Epoxidation of α-isophorone with amine-modified titania-silica hybrid aerogel: Evidence for Ti-amine interaction

Article abstract of DOI:10.1006/jcat.2000.2859

The oxidation of α-isophorone was selected as a test reaction to evaluate the newly developed organically modified aerogels in the epoxidation of deactivated olefins and to elucidate the role of organic modification in the epoxidation reaction. The catalyst used was an N,N-dimethyl-3-aminopropyl-modified titania-silica mixed oxide containing ~ 9 wt % TiO₂, showing exceptional activity and 94% epoxide selectivity at 91% peroxide conversion in the epoxidation of cyclohexanol with tert-butylhydroperoxide. Organic modification diminished the epoxidation activity of titania-silica and eliminated the activity in acid-catalyzed side reactions, such as epoxide and peroxide decomposition. Methanol addition to an unmodified aerogel had a similar effect. Electron donation by the alkylamino groups or methanol to the titanium active site (Lewis acid) suppressed its acidity and, thus the rate of acid-catalyzed oxidation and isomerization reactions. The surface Si-OH groups (Broensted sites) of titania-silica were poor catalysts for epoxide decomposition.