Surface characteristics of titania/carbon composite aerogels

Titania/carbon composite aerogels with a nominal titania content between 10 and 50% were prepared by the sol-gel method. The samples obtained were heat treated at 500 and 900 degreesC in He flow. All composite aerogels and their carbonized derivatives were characterized by physical adsorption and mercury porosimetry to determine their surface area and pore texture. The surface chemistry was studied by X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia previously adsorbed at 100 degreesC. Results showed that development of the meso- and macroporosity as well as the surface area depended on the titania content and the heat treatment. The titania phase in the composite aerogels was uniformly and well dispersed up to a real titania content of around 70%, either as anatase or as a mixture of anatase and rutile. The surface acid sites of the metal oxide phase were of the Lewis type, and it was well dispersed up to the above titania content. In the composites with higher titania content there was a sintering of the metal oxide particles, which increased with temperature.