K^+和Ca^(2+)对钙钛矿LaCoO_3中A位离子的掺杂及对柴油车尾气中Soot和NO去除率的影响

Effect of A-Site Ion in Perovskite LaCoO_3 by Addition of K^+ and Ca^(2+) on Removal Rate of Soot and NO in Exhaust of Diesel Vehicle

通过柠檬酸络合法制备用于柴油车尾气颗粒物的钙钛矿型催化剂LaCoO_3。并采用不同取代量的K^+,Ca^(2+)对催化剂La基位离子进行取代,记为La_(1-x)A_xCoO_3(A=K,Ca;x=0,0.1,0.2,0.3,0.4,0.5),所制得催化剂的结构采用X射线衍射(XRD)、扫描电镜(SEM)和比表面积(BET)进行表征,并通过固定床实验来对所制得的催化剂进行催化活性测试。通过催化剂对Soot和NO的去除率与未改性的LaCoO_3相比,得出K^+和Ca^(2+)的最佳取代量分别为x=0.3和x=0.4,而钙钛矿型催化剂La_(0.7)K_(0.3)CoO_3对Soot和NO的去除率分别达到86.9%和82.6%。这与钙钛矿型催化剂LaCoO_3的A位离子被K^+,Ca^(2+)取代后,K^+或Ca^(2+)迁移到钙钛矿的晶格内有关,形成了La_(1-x)M_xCoO_3,增加钙钛矿型结构中的氧空位,使得碳烟的起燃温度降低,从而提高了Soot的去除率,即A位离子被取代后所形成的氧空位促成其钙钛矿型催化剂对Soot氧化的高催化活性。

The perovskite-type catalyst LaCoO3 for diesel engine exhaust particulates was prepared by citric acid complexation. The La-site ions of the catalyst were substituted with different substitution K^＋ and Ca^2＋ as La1-xAxCoO3（ A = K,Ca; x = 0,0. 1,0. 2,0. 3,0. 4,0. 5）. The structures and physico-chemical properties for these catalysts were characterized by X-ray diffraction（ XRD） SEM and BET. The catalytic activity of the prepared catalyst was tested by a fixed bed experiment. The optimum substitution rates of K^＋ and Ca^2＋ were x = 0. 3 and x =0. 4. The removal rates of Soot and NO by La0.7K0.3CoO3 was obtained： 86. 9% and 82. 6%. When LaCoO3 is replaced by both K^＋ and Ca^2＋ ,K^＋ or Ca^2＋ migrates into the lattice of perovskite to form La1-xMxCoO3,which increases the oxygen vacancy in the perovskite structure,results in a decrease in the ignition temperature of the soot,thereby increase the removal rate of the carbon particles. Therefore,the oxygen vacancies formed by the substitution of A-site ions,contribute to the high catalytic activity of perovskite-type catalysts for the oxidation of soot.