Magnetically Separable Single-Site Ti–Fe₃O₄@MCM-41 Catalyst for Selective Epoxidation of Olefins

Abstract

Magnetically separable Ti–Fe3O4@MCM-41 (Ti-MS) catalysts were prepared by postgrafting Ti with varying loading on mesoporous silica containing dispersed magnetite. The hexagonal structure of Ti-MS catalysts with a periodicity in the pores and a highly ordered hexagonal matrix was established by X-ray diffraction and transmission electron microscopy, while diffuse reflectance UV showed the isolated tetrahedral Ti species coordinated with O2–. From the Fourier transform infrared studies, the extent of Ti–O–Si linkage was found to increase with increase in Ti-loading from 1 to 5 wt % beyond which (10%), the intensity of Ti–O–Si band decreased due to the polymerization of the Ti on the silica surface. Silanol groups on the surface of silica interact with the precursor Ti(OiPr)4 to give site isolated tetrahedral Ti-species responsible for complete selectivity to the epoxide in the epoxidation of cyclooctene. The magnetic property facilitated easy recovery of the catalyst for its successful eight recycles showing its stability under reaction conditions.