NOVEL PREPARATION OF HIGHLY DISPERSED TUNGSTEN-OXIDE ON SILICA

WO3/SiO2 samples prepared by three different methods and calcined at two temperatures (450 and 900-degrees-C) are studied by different physicochemical techniques [X-ray diffraction (XRD), specific surface area, X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), electron microscopy and temperature-programmed reduction (TPR)]. When the solids were prepared by mixing two gels (tungsten and silica gel) a good WO3 dispersion was achieved and calcination at high temperature gave an amorphous phase. The impregnation of silica gel by ammonium paratungstate allows the interaction of tungsten with silica as dispersed oxoanions and, upon calcination, smaller WO3 particles and amorphous glassy particles were formed. In contrast, when the solid was prepared by the wet impregnation method using a silica carrier the interaction of the oxotungsten species with the support was weak. When the sample was calcined the silica and the oxides were segregated.