SURFACE-ACIDITY AND PROPERTIES OF TITANIA-SILICA CATALYSTS

Titania-coated silica microspheres containing between 8 and 48 wt % TiO2 have been prepared by the homogeneous precipitation of TiC3 with a diluted ammonia solution up to a final pH close to 7. All these TiO2-SiO2 materials were physically characterized by X-ray diffraction, UV-visible reflectance, Raman, Fourier transform infrared, and photoelectron spectroscopic techniques. Calcination of the silica-supported precipitates leads to the formation of titanium dioxide. These TiO2 species are scattered on the surface as small crystals of anatase. Their structures become better defined as the titania loading increases. It was also observed that the TiO2-SiO2 oxides show much stronger acidic properties than the single TiO2 and SiO2 oxides. Bronsted acid sites appear to be associated with thee interface between octahedral titanium sites and silica. The infrared spectra of chemisorbed ammonia was very useful to charaterize acid properties in these materials.