Selective synthesis of imines by direct oxidative coupling of amines on Cu-doped CeO2 catalysts

Abstract

The study and development of CeO2 nanocrystals containing transition-metal species are of crucial importance for understanding the effect of transition-metal species on their catalytic activity. In this work, CeO2 nanocrystals containing only 0.61 wt% Cu have been demonstrated as an effective catalyst for imine synthesis from amines at 110 °C using NHPI as radical initiator and air as oxidant. Especially, Cu-doped CeO2 nanocrystals after thermal treatment at 300 °C for 2 h show high conversion (97.8%) and high selectivity (98.6%) for the synthesis of N-benzylidene benzylamine from benzylamine, as well as acceptable yield for the synthesis of several other kinds of imines from amines. The Cu-doped CeO2 nanocrystals also exhibited excellent cycling stability for at least four cycles with only a slightly decreased yield. It has been demonstrated that the high catalytic activity of Cu-doped CeO2 can be ascribed to the highly dispersed Cu species and abundant oxygen vacancies on their surfaces which activated the NHPI and O2 and promoted the adsorption/conversion of amine.