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

Abstract

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°C; CH₄/O₂ ratio, 2.0-8.0 and GHSV (at STP) 51 600 cm³ g^-1h^-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 LaMgO, CeMgO and EuMgO showed high activity and selectivity in the OCM process and the performance of these catalysts 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.