Abstract

Photocatalytic selective oxidation of alcohols over titania supported with bimetallic nanoparticles represents energy efficient and sustainable route for synthesis of esters. Specifically, the bimetallic PdAu/​TiO2 system was found to be highly active and selective towards photocatalytic production of methyl formate (MF) from gas – phase methanol. In the present work, we applied the electronic structure density functional theory (DFT) method to understand the mechanistic aspects and corroborate our recent experimental measurements for the photocatalytic selective oxidation of methanol to methyl formate over PdAu/​TiO2 catalyst. Our theoretical results revealed the preferential segregation of Pd atoms from initially mixed PdAu nanocluster to the interface of PdAu/​TiO2 and subsequent formation of the unique structure, resembling 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 anatase surface and hence, the remarkably enhanced photocatalytic activity, in comparison to its 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 methyl formate formation) in gas phase. Our investigation provides theoretical guidance for designing highly active and selective bimetallic nanoparticles – TiO2 catalysts for the photocatalytic selective oxidation of methanol to MF.