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 stepwise-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 catalytic 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+-□-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 enhancement 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 °C) 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 valence 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 oC.This was ascribed to presence of more Mn species with higher oxidation state on the surface and the better reducibility over the Ce-Mn-1 catalyst than other CeO2-MnOx catalysts.
