Water-promoted selective photocatalytic methane oxidation for methanol production

Converting relatively inert methane into active chemical fuels such as methanol with high selectivity through an energy-saving strategy has remained a grand challenge. Photocatalytic technology consuming solar energy is an appealing alternative for methane reforming. However, the low efficiency and the undesirable formation of low-value products, such as carbon dioxide and ethane, limit the commercial application of photocatalytic technology. Herein, we find a facile and practical water-promoted pathway for photocatalytic methane reforming into methanol, enabling methanol production from methane and oxygen with a high selectivity (>93%) and production rate (21.4 μmol cm^-2 h^-1 or 45.5 mmol g^-1 h^-1) on metallic Ag nanoparticle-loaded InGaN nanowires (Ag/InGaN). The experimental XPS and theoretical PDOS analyses reveal that water molecules adsorbed on Ag nanoparticles (AgNPs) can promote the electron transfer from InGaN to AgNPs, which enables the formation of partial Ag species with a lower oxidation state in AgNPs. Through the in situ IR spectrum and the reaction pathway simulation studies, these newly formed Ag species induced by water adsorption were demonstrated to be responsible for the highly selective methanol production due to the effective formation of a C-O bond and the optimal desorption of the formed methanol from the surface indium site of the InGaN photocatalyst. This unique water promotion effect leads to a 55-fold higher catalytic rate and 9-fold higher selectivity for methanol production compared to photocatalytic methane reforming without water addition. This finding offers a new pathway for achieving clean solar fuels by photocatalysis-based methane reforming.