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

Abstract

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 minimise capillary pressures and hence preserve pore structure and maximise the surface area. SAXS data have identified that heptane washing during drying, in general, results in a preservation of the pore structure and surface areas of up to 450 m² g⁻¹. ¹⁷O 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 expected. The calcined xerogels were tested for their catalytic activity using the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) as a test reaction, with excellent selectivities and reasonable percentage conversions. FT-IR spectroscopy has revealed that the catalytic activity is correlated with the intensity of the Si–O–Ti signal, after accounting for variations in Si–OH and Si–O–Si. The most effective catalyst was produced with heptane washing, a calcination temperature of 500°C, and a heating rate of 5°C min⁻¹.