The Oxidation Activity Studies Of Low Temperature Combustion For Diesel Soot

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.