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Preparation and Properties of CZ/A Complex Oxides

Author: HanYi
Tutor: MaXinSheng; GaoZuo
School: East China University of Science and Technology
Course: Chemical Engineering
Keywords: Ceria-zirconium solid solution Al2O3 OSC Thermal stability
CLC: O611.62
Type: Master's thesis
Year: 2013
Downloads: 40
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Abstract


As air pollution has posed a more and more urgent threat to the health of human beings, the demand for better catalytic performance to purify automotive exhaust gas, one of the main sources of air pollution, is higher and higher. But the specific surface area (BET) and catalytic performance of ceria-zirconium solid solution(CZ), which is used as the oxygen storage materials(OSC) for purifying automotive exhaust gas, would be reduced significantly at high temperatures. For Al2O3could maintain its large specific surface area at high temperatures, the complex oxides (CZ/A) of ceria-zirconium and Al2O3are prepared by co-precipitation method in our work to enhance the performance of CZ when the temperature is above1000℃. This work is mainly focused on the effects that the different sources of Al2O3and the different ways of mixing may have on the properties of CZ, and the effects of operational parameters for preparing the precursors and the contents of Al2O3may have on the propertities of complex oxides (CZ/A) are also studied. The results suggest that:The specific surface area, thermal stability and OSC of ceria-zirconium solid solution are significantly improved by doping Al2O3. And samples which are nanometer-level of chemical mixing between Al2O3and CZ, would better inhibit crystallite growth, get higher BET and gain more OSC after being calcined at high temperature than those of samples which are the micron scale mixing. The CZ/AL (using A1(NO3)3·9H2O as the Al2O3source) and CZ/AS (using pseudo-boehmite as the Al2O3source) samples both have cubic crystalline structures with better dispersion effect, with CZ/AS the highest BET and CZ/AL the largest oxygen storage capacity(OSC).In the process of preparing CZ/A samples, when the aging time is4h, the samples could keep high BET and cubic crystalline structure with better dispersion effect. And when the non-ionic surfactant Tw80is added as a dispersant, with weight ratio of20wt%-30wt%as preperred, the specific surface area and pore volume of CZ/AS is highly improved.Generally, the values of BET for CZ/AS samples is directly proportional to the content of Al2O3, but when the content of Al2O3in CZ/AS samples is above70wt%, the OSC of CZ/AS samples is reduced remarkably. Thus, when the contents of Al2O3remain at30wt%-50wt%, the CZ/AS samples could keep the cubic crystalline structure and obtain higher specific surface area, better reduction properties and more desirable OSC

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Chemical elements and inorganic compounds > Inorganic compounds > Oxides,peroxides
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