Spectroscopic Characterization of Mixed Titania-Silica Xerogel Catalysts

The synthesis of high surface area (TiO2)(0.18)(SiO2)(0.82) xerogels has been achieved using the sol-gel route. Heptane washing was used before the drying stage to minimise capillary pressure and hence preserve pore structure and maximise the surface area. The as-prepared xerogels were tested for their catalytic activity using the epoxidation of cyclohexene with tert-butyl hydrogen peroxide (TBHP) as a test reaction. Surface areas up to 450 m(2)g(-1) were achieved with excellent selectivities and reasonable percent conversions. SAXS data has identified that heptane washing during drying, in general, results in a preservation of the pore structure, and produces more effective catalysts with higher surface areas and larger pore diameters. FT-IR spectroscopy has revealed that the catalytic activity is dependant upon the number of Si-O-Ti linkages, inferring intimate mixing of the precursors at the atomic level. XANES data reveals the presence of reversible 4/6-fold Ti sites that are thought to be 'active' catalytic sites. The most effective catalyst was produced with a calcination temperature of 500 degrees C, and a heating rate of 5 degrees Cmin(-1).