Preparation and characterization of mesoporous titania–alumina ceramic by modified sol–gel method

Mesoporous titania–alumina ceramics are interesting as catalysts and catalyst supports. Monolithic wet-gels of 0.2TiO2–0.8Al2O3, prepared by hydrolysis of metal alkoxides in alcoholic solutions, were dried at 90 °C (xerogel), immersed into a surfactant solution before drying (surfactant-modified gel), or the solvent in wet gels was supercritically extracted in one step from CO2 at 60 °C and 24 Mpa for 2 h (aerogel). Thermal evolution of the microstructure of the gels was evaluated by thermal analyses (TG-DTA), N2 adsorption, scanning electron microscopy, and X-ray diffraction. After calcination at 500 °C, the specific surface area of the gels was >400 m2 g−1. The average pore radius for the supercritically extracted titania–alumina gel, about 8 nm (∼50% of that for alumina aerogels), was 2–4 times larger than that of the surfactant-modified gels and of the xerogel. The specific surface area of the surfactant-modified gels and of the supercritically extracted gels was more than 150 m2 g−1 after calcination at 800 °C. The pore size and pore volume of these gels minimally decreased after calcination at 800 °C, while those values of the xerogel markedly decreased. The thermal stability of the microstructure of mesoporous titania–alumina is improved by surfactant immersion or supercritical extraction.