Preparation and characterization of mesoporous titanic-alumina ceramic by modified sol-gel method

Mesoporous titanic-alumina ceramics are interesting as catalysts and catalyst supports. Monolithic wet-gels of 0.2TiO(2)-0.8Al(2)O(3), prepared by hydrolysis of metal alkoxides in alcoholic solutions, were dried at 90degreesC (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 60degreesC and 24Mpa for 2h (aerogel). Thermal evolution of the microstructure of the gels was evaluated by thermal analyses (TG-DTA), NZ adsorption, scanning electron microscopy, and X-ray diffraction. After calcination at 500degreesC, the specific surface area of the gels was >400m(2)g(-1). The average pore radius for the supercritically extracted titanic-alumina gel, about 8nm (similar to50% 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 150m(2)g(-1) after calcination at 800degreesC. The pore size and pore volume of these gels minimally decreased after calcination at 800degreesC, while those values of the xerogel markedly decreased. The thermal stability of the microstructure of mesoporous titanic-alumina is improved by surfactant immersion or supercritical extraction. (C) 2004 Elsevier B.V. All rights reserved.