Ce⁴⁺/Ce³⁺ Redox Effect-Promoted CdS/CeO₂ Heterojunction Photocatalyst for the Atom Economic Synthesis of Imines under...

The employment of stoichiometric alcohols and amines for imine synthesis under mild and green reaction conditions is still a challenge in the field. In this work, based on our research foundation in the thermocatalytic synthesis of imines over ceria, a CdS/CeO₂ heterojunction photocatalyst was constructed and successfully realized the atom-economic synthesis of imines under visible light without additives at room temperature. Mechanistic experiments and corresponding characterizations indicated that the CdS/CeO₂ heterojunction can improve the separation efficiency of photogenerated carriers, which can be further enhanced by the Ce⁴⁺/Ce³⁺ redox pair by rapidly combining photogenerated e^-. The in situ-reduced Ce³⁺ can better activate O₂ to form Ce-O-O·, which, together with h⁺, efficiently accelerates alcohol oxidation, which is the rate-determined step for the synthesis of imines via oxidative coupling reaction of alcohol and amine. In addition, our photocatalyst exhibited fairly decent reusability and substrate universality. This work solves problems of using base additives and excess amine or alcohol in the reported photocatalytic systems and provides new insight for designing CeO₂-based photocatalytic oxidation catalysts.