Systematic exploration of alkali–anion pairs for descriptor identification in OH-mediated methane coupling†

Abstract

The oxidative coupling of methane (OCM) was investigated using various alkali metal salts supported on SiO₂. The addition of H₂O enhances both the methane conversion rate and selectivity across all alkali metal salts, which suggests there is an OH-radical-mediated pathway that is facilitated by the surface formation of alkali peroxide. To explain the observed experimental differences, we explored the interactive energetics of alkali–anion pairs with a particular focus on the stabilization of alkali peroxide intermediates by anion species. Anion polarizability is indicative of the alkali ion's degree of freedom and positively correlated with the catalytic performance due to formation capability of catalytic alkali peroxide species. This insight highlights the critical role of the reaction of surface alkali peroxide with H₂O as a key elementary step in OCM.