Synthesis of hierarchical titanium silicalite-1 by seed silanization for selective oxidation reactions

Abstract

The sole microporous structure of titanium silicalite-1 (TS-1) zeolite usually leads to diffusion resistances, which would negatively influence its catalytic performance. Herein, a small-crystal TS-1 zeolite with micropore/mesopore structure has been successfully synthesized by silanization of seed in a tetrapropylammonium bromide (TPABr)-ethanolamine hydrothermal system. Dodecyltrichlorosilane (DTS) was used to modify the surface of nanosized S-1 seed, then the synthetic precursor of TS-1 was crystallized around the silanized seed, and the mesopores were generated in the spaces occupied by the organosilanes as a result of the calcination of solid zeolite material. The pore diameter of mesopore could be adjusted from 2.9 nm to 7.3 nm relative to the changing of the molar ratio of DTS to SiO2 in seed from 0.05 to 0.45. The resultant hierarchical TS-1 with micropore/mesopore structure exhibited excellent catalytic performances in the propylene epoxidation and cyclohexanone ammoximation, which were even superior to that of hollow TS-1 obtained from post-synthesis treatment. This approach for the preparation of TS-1 with micro-mesopores could be easily realized in industrial application to provide a feasible strategy for the exploration of other hierarchical zeolites.