La Doping Imparts Bifunctional Interfacial Catalysis for Dehydrolactonization of 1,6-Hexanediol

Abstract

The dehydrolactonization of 1,6-hexanediol (1,6-HDO) to ε-caprolactone (ε-CL) requires a catalyst capable of cooperatively catalyzing two distinct half-reactions, namely dehydrogenation and cyclization. However, conventional catalysts lack the electronically asymmetric sites needed to drive both steps efficiently. Herein, a bifunctional Cu+–Ov–Ce3+ interfacial frustrated Lewis pair (FLP) is constructed by loading Cu onto La doping CeO2. La doping introduces additional oxygen vacancies (Ov) and Ce3+ species, thereby enriching the Ov–Ce3+ sites. Systematic characterizations (XPS, EPR, XAS, TPD, in situ FTIR) combined with DFT calculations reveal that Cu+ sites are responsible for α-H elimination to form 6-hydroxyhexanal (6-HA), whereas the cyclization reaction is driven by the FLP composed of Ov–Ce3+ and adjacent lattice oxygen. La incorporation lowers the energy barrier and enhances FLP formation. Under optimized conditions (3 wt % La, 280 °C, weight hourly space velocity of 1.5 h–1), a ε-CL yield of 61.17% is achieved with good stability over 120 h. From these findings, the interfacial bifunctional mechanism is clearly elucidated, and a defect engineering strategy for decoupling interfacial components is demonstrated, providing a rational approach to the design of multifunctional catalysts for tandem reactions.