Activity and Selectivity of Oxidative Coupling of Methane on Doped La2O3 Catalysts: A Density Functional Theory Study

The oxidative coupling of methane (OCM) on rare earth metal oxides has been studied by periodic density functional theory (DFT) calculations. Detailed energetic, structural and electronic properties of the related reactions have been determined. The calculated activation energies of breaking the first C-H bond in methane on the La₂O₃(001) and CeO₂(111) surfaces are compared, which suggest the high selectivity and low activity on the La₂O₃(001) surface and the opposite on the CeO₂(111) surface for the OCM reaction. It has been found that the methyl radical is the key species, and the activity of the OCM reaction can be increased by modifying the catalyst from the perspectives of structural and electronic properties for tuning the formation of the methyl radical. The La₂O₃(210) surface has low-coordinated oxygen and it is beneficial for breaking the first C-H bond in methane; and with doped Sr and Ce, the surface can maintain the activity to dissociate first C-H bond while favor the occurrence of methyl radicals for further coupling. This work illustrates that the SrCeLa₂O₃ catalyst can be highly active and selective for catalytic OCM reactions.