Toward a Comprehensive Understanding of Enhanced Photocatalytic Activity of the Bimetallic PdAu/TiO₂ Catalyst for Selective Oxidation of Methanol to Methyl Formate

Photocatalytic selective oxidation of alcohols over titania supported with bimetallic nanoparticles represents an energy efficient and sustainable route for the synthesis of esters. Specifically, the bimetallic PdAu/TiO₂ system was found to be highly active and selective toward photocatalytic production of methyl formate (MF) from gas-phase methanol. In the current paper, we applied the electronic structure density functional theory method to understand the mechanistic aspects and corroborate our recent experimental measurements for the photocatalytic selective oxidation of methanol to MF over the PdAu/TiO₂ catalyst. Our theoretical results revealed the preferential segregation of Pd atoms from initially mixed PdAu nanoclusters to the interface of PdAu/TiO₂ and subsequent formation of a unique structure, resembling a core@shell architecture in close proximity to the interface. The analysis of the calculated band gap diagram provides an explanation of the superior electron–hole separation capability of PdAu nanoparticles deposited onto the anatase surface and hence the remarkably enhanced photocatalytic activity, in comparison to their monometallic counterparts. We demonstrated that facile dissociation of molecular oxygen at the triple-point boundary site gives rise to in situ oxidation of Pd. The in situ formed PdO/TiO₂ is responsible for total oxidation of methanol to CO₂ (no MF formation) in the gas phase. Our investigation provides theoretical guidance for designing highly selective and active bimetallic nanoparticlesTiO₂ catalysts for the photocatalytic selective oxidation of methanol to MF