Photocatalytic Oxidation of Alcohols over TiO2 Covered with Nb2O5

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 (O-2(-) and O-3(-)) over the catalyst, as estimated by ESR, drastically decreased with increased loadings of Nb2O5. The O-3(-) 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 compared with Nb2O5 without lowering the selectivity.