EFFECTS OF CARBON-DIOXIDE AND CATALYST PREPARATION ON THE OXIDATIVE DIMERIZATION OF METHANE

The use of carbon dioxide as a reactive diluent for the oxidative coupling of methane increased the yields of ethane and ethene (C2 compounds) from 13.4 to 18.3% with an increase in C2 selectivity from 42.3 to 49.4% over MgO catalyst at 1073 K, CH4-to-O2 ratio = 2 and W/F = 6.07 g/h.mol. Alkaline earth metal oxide catalysts prepared by thermal decomposition of their oxalates at 1023 K gave high C2 space-time yield (e.g., 8.6 mmol/g·h). Sm2O3 (15 wt.-% )/porous MgO catalyst prepared at 1173 K showed high C2 selectivity (47.9% with a C2 yield of 13.3%). The selectivity for C2 compounds was further improved to 57.4% in a stream of CH4O2CO2 without reducing the C2 yield (13.6%). Addition of carbon dioxide suppressed the deactivation of the catalyst and decreased the amount of coke deposited on the catalyst surface in a prolonged run. Partial adsorption of carbon dioxide on the catalyst surface inhibits the deep oxidation of methane or C2 products, resulting in increased C2 selectivities on dilution of the feed stream with carbon dioxide. © 1990.