Efficient Imine Formation by Oxidative Coupling at Low Temperature Catalyzed by High‐Surface‐Area Mesoporous CeO<sub>2</sub> with Exceptional Redox Property
Shipeng Wu, Yinghao Wang, Qiue Cao, Qi‐Hua Zhao, Wenhao Fang
Abstract
Abstract High‐surface‐area mesoporous CeO 2 ( hsm CeO 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 CeO 2 and hsm CeO 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 hsm CeO 2 calcined at 400 °C shows the highest specific surface area (158 m 2 g −1 ), the highest fraction of surface coordinatively unsaturated Ce 3+ 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 hsm CeO 2 catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol h −1 based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram‐scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsm CeO 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.