Co-Condensation Assisted Preparation of MoVI Schiff Base Modified Mesoporous Silica Catalyst for Enhanced Epoxidation of Olefins

Abstract

An organic–inorganic catalyst was prepared by the reaction of p-salicylidine aminobenzoic acid with mesoporous silica modified with 3-chloropropyl groups. The hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and 3-chloropropyltrimethoxysilane (CPTES) took place during the preparation process. MoO2(acac)2 was then introduced into the mesoporous silica functionalized with a Schiff base ligand. The structural properties of the prepared catalysts were investigated by a series of techniques, such as elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption curves, and thermogravimetric analysis (TGA). The results demonstrated that the MoVI Schiff base complex was successfully tethered on the silica support, and the hexagonally ordered mesoporous structure of the SBA-15-type silica was well retained after the anchoring reaction. The heterogeneous catalyst showed good catalytic activities in the liquid-phase epoxidation of olefins with t-BuOOH as the oxygen source in 1,2-dichloroethane solvent at 80°C. Several important factors, including oxidant-to-substrate ratio, solvent, and catalyst reusability, were investigated. Under the optimum reaction conditions, using this heterogeneous catalyst for the cyclohexene epoxidation reaction, a high conversion of 97.20 % and selectivity of >99 % was achieved after 4 h, while the catalytic activity nearly remained unchanged over four runs.