Characteristic and Uses of Titanium Silicalite-1

Titanium Silicalite-1, TS-1, 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. TS-1 has unique properties as a heterogenous catalyst when H2O2 is used as the oxidant and H2O2 is attractive for industrial applications because of its relatively low cost and because it is clean.

Characteristic

The high activity of titanium silicate-1 (TS-1) in oxidations with hydrogen peroxide is the result of different factors, directly referable to the MFI structure. The configuration of Ti site (tetrahedral), the nature of active species (Ti-OOH) and the nature of the surface (hydrophobic) are the three factors that are immediately apparent. Hydrophobicity alone, however, cannot fully explain certain catalytic performances and trends in the oxidation of the olefins, without envisaging a major involvement of porosity. Actually, the molecular dimensions of pores (ca. 0.55 nm), normally perceived as just a drawback for the limits set to the range of potential substrates, play a relevant and positive role in TS-1 catalysis. 

Uses

Titanium silicalite (TS-1) is a silicalite in which Ti has been substitionally incorporated to its framework (MFI topology), creating isolated tetrahedral Ti(IV) sites with unique catalytic properties for a number of different reactions (alkane oxidation, epoxidation of C-C double bonds, oxidation of alcohols, ammoximation of ketones, etc). TS-1 is a typical microporous catalyst that, despite its relatively small pore sizes (0.55 × 0.51 and 0.56 × 0.53 nm), has found its way to industrial application as catalyst for the production of propylene oxide (via epoxidation of propylene) and cyclohexanone oxime (via ammoximation of cyclohexanone). The hydrophobic environment within the channels and cavities of TS-1 also plays a key role in the remarkable catalytic activity of this material.

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