Kinetic and mechanistic features of carbon dioxide reforming of methane over Co-Ce/ZrO2 catalysts

Carbon dioxide reforming of methane (CDRM) is an effective route to utilize CO2 and CH4, the most abundant, thermodynamically stable and hazardous greenhouse gases. To overcome the economical impediments to favor CDRM's industrial applicability, its mechanistic features need to be revealed both for developing efficient catalysts and optimizing operational conditions. In this context, this work aims to obtain power-law type CDRM kinetic expressions over 5%Co-2%Ce/ZrO2 and 10%Co-2%Ce/ZrO2 catalysts and compare and analyze mechanistic routes to elucidate the effect of the Co:Ce ratio on kinetics. The empirical power-law type rate expressions were estimated with the reaction orders of 1.63 and 1.12 for CH4 and 0.29 and -0.12 for CO2 for 5%Co-2%Ce/ZrO2 and 10%Co-2%Ce/ZrO2 catalysts, respectively. Limited CH4 activation and, thus, carbon formation due to low Co loading lead to accumulation of surface oxygen on ZrO2 as redox ability of Ce becomes suppressed. This causes higher CO2 activation barrier. The presence of H-2 in the feed slows down mechanistic steps involving CHx. The reactions including CH4 activation, most probably reversible direct CH4 dissociation, are found to be rate determining.