Passivating Lattice Oxygen in ZnO Nanocrystals to Reduce its Interactions with the Key Intermediates for a Selective Photocatalytic Methane Oxidation to Methanol

Abstract

An inevitable overoxidation process is considered as one of the most challenging problems in the direct conversion of methane (CH4) to methanol (CH3OH), which is limited by the uncontrollable cracking of key intermediates. Herein, we have successfully constructed a photocatalyst, the Fe-doped ZnO hollow polyhedron (Fe/ZnOHP), for the highly selective photoconversion of CH4 to CH3OH under mild conditions. In-situ experiments and density functional theory calculations confirmed that the introduction of Fe was able to decrease the energy level of the O 2p orbital, which passivated the activity of lattice oxygen in ZnO nanocrystals. This passivation effect greatly weakened the interaction between *CH3 and lattice oxygen, thus facilitating the conversion of *CH3O to *CH3 intermediate rather than the direct desorption of *CH3O. As a result, Fe/ZnOHP exhibited excellent CH3OH generation rate (ca. 1009 μmol gcat−1 h-1) and selectivity (ca. 96%) in the photocatalytic conversion of CH4 at room temperature and low pressure.