The Preparation And Characterization Study Of Catalytic Performance Over Ceria-Based Catalysts

Reducing air pollution has become an important issue in environmental protection. Among them, CO and NO are the main air pollutants. Therefore, more and more researchers pay close attention to CO oxidation and NO reduction by CO. In the catalytic reaction, the choice of catalyst is very important. On the one hand, it needs to cheap and easy to obtain. On the other hand, high catalytic activity is necessary. Noble metals are highly activity, but expensive and scarce. Therefore, it is great significance to study non-noble metals catalysts instead of noble metals.Ceria, a rare earth functional material with fluorite structure, has a good oxygen storage capacity and excellent redox properties, and easily contains oxygen vacancies. In this paper, Cerium-based catalysts were synthesized in this study. The obtained samples were investigated in detail by X-ray diffraction （XRD）, N₂-physisorption （BET, BJH）, scanning electron microscope （SEM）, transmission electron microscope （TEM）, X-ray photoelectron spectroscopy （XPS）, laser raman spectroscopy （LRS）, UV-vis diffuse reflectance （UV-vis DRS）, temperature-programmed reduction of H₂ （H₂-TPR）, temperature-programmed desorption of O₂ or NO （O₂-TPD, NO-TPD）, and in situ DRIFTS techniques. The catalytic performances of catalysts were evaluated by CO+O₂ or CO+NO model reaction. The main results were shown as follows:（1） The MnO_x-doped CeO₂ composite oxide was obtained by co-precipitation and then used as supports to prepare CuO/MnO_x-CeO₂ catalysts through wetness impregnation method. The article attention was mainly focused on investigating the effect of the amount of CuO and Mn ions on properties and the catalytic activities of the catalysts. When the loading amount of copper was 12% and the molar ratio of Ce/Mn was 10:1, the catalytic performance of this catalyst was best for CO oxidation. Doping appropriate amount of Mn ion was beneficial to form oxygen vacancies. Loading appropriate amount of CuO was beneficial to form more active sites of Cu⁺ and adsorb CO. Simultaneously, the interaction between Mn and Cu can form more Cu⁺ (Cu²⁺+Mn²⁺（?）Cu⁺+Mn³⁺,Cu²⁺+Mn³⁺（?）Cu⁺+Mn⁴⁺). And there were electron transfer effect of three pairs redox (Cu²⁺/Cu⁺, Ce⁴⁺/Ce3+, Mnⁿ⁺/Mnn-1), which formed more activated lattice oxygen species to improve catalytic activity for CO oxidation. Therefore, the CuO/MnO_x-CeO₂ catalyst had high catalytic activity.（2） We have prepared three kinds of different shapes of CuO modified CeO₂:spindles, spheres, and hollow spheres. The CeO₂ spindles and CeO₂ spheres were synthesized by the hydrothermal method. And CeO₂ hollow spheres were prepared by using carbon spheres as the template. The CuO/CeO₂ catalysts was prepared by the wetness impregnation method. This article studied the properties of CeO₂ and CuO/CeO₂ with different morphologies and its catalytic activity for NO reduction by CO. The results showed that the CeO₂ catalyst with different morphologies affected specific surface area, reductibility, oxygen vacancy content, the stability of CO and NO adsorption species, which therefore resulted in different catalytic activity. At the same time, it changed coordination environments of the supported CuO and influenced synergistic effects between CeO₂ and CuO.