Anatase-free titanosilicate with quasi-pure octahedral titanium species for efficient selective oxidations with hydrogen peroxide

Tetrahedral framework Ti sites are well-known as the origin of Lewis acidity for microporous titanosilicate, which was regarded as the key catalyst in heterogeneous selective oxidations. Although recent studies reveal the excellent catalytic activity of octahedral Ti species, the current synthetic approaches always result in a low content of octahedral Ti species, simultaneously generating inactive anatase impurity. Herein, this work solves this decades-long synthetic bottleneck, achieving unprecedented quasi-pure octahedral Ti coordination (>85 %) in an anatase-free titanosilicate. The catalytic performance of octahedral Ti enriched titanosilicate in industrial-relevant olefin epoxidation and cyclohexanone ammoxidation was found to be closely correlated with well-controlled acidic microenvironment (Lewis/Brønsted acid ratio), which was governed by the proximity of defective silanols and octahedral Ti species. Notably, the novel catalyst with such high content of octahedral Ti species exhibits 8-fold enhanced batch activity and nearly 3-fold prolonged stability in industrially-related cyclohexanone ammoxidation versus conventional catalyst possessing only tetrahedral Ti species, demonstrating a new design principle of developing highly efficient catalysts for the next-generation selective oxidation through active species engineering.