Photocatalytic Oxidation of Alcohols over TiO₂ Covered with Nb₂O₅

A selectivity enhancement in alcohol photooxidation using TiO 2 covered with Nb 2 O 5 is demonstrated. A series of TiO 2 covered with Nb 2 O 5 catalysts (Nb 2 O 5 /TiO 2, loading of Nb 2 O 5; 0–5 mol %) were prepared and characterized. XPS studies suggest that the TiO 2 surface was completely covered with Nb 2 O 5 at a 3.5 mol % loading. UV–vis spectra of TiO 2 and the Nb 2 O 5 /TiO 2 series revealed that the band gap energy of the catalyst was not changed upon addition of Nb 2 O 5 . 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 Nb 2 O 5 . The O 3 – anion, in particular, which can be formed on anatase TiO 2, completely disappeared at Nb 2 O 5 loadings over 4 mol %. In the oxidations of several alcohols (1-pentanol, 2-pentanol, 3-pentanol, and cyclohexanol), the Nb 2 O 5 /TiO 2 catalysts exhibited higher selectivities than TiO 2 with comparable conversion levels. Furthermore, the Nb 2 O 5 /TiO 2 system gave a higher photocatalytic activity compared with Nb 2 O 5 without lowering the selectivity.