Selective oxidation of cyclic olefins over framework Ti-substituted, three-dimensional, mesoporous Ti-SBA-12 and Ti-SBA-16 molecular sieves

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 Ti4+ (for Si4+) in the framework locations. The catalytic activity correlated with the concentration of framework-substituted, tetrahedral Ti4+ 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.

Graphical abstractTi-SBA-12 and Ti-SBA-16 were prepared by direct hydrothermal synthesis and their comparative catalytic activity for the oxidation of cyclohexene and cyclooctene with TBHP was investigated.Figure optionsDownload full-size imageDownload high-quality image (145 K)Download as PowerPoint slideHighlights► Direct hydrothermal synthesis of Ti-substituted Ti-SBA-12 and Ti-SBA-16. ► Highly efficient and selective oxidation catalysts. ► Cyclohexene and cyclooctene get oxidized selectively to their epoxides in high yields. ► 3D pore structure and hydrophobicity are the features for superior activity of these catalysts. ► Ti-SBA-16 is relatively more active than Ti-SBA-12.