ABSTRACT
Abstract A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(OiPr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with tBuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. Introduction Synergy between different metal sites in bimetallic catalysts is a well-known phenomenon. For example, V-Ti-SiO2 is a more active and more selective catalyst than any of V-SiO2, Ti-SiO2 or V-TiO2 for the oxidation of o-xylene to phthalic anhydride (1) as well as the selective catalytic reduction of NOx (2). Both V-based and Ti-based epoxidation catalysts are well-known, in homogeneous and heterogeneous forms (3). A mixed V-Ti catalyst for epoxidation has not previously been reported. Such a system may be designed to catalyze the epoxidation of functionalized olefins.
