Spectroscopic characterisation 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 tertbutyl hydrogen peroxide (TBHP) as a test reaction. Surface areas up to 450 m2g-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 °C, and a heating rate of 5 °Cmin-1. ©2000 Materials Research Society