Active M/CeO₂ (M=Ni, Cu, Zn) catalysts for selective oxidative C-N coupling of amines and alcohols into imines

The oxidative coupling of alcohols and amines to produce imines, commonly known as Schiff bases, is an important transformation in the synthesis of fine chemicals, dyes, insecticides, and pharmaceuticals. Traditional methods often rely on noble metal catalysts, which are expensive, less sustainable, and encounter difficulties in catalyst recovery and reusability. CeO₂ is an alternative and promising support due to its unique redox properties and high density of oxygen vacancies that facilitate the oxidative C-N coupling of amine and alcohol. In the work, the incorporation of transition metals (TM) (Ni, Cu, and Zn) into CeO₂ was studied to enhance its catalytic activity. The introduction of divalent metal ions into the CeO₂ promoted the lattice expansion, which was confirmed by a slight shift of Bragg’s angle toward a lower 2θ value in the XRD analysis. XPS analysis revealed that Zn_0.10CeO₂ possesses a higher share of Ce³⁺ species, which is closely associated with the presence of oxygen vacancies. These oxygen vacancies play a crucial role in the activation of molecular oxygen during the C-N coupling reaction. Under optimized reaction condition Zn_0.10CeO₂ gave 97.0% conversion of aniline and 100.0% selectivity for N-Benzylideneaniline. The versatility of the catalyst was tested across various amines and alcohols, showing excellent substrate tolerance and high imine yields.