CHARACTERIZATION OF THE ZIRCONIA-SUPPORTED TUNGSTEN-OXIDE SYSTEM BY LASER RAMAN AND DIFFUSE-REFLECTANCE SPECTROSCOPIES

Zirconia-supported tungsten oxide samples, prepared by the equilibrium . adsorption method in the pH range 2-13 by using as a support either hydrous [ZrO2(383)] or thermally pretreated [ZrO2(T)] zirconium oxide, were studied by laser Raman and diffuse reflectance spectroscopies. T he W uptake increased (from similar to 1.0 to similar to 2.8 atoms nm( -2)) as the pH decreased for the ZrO2(T) supports, whereas for hydrous zirconia support showed the opposite trend. Different tungsten specie s were revealed depending on the amount of the adsorbed tungsten but n ot on the pH of the contacting solution. The continuous frequency shif t of the Raman bands with the tungsten content, from 930 to 975 cm(-1) , indicated the presence of monomeric species at low tungsten concentr ations and of polymeric species at high loading. The uptake of the tun gsten species depends on the morphology and the texture of the support .