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 different organic molecules, and TiCl₄ vapor at elevated temperature. XRD, FT-IR, UV-Vis, ²⁹Si and ²⁷Al solid NMR techniques are used to characterize precursors and Ti-ZSM-5 zeolites. Highly siliceous ZSM-5 synthesized with different templates possesses different amount of internal silanol groups clustered as silanol nests in framework. When the precursor is contacted with TiCl₄ vapor at elevated temperature, titanium atoms are incorporated into the tetrahedral sites by the reaction between TiCl₄ and silanol nests, not by the isomorphous substitution of titanium for framework aluminium or/and silicon. Highly siliceous ZSM-5 precursor synthesized with NBA, TEABr or HDA template possesses relatively large amount of internal silanol groups, and then obtains high concentrations of framework titanium after contacted with TiCl₄ vapor, compared to those synthesized with TPAOH or TPABr template. In addition, Ti-ZSM-5 with precursors obtained by using NBA, TEABr or HDA template can occupy higher catalytic activity in the epoxidation of propylene with diluted hydrogen peroxide.