Photocatalytic Methane Oxidation and Removal Mediated by Free Radicals

Activation and selective oxidation of C-H bond in methane under mild conditions constitutes long-standing challenges which are of fundamental and technological importance, from biological to industrial and environmental. Earth relies on free radicals to remove the climate-damaging methane and other organic pollutants from the air. In recent decades, intensive efforts have been focused on leveraging free radicals for selective methane oxidation. Free radicals are one of key mediators underpinning many active sites in thermal catalysis and these enhancement effects induced by the light and electric fields. However, it remains unclear how free radicals as active species mediate the C-H bond activation in methane and dictate the products distribution. In this talk, we will discuss our recent advances in understanding and promoting the photocatalytic oxidation of methane to methanol by combining the rational design of photocatalysts, photochemical experiments, as well as the in-situ electron paramagnetic resonance studies of free radicals. Our results unravel interactions between these free radicals and the solid co-catalysts, ions, and gases 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 the products distribution. Furthermore, we report an inherent trade-off in the photochemical methane to methanol conversion. A new design principle featuring isolating different reaction steps is developed to circumvent this trade-off. Such molecular-level insights into photocatalysts and their interactions with free radicals are expected to promote the methane removal and its selective functionalization and offer informative design principles for chemical bonds activations that are driven by light, heat, and electric fields.