Dinuclear titanium on TS-1 for propylene epoxidation at alkaline condition

Propylene epoxidation is an important industrial process, but current techniques have shown adverse environmental impacts.1-3 Recently, the eco-friendly photo-electro-heterogeneous catalytic production of propylene oxide (PO) has been reported using in situ generated H2O2 and a zeolite catalyst (titanium silicalite-1, TS-1).4 However, the PO production rate was too low due to the low solar H2O2 production rate. In this work, we recorded high solar H2O2 production rate required for the practical PO production for first time. However, TS-1 exhibits low activity in the presence of alkali metal ions under alkaline condition, which are crucial for efficient solar H2O2 production. Herein, we hydrothermally synthesize a TS-1 catalyst containing dinuclear titanium sites and Ti–O–Ti bonds and show that it efficiently promotes propylene epoxidation under alkaline conditions (pH 11). The results of density functional theory (DFT) calculations and instrumental analyses reveal that the dinuclear titanium sites are active for propylene epoxidation and synergistically interact with alkali metals ions to prevent hydrolysis of PO to propylene glycol. Thus, our work demonstrates the superiority of the developed catalytic system over its predecessors, paving the way for the use of TS-1 in other partial oxidation reactions and the development of novel environmentally benign chemical processes.