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

Abstract

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.