On the limited selectivity of silica-based epoxidation catalysts

Epoxidation of 2-cyclohexen-1-ol with TBHP and TiO2-SiO2, Fe2O3-SiO2 and Si O2 aerogels has been studied. The influence of surface silanol groups and t ransition metal impurities in titania-silica on the product distribution ha s been analyzed. The results, supported by literature data, indicate that h igh surface area silica cannot generally be regarded as an inert matrix in epoxidation catalysts, Contribution of Ti-free silica limits the selectivit y of Ti- and Si-containing catalysts in demanding epoxidation reactions. Th e activity of silica - together with the background oxidation of the olefin - may lead to overestimated intrinsic activities when the reaction rate is related to the Ti content of the catalyst.