Designing alkaline-rich Ba/MnO2 catalysts for efficient oxidative coupling of alcohols and amines at low temperatures

Abstract

In this work, a series of alkaline earth metal-modified manganese oxide catalysts were prepared via the impregnation method and applied to the oxidative coupling reaction of alcohols and amines to imine. The prepared catalysts were characterized by X-ray diffraction (XRD), N₂-adsorption, field emission-scanning electron microscopy (FE-SEM), H₂ temperature-programmed reduction (H₂-TPR), NH₃-temperature-programmed desorption (NH₃-TPD), CO₂-temperature-programmed desorption (CO₂-TPD) and X-ray photoelectron spectroscopy. Among the catalysts, Ba/MnO₂ showed the best catalytic performance in the reaction and exhibited the highest Mn³⁺/Mn⁴⁺ ratio, surface weak basic sites and a relatively small number of weak acidic sites. Lattice oxygen mobility and Mn³⁺/Mn⁴⁺ ratio were found to play important roles in the catalytic activity of aerobic reactions. The weak and medium basic sites on the catalyst surface can further promote the alcohol–amine oxidative coupling process, as they serve as active centers for the activation of benzyl alcohol, which is the rate-determining step for this oxidative coupling reaction.