Titania-silica epoxidation catalysts modified by mono- and bidentate organic functional groups

Amorphous, mesoporous titania-silica mixed oxides with covalently bound mon o- and bidentate acetoxyalkyl and aminoalkyl functional groups were prepare d using the solution sol-gel process and ensuing low temperature supercriti cal extraction with CO2. Titanbisacetylace-tonatediisopropoxide, tetrametho xysilane and amino- or acetoxyalkyl-trimethoxysilane precursors were used f or the syntheses of hybrid aerogels with a constant Ti: Si atomic ratio of 1 : 12. The mixed oxides were characterized by thermal analysis, N-2 physis orption, C-13- and Si-29-CP-MAS NMR spectroscopy, and electron microscopy. The amorphous mesoporous structure of the aerogels depended markedly on the nature of the modifier. Organic modification enhanced remarkably the rate of epoxidation of cyclohexene and cyclohexenol. The highest selectivity in the tnore demanding epoxidation of cyclohexenol, 91% at 80% TBHP conversion , was achieved with a bidentate (diaminoalkyl)-modified aerogel.