Effects of carbon dioxide and catalyst preparation on the oxidative dimerization of methane

Abstract

The use of carbon dioxide as a reactive diluent for the oxidative coupling of methane increased the yields of ethane and ethene (C 2 compounds) from 13.4 to 18.3% with an increase in C 2 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 C 2 space—time yield (e.g., 8.6 mmol/g·h). Sm 2O 3 (15 wt.-% )/porous MgO catalyst prepared at 1173 K showed high C 2 selectivity (47.9% with a C 2 yield of 13.3%). The selectivity for C 2 compounds was further improved to 57.4% in a stream of CH 4 O 2 CO 2 without reducing the C 2 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 C 2 products, resulting in increased C 2 selectivities on dilution of the feed stream with carbon dioxide.