Critical Impacts of Interfacial Water on C–H Activation in Photocatalytic Methane Conversion

On-site and on-demand photocatalytic methane conversion under mild conditions is one of the urgent global challenges for the sustainable use of ubiquitous methane resources. However, the lack of accurate knowledge of the reaction mechanism prevents the development of engineering strategies for methane photocatalysis. Combining real-time mass spectrometry and operando infrared absorption spectroscopy with ab initio molecular dynamics simulations, here we report key molecular-level insights into photocatalytic green utilization of methane. The photoactivated water dramatically promotes the activation of robust C–H bond of methane, and stabilizes the •CH3 intermediates in the interfacial hydrogen-bond network of water. Owing to the moderate stabilization of •CH3, the overall photocatalytic conversion rates are dramatically improved by typically more than 30 times at ambient temperatures (~300 K) and pressures (~1 atm). The increase in reaction activity is noticeable also in C1 to C2 evolution of methane, although water is not explicitly involved in the reaction equation (2CH4 → C2H6 + H2). These marked water-assisted effects in the interfacial chemistry should affect the basic understanding and the designing strategies on the non-thermal heterogeneous catalysis of methane under ambient conditions.