Titania-alumina prepared by sol-gel method: Influence of pH and drying on textural and structural properties

The influences of synthesis conditions (pH) and drying (oven or freeze-drying) on textural and structural properties of titania-aluminas prepared by hydrolysis of alkoxides were studied. Titania-aluminas with a 1:1 molar ratio were prepared by hydrolysis of alcoholic solutions of titanium and aluminium isopropoxides. The syntheses were conducted in acidic (pH 1.4) or basic hydrolysis conditions (pH 9). Solvent and water were removed by freeze-drying or oven-drying at 393 K, followed by calcination at 773 K or 1073 K. The solids were characterized by nitrogen adsorption, X-ray diffraction, Al-27 NMR, DTA and XPS. The results suggested that the textural properties of titania-aluminas prepared by the sol-gel method were mainly determined by the pH of hydrolysis. However, structural properties were very sensitive to the drying procedure. A less stable structure, with a more random distribution of titanium and aluminum, was formed by freeze-drying than the one obtained by oven-drying, which led to separate alumina and titania domains.