Facet-Dependent Photocatalytic Conversion of Methane to C₁ Oxygenates with Au/TiO₂ Nanoparticles

The conversion of methane into high-value-added liquid chemicals such as methanol is an ideal means of carbon resource storage and recycling. However, the intricate catalytic steps and the presence of diverse reactive oxygen species (•OH and •O 2 –, etc.) obscure the oxygen sources and reaction pathways of the product C 1 oxygenates. In particular, the frequent coexistence of CH 3 OOH and CH 3 OH in liquid products further complicates the matter. In this study, two distinct types of Au/TiO 2 nanoparticle catalysts, i.e., one with nonselective deposition and another with selective deposition, were synthesized via chemical reduction and photodeposition, respectively. On this basis, we systematically investigated their photocatalytic performances in methane oxidation and successfully established the structure–activity relationship between the crystal surface and product selectivity. Mechanistic studies revealed that the {001} and {101} facets of TiO 2 nanocrystals played dominant roles in the generation of CH 3 OH and CH 3 OOH primary oxygenates, respectively, due to their varying abilities to further convert •O 2 – . In addition, Au, serving as an electron acceptor, facilitates the reduction of oxygen to form •O 2 – and promotes facet-related reactions. These findings offered a great perspective for the development of methane photooxidation to produce liquid oxygenates.