Preparation and characterization of titanium-containing MFI from highly siliceous ZSM-5: effect of precursors synthesized with different templates

Titanium-containing MFI zeolites (Ti-ZSM-5) have been prepared by gas-solid reaction between highly siliceous ZSM-5 precursors synthesized with differ ent organic molecules, and TiCL4 vapor at elevated temperature. XRD, FT-IR, UV-Vis, Si-29 and Al-27 solid NMR techniques are used to characterize prec ursors and Ti-ZSM-5 zeolites. Highly siliceous ZSM-5 synthesized with diffe rent templates possesses different amount of internal silanol groups cluste red as silanol nests in framework. When the precursor is contacted with TiC l4 vapor at elevated temperature, titanium atoms are incorporated into the tetrahedral sites by the reaction between TiCl4 and silanol nests, not by t he isomorphous substitution of titanium for framework aluminium or/and sili con. Highly siliceous ZSM-5 precursor synthesized with NEA, TEABr or HDA te mplate possesses relatively large amount of internal silanol groups, and th en obtains high concentrations of framework titanium after contacted with T iCl4 vapor, compared to those synthesized with TPAOH or TPABr template. In addition, Ti-ZSM-5 with precursors obtained by using NEA, TEABr or HDA temp late can occupy higher catalytic activity in the epoxidation of propylene w ith diluted hydrogen peroxide. (C) 1999 Elsevier Science S.A. All rights re served.