Epoxidation of alkenes with hydrogen peroxide catalyzed by ReO4-SiO2 center dot Al2O3 and ReO4-Al2O3

Rhenium oxides supported on zeolite Y, mixed silica-alumina and pure alumin a were prepared by impregnation of the supports with Re2O7 or NH4ReO4. The materials are active catalysts in the epoxidation of cyclooctene and cycloh exene with anhydrous H2O2 in EtOAc. Catalyst stabilities with regard to met al leaching are closely correlated with the alumina content of the support and almost no leaching was observed with ReO4- supported on pure alumina. S table catalysts ReO4-Al2O3 with ReO4- contents up to 12 wt.% can be prepare d. Higher contents result in extensive metal leaching and catalysis in the homogeneous phase. The catalyst ReO4(12 wt.%)-Al2O3 was re-used in three ca talytic runs, without loss of activity. Selectivities for cyclooctene epoxi de were around 96%, whereas cyclohexanediol was obtained as the only produc t in cyclohexme epoxidation. Adding pyridine to the reaction mixtures. the selectivity for cyclohexene epoxide increased from 0 to 67%, however, a sig nificant decrease in conversion was observed. (C) 2001 Elsevier Science B.V . All rights reserved.