Textural Analysis of Sulphated ZrO 2 –SiO 2 Sol–Gel Catalytic Supports by N 2 Sorption and X-Ray Diffraction

The textural properties of sulphated ZrO₂–SiO₂ catalytic supports of different compositions were investigated through N₂ sorption and X-ray diffraction (conventional and SAXS) methods. The materials were synthesised by the sol–gel procedure from a mixture of zirconium(IV) tert-butoxide and tetraethyl orthosilicate. The final products were obtained after drying at 125°C followed by calcination at 400°C. The porous structures of the substrates were found to depend on their composition: at low zirconia contents these were formed by slit cavities while at high ZrO₂ concentrations the void structure became open; both cavities and necks were of similar size. In the first case, the pore size distribution function could be obtained from an analysis of the ascending boundary curve of the N₂ isotherm since adsorption occurred on a flat surface. In the second case, a unique pore-size distribution was obtained either from the ascending or descending boundary curves of the N₂ isotherm. A tubular geometry seemed appropriate for the description of the sorption characteristics of these substrates. Primary descending scanning curves traced within the hysteresis loops of samples having high ZrO₂ contents offered further textural information. X-Ray diffraction methods provided compound identification, evidence of phase segregation between ZrO₂ and SiO₂, and particle and pore-size distributions.