Titanium Silicalite-1 - TS-1 Catalyst

Titanium silicalite-1 (TS-1) is a zeolitic material with MFI framework structure, in which 1 to 2 per cent of the silicon atoms are substituted for titanium atoms. It was the first framework-substituted redox molecular sieve to be identified. Redox molecular sieves offer a significant advantage over standard heterogenous catalysts; a redox sieve makes it possible to get a significantly higher selectivity to primary oxidation products. 

Applications

Titanium silicalite-1 is widely used in industry owing to its ability to catalytically epoxidize olefins with hydrogen peroxide (H2O2), leaving only water as a byproduct around one million tonnes of propylene oxide are produced each year using this process. The catalytic properties of TS-1 are generally attributed to the presence of isolated Ti(IV) sites within the zeolite framework. However, despite almost 40 years of experimental and computational investigation the structure of these active Ti(IV) sites is unconfirmed, owing to the challenges of fully characterizing TS-1. 

Synthesis of Titanium Silicalite-1 

Titanium silicalite-1 (TS-1) with little extraframework Ti was hydrothermally synthesized in a tetrapropylammonium hydroxide system using starch as the additive. The influences of the amount of starch added on the coordination states of titanium ions and the functional mechanism of starch were studied by various characterization means. The addition of starch slowed the crystallization rate of TS-1 so that the insertion rate of titanium to the framework matched well with that of silicon. Therefore, the generation of extraframework Ti, including the anatase TiO2 and octahedrally coordinated titanium, was eliminated. The catalytic performances of the TS-1 samples were evaluated in the epoxidation of 1-butene to produce butene oxide. The catalytic activity of TS-1 was improved significantly due to the increasing amount of framework Ti.