When Free Radicals Meet the Solid, Ion and Gas in Photochemical Methane Oxidation to Methanol

C-H bond oxidation in methane under mild conditions constitutes long-standing challenges that are of fundamental and technological importance, from biological to industrial and environmental. Methanol is a key vector to fuel a future. Currently, the methane-to-methanol conversion relies on energy intensive processes involving a syngas intermediate. In recent decades, intensive efforts have been focused on developing direct methane-to-methanol conversion as an alternative and more sustainable pathway. Free radicals are one of key mediators underpinning many active sites in thermal catalysis and the enhancement effects induced by light and electric fields, including methane to methanol oxidation. However, it remains unclear how free radicals as active species mediate the C-H bond activation and dictate the products distribution.<br/>In this talk, we combine rational design of TiO₂-noble metal composite photocatalysts, experimental design of methane oxidation experiments with the in-situ free radical detection. Our results unravel interactions between these free radicals and the solid co-catalysts, ions, and gas molecules in water, as well as their impact on methane removal and its selective oxidation. Our studies highlight the neglected while important interplay between photogenerated radicals and co-catalysts, ion impurities, and gas molecules in promoting methane removal and controlling products distribution. Furthermore, we report an inherent trade-off in both photochemical oxidation of methane to methanol. A new design principle featuring isolating different reaction steps is developed to circumvent this trade-off. Furthermore, our findings and strategies are generally applicable to thermochemical methane oxidation using H₂O₂.<br/>Our molecular-level insights into free-radical-mediated photochemical and thermochemical methane oxidation are expected to promote methane removal and its selective functionalization and offer informative design principles for chemical bond activations driven by light, heat, and electric fields.