Three different TiO2-SiO2 gels (Xerogel, Carbogel and
Aerogel) are more active acid catalysts than other reference samples used
here. As deduced from FTIR, XRD and XANES studies, the structural properties
of these gels are quite different to each other, thus revealing the strong
influence of the drying treatment. It is found that the degree of Si-O-Ti
linking and the surface acidity follows the same trend (X 〉 C 〉 A). We
conclude that supercritical drying at 600 K and 190 bars can induce Ti
leaching followed by redeposition in the narrower pores of the gel. These
effects modify both the textural and surface chemical properties of the
resulting material.