Hydrophobic TaO x Species Overlayer Tuning Light-Driven Methane Chlorination with Inorganic Chlorine.

Halogenated methane serves as a universal platform molecule for building high-value chemicals. Utilizing sodium chloride solution for photocatalytic methane chlorination presents an environmentally friendly method for methane conversion. However, competing reactions in gas-solid-liquid systems leads to low efficiency and selectivity in photocatalytic methane chlorination. Here, an in situ method is employed to fabricate a hydrophobic layer of TaO x species on the surface of NaTaO 3 . Through in-situ XPS and XANES spectra analysis, it is determined that TaO x is a coordination unsaturated species. The TaO x species transforms the surface properties from the inherent hydrophilicity of NaTaO 3 to the hydrophobicity of TaO x /NaTaO 3 , which enhances the accessibility of CH 4 for adsorption and activation, and thus promotes the methane chlorination reaction within the gas-liquid-solid three-phase system. The optimized TaO x /NaTaO 3 photocatalyst has a good durability for multiple cycles of methane chlorination reactions, yielding CH 3 Cl at a rate of 233 µmol g -1 h -1 with a selectivity of 83%. In contrast, pure NaTaO 3 exhibits almost no activity toward CH 3 Cl formation, instead catalyzing the over-oxidation of CH 4 into CO 2 . Notably, the activity of the optimized TaO x /NaTaO 3 photocatalyst surpasses that of reported noble metal photocatalysts. This research offers an effective strategy for enhancing the selectivity of photocatalytic methane chlorination using inorganic chlorine ions.