The electronic structure of oxide-supported tungsten oxide catalysts as studied by UV spectroscopy

The UV spectra of tungsten oxide catalysts supported on alumina, titania and zirconia and on titania-alumina and titania-zirconia mixed oxides are reported and discussed. Evidence is provided for the different electronic structure of supports and catalysts, which could affect the behavior of the tungsten oxide centres in the different cases. On alumina, tungsten oxide centres are "isolated" by the insulating support, while on titania-based materials they are likely in electronic contact with each other and with Ti centres through the support conduction band. In the case of WO3-ZrO2, the 5d levels of tungsten ions fall just below of the lower energy limit of the support conduction band.