Oxidative coupling of methane over supported La₂O₃ and La-promoted MgO catalysts: influence of catalyst-support interactions

Abstract

Methane-to-C₂-hydrocarbon conversion activity and selectivity (or yield) of MgO and La-promoted MgO catalysts in the oxidative coupling of methane and strong basicity of the catalysts are decreased appreciably when these catalysts are deposited on commonly used commercial low surface area porous catalyst carriers containing Al₂O₃, SiO₂, SiC, or ZrO₂ + HfO₂ as the main components. The decrease in the strong basicity and catalytic activity/selectivity or yield is mostly due to strong chemical interactions between the active catalyst component (viz. MgO and La₂O₃) and the reactive components of the catalyst support (viz. Al₂O₃ and SiO₂), resulting in the formation of catalytically inactive binary metal oxides on the support surface. However, the influence of support on the activity/selectivity of La₂O₃ is relatively very small, and also the chemical interactions of La₂O₃ with the supports (except that containing a high concentration of SiO₂) are almost absent. The catalyst-support interactions are thus found to be strongly dependent upon the nature (chemical composition) of both catalyst and support. For developing better supported catalysts for the oxidative coupling of methane, supported La₂O₃ with some promoters shows high promise.