Enhancing oxygen activation toward promoted photocatalytic oxidation of methane to liquid oxygenates with ReO2@TiO2: the regulation of oxygen affinity

Abstract

The ReO₂@TiO₂ catalyst has been designed and applied in photocatalytic methane oxidation to liquid oxygenates. The oxygen affinity regulation was employed as a strategy in the rational design of the active site from a molecular level. Thus, upon revealing the electronic origins for the oxygen affinities of the gas-phase ReO_x⁺ (x = 0–3) clusters, theoretical screening of Re active sites was performed, affording ReO₂ as the optimal species. Next, the optimized 1.0% ReO₂@TiO₂ catalyst exhibits excellent yields of liquid oxygenates (CH₃OH, CH₃OOH, HCHO, and HCOOH) of 11 581.2 μmol g⁻¹ h⁻¹ with 94.5% selectivity and 4061.7 μmol g⁻¹ h⁻¹ with 98.4% selectivity under full-spectrum Xe lamp irradiation at the catalyst loading of 2 mg and 10 mg, respectively, superior to most previously reported ones. In situ EPR, isotope labeling experiments and further DFT calculations were carried out to investigate the origins of the catalytic performance. The regulation of oxygen affinity guided by gas-phase results eventually turned out to be a rational way to enhance the oxygen reduction process, thus facilitating the photocatalytic methane oxidation.