Selective oxidation of cyclic olefins over framework Ti substituted, three dimensional, mesoporous Ti SBA 12 and Ti SBA 16 molecular sieves
Abstract Framework Ti substituted, three dimensional, mesoporous titanosilicates, Ti SBA 12 and Ti SBA 16, were prepared by direct hydrothermal synthesis method. These catalysts showed catalytic activity higher than the hitherto known titanosilicates for the oxidation of cyclic olefins (cyclohexene and cyclooctene) with tert. butyl hydroperoxide. An epoxide selectivity of 100% and olefin conversion greater than 92% were obtained. Cubic Ti SBA 16 with interconnected cage like mesopore structure was more active than hexagonal Ti SBA 12. X ray diffraction and diffuse reflectance UV vis, Fourier transform infrared, Raman and electron paramagnetic resonance spectroscopies provided evidence for the substitution of Ti 4+ (for Si 4+ in the framework locations. The catalytic activity correlated with the concentration of framework substituted, tetrahedral Ti 4+ ions. Easy accessibility of the active sites and the three dimensional mesoporous structure are the possible causes for the superior activity of these titanosilicate catalysts.