Spatially Decoupling Redox Sites on TiO2 via Ag–Cr Co-Modification for Highly Selective Photocatalytic Methane Coupling

Abstract

Photocatalytic oxidative coupling of methane (OCM) presents a promising route for the direct conversion of methane into value-added hydrocarbons, yet it remains challenged by the need to balance efficient methane activation with the suppression of overoxidation. Herein, we report a Ag–Cr co-modified TiO2 photocatalyst featuring spatially decoupled redox active sites, which enables high-performance continuous-flow OCM. The optimized AgCr/TiO2 system delivers a C2+ hydrocarbon production rate of 2005.1 μmol g−1 h−1 with 92% selectivity, alongside stable operation for over 45 h, surpassing most reported semiconductor-based photocatalysts. In situ and time-resolved spectroscopic analyses reveal a synergistic mechanism in which metallic Ag sites and adjacent Cr species collaboratively promote charge separation and transfer. Specifically, Cr acts as a hole-trapping center that facilitates C−H activation, while metallic Ag serves as an electron sink to support oxygen reduction. This spatially separated dual-site configuration enables the selective formation of *CH3 intermediates, thereby steering the reaction pathway toward C2+ products and effectively suppressing overoxidation. This work provides valuable insights into the photocatalytic OCM, highlighting how a spatial decoupling strategy of active sites can enable efficient and selective methane activation.