Alkene Epoxidation with Ethylbenzene Hydroperoxides Using Molybdenum Heterogeneous Catalysts

Molybdenum-containing catalysts were prepared by anchoring Mo(VI) groups onto different amino-functionalized silica surfaces and then tested in the epoxidation reaction of 1-octene with ethylbenzene hydroperoxide (EBHP) as an oxidant. Catalytic performance was found to depend on the chemical structure and nature of the functional group. EBHP conversion-time profiles exhibited an S-shaped behavior, suggesting that an induction period is required to develop the active site. Selectivity-conversion plots indicated that selectivities as high as 80% could be obtained at EBHP conversions of about 80% when the Mo complexes were immobilized on a silica substrate functionalized with a diamino-containing moiety. In contrast, surface functionalization with -COOH was found to be detrimental, as acid groups catalyze EBHP decomposition. Experiments designed to determine possible leaching of molybdenum into the reaction medium during the tests indicated that the catalyst prepared on a triamine-containing substrate exhibited good stability with almost no change in performance after three consecutive runs. The high stability of the Mo(VI) complex, in this catalyst was shown by UV-vis and photoelectron spectroscopic techniques.