Understanding of photocatalytic partial oxidation of methanol to methyl formate on surface doped La(Ce)[sbnd]TiO2: Experiment and DFT calculation

Abstract

The photocatalytic partial oxidation of methanol to methyl formate (MF) under visible light irradiation on surface doped La(Ce)TiO2 was studied by the experimentation and DFT calculation. The La or Ce atoms could be doped in the surface lattice of TiO2 to form the bond of La(Ce)OTi but could not be doped in the body of TiO2. The crystal size of TiO2 was restrained from growth due to the surface lattice distortion resulted from La(Ce) bonding with surface oxygen. The band structure and surface hydroxyls can be tuned by the La or Ce distribution on the surface of TiO2. The rare earth on the surface of TiO2 can form impurity levels in the valence band and conduction band, reduce the band gap, change surface electron states, decrease the potential energy for surface hydroxyl formation, and reduce the energy barriers of the transition states from methoxy via formaldehyde to MF. The doped catalyst exhibited superior methanol conversion and MF selectivity in photocatalytic partial oxidation of methanol to MF under visible light irradiation. The surface hydroxyl group plays an important role in the reaction and were positively related to the methanol conversion and MF selectivity. The La doped catalysts exhibited better methanol conversion and MF selectivity than the Ce doped catalysts due to the faster recoverable surface hydroxyls and lower energy barriers to transition states. This study may contribute to design new visible light responsive catalyst for photocatalytic partial oxidation reaction and provide applicable green route to MF synthesis.