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本工作是对钙钛矿型稀土催化剂的合成方法,特别是对其烧成过程的研究。以LaCoO_3的合成为例,对硝酸盐热解法、共沉淀法和柠檬酸络合法三种合成基体的方法进行了比较。报导了用X-射线衍射分析、差热分析、化学组成分析、扫描电镜、电子探针、比表面积测定和催化活性的研究情况,着重阐述了有关络合法的研究结果。实验表明,烧成温度与合成基体的方法有关。络合法可在低温下烧成钙钛矿结晶、450℃即有LaCoO_3生成,比文献报导的一般烧成温度低得多。其他两种方法台成时,则需800℃以上才有显著量LaCoO_3生成。络合法可避免高温下钴的流失,有利于制得规定组成和结构的产物。550℃烧成者为片状构造,870℃时转变为球状粒子串接成的理纹构造,球径大约为0.5μ。此外,络合法还可大大缩短烧成时间。以CO氧化反应为模型反应,对比结果为用络合法烧成者催化活性最高。对烧成机理作了初步探讨。络合法合成的特点是可制得具有大量缺陷结构的、各组元高度分散的基体,组元离子只需经短距离扩散即可达成反应。其他两种方法合成者则组元离子需经历长距离扩散才能达成固相反应,烧成过程可能还与氧的气相转移机理有关。
This work is a synthesis method of perovskite rare earth catalyst, especially its firing process. Taking the synthesis of LaCoO_3 as an example, the methods of synthesizing matrix by nitrate pyrolysis, coprecipitation and citric acid complexation were compared. The results of X-ray diffraction analysis, differential thermal analysis, chemical composition analysis, scanning electron microscopy, electron probe, specific surface area measurement and catalytic activity have been reported. Experiments show that the sintering temperature and the method of synthesis of the substrate. Complexation method can be fired at low temperature perovskite crystallization, LaCoO_3 generated at 450 ° C that is much lower than the reported general firing temperature. For the other two methods, a significant amount of LaCoO_3 is required to be formed above 800 ° C. Complex method can avoid the loss of cobalt at high temperature, is conducive to the preparation of the provisions of the composition and structure of the product. 550 ℃ calcined flake structure, at 870 ℃ into spherical particles connected to the texture structure, the ball diameter of about 0.5μ. In addition, the complex method can also greatly reduce the firing time. CO oxidation reaction as a model reaction, the results of the comparison with the complexation method, the highest catalytic activity. The mechanism of sintering was made preliminary discussion. Complex synthesis is characterized by the availability of a large number of defects in the structure, the highly dispersed matrix of each component, only a short diffusion of component ions to reach a reaction. The other two methods synthesize the component ions need to go through long-distance diffusion in order to achieve solid-state reaction, the firing process may also be related to the oxygen vapor phase transfer mechanism.