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本文用柠檬酸络合物分解法、碳酸盐共沉淀分解法、硝酸盐直接分解法和陶瓷法合成了轻、重稀土钙钛矿型氧化物LnMnO_3(Ln=Sm.Er).用X-射线衍射(XRD)和程序升温还原(TPR)技术考察了制备方法和灼烧温度对钙钛矿型结构形成的影响.实验结果表明,用柠檬酸络合物分解法可以在较低的温度下得到单一相的钙钛矿氧化物,而陶瓷法的灼烧温度比其他方法所需的温度要高得多。不同方法得到的产物SmMmO_3对CO氧化反应的活性为:柠檬酸法～碳酸盐法～硝酸盐法>陶瓷法。实验表明,TPR技术在某些体系中可作为灵敏的物相分析辅助手段,它可在制备或反应过程中原位观察体系结构的变化,实验中观察到,稀土氧化物能促进某些过渡金属氧化物在稀土氧化物表面分散,能阻止它们形成晶态.本文还讨论了钙钛矿型氧化物的形成机理,提出了过渡金属氧化物的扩散是形成钙钛矿结构反应速率的决定步骤观点。
In this paper, light and heavy rare earth perovskite oxides LnMnO_3 (Ln = Sm.Er) were synthesized by citrate complex decomposition method, carbonate coprecipitation decomposition method, nitrate direct decomposition method and ceramic method. Ray diffraction (XRD) and temperature programmed reduction (TPR) techniques were used to investigate the effect of preparation method and burning temperature on the formation of perovskite structure.The experimental results show that the decomposition of citrate complex can be carried out at lower temperature A single phase of perovskite oxide is obtained, whereas the ceramic method has a much higher firing temperature than the other methods require. The activity of the product SmMmO_3 obtained by different methods on the CO oxidation reaction is: Citrate method ~ Carbonate method ~ Nitrate method> Ceramic method. Experiments show that the TPR technology can be used as a sensitive phase analysis aid in some systems. It can observe the changes of the structure in situ during preparation or reaction. It is observed in experiment that rare earth oxides can promote the oxidation of some transition metals The results show that the diffusion of transition metal oxide is the decisive step in the formation of perovskite structure reaction rate. This paper also discusses the formation mechanism of perovskite type oxides.