Efficient Imine Formation by Oxidative Coupling at Low Temperature Catalyzed by High-Surface-Area Mesoporous CeO2 with Exceptional Redox Property

High-surface-area mesoporous CeO2 (hsmCeO(2)) was prepared by a facile organic-template-induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO2 and hsmCeO(2) after different thermal treatments were also investigated. XRD, N-2 physisorption, UV-Raman, H-2 temperature-programmed reduction, O-2 temperature-programmed desorption, EPR spectroscopy, and X-ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO(2) calcined at 400 degrees C shows the highest specific surface area (158 m(2)g(-1)), the highest fraction of surface coordinatively unsaturated Ce3+ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4 +/- 10(15) spins g(-1)). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO(2) catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmolg(-1) ceria h(-1) based on > 99% yield at 60 and 80 degrees C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 degrees C and in gram-scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO(2) catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated.

Automated summary

High-surface-area mesoporous CeO2 (hsmCeO(2)) prepared by a facile organic-template-induced homogeneous precipitation process shows excellent catalytic activity in air for imine synthesis from primary alcohols and amines, as well as outstanding results in oxidative coupling reactions.