Surface Of TS-1 Research Articles

A study of the external and internal sites of MFI-type zeolitic materials through the FT-IR investigation of the adsorption of nitriles

The adsorption of acetonitrile (AN) and pivalonitrile (2,2-dimethylpropionitrile, PN) has been investigated on pure silicalite S1, on a ZSM5 zeolite apparently free from extraframework material and another ZSM5 zeolite apparently rich in extraframework material, on a titanium silicalite TS1 and on a boralite sample. AN enters the cavities of MFI type structures and interacts with both internal and external acid sites while PN does not enter such cavities and only interacts with the external sites. Terminal silanols, whose acidity can vary from weak to medium, are present in all cases mostly at the external surface, while very acidic bridging Si–OH–Al sites of ZSM5 zeolite are apparently exclusively located at the internal channel surface. Lewis acidic Ti cations are evident both in the internal and on the external surface of TS1. Weakly acidic BOH sites of boralite are distributed among internal and external surface. Extraframework alumina-like species of ZSM5 zeolite are apparently located in the internal cavities. Terminal silanols and hydrolized defects are located mostly at the external surface of silicalite. The mechanism of incorporation and charge balance of boron atoms as well as the structure of the hydroxy groups of boralite are still not well established.

Epoxidation of allyl chloride with hydrogen peroxide catalyzed by titanium silicalite 1

In this paper, different parameters affecting the epoxidation of allyl chloride with hydrogen peroxide, as well as the kinetic characteristics are described. The influence of the amount of catalyst and the concentration of oxidant and substrate, the effect of solvent and additive have been investigated. The epoxidation of allyl chloride is first order with respect to the amount of catalyst and between zero and unity order in the substrate and oxidant concentration. The epoxidation was accelerated and the selectivity was improved with increasing the concentration of substrate and the amount of TS-1. Finally, a possible kinetic model was supposed according to Eley-Rideal isotherms, which was in agreement with experimental data. Both the weak acidity of TS-1 surface and the proton produced by the interaction of active sites of TS-1 with hydrogen peroxide can catalyze the solvolysis of oxirane product. The best solvent for epoxidation of allyl chloride is methanol or methanol/water mixture. Small amount of additives can affect the reaction seriously. Inorganic basic compounds and fluorides can suppress the epoxidation completely, while acidic materials can promote the solvolysis of product.