Assemblies of Ti Active Sites Over HMS Supports Containing Surface's OH or NH2Groups

Abstract

Three types of HMS supports, which were as-synthesized, HMS(u), HMS(c) calcined from HMS(u), and HMS(m) prepared by the modification of HMS(c) with 3-amino propyltriethoxysilane, were first used to assemble the Ti catalytic sites through the exchange reactions between them and Ti compounds such as Ti tetraisoproxide (Ti(OiPr)4), Ti tetrachloride (TiCl4)) and their Ti tartrate complexes. The Ti-assembled HMS catalysts were investigated in detail by means of FT-IR, UV–vis reflection spectra, chemical and elemental analyses. It is found that in Ti(OiPr4 and especially TiCl4, the exchange that takes place with the surface hydroxyls of the HMS(c) is easier than with the surface NH2 groups of HMS(u) and HMS(m). Ti tartrate complex can be successfully assembled on the HMS(c) through three assembled pathways. The UV–vis reflection spectra indicates that the Ti species are highly dispersed upon the surface of HMS. In catalyzing epoxidation of styrene with TBHP, the above-described catalysts show a higher catalytic activity and selectivity for the epoxides than unloading Ti tartrate complex, and the Ti-substituted HMS catalysts. Their outstanding advantage is that they can be reused many times with little loss of activity.