Continuous selective oxidation of methane to methanol by thermal-assisted photocatalysis over NiO/ZnO.

The selective oxidation of methane to methanol under mild conditions remains challenging due to the delicate balance between methane activation and the prevention of overoxidation. Herein, we present a continuous thermal-assisted photocatalytic process for selective methane oxidation to methanol using NiO/ZnO catalysts in a flow fixed-bed reactor. Under optimal conditions, the process achieves a methanol yield of 47.5 μmol g-1h-1 with 94.7 % selectivity and long-term stability over 120 h. In situ EPR, time-resolved decay spectra, and transient photocurrent response analyses confirm that thermal assistance enhances the generation and migration of photogenerated carriers and promotes the activation of CH4, resulting in a 16.49-fold increase in methanol yield compared to photocatalysis alone. Additionally, NiO modification of ZnO facilitates the formation of oxygen vacancies (OVs) in ZnO, boosting electron transfer, while NiO nanoparticles promote hole transfer. This dual-site synergistic charge transfer mechanism, combined with thermal assistance, significantly enhances the separation of photogenerated electron-hole pairs, thereby improving the overall performance of methane oxidation to methanol.