Synthesis of mixed silica–titania by the sol–gel method using polyethylenimine: porosity and catalytic properties

By means of the sol–gel method, hybrid xerogels of silica, titania and silica–titania mixed networks of different composition with polyethylenimine (PEI) were formed. After removal of PEI followed by calcination, mesoporous oxides of high surface area with monomodal and narrow porosity distribution were obtained. The surface area of the mixed oxides decreases with increasing titania content, but pore size remains almost constant when a PEI:(SiO2 + TiO2) ratio of 1 is kept constant in the xerogel precursor. By doubling and tripling the proportion of PEI, the surface area increases by 15% and 30%, respectively, but pore size remains constant, indicating the formation of a larger number of PEI domains of similar size in the hybrid. Isopropanol decomposition reactions were carried out using the mixed oxides as catalysts, and it was found that the networks contain Lewis acid sites but lack Bronsted acid sites.