Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO2 catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO2. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO2 catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO2 was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO2, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO2 reforming of ethane and the ODHE with CO2. As a consequence, the synthesis gas produced from CO2 reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO2, thus increasing the selectivity of ethylene.