Amino acid-assisted synthesis of TS-1 zeolites containing highly catalytically active TiO₆ species

Tailoring the Ti coordination states in titanosilicate zeolites to simultaneously improve feedstock conversion and maximize the target product selectivity remains a challenge in the pursuit of high-performance catalysts for selective oxidation reactions. Herein, we provide a facile strategy to synthesize hierarchical anatase-free TS-1 (MFI-type) zeolites with tetrahedrally coordinated (TiO₄) and octahedrally coordinated Ti species (TiO₆). The TiO₄ species provide high epoxide selectivity, while the TiO₆ species afford improved alkene conversion. This strategy is achieved by synergistically using an L-lysine-assisted approach and a two-step crystallization; the two-step crystallization approach prevents the formation of anatase TiO₂, while L-lysine stabilizes the TiO₆ species and ensures efficient incorporation of TiO₆ into the anatase-free TS-1 zeolites. Compared with their conventional counterparts, which only contain TiO₄ species, the as-prepared TS-1 zeolites (Si/Ti = 36.9) result in a higher 1-hexene conversion (33%), higher TON value (153), and comparable epoxide selectivity (95%). This synthetic strategy provides avenues to tailor the amount and distribution of Ti species in titanosilicate zeolites to achieve high catalytic performances in various processes.