Oxidative coupling of methane over La2O3. Influence of catalyst preparation on surface properties and steady and oscillating reaction behaviour

Abstract

The catalyst precursor and calcination conditions used in the preparation of La₂O₃ have been found to have a marked influence on the surface properties, basicity and base strength distribution, and catalytic activity and selectivity in the oxidative coupling of methane (OCM) under different reaction conditions. Among the La₂O₃ catalysts, only that prepared from lanthanum acetate by decomposition in N₂(but not in O₂) showed symmetric temperature and concentration oscillations in OCM at or below 933 K over a narrow temperature range. The unsteady reaction behaviour is found to be very complex and strongly dependent upon the OCM process parameters and the catalyst parameters. Furthermore, the results on the La₂O₃ obtained from the acetate indicated a strong possibility of the formation of new catalytic sites active at lower temperatures (below 873 K) during the OCM reaction at higher temperatures.