La_(0.2)Ca_(0.8)MnO_3催化剂活性相的结构和形成机理

THE STRUCTURE OF CATALYST La_0.2Ca_0.8MnO_3 AND ITS FORMATION MECHANISM

利用ＴＧ，ＤＴＡ，ＸＲＤ和ＸＰＳ方法研究了Ｌａ０．２Ｃａ０．８ＭｎＯ３催化剂的结构和形成机理．样品用Ｌａ，Ｃａ，Ｍｎ混合硝酸盐制备．随着焙烧温度的升高发生了一系列的固相反应，发现氨氧化催化剂催化活性与生成的ＣａＭｎＯ３含量成正比．在９００℃制备的含有ＣａＭｎＯ３，Ｌａ０．５７５Ｃａ０．４２５ＭｎＯ３，Ｍｎ２Ｏ３和Ｌａ２Ｏ３的混合物是氨氧化最佳催化剂，活性相是ＣａＭｎＯ３，并具有大量的氧空穴．

The structure of catalyst La_0.2Ca_0.8MnO_3 and its formation mechanism have been studied by using TG, DTA, XRD, SEM and XPS. The sample was prepared by coprecipitation from La, Ca, Mn nitrates. As calcination temperature increases a series of solid reactions occur. The catalytic activity for NH_3 oxidation is proportional to the content of CaMnO_3 in samples. The best catalyst, prepared at 900℃, is a mixture of CaMnO_3, La_0.575Ca_0.425MnO_3, Mn_2O_3, and La_2O_3. The active phase is CaMnO_3 with a large number of oxygen vacancies.