Confined water accelerated alkene epoxidation inside channels of Ti-beta zeolite

Comprehensive mechanistic explorations and profound understandings of the interactions between water molecules and active intermediates harbors tremendous significance in the field of zeolite catalysis. Herein, we envision a strategy to accelerate alkene epoxidation reactions (e.g., 1-pentene, 1-hexene, cyclohexene, cyclooctene) with preformed H₂O₂ inside confined channels of Ti-beta by water molecules. Combined with in situ UV–vis, kinetic experiments, and DFT calculations, it is found that keen control of water molecules could effectively enhance H₂O₂ adsorption and stabilize crucial oxygen intermediates (Ti-OOH) by hydrogen bonding interactions. As a result, the yields of corresponding epoxides increased up to 20.5%. However, excessive water clusters construct a dense and robust hydrogen-bond network, blocking the activation of reactants and further epoxidation over Ti sites. This finding not only sheds new light on the mechanism of water-accelerated reaction, but also opens up new opportunities to enhance the efficiency of industrial epoxidation reactions involving H₂O₂.