Macro-meso-microporous titanium silicalite-1 catalyst featuring self-assembled nanocrystals and multiple active species for propylene epoxidation

Abstract

Titanium silicalite-1 (TS-1) is an important catalyst for many oxidation reactions. Catalytically active titanium species with favourable particle morphology and pore structure to support diffusion are vital to the performance of this catalyst. Herein, by growing TS-1 nanocrystals on solid silicalite-1 cores followed by hollowing both the cores and TS-1 nanocrystals, a macro-meso-microporous (3 M) structured 3 M−TS−1(ML) catalyst was produced using only a solo template, tetrapropylammonium hydroxide. This catalyst demonstrates superior catalytic performance for propylene epoxidation to propylene oxide, and contains only catalytically active Ti(OH)(OSi)3, Ti(OH)2(OSi)3 and Ti(OH)4(OSi)2 species and is free from inactive Ti species such as anatase-TiO2. Through rationally designed comparative evaluations, this work shows that the high catalytic activity of 3 M−TS−1(ML) is the results of both having excellent diffusion conditions from its unique 3-tiered pore structure and containing high activity Ti species such as Ti(OH)4(OSi)2.