from first principles PP-I-1

OP-V-2Reaction Mechanism of Selective Oxidation of Alcohols and Amines overSemiconductor PhotocatalystsShishido T. 1 , Furukawa S. 1 , Ohno Y. 1 , Teramura K. 1,2 , Tanaka T. 11 Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,Kyoto, Japan2 Precursory Research for Embryonic Science and Technology (PRESTO), Japan Scienceand Technology Agency (JST), Saitama, Japanshishido@moleng.kyoto-u.ac.jpRecently, we found that niobium oxide (Nb 2 O 5 ) is an effective catalyst for thephotooxidations of various alcohols and various amines to the corresponding imines underatmospheric pressure at room temperature by using molecular oxygen [1,2]. It is well knownthat the band structure of semiconductor photocatalysts determines the utilizable light energy,oxidizability, and reducing ability. Although Nb 2 O 5 usually works only in the ultraviolet (UV)region because of the limit of its bandgap energy, Nb 2 O 5 can catalyze these oxidations evenunder visible light irradiation up to ca. 460 nm. This suggests that these two oxidations takeplace by the different photo-activation mechanisms from the classical electron transfermechanism in semiconductor photocatalysis, that is, the formation of an excited electron inthe conduction band and the positive hole in the valence band.We investigated the reaction mechanisms of the photooxidation of alcohols and amines overNb 2 O 5 . A mechanistic study by UV-Vis, ESR, FT/IR, kinetic study, and DFT calculationsrevealed the reaction mechanisms of photooxidation of alcohols and amines, and that thesurface complex consisting of adsorbed molecule and catalyst plays an important role in thephoto-activation step. The surface complex is converted to the photo-activated species evenunder visible light irradiation, because the direct electron transition from a donor level derivedfrom adsorbed molecule to the conduction band of photocatalyst takes place and photogeneratedhole is trapped on adsorbed molecule to form the photo-activated radical species.The effective wavelength becomes longer due to the formation of donor level derived fromadsorbed molecule during a chemical reaction (called here “in situ doping”). This uniquephoto-activation mechanism by “in situ doping” gives us attractive ways for the removing thelimit of bandgap energy, and the utilization of visible light.References:[1] T. Shishido, T. Miyatake, K. Teramura, Y. Hitomi, T. Tanaka, J. Phys. Chem. C 113 (2009) 18713.[2] S. Furukawa, Y. Ohno, T. Shishido, K. Teramura, T. Tanaka, ACS Catal. 1 (2011) 1150.84