Titania-silica mixed oxides. II. Catalytic behaviour in olefin epoxidation
- Swiss Federal Institute of Technology, Zurich (Switzerland)
Various titania-silica aerogels prepared by an alkoxide-sol-gel route have been tested in the epoxidation of bulky olefins using cumene hydroperoxide as oxidant. The drying method, the titanium content between 2 and 20 wt%, and the calcination temperature between 473 and 1073 K were the most important preparation parameters, influencing the catalytic behaviour of the aerogels. The aerogels dried by semicontinuous extraction with supercritical CO{sub 2} at low temperature (LT aerogel) were found to be much more efficient epoxidation catalysts than aerogels prepared by high-temperature supercritical drying and conventionally dried xerogels. The reaction rate of cyclohexene epoxidation over LT aerogels increased monotonically with increasing Ti content. In the range of 333-363 K the catalysts containing 20 wt% TiO{sub 2} (20LT) showed high activity and selectivity (79-93% to peroxide and 87-100% to epoxide) in the oxidation of various cyclic olefins, including cyclododecene, norbornene, cyclohexene, and limonene. Catalytic experiments, FTIR, and UV-vis spectroscopy indicated that the LT aerogels consist of two different types of active species: titanium well-dispersed in the silica matrix and titania nanodomains. The key factors determining the activity and selectivity of sol-gel titania-silica catalysts are the morphology (surface area and pore size) and the relative proportions of Ti-O-Si and Ti-O-Ti structural parts. A comparative study of the epoxidation of cyclohexene, cyclododecene, and norbornene over structurally different titania-silica catalysts, indicates that 20LT shows better catalytic behaviour in these reactions than Ti zeolites and silica-supported titania. 46 refs., 12 figs., 3 tabs.
- OSTI ID:
- 98955
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 153; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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