Facet-Engineered Highly Active and Stable Ag/TiO₂ Photocatalysts for Selective Oxidative Coupling of Methane

The oxidation of methane into valuable chemicals, like C₂₊ molecules, has long been pursued, yet the trade-off between a high yield and high selectivity remains unresolved. Here, we demonstrate efficient methane upgrading via photocatalytic oxidative coupling of methane (POCM) using Ag-decorated facet-engineered TiO₂. {001}-dominated TiO₂ exhibits exceptional performance, delivering a C₂₊ production rate of 2.2 mmol g^-1 h^-1 with 96% selectivity and remarkable stability exceeding 70 h, surpassing most literature benchmarks and the performance of {101}- and {100}-faceted TiO₂. In situ spectroscopic characterization combined with density functional theory calculations demonstrates that the introduced Ag nanoparticles serve as dual-functional mediators for electron extraction and C-C coupling. More importantly, dynamically formed Ti³⁺ active sites on the reactive {001} facets function as efficient hole-trapping centers, which not only facilitate charge separation through directional hole transfer but also prevent excessive methane activation at static Ti⁴⁺ sites, thus achieving highly efficient and selective OCM performance. This work establishes a facet-mediated strategy for spatially organizing photocatalytic systems and provides fundamental insights into charge carrier management for selective methane activation, opening new avenues for solar-driven methane upgrading.