The Effect of Silanization on the Catalytic and Sorption Properties of Zeolites

Abstract

Silanizing a zeolite can result in significant beneficial changes to their catalytic and sorptive properties. It has been shown, however, that it is necessary to carefully control the reaction conditions when silanizing a zeolite. Apart from considerations such as the different effects of using vapor or liquid deposition procedures and static or flow systems, deposition temperature and the number of silanization/calcination cycles are of great importance. By careful control of the number of cycles it is possible to systematically modify the diffusional properties of the zeolite while at the same time inertizing the external surface acidity. On the basis of the changes in adsorption properties of the silanized zeolite it is suggested that diffusional changes are more likely due to blockage of pore entrances,resulting in a greater diffusion pathway, than due to a controlled narrowing of the pore openings. By careful control of the number of cycles (i.e., silanization followed by calcination)it is possible to systematically change the diffusional properties to whatever extent is desired. It is shown that the amount of Si deposited/nm2 is a good indicator of the process of silanization. The conversion of TEOS and the products of the silanization reaction at different temperatures have been used to propose a reaction pathway. Results shown for a variety of reactions indicate that silanized zeolites are able to significantly increase the yield of particular isomers as a result of the diffusional constraints resulting from the silanization process.