Highly dispersed molybdenum incorporated hollow mesoporous silica spheres as an efficient catalyst on epoxidation of olefins

Highly dispersed Molybdenum (VI) incorporated hollow mesoporous silica catalyst was facilely synthesized with a selective etching strategy and then followed with a modified immersion method. Firstly, hollow mesoporous silica spheres were obtained from solid silica spheres with the interaction of cetyltrimethyl ammonium bromide (CTAB) and Na₂CO₃. Then the catalytic sites were loaded by modified and direct immersion methods as comparison. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption/desorption and X-ray photoelectron spectra (XPS). The reactivity of the catalysts was also detected under the same condition in olefin epoxidation. Compared with these two immersion methods, modified method exhibited the best turnover number of 3873 at 6 h with a better reactivity and textural properties than direct one. Highly dispersed molybdenum indeed brought excellent activity and high stability. The conversion could reach 100% with a selectivity above 99% after 12 h. And the catalyst still had a conversion above 86% and a selectivity above 93% after five runs. More importantly, this modified immersion method could also be widely used in the preparation of catalysts as a simple but efficient way.