Ammonia-assisted dry-gel conversion for preparation of TS-1 with enriched Ti(OSi)₃OH active sites

Defective Ti(IV) species, i.e. Ti(OSi)₃OH, are highly active catalytic sites within the TS-1 framework, and developing efficient methods to enrich these species has attracted significant attention from both academia and industry sectors. Herein, we developed an ammonia-assisted dry-gel conversion (DGC) method to synthesize TS-1-AM enriched with Ti(OSi)₃OH species using NH₃ (ammonia, AM) as a modifier. Comprehensive characterization using XRD, UV–Vis, SEM, XPS, pyridine-IR, solid-state MAS NMR confirmed the abundant presence of Ti(OSi)₃OH species in TS-1-AM. The modified catalyst demonstrated exceptional performance in alkene epoxidation, achieving approximately 150% higher catalytic activity compared to the parent TS-1, while maintaining excellent cycling stability. Further studies revealed that the synergistic effect of NH₃ and H₂O molecules facilitated the selective cleavage of framework Si-O-Ti bonds, promoting the conversion of Ti(OSi)₄ species to Ti(OSi)₃OH species. Furthermore, the condensation of surface silica hydroxyls, particularly silica hydroxyl nests, enhanced surface hydrophobicity. This straightforward DGC method provides an efficient approach for synthesizing titanosilicates enriched with highly active Ti(OSi)₃OH species.