Catalytic performance of a phosphorus-modified H-IM-5@meso-SiO2 composite in the alkylation of toluene with methanol

Abstract

Herein, a core–shell H-IM-5@meso-SiO₂ hybrid material was synthesized by reversing the charge of the external surface of IM-5 crystals to a positive charge by PDDA that could induce an oriented self-assembly formation of the meso-SiO₂ shell. The as-synthesized H-IM-5@meso-SiO₂ composite was thereafter modified with phosphorus species to further enhance the selectivity of the target product. The sample morphology and structure were analyzed by electron microscopy technology, XRD, XPS and N₂ adsorption–desorption. The effects of the meso-SiO₂ shell and phosphorus species on sample acidity were investigated by NH₃-TPD, FTIR spectroscopy and solid-state NMR measurements. The catalytic properties and characterization results revealed that the meso-SiO₂ shell could passivate the external surface acids of the H-IM-5 crystals. The phosphorus modification could simultaneously adjust the surface acidity as well as the size of the pores and pore-openings. The TPD analysis of xylene showed that the sample surface acidity and geometric factors played important roles in the diffusion process of the diffusing molecules.