A Review on Understanding and Strengthening of Active Species in Titanium Silicalite-1 (TS-1) Catalysts

Titanium silicalite-1 (TS-1) zeolite stands out as a top-tier catalyst for producing key chemical intermediates under mild conditions. This paper briefly summarizes its applications in oxidation reactions such as ammoximation and epoxidation, and explores the various reaction pathways dominated by Ti active species. Its catalytic oxidation performance depend upon the content and coordination of Ti active species. Strategies for designing highly efficient TS-1 catalysts focus on regulating its structure and active species by adjusting synthesis conditions. Balancing hydrolysis rates of titanium and silicon sources facilitates more framework Ti species and little anatase TiO₂. Nucleation and crystallization can be controlled to adjust the microenvironment around the active sites by such as pH control, using modifiers, and tuning crystall pathways. Effective regulation of the crystallization process is conducive to the generation of new coordination Ti species beyond the tetra-coordinated TiO₄. By employing bases and templates, Ti species in TS-1 can be redistributed via dissolution-recrystallization process. Additionally, the introduction of heteroatoms can alter the electronic state of Ti species. These strategies can convert extra-framework titanium into framework titanium or highly coordinated titanium species, thereby introduce mesopores in TS-1 crystals. The design of TS-1 zeolites with diverse active species demonstrates promising industrial applications.