Dual-Function Reaction Center for Simultaneous Activation of CH4 and O2 via Oxygen Vacancies during Direct Selective Oxidation of CH4 into CH3OH.

Abstract

The direct oxidation of methane (CH4) to methanol (CH3OH) has been a focus of global concern and is quite challenging due to the thermodynamically stable CH4 and uncontrolled overoxidation of the products. Here, we provided a new viewpoint on the role of oxygen vacancies that induce a dual-function center in enhancing the adsorption and activation of both CH4 and O2 reactants for the subsequent selective formation of a CH3OH liquid fuel on two-dimensional BiOCl photocatalysts at atmospheric pressure. The key for the favorable activity lies in the simultaneous ability of the electron-trapped Bi atom in activating CH4 and the formation of •O2- radicals due to the activation of O2 at the adjacent oxygen vacancy site, which immediately attack the activated CH4 to directly produce CH3OH, in initiating the oxidation reaction. What is more, the relatively low reaction barriers and the easy desorption of CH3OH concertedly facilitate the highly selective conversion of CH4 up to 85 μmol of CH3OH, with a small amount of CO2 and CO as the byproducts over the BiOCl nanosheets with an oxygen vacancy concentration of 2.4%. This work could broaden the avenue toward the application of oxygen-defective metal oxides in the photocatalytic selective conversion of CH4 to CH3OH and offer a disparate perspective on the role of oxygen vacancy acting as the surface electron transfer channel in enhancing the photocatalytic performance.