Enhanced Catalytic Performance of Titanium Silicalite-1 in Tuning the Crystal Size in the Range 1200-200 nm in a Tetrapropylammonium Bromide System

A facile method for the size-controllable synthesis of titanium silicalite-1 (TS-1) is presented. A tetrapropylammonium bromide hydrothermal system was used, and the amount of seeds (silicalite-1 suspension) and crystallization time were tuned to control the crystal size. The crystal size could be adjusted from 200 to 1200 nm by varying the seed amount from 12 to 0.05 wt%. Crystallization time plays a less important role than the seed amount on the crystal size. TS-1 samples with different crystal sizes were characterized and evaluated in propene epoxidation. The catalytic activity and selectivity of propene oxide are enhanced by decreasing the crystal size from 1200 to 200 nm because the diffusion limitation is eliminated gradually. The seed is significant for this system, as a lack of seeds leads to poor crystallization and low catalytic activity. The mechanism of the seed function was studied by simulating the transformation process of the seed in the TS-1 synthesis system.