Surface properties of rare earth promoted MgO catalysts and their catalytic activity/selectivity in oxidative coupling of methane

Surface properties (viz. acidity/acid strength distribution, basicity/base strength distribution, surface area, etc.) and catalytic activity/selectivity in oxidative coupling of methane at different reaction conditions (reaction temperature, 650-850 degrees C; CH4/O-2 ratio, 2.0-8.0 and GHSV (at STP) 51 600 cm(3) g(-1) h(-1)) of rare earth (La, Ce, Nd, Eu and Yb) promoted MgO with different rare earth/Mg ratio have been thoroughly investigated. The surface and catalytic properties are found to be strongly influenced by the rare earth promoter and also by its concentration. The La-MgO, Ce-MgO and Eu-MgO showed high activity and selectivity in the OCM process and the performance of these catalysts is found to be comparable. The promotion of MgO by rare earths resulted in a large increase in the catalytic activity and selectivity and also in the basicity (both total and strong basic sites) but caused a decrease in the acidity (both number and strength of acid sites). A comparison of the catalysts showed that, the activity/selectivity in the OCM process depends not only on the strong basicity of the catalyst but also on the number and strength of its acid sites.