Synthesis, characterisation and performance of (TiO2)(0.18)(SiO2)(0.82) xerogel catalysts

The synthesis of high surface area xerogels has been achieved using the sol -gel route. Heptane washing was used during the stages of drying to minimis e capillary pressures and hence preserve pore structure and maximise the su rface area. SAXS data have identified that heptane washing during drying, i n general, results in a preservation of the pore structure and surface area s of up to 450 m(2) g(-1). O-17 NMR showed that Ti is fully mixed into the silica network in all of the samples. XANES data confirm that reversible 4- fold Ti sites are more prevalent in samples with high surface areas, as exp ected. The calcined xerogels were tested for their catalytic activity using the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) as a t est reaction, with excellent selectivities and reasonable percentage conver sions. FT-IR spectroscopy has revealed that the catalytic activity is corre lated with the intensity of the Si-O-Ti signal, after accounting for variat ions in Si-OH and Si-O-Si. The most effective catalyst was produced with he ptane washing, a calcination temperature of 500 degreesC, and a heating rat e of 5 degreesC min(-1).