Activity, selectivity and stability of metallosilicates containing molybdenum for the epoxidation of alkenes

Abstract

Microporous metallosilicates containing various transition metals have been prepared by the acid-catalyzed sol–gel process. The catalytic activity of the materials has been tested for the epoxidation of cyclooctene with tert-butyl hydroperoxide. Silicates containing molybdenum showed high activities and epoxide selectivities. The catalytic activities of catalysts prepared with molybdenyl acetylacetonate as metal precursor are mainly due to metal leached into the homogeneous phase. A catalyst for the heterogeneous phase epoxidation was obtained, using Mo(V)isopropoxide as metal precursor. This catalyst was tested in the epoxidation of various alkenes and conversions increase in the order 1-decene≈α-pinene<1-octene<limonene<1-hexene<cyclooctene<cyclohexene. Quantitative conversions of cyclooctene and cyclohexene with epoxide selectivities around 98% were obtained at 373 K. The catalyst was used in five consecutive reactions and metal leaching is fairly low up to the third reaction. Information about the catalyst structure was obtained by elemental analysis, thermogravimetry, X-ray diffraction and fluorescence, N 2-physisorption, UV–VIS and FTIR spectroscopy.