Selective oxidation of alcohols in aqueous suspensions of rhodium ion-modified TiO2 photocatalysts under irradiation of visible light

Abstract

Photocatalytic oxidation of benzyl alcohols in aqueous suspensions of rhodium ion-modified titanium(IV) oxide (Rh³⁺/TiO₂) in the presence of O₂ under irradiation of visible light was examined. In the photocatalytic oxidation of benzyl alcohol, benzaldehyde was obtained in a high yield (97%) with >99% conversion of benzyl alcohol. Rh³⁺/TiO₂ photocatalysts having various physical properties were prepared using commercially available TiO₂ powders as supporting materials for Rh³⁺ to investigate the effect(s) of physical properties of TiO₂ on photocatalytic activities of Rh³⁺/TiO₂ for selective oxidation. Adsorption properties of benzyl alcohol, benzaldehyde and benzoic acid on TiO₂ were also investigated to understand the high benzaldehyde selectivity over the Rh³⁺/TiO₂ photocatalyst. The reaction mechanism was discussed on the basis of the results of photocatalytic oxidation of various p-substituted benzyl alcohol derivatives.