MnCeO x /TiO 2 has been widely used in selective catalytic reduction (SCR) of NO x at low temperature. However, it is often poisoned in the presence of water vapor and sulfur dioxide . In this work, the promotion mechanism of Ba modification was investigated. Results show that the doped BaO reacts with CeO 2 and forms BaCeO 3 . This unique perovskite structure of BaCeO 3 significantly enhances NO oxidation and NH 3 activation of MnCeO x /TiO 2 catalyst so that the NO conversion and the resistances to SO 2 improve. It is found that Ba species obviously promotes the NO adsorption ability and improve the redox properties of MnCeO x /TiO 2 catalyst. While the acid properties of the catalyst are inhibited by Ba modification and among which Lewis acid sites are dominant for both MnCeO x /TiO 2 and MnCe(Ba)O x /TiO 2 catalysts. Furthermore, in situ DRIFT experiments reveal that the NO reduction upon MnCeO x /TiO 2 and MnCe(Ba)O x /TiO 2 catalysts follows both E-R and L-H mechanisms, in which L-H is preferred. Ba species enhances the formation of active nitrate species, which accelerates the NO reduction through L-H mechanism. It is interesting that although Ba species weakens the NH 3 adsorption, it induces the ammonia conversion to coordination ammonia, which in turn accelerates the catalytic reaction .
Qiang Bao,Wenhui Feng,Yunfeng Hu,Zhenlu Wang,Guoliang Wu,Zhirui Chen,HaoCheng Li,Chenguang Shi
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.
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