Nitrogen-Tuned Cationic Au Sites on TiO₂ Enable Selective Methane Oxidation to Methanol

Selective oxidation of methane to methanol under mild conditions remains a long-standing challenge because of the high inertness of the C-H bond in methane and the susceptibility of methanol to overoxidation. Here, we report a nitrogen-incorporation strategy for constructing TiO₂-supported Au catalysts with cationic Au sites for selective methane oxidation using O₂ as the oxidant in aqueous CH₄/O₂/CO media. The optimized Au/N-TiO₂ catalyst delivers a methanol productivity of 3956 μmol g_cat^-1 h^-1, corresponding to 177 mol mol_Au^-1 h^-1, with 98% selectivity at 180 °C, demonstrating superior catalytic performance to most reported systems under comparable conditions. Spectroscopic and structural analyses reveal that nitrogen incorporation modulates the electronic state of Au and, in combination with an appropriate Au particle size, establishes a favorable size-charge match for constructing highly efficient interfacial active sites. Isotope-labeling experiments, in situ DRIFTS, kinetic analysis, and density functional theory calculations show that the reaction proceeds through a CO-assisted, surface-mediated O₂ activation pathway involving surface methoxy species as key intermediates.