Different transition metal (Fe2+, Co2+, Ni2+, Cu2+ or VO2+) Schiff complexes immobilized onto three-dimensional mesoporous silica KIT-6 for the epoxidation of styrene

Abstract

Highly ordered three-dimensional Ia3d mesoporous silica KIT-6 was functionalized with 3-aminopropyltriethoxysilane (3-APTES), following by post-grafting of various transition metal (Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ or VO²⁺) Schiff complexes onto amino-functionalized KIT-6. The surface functionalized materials were analyzed by a series of characterization techniques such as XRD, X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, IR spectroscopy, inductively coupled plasma (ICP), scanning electron microscopy (SEM), and thermal gravimetric analyses (TGA), etc. The characterization results demonstrated structural intact of the mesoporous hosts throughout the grafting procedures and successfully anchoring of transition metal Schiff complexes on the modified KIT-6. The obtained organic–inorganic hybrid materials were subsequently employed as catalysts for the epoxidation of styrene under optimized reaction conditions. It was indicated that Cu-NH₂-KIT-6 showed very high substrate conversion (98.6%) and excellent epoxide selectivity (97.8%) when using tert-butyl hydroperoxide (TBHP) as the oxidant at 80 °C after 6 h. It was also observed that the catalyst could be recycled three times without obvious loss in catalytic activity and selectivity.