Highly catalytically active micro/meso-porous Ti-MCM-36 prepared by a grafting method

Abstract

The effect of titanium alkoxides and solvents in the preparation of Ti(IV)-incorporated micro/meso-porous MCM-36 (Ti-MCM-36) by a simple grafting method using different titanium alkoxides, including Ti(OEt)₄, Ti(OiPr)₄ and Ti(OBu)₄ in various solvents, including ethanol, 1-butanol, and toluene, was examined. The X-ray diffraction patterns and N₂ sorption isotherms confirmed the retention of the basal MWW layer structure in Ti-MCM-36. The Si/Ti molar ratios analyzed by ICP-MS increased with the size of titanium alkoxides and varied in the order of Ti(OEt)₄ < Ti(OiPr)₄ < Ti(OBu)₄ based on the same amounts of titanium alkoxides used in the grafting solutions, while the solvent had little influence on the Ti loading. However, UV-vis and XANES spectra showed that titanium species were mainly tetrahedrally coordinated Ti(IV) as well as a small amount of titania clusters when grafting in ethanol and 1-butanol, while large bulky titania crystallites were formed in toluene. Ti-MCM-36 prepared by grafting with Ti(OEt)₄ in 1-butanol demonstrated better catalytic activities in the epoxidation of olefins using t-butyl hydrogen peroxide (TBHP) as the oxidant than TS-1, Ti-YNU-1 and those grafted in toluene or with Ti(OiPr)₄ and Ti(OBu)₄ in butanol. In the oxidation of dicyclopentadiene (DCPD), about 100% DCPD conversion and 95% diepoxide selectivity could be achieved with a TBHP/DCPD molar ratio of 3.5.