A Titanium Silicalite-1 (TS-1) Catalyst with Abundant Active Ti-VI Species for Efficient Conversion of Ethylene to Glycol

One-pot synthesis of glycol from ethylene and H2O2 is simple and environmentally friendly, making it a potential alternative for glycol production. The key to the success of this is to have a bifunctional catalyst with both oxidative activity for ethylene epoxidation and acidic centers for the hydration of ethylene oxide. Typically, the incorporation of trivalent metal ions into titanium silicalite-1 (TS-1) framework can provide the two types of active centers, but this often results in decreased oxidative activity. Here, we propose a dual-chemical post-treatment regime to introduce acid centers in TS-1 while simultaneously improving oxidative activity. The combined tetrapropylammonium hydroxide (TPAOH) + (NH4)2CO3 post-treatment not only produces abundant Ti(OSi)2(OH)4 (Ti-VI) species from Ti(OSi)4, but also creates internal cavities within TS-1. Ti-VI possesses both high oxidative activity and acidic sites. The presence of internal cavities enhances the diffusion on the catalyst as well as increases the accessibility of Ti-VI species. Consequently, when applied as a catalyst, the combined-treated TS-1 demonstrates an outstanding catalytic performance, achieving 98.6 % conversion of H2O2 and 99.8 % selectivity of EG, which is approximate to 2 times of the conventional TS-1. This study also unveils the formation mechanism of Ti-VI during the post-treatment.