Silylation of [Nb]-MCM-41 as an efficient tool to improve epoxidation activity and selectivity

Well-ordered [Nb]-MCM-41 was synthesized at room temperature with essentially all niobium present in the sample substituted into the silica framework. The material was calcined and then silylated using hexamethyldisilazane (HMDS). Both calcined and silylated materials were characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis, inductively coupled plasma emission (ICP-OES), infrared spectroscopy (FTIR), N2 adsorption at low temperatures, thermogravimetry (TG), and nuclear magnetic resonance of 29Si with magic-angle spinning (NMR-MAS). The materials were used as catalysts in the epoxidation of cis-cyclooctene with tert-butyl hydroperoxide (TBHP) and 70 wt% aqueous hydrogen peroxide as oxidants, to verify the influence of the silylation on the activity and selectivity. It was observed that the silylated material was more active for both oxidants, reaching 62% conversion and 94% selectivity after 48 h with TBHP and 13% conversion and 80% selectivity after 5 h with aqueous hydrogen peroxide.