Abstract:
The aim of the current work is to design and develop effective non-PGM based CDRM catalysts, to confirm the roles of each catalyst component, to determine optimum reaction conditions for the highest performance, and to reveal the details of CDRM reaction mechanism. In activity and selectivity tests, the reaction temperature, feed ratio and space velocity were used as the parameters. The properties of both the catalysts and the type of carbon deposited on them during CDRM were analyzed via SEM-EDX, TPO, XPS, HRTEM-EDX and Raman Spectroscopy. The kinetic behaviors of the catalysts were parametrically analyzed by varying temperature and partial pressures of both reactants and products. FTIR-DRIFT studies were also performed to obtain information on both catalyst surface and CDRM mechanism. It was indicated that Co particles partially cover evenly distributed Ce particles. The lowest degree of ceria reduction, and the highest asymmetry of the O1s XP spectrum, due to lattice oxygen vacancies and adsorbed oxygen, were obtained for the catalyst with the highest Co/Ce ratio. It was also verified that Co species in the catalyst samples with higher Co loading are more oxidized. The roles of each species in the catalyst design were confirmed: Co is responsible for CH4 dehydrogenation, ceria has a pronounced effect on surface oxygen transfer, and ZrO2 serves for surface oxygen production via CO2 dissociation stages of CDRM. The fraction of different carbon types formed on the catalyst surface were dependent both on catalyst composition and reaction conditions. The kinetic studies have shown that CH4 utilization is a key factor in CDRM, even affecting CO2 utilization, and H2 introduction has an inhibitory effect on the mechanism. The effect of Co/Ce ratio on C balance of CDRM was also highlighted with the combined evaluation of performance, kinetic and FTIR-DRIFT studies.
