In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO, two series of catalysts （xCuyMn/Ce and xCu/yMn/Ce） were prepared by co-impregnation and step- wise-impregnation methods, and characterized by means of X-ray diffraction （XRD）, Raman spectra, H2-temperature programmed reduction （H2-TPR）, in situ diffuse reflectance infrared Fourier transform spectra （in situ DRIFTS） techniques. Furthermore, the cata- lytic performances of these catalysts were evaluated by NO＋CO model reaction. The obtained results indicated that： （1） The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method, which was beneficial to the improvement of the reduction behavior; （2） The excellent reduction behavior was conducive to the formation of low valence state copper species （Cu＋/Cu0） and more oxygen vacancies （especially the surface synergetic oxygen vacancies （SSOV, Cu＋-n-Mn（4-x）-）） during the reaction process, which were beneficial to the adsorption of CO species and the dissociation of NO species, respectively, and further promoted the en- hancement of the catalytic performance. Finally, in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods, a possible reaction mechanism （schematic diagram） was tentatively proposed.
The CuO/CeO2 catalysts were investigated by means of X-ray diffraction （XRD）, laser Raman spectroscopy （LRS）, X-ray photoelectronic spectroscopy （XPS）, temperature-programmed reduction （TPR）, in situ Fourier transform infrared spectroscopy （FTIR） and NO＋CO reaction. The results revealed that the low temperature （〈150℃） catalytic performances were enhanced for CO pretreated samples. During CO pretreatment, the surface Cu＋/Cu0 and oxygen vacancies on ceria surface were present. The low va- lence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation. These effects in turn led to higher activities of CuO/CeO2 for NO reduction. The current study provided helpful understandings of active sites and reaction mechanism in NO＋CO reaction.
Mesoporous CeO2-MnOx binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy （SEM）, N2 sorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2-TPR）. The characterization results indicated that the CeO2-MnOx catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO2 lattice to form solid solution. The CeO2-MnOx catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO2-MnOx catalyst with Mn/Ce molar ratio of 1 in the synthesis gel （Ce-Mn-1） exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 ℃. This was ascribed to presence of more Mn species with higher oxida- tion state on the surface and the better reducibility over the Ce-Mn-I catalyst than other CeO2-MnOx catalysts.
