Effect of Ceria on redox-catalytic property in mild condition: A solvent-free route for imine synthesis at low temperature

Five different nanocerias were prepared and used to catalyze the direct coupling of alcohol and amine to the corresponding imines under air atmosphere at low temperature. The catalytic efficiencies have great differences, CeO₂ prepared by coprecipitation at room temperature (called CeO₂-5) has the best catalytic activity, whose yield reaches 99% at 303 K for 36 h, 100 times higher than the nano-octahedras ceria (called CeO₂-4) and also higher than the catalytic performance of most reported catalysts. Such phenomena are ascribed to the higher acidic sites, specific surface area, and proportions of surface oxygen. The results of DRIFTS demonstrated that the alcohol oxidized to benzaldehyde was the rate determining step in this reaction. Furthermore, CeO₂-5 still shows excellent catalytic performance on 10-fold magnification experiments without any addition of solvent. Besides, it has the advantages of simple process, low energy consumption and practical scaling-up as well as good universality towards this kind of reaction, showing every prospect in industrial application.