Photocatalytic Methane Coupling: A Unified Mechanistic Framework for Oxidative and Non-Oxidative Pathways

Direct and selective upgrading of methane to multicarbon hydrocarbons under mild conditions remains one of the most compelling yet elusive goals spanning chemistry, energy, and environmental science. Solar-driven photocatalysis now offers an avenue to activate the inert C–H bonds of methane at ambient temperature and pressure; however, a clear, comparative mechanistic understanding of oxidative coupling versus non-oxidative coupling remains lacking, hindering rational catalyst design and pathway optimization. This review systematically dissects the photocatalytic reaction mechanisms of oxidative versus non-oxidative coupling, outlines key challenges associated with catalyst efficiency, selectivity, and stability, and highlights promising research directions for both pathways. The primary objective of this review is to further advance photocatalytic methane conversion technologies and to provide strategic guidance for the rational design of high-performance photocatalysts.