Tailoring the properties of hierarchical TS-1 zeolite synthesized from silanized protozeolitic units

Abstract

Hierarchical TS-1 zeolites, characterized by having a secondary porosity within supermicro-mesopore range, have been synthesized by silanization of protozeolitic units, previously generated by means of a precrystallization step. The silanization agent anchors over protozeolitic units surface, acting as crystal growth inhibitor during the hydrothermal crystallization treatment and hindering partially the protozeolitic units growth and aggregation. The secondary porosity arises from the voids existing between these protozeolitics units. Both the duration of the precrystallization step and the proportion of the organosilane compound added to the synthesis gel have a significant influence on the physicochemical and textural properties of the resultant materials. Thus, a precrystallization time comprised between 22 and 24h leads to the highest enhancement of the textural properties. On the other hand, by controlling the organosilane compound proportion added to the synthesis gel, the relative contribution of the secondary porosity can be tailored. The catalytic activity of these materials was evaluated in olefin epoxidation reactions, using tert-butylhydroperoxide (TBHP) as oxidant. The olefin conversion and TOF values reached by hierarchical TS-1 zeolites are remarkably superior to those obtained with the conventional microporous TS-1 zeolite, the best catalytic results being achieved using a 8%mol of silanization agent. Likewise, these zeolites exhibit a high oxidant efficiency and total selectivity to epoxide, parameters which are not affected by the presence of the secondary porosity.