A Review of Methane Photocatalytic Systems
Methane (CH4), the primary component of natural gas, is an ideal feedstock for producing high-value chemicals and clean fuels due to its high hydrogen-to-carbon ratio. However, its chemical inertness poses significant challenges, and traditional thermal catalytic reforming processes suffer from long reaction pathways and high energy consumption. Photocatalytic technology enables highly selective CH4 conversion under mild conditions, even at room temperature, offering environmental and economic benefits. This review systematically summarizes recent advances in room-temperature photocatalytic systems for direct CH4 conversion. It begins by elucidating the mechanisms, product distributions, and inherent challenges of four key reaction pathways: partial oxidation, non-oxidative coupling, oxidative coupling, and oxidative carbonylation. The discussion then addresses the critical role of catalyst architecture, focusing on semiconductor supports, metal site modulation, and advanced porous frameworks. Furthermore, reactor design and process intensification strategies are examined, including batch and continuous-flow reactors, novel structured reactors, and photo-electro and photo-thermo synergistic approaches. Finally, reaction mechanisms are summarized. Despite progress, challenges remain in fundamental understanding, performance evaluation, and technological integration. Future efforts should focus on mechanistic studies, standardization of evaluation protocols, development of non-noble metal catalysts, system optimization, and comprehensive sustainability assessments.