Oxidative conversion of methane to C₂-hydrocarbons over lithium, manganese, cadmium and zinc promoted MgO catalysts I. Catalyst performance in presence of free oxygen

Abstract

Oxidative coupling of methane to C₂-hydrocarbons over MgO, Li - MgO, MnO_x - MgO, Li - MnO_x MgO, CdO - MgO, Li - CdO - MgO, ZnO - MgO and Li - ZnO - MgO catalysts at 823-1103 K in presence of free oxygen has been investigated. The C₂-selectivity of the catalysts and the ethylene-to-ethane ratio in the products were found to increase with the increase in the reaction temperature. The addition of lithium, zinc and cadmium promoters to MgO caused a very significant catalyst sintering resulting in a decrease in the catalyst surface area but an increase in the catalyst C₂-selectivity. The catalyst C₂-selectivity was found to be increased almost linearly with the decrease in the catalyst surface area. The lithium-promoted catalysts, however, showed a strong dependence of their methane conversion activity and C₂-selectivity on the time on-stream and are sintered extensively during the catalytic process. Among the catalysts, the Li - ZnO - MgO and Li - CdO - MgO showed superior performance in the methane conversion process.