| Three-way catalysts (TWCs) have been widely used to diminish the environmental impact of pollutants emitted by gasoline engine powered vehicles attracted more and more attention. TWCs can work efficiently to reduce NO as well as to oxidize CO and hydrocarbons (HC) in a narrow window of air-to-fuel ratio (A/F), close to the stoichiometric point. Ceria-zirconia mixed oxides as the catalyst coating material, has been widely used in the three-way catalyst because of the oxygen storage/release ability of cerium to switch between the Ce4+and Ce3+oxidation states and to adjust the oxygen content vibration of the exhaust. In recent years, since automotive emission regulations are becoming more and more stringent with the increasing demands for global environmental protection, further improvement of catalytic efficiency and stability of TWCs is still required. To further improve the textural/structural and oxygen storage properties of ceria-zirconia solid solution, the introduction of metals into ceria-zirconia formed multi-component oxides, such as rare earth metals, transition metals and alkaline earth metals doping, has earned much attention. As reported in literature, such as by doping a small amount of dopant Y3+, La3+ and Pr3+etc., can improve the oxygen mobility of CeO2-ZrO2 mixed oxides in the process of the oxygen storage and release, oxygen vacancies concentration and thermal stability. Our research also shows that the introduction of transition metals can promote the three-way catalyst performance because of the variety oxidation state of transition metals, good redox properties, exceptional performance coupled with nano-scale materials and the strong interaction between the support and the precious metal.In the present dissertation, we used X-ray powder diffraction (XRD), N2 adsorption/desorption, UV-Raman spectra (UV-Raman), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), in situ Raman, oxygen storage complete capacity (OSCC), Dynamic oxygen storage capacity (DOSC), temperature-programmed reduction (H2-TPR) and catalytic activity test techniques to study systematically the effect of different transition metals doping, different loading of iron and nickel oxide doping and synthesis method of nickel oxide doping into CeO2-ZrO2 on the textural-structural property, oxygen storage-release capacity, redox property, thermal stability and the performance of its supported Pd-only TWCs. Some specific conclusions are drawn from this work as follows:1. The effect of different transition metals (Cr,Mn,Fe,Co,Ni) doping on the textural-structural property, redox property, oxygen storage-release capacity of CZ and the performance of its supported Pd-only TWCs was investigated. The results show that the catalytic performance and the value of W of the catalysts before and after ageing is on the order of Pd/CZCo, Pd/CZFe> PdCZNi>PdCZ>Pd/CZMn>Pd/CZCr. The different catalytic performance of doping transition metals is related to the textural-structural property, redox property and oxygen storage-release capacity of support. Transition metal ions have entered into the ceria lattice and atomically more homogeneous mixed oxides have formed on the order of CZFe≈CZCo> CZNi≈CZ> CZMn> CZCr. The introduction of Fe, Co and Ni significantly improves the textural-structural property of CeO2ZrO2 mixed oxides, increases the surface area and pore volume, and decreases the grain size. Moreover, the introduction of Fe, Co and Ni forms more homogeneous Ce-Zr-M-O ternary mixed oxides, seems to facilitate the reduction of Ce4+→Ce3+ or the formation of oxygen vacancy, increases the oxygen mobility, enhances the redox property and the oxygen storage/release capacity of sample at lower terperature. Furthermore, the introduction of Fe, Co and Ni promotes the interation between PdOx and Ce-Zr-M-O mixed oxides, favors to the dispersion of PdOx species and thermal stability, also increases the reduction of the catalyst, and thus benefits to the improvement of three-way catalytic performance. However, the introduction of Cr and Mn increases the grain size, appears a few clusters of Cr or Mn ions in the formation of Ce-Zr-M-O ternary mixed oxides which has poor homogeneity of its structure, and makes against the reduction of PdOx species.2. The effect of different loading of iron oxide doping on the textural-structural property, redox property, oxygen storage-release capacity of CZ and the performance of its supported Pd-only TWCs was investigated. The results demonstrate that Pd/CZFe catalyst doped with 1% iron oxide, exhibits the best catalytic performance for CO, HC, NO and NO2 elimination, in accordance with the decrease in the light-off temperature and the full-conversion temperature, and the widest operation window. The doping of iron oxide with 1% loading suggests the formation of more homogeneous Ce-Zr-Fe-O ternary solid solution, seems to facilitate the reduction of Ce4+→Ce3+ or the formation of oxygen vacancy under the oxidation or reduction atmosphere, and thus improves the oxygen storage/release capacity of sample. Moteover, the appropriate amount of Fe doping promotes the interaction between Ce-Zr and Fe, and then improves the reduction of support and Pd-catalyst.3. The effect of different loading of nickel oxide doping on the textural-structural property, redox property, oxygen storage-release capacity of CZ and the performance of its supported Pd-only TWCs was investigated. The results demonstrate that the appropriate amount of nickel oxide doping significantly improves the textural-structural property of CeO2-ZxO2 mixed oxides, formes more homogeneous Ce-Zr-Ni-O ternary mixed oxides, clearly increases the surface area and decreases the grain size. The best amont of nickel oxide doping is 3%. Moreover, the appropriate amount of nickel oxide doping promotes the interaction between Ce-Zr and Ni, and then enhances the reduction property, the oxygen storage/release capacity and the high thermal stability of sample. Thus, Pd/CZNi catalyst doped with 3% nickel oxide, exhibits the best catalytic activity in accordance with the decrease of light-off and full-conversion temperature and the widest operation window before and after aging compared with that of other catalysts.4. The effect of different synthesis method of nickel oxide doping on the textural-structural property, surface state, redox property, oxygen storage-release capacity of CZ and the performance of its supported Pd-only TWCs was investigated. The results show that among all the catalysts examined, Pd/CZN-s exhibits the best catalytic activity, in accordance with the decrease in the light-off temperature and the full-conversion temperature, and the widest operation window before and after aging. More homogeneous ternary solid solution between Ce, Zr and Ni is successfully obtained by co-precipitation and supercritical drying method, leading to the biggest surface area and pore volume and average pore diameter and the widest pore size distribution, which may be beneficial to the adsorption/desorption of target pollutant. Furthermore, more Zr atoms of the surface layer are replaced by Ni atoms. In order to satisfy the charge balance, more xygen vacancies or lattice defects are formed, which enhances the oxygen storage/release capacity and the reduction property of CZN-s sample. Compared with that of other preparation methods, after ageing treatment, CZN-s prepared by co-precipitation and supercritical drying method also exhibits the better textural-structural stability, good oxygen storage/release property and reduction property, and further improves the thermal stability of its Pd-only catalysts, and thus enhances its three-way catalytic performance.
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