CuOx Nanopatches Positioned at Lewis Acidic Sites of TiO2 for Propylene Epoxidation Using Molecular Oxygen

Abstract

Controlling the precise placement of active metals on supports is highly desirable yet challenging, which governs both the reaction pathway and the ultimate outcomes of catalytic reactions. Herein, the Cu species are positioned to the Lewis acidic sites created by the ultrahigh-temperature calcination of TiO₂, where the atomic structures of the Lewis acids are identified as five-coordinated Ti⁴⁺ cations bound to three-coordinated O^2– anions (L_β sites) by in situ characterizations. Owing to the robust chemical affinity, CuO_x manifests itself as a nanopatch. The Cu/TiO₂ catalyst without any modifications exhibits a propylene oxide (PO) formation rate of 44 mmol g_Cu^–1 h^–1 for direct epoxidation of propylene using molecular oxygen (DEP). The PO yield on Cu/TiO₂ can be efficiently correlated with the quantity of the decreased Lewis acids, which demonstrates that the intimated interaction between the Cu species and Lewis acids should be responsible for PO production. Furthermore, density functional theory calculations suggest that Cu⁺ in the Ti–O–Cu interface formed at the L_β sites is the active site of the DEP reaction, with the aid of the adjacent Cu atom. This study provides a Cu-based catalyst for the DEP reaction.