Incorporation process of Ti species into the framework of MFI type zeolite

The incorporation process of titanium species into the framework of MFI type zeolite is investigated to clarify the reasons for the difficulty in the isomorphous substitution of Ti into the zeolitic lattice. TS-1 samples are synthesized via two synthesis routes, conventional route and peroxo-complex route, in which different sources of Ti are used. Changes in the content and the coordinated environment of Ti in the products are observed along with the time course of crystallization; although the MFI-type framework is already formed at the initial stage of the crystallization, Ti is hardly incorporated into the framework. After prolonging the crystallization, the content of tetrahedrally-coordinated Ti is drastically increased. It is concluded that Ti would be incorporated into the pre-crystallized Si-rich zeolite (almost all-silicalite-1), resulting in the formation of TS-1. Considering the differences between the synthesis routes employed, the reactivity of Ti species relative to Si species could strongly affect the incorporation of Ti into the zeolite framework. Based on these results, a novel post-synthesis method for preparing TS-1 is proposed.