is diminished. Inhibitory effects of H-2, CO, and CO2 on the methane conversion rates are detected. Temperature-programmed steam reforming experiments over ceria-zirconia support revealed insignificant methane adsorption on the surface from 550 to 725 degrees C. Catalyst deactivation and steady state stability over time were examined. A molecular reaction mechanism is proposed to qualitatively explain the kinetic observations. Two distinct sites are thought to be responsible for the dissociative adsorption of methane and steam on the catalyst and the support surfaces. Methane is dissociatively adsorbed on the rhodium active metal sites and steam is dissociatively adsorbed on the support surface. Surface reactions of carbon containing methane precursors on the interface between the active metal and the support are considered to be the rate determining steps. (C) 2010 Elsevier B.V. All rights reserved.