Comparison of alkali metal promoted MgO catalysts for their surface acidity/basicity and catalytic activity/selectivity in the oxidative coupling of methane

Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0.1) calcined at 750&#176;C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C<SUB>2</SUB>-hydrocarbons at different temperatures (700-750&#176;C), CH<SUB>4</SUB>/O<SUB>2</SUB> ratios (4.0 and 8.0) in feed, and space velocities (10320 cm<SUP>3</SUP> g<SUP>-1</SUP> h<SUP>-1</SUP>). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C<SUB>2</SUB>-hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750&#176;C, the best performance in the OCM is shown by Li-MgO (at 750&#176;C)