Elucidating the action mechanism of different kinds of oxygen species on methane dissociation to generate methyl radical on lanthanum oxide catalyst

The reaction of oxidative coupling of methane (OCM) to C2+ hydrocarbons is an important way of high-value conversion of methane, and methane dissociation to generate methyl radicals (CH3•) is the key step of the reaction, where the different kinds of oxygen species are the key factors affecting CH3• generation. In this study, we choose lanthanum oxide (La2O3) catalyst as the research example to systematically explore the action mechanism of different kinds of oxygen species on the CH3• generation through the density functional theory (DFT) calculation. The results show that for the lattice oxygen (O2−) and oxygen vacancy (Ov), the dissociation of CH4 is essentially an acid-base reaction, where CH4 is activated to generate adsorbed CH3 via heterolytic way; for the superoxide (O2–) and peroxide (O22–), the dissociation of CH4 is essentially an oxidation–reduction reaction, where CH4 is activated to directly generate CH3• on superoxide (O2–) via homolytic way, while CH4 is activated to generate CH3OH or CH3O on peroxide (O22–). The study clearly elucidates the action mechanism of different types of oxygen species on generation of CH3•, which is helpful to understand the OCM complex reaction mechanism and further develop high-performance catalysts.