A novel titanosilicate with MWW structure: III. Highly efficient and selective production of glycidol through epoxidation of allyl alcohol with H 2O 2

Abstract

The catalytic properties of Ti-MWW in the epoxidation of allyl alcohol (AAL) with hydrogen peroxide to glycidol (GLY) have been studied in detail by a comparison with those of TS-1 and pure silica Ti-Beta, and mechanical considerations have been given to the relation between the catalytic performance and the structural, acidic, and hydrophilic/hydrophobic nature of titanosilicates. Ti-MWW catalyzed the AAL epoxidation more actively and selectively than TS-1 and Ti-Beta in the presence of H 2O or MeCN, and exhibited a conversion of 95% for AAL and a selectivity of 99% for GLY when the AAL epoxidation was carried out at 333 K for 30 min and at 12 wt% of catalyst to substrate. Ti-MWW proved to be a reusable and sustainable catalyst as it stood up to Ti leaching and maintained the catalytic activity and the product selectivity in the reaction-regeneration cycles. The acidic character due to the boron framework was very weak, and thus contributed negligibly to the solvolysis of GLY. The AAL epoxidation proceeded mainly within the intralayer sinusoid 10-MR channels which supplied more steric fitness to the substrate molecules than the tunnel-like channels of TS-1 ad Ti-Beta. Ti-MWW was more hydrophilic than TS-1, but much more hydrophobic than Ti-Beta. The hydrophilicity of Ti-MWW was presumed to derive mainly from the defect sites due to the incomplete dehydroxylation between the layers and partially as a result of deboronation. The sinusoidal 10-MR channels serving as the reaction space for the AAL epoxidation were considered to be hydrophobic, thus rendering the Ti-MWW catalyst applicable to the substrates and solvents, both of a polar nature.