On the active site of MgO/CaO mixed oxide for oxidative coupling of methane

Abstract

The catalytic performance of Mg/Ca mixed oxides for oxidative coupling of methane and their physical properties were studied. It was found that while the activity for formation of carbon oxides was not influenced by the ratio MgO/CaO, both selectivity and activity to CZ hydrocarbons were maximum (67% and 14.5 C-mmol · h −1 · g −1, respectively) with 85% MgO/CaO at 1023 K. The values increased with increasing reaction temperature. Physical properties such as the strain in the MgO lattice and the amount of strongly adsorbed CO 2 were also maximum at the same composition. It was found that most of the surface species was MgO for Mg-rich oxides. Surface basicity, which was estimated by the wavenumber difference of the asymmetric and symmetric IR absorption bands of surface carbonates, was associated with these properties. The basicity of MgO, which was promoted by incorporated CaO, is considered to be the main factor for promoting the coupling activity.