Direct conversion of methane into methanol and other liquid oxygenates still confronts considerable challenges in activating the first C−H bond of methane and inhibiting overoxidation. Here, we report that ZnO loaded with appropriate cocatalysts (Pt, Pd, Au, or Ag) enables direct oxidation of methane to methanol and formaldehyde in water using only molecular oxygen as the oxidant under mild light irradiation at room temperature. Up to 250 micromoles of liquid oxygenates with ∼95% selectivity is achieved for 2 h over 10 mg of ZnO loaded with 0.1 wt % of Au. Experiments with isotopically labeled oxygen and water reveal that molecular O 2 , rather than water, is the source of oxygen for direct CH 4 oxidation. We find that ZnO and cocatalyst could concertedly activate CH 4 and O 2 into methyl radical and mildly oxidative intermediate (hydroperoxyl radical) in water, which are two key precursor intermediates for generating oxygenated liquid products in direct CH 4 oxidation. Our study underlines two equally significant aspects for realizing direct and selective photooxidation of CH 4 to liquid oxygenates, i.e., efficient C−H bond activation of CH 4 and controllable activation of O 2 .

The conversion of methane to upgraded fuels and higher-value chemicals such as hydrogen, methanol, and olefins is a promising technology in the supply of chemicals and energy. However, current commercial methane conversion technology suffers from intense energy consumption. It is highly desirable to develop novel technologies for methane conversion with improved efficiency and lower cost. Solar energy, the most abundant and clean renewable energy, has been utilized as a new stimulus to drive methane conversion under mild conditions. In this review, recent achievements in solar-energy-mediated catalytic methane conversion are highlighted. We focus on the photocatalytic conversion of methane in photocatalytic systems, photoelectrochemical systems, and photoenhanced thermocatalytic systems. We discuss the challenges and prospects of future research on solar-energy-mediated methane conversion and aim to acquire in-depth understanding of the photo-mediated activation of the C-H bond and provide guidelines for the design of highly efficient catalysts.

Enormous efforts have been devoted to the reduction of carbon dioxide (CO2) by utilizing various driving forces, such as heat, electricity, and radiation. However, the efficient reduction of CO2 is still challenging because of sluggish kinetics. Recent pioneering studies from several groups, including us, have demonstrated that the coupling of solar energy and thermal energy offers a novel and promising strategy to promote the activity and/or manipulate selectivity in CO2 reduction. Herein, we clarify the definition and principles of coupling solar energy and thermal energy, and comprehensively review the status and prospects of CO2 reduction by coupling solar energy and thermal energy. Catalyst design, reactor configuration, photo‐mediated activity/selectivity, and mechanism studies in photo‐thermo CO2 reduction will be emphasized. The aim of this Review is to promote understanding towards CO2 activation and provide guidelines for the design of new catalysts for the efficient reduction of CO2.