Efficiently Light-Driven Nonoxidative Coupling of Methane on Ag/NaTaO₃: A Case for Molecular-Level Understanding of the Coupling Mechanism

Metal-decorated oxide semiconductors are overwhelming photocatalysts for nonoxidative coupling of methane (NOCM). However, the overall NOCM mechanism remains an unopened black box, which hinders the design of high-performance catalysts. Herein, we systematically studied a series of noble metal (Ag, Au, Pt, Pd, Cu, and Ni)-decorated oxides (NaTaO_3, CaTiO₃, LiNbO₃, and TiO₂) for NOCM. We proposed that the active sites for H abstraction and C–C coupling of CH₄ are spatially separated. Specifically, NaTaO₃ only completes the initial H abstraction of CH₄ activation, while metal nanoparticles are responsible for the final C–C coupling. Noble metals dominate NOCM by significantly decreasing the energy barrier of CH₄ dissociation and promoting C–C coupling. Among various metals, Ag is preferential for the weak adsorption of ^·CH₃ intermediates and subsequent metal-induced C–C coupling. This contributes to Ag/NaTaO₃ the highest C₂H₆ yield of 194 μmol g^–1 h^–1 and stoichiometric H₂ with 11.2% quantum efficiency. This work provides a molecular-level insight into the CH₄ coupling mechanism on metal-decorated photocatalysts.