Surface basicity and acidity of alkaline earth-promoted La2O3 catalysts and their performance in oxidative coupling of methane

Abstract

The catalytic activity and selectivity of La2O3 and alkaline earth (viz. Mg, Ca, Sr and Ba) promoted La2O3 (alkaline earth metal/La = 0.1) catalysts in the oxidative coupling of methane (OCM) to C2-hydrocarbons (at 800°C, CH4/O2 ratio = 4 or 8 and gas hourly space velocity = 102000 cm3 g-1 h-1) have been investigated. The acidity and basicity distributions on these catalysts are measured by the temperature programmed desorption (TPD) of NH3 and CO2 from 50°C to 950°C, respectively. Both the acidity and basicity of the La2O3 catalysts and their activity in the OCM are strongly influenced by the alkaline earth promoter and its concentration. Among the catalysts, Sr-promoted La2O3 (Sr/La = 0.1) is the most active and selective catalyst for the OCM process. This catalyst contains a larger number of strong basic sites and intermediate strength acid sites.