Photocatalytic Methane Oxidation: Reactive Oxygen Species Regulation, Active Interface Engineering, and Reaction Microenvironment Design

Photocatalytic methane oxidation offers a promising route for methane valorization under mild conditions, yet it is constrained by the need to activate inert C─H bonds while protecting more reactive oxygenated products from sequential oxidation. Recent studies show that product selectivity is not dictated simply by the identity or oxidative strength of reactive oxygen species (ROS), but by how semiconductor excitation, charge migration, oxidant activation, active interfaces, ROS localization and utilization, and local reaction environments are coordinated. This Review discusses photocatalytic methane oxidation as a problem of reaction pathway control. The elementary chemistry of methane activation, methyl intermediate transformation, oxygenate formation, and overoxidation is first summarized. Semiconductor reaction fields and cocatalyst/interface strategies are then examined in relation to charge transfer, oxygen activation, C─H functionalization, intermediate stabilization, and product desorption. The roles of ROS identity, surface confinement, diffusion behavior, and utilization efficiency are analyzed with emphasis on methane activation, intermediate conversion, and product preservation. Microenvironment and reactor engineering are further discussed as emerging approaches to improve methane accessibility, oxidant delivery, residence time control, product extraction, and stability. Finally, key design principles and mechanistic requirements are outlined for developing photocatalytic methane oxidation systems with improved selectivity, durability, and scalability.