Synergetic C–H bond activation and C–O formation on CuOx facilities facile conversion of methane to methanol

Abstract

Direct methane to methanol conversion is desirable but difficult to implement due to the inertness of methane and unattainable matching oxidant. The capability of Cu oxides releasing lattice oxygen makes it a potential oxidant to facilitate the conversion. Herein, the mechanism of methane to methanol on the surfaces of CuOx has been studied using density functional theory calculations. Heterolytic cleavage of the C–H bond is preferred at the Cu–O site whereas methanol formation from dissociated CH3 and H on surface O can take place over either Cu–O or O–O site. On CuO(1¯1 1), methane activation at the Cu–O site and methanol formation over the O–O site synergistically enable the selective oxidation of methane to methanol. In contrast, the formation of methanol on the O-deficient surfaces is a result of direct coupling of CH3 on Cu and OH formed from of H adsorbed on the surface O site. Microkinetics analysis confirms the synergistic effect of Cu–O and O–O on CuO(1¯1 1) for methanol formation in a temperature range of 473–648 K. These findings demonstrate the feasibility of selective oxidation of methane to methanol with the surface lattice oxygen of CuOx and help to design the CuOx-based oxygen carriers and/or catalysts.