Alkali metal and alkaline earth metal perovskites for oxidative coupling of methane and oxidative dehydrogenation of ethane

Abstract

In this study, alkali metal and alkaline earth metal perovskites have been synthesized using simple preparation methods for catalyzing the oxidative coupling of methane (OCM) and oxidative dehydrogenation of ethane (ODHE). The influence of their structural parameters (such as tolerance factor t, unit cell free volume (Vf), electronegativity of A- and B-site elements, average metal-oxygen energy, and crystalline phase transition) on basic sites and reaction performance is also systematically investigated. The results show that these two perovskites have similar active sites for OCM and ODHE reactions, with the moderate and strong basic sites favoring the OCM reaction and the moderate basic site facilitating the ODHE reaction. The surface basicity of these perovskites reflects the electron-donating ability of lattice oxygen, which in turn affects the production of reactive oxygen species (O2−, O22−, and O−). Moderate basic sites are abundant and closely related to oxygen vacancies, with high oxygen vacancy concentrations generating abundant reactive oxygen species. Meanwhile, Vf values of perovskites govern the CH4, C2H6, and O2 conversions, the electronegativity of elements affects the catalyst basicity, and the average metal-oxygen energy and crystalline phase transition alter the moderate basic sites. Overall, it concludes that perovskites should meet the following conditions to achieve excellent catalytic performance for OCM and ODHE: moderate Vf, low electronegativity of A- and B-site elements, low average metal oxygen energy, and a crystalline structure that changes with temperature.