【作者】 马娜；

【导师】 单文娟；

【作者基本信息】 辽宁师范大学 ， 物理化学， 2010， 硕士

【摘要】 柴油机由于其循环热效率高、燃油经济性好,所以日益受到重视。然而柴油机尾气排放造成的环境污染问题也日益严重,尤其是其中的碳黑颗粒,不仅对人类的视觉和嗅觉产生不良影响,而且碳黑上往往吸附着SO₂和其它致癌物质,其造成的影响更不容忽视。碳黑颗粒的热氧化温度高达550-600℃,但是柴油机的排气温度却在175-400℃之间。如何制备高活性催化剂降低碳黑颗粒的燃烧温度是应用催化和环保研究领域中一个极为重要方向。本论文主要研究了以10%O₂为反应气,在松散接触条件下,铈-钾、铈-锰基氧化物和钙钛矿催化剂在碳黑低温燃烧反应中的催化性能。采用不同的合成方法制备了CeO₂催化剂载体和不同K负载量的KNO₃/CeO₂和K₂CO₃/CeO₂催化剂,考察其催化碳黑氧化的催化活性。研究结果表明:负载K可以明显改善CeO₂催化剂活性,其中19wt%K/（KNO₃+CeO₂）催化剂的活性最好。其原因在于KNO₃的熔融温度和分解温度较低,在反应温度下处于KNO₃熔融状态,有利于改善碳黑与催化剂的接触程度,从而促进反应的进行。另外,反应温度下可能有一部分的KNO₃分解成KNO₂甚至进一步分解成K₂O,放出O₂和NO_x,对反应的进行也有促进作用。改变制备方法及过程制备固定Mn/Ce比例的Mn-Ce复合氧化物催化剂,研究结果表明:Mn/Ce比例和催化剂制备过程中pH值对催化剂的活性均有不同程度的影响。另外,在催化剂制备过程中用于调节pH值的物质对催化剂活性同样有一定影响,利用尿素调节pH值制备得到的催化剂催化活性最好。采用络合燃烧法制备了不同的钙钛矿催化剂,并考察其催化碳黑氧化的催化活性。研究结果表明:当Co元素作为B位离子的催化剂拥有较好的催化活性;同时在A位采用不同比例的K元素取代时,催化剂的催化活性随K元素的取代量上升而呈现先减后增的趋势。而另一方面,如果将贵金属Pt分别以负载或掺杂B位的形式引入LaCoO₃催化剂当中时,催化剂的催化活性都有不同程度的提高。尤其是负载Pt时,催化剂活性得到明显提高。更多还原

【Abstract】 Diesel engines are more popular due to the relatively high thermal efficiency and fuel economy than gasoline engines. Diesel engine emissions have led to serious environmental problems especially their carbon particles content. The small size of diesel soot particles may be linked to a number of health problems by its ability to penetrate the body through the respiratory system.The non-catalytic ignition temperature of soot generally exceeds 550℃, while the temperature of typical exhausts is 400℃or below in light duty applications. The combination of traps and oxidation catalysts appear to be the most plausible after-treatment technique to eliminate soot particles. However, the temperature of diesel exhaust is in the range of 175-400℃. To lower the soot ignition temperature, one solution is using catalyst. Under loose contact, Ceria based, potassium based, manganese based oxides and perovskite were investigated as catalysts for the soot combustion with 10%O₂ as reactant gas in this work, considering the excellent redox properties of these oxides.First, ceria and ceria-based oxide catalysts have been investigated for catalytic soot oxidation reaction, which were got by different synthesis methods. It was found that the catalytic activities of ceria-based oxide catalysts can be improved by loading potassium. The 19wt%K/（KNO₃+CeO₂） catalyst showed the excellent catalytic activity for soot oxidation. The main reason was that the melting temperature and decomposing temperature of KNO₃ were lower than K2CO₃, in other words, KNO₃ was melting at reaction temperature, which was useful to improve the contact state between soot and catalyst.Second, different Mn-Ce oxide catalysts for soot oxidation were fabricated through different preparation method or process. It was indicated that the molar ratio of Mn to Ce and the pH value of the preparation process can influence the catalytic activity for the soot oxidation to some extent. Otherwise, the reagent for adjusting the pH value of the preparation solution can also influence the catalytic activity of the Mn-Ce oxide catalysts. Last, different perovskite oxide catalysts have been investigated for the catalytic soot oxidation process, which were prepared through the complex-combustion method. The results indicated that the Co as B-site cationic show much high activity for the soot oxidation, and the substitutional incorporation of K into A-sites of perovskite oxides was found to be quite effective in enhancing the activity. In addition, two important measures were adopted in order to modify the activity of perovskite-type oxide catalysts. One is to perform substitutions of platinum on the cationic sites; the other is to support noble platinum on the surface of perovskite-type oxides by impregment method. It was indicated that noble platinum as supported particles could promote effectively the catalytic performance of the perovskite-type oxide catalysts.更多还原