Preparation of Heterogeneous Mesoporous Silica-Supported 12-Tungstophosphoric Acid Catalyst and Its Catalytic Performance for Cyclopentene Oxidation

Keggin-structured 12-tungstophosphoric acids were immobilized onto the surface of amine-modified mesoporous sieve SBA-15 as onium salts. All the catalyst materials were characterized by x-ray diffraction, N-2 physisorption, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and X-ray photoelectron spectroscopy for their structural integrity and physicochemical properties. Characterization of the catalysts confirmed an ordered hexagonal mesostructure for SBA-15 and that the Keggin structure of the heteropolyanions on the amine-modified SBA-15 was preserved. The catalytic activities of the catalysts were evaluated for the liquid-phase oxidation of cyclopentene with 50% hydrogen peroxide as the oxidant in tert-butanol. A 100% conversion of cyclopentene and an 81% selectivity for glutaraldehyde were obtained and these were higher than that for the catalysts prepared by direct impregnation. The stability and reusability of the catalysts were studied and the catalysts could be reused at least five times, which indicates their excellent reusability. The influence of reaction temperature and reaction time was also investigated. In addition, a reaction mechanism was proposed.