TS-1 Synthesis via Subcrystal Aggregation: Construction of Highly Active Hydrogen-Bonded Titanium Species for Alkene Epoxidation.

The construction and determination of highly active Ti sites comprise one of the most significant challenges in the rational design and synthesis of Ti-containing porous catalysts. The pathway to efficiently build highly catalytically active titanium species remains to be proposed in spite of deliberate post treatments or ambiguous batch composition adjustments. In this study, we developed a bottom-up strategy to construct a TS-1 catalyst with highly active hydrogen-bonded Ti species via subcrystal aggregation crystallization. The microstructure of the hydrogen-bonded Ti species was verified by vacuum FT-IR and 1 H MAS SSNMR spectroscopies. Noteworthy features of the hydrogen-bonded Ti species were also revealed, including a pentahedral coordination state and Brønsted acidity, as identified by the UV-Raman, XPS, XAFS, and FT-IR spectra of adsorbed pyridine. Significantly, the hydrogen-bonded Ti species exhibits extraordinary activity in allyl chloride epoxidation (nearly 70% higher than that of traditional Ti species). This study provides a new approach to building highly active Ti sites, which may provide new insights into the design and synthesis of high-performance titanosilicate catalysts.