Hierarchical TS-1 zeolite synthesized from SiO 2 TiO 2 xerogels imprinted with silanized protozeolitic units

Abstract

A new method is reported for the synthesis of TS-1 zeolite with hierarchical porosity based on the crystallization of SiO 2–TiO 2 xerogels that have been previously imprinted with silanized protozeolitic units. The organic functionalization of the latter disrupts the growth and aggregation of the zeolitic crystals during the hydrothermal crystallization, causing the formation of a hierarchical porosity. The TS-1 materials so obtained exhibit enhanced textural properties, due to the formation of an additional porosity within the supermicro/mesoporous range, and present less diffusion restrictions than TS-1 samples prepared by conventional methods. The development of this additional porosity depends both on the molecular size of the organosilane compound and on the TPAOH/xerogel ratio employed in the synthesis. However, these changes are accompanied by a higher hydrophilic character of TS-1 zeolite, reducing its potential application in oxidation reactions using hydrogen peroxide as oxidant, since water molecules adsorbed on the zeolite surface prevent the access of the substrates to the titanium active sites. In contrast, these hierarchical TS-1 zeolites present remarkable catalytic activity in olefin epoxidation reactions using alkyl hydroperoxides as oxidant. This fact is ascribed to the enhanced accessibility to the Ti active sites originated by the presence of the secondary porosity.