Correlation of Methane Activation and Oxide Catalyst Reducibility and Its Implications for Oxidative Coupling

Abstract

We investigate methane activation over a range of metal-oxide surfaces. Density functional theory calculations are used to correlate the C-H bond activation energy to the surface reducibility (oxygen vacancy formation energy, work function). The correlation includes several reducible and nonreducible metal-oxides, doped CeO2, doped TiO2, ZnO, and doped MgO, and also holds for various oxidation states of TbOx, different surface facets of TiO2, and variation of Hubbard U parameter for CeO2. We find a linear correlation between the C-H activation reaction energy,·CH3 adsorption energy, and the oxygen vacancy formation energy of pure/doped metal-oxides, making surface reducibility a descriptor for predicting catalyst activity and selectivity against further oxidation of the·CH3 radical.