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 an d zirconia and on titania-alumina and titania-zirconia mixed oxides are rep orted and discussed. Evidence is provided for the different electronic stru cture of supports and catalysts, which could affect the behavior of the tun gsten oxide centres in the different cases. On alumina, tungsten oxide cent res are "isolated" by the insulating support, while on titania-based materi als they are likely in electronic contact with each other and with Ti centr es through the support conduction band. In the case of WO3-ZrO2, the 5d lev els of tungsten ions fall just below of the lower energy limit of the suppo rt conduction band.