Photocatalytic Oxidation of Alcohols over TiO2 Covered with Nb2O5

Abstract

A selectivity enhancement in alcohol photooxidation using TiO2 covered with Nb2O5 is demonstrated. A series of TiO2 covered with Nb2O5 catalysts (Nb2O5/TiO2, loading of Nb2O5; 0–5 mol %) were prepared and characterized. XPS studies suggest that the TiO2 surface was completely covered with Nb2O5 at a 3.5 mol % loading. UV–vis spectra of TiO2 and the Nb2O5/TiO2 series revealed that the band gap energy of the catalyst was not changed upon addition of Nb2O5. The amounts of photogenerated oxygen anion radical species (O2– and O3–) over the catalyst, as estimated by ESR, drastically decreased with increased loadings of Nb2O5. The O3– anion, in particular, which can be formed on anatase TiO2, completely disappeared at Nb2O5 loadings over 4 mol %. In the oxidations of several alcohols (1-pentanol, 2-pentanol, 3-pentanol, and cyclohexanol), the Nb2O5/TiO2 catalysts exhibited higher selectivities than TiO2 with comparable conversion levels. Furthermore, the Nb2O5/TiO2 system gave a higher photocatalytic activity co...