Study On Preparation And Mechanism Of Cerium-based Soot Combustion Catalyst

With the global energy crisis continuing and the increasing pressure on environmental protection,the efficiency and cleanliness of diesel fuel use are gaining increasing attention.The soot particles in the exhaust gas of the diesel engine cause great harm to the environment and human health,and the ignition temperature of the soot is usually above 580?.In order to achieve the removal of soot particles at the working temperature?170-400??,it is necessary to add a soot combustion catalyst to the diesel exhaust gas aftertreatment device.Compared with the traditional Pt/Pd noble metal catalyst,the cerium-based catalyst is not only cheap,but also exhibits excellent soot combustion activity as much as the noble metal catalyst after the modification of the doped copper and manganese.In this paper,cerium-based composite oxide catalysts with different contents of copper and manganese were prepared by sol-gel method.First,The optimum Cu?Mn?/Ce ratio was determined by N₂-desorption curve,XRD,H₂-TPR,O₂-TPD and activity test,and then the catalyst preparation conditions were optimized by single factor modulation:synthesis temperature,feeding method,rotational speed,water content,citric acid/M^x+ratio,surfactant and drying temperature.The results showed that the optimum molar ratio was 1/9?Cu/Ce?and 1/1?Mn/Ce?,the synthesis temperature was 80?,the feeding method was by adding dropwise,the surfactant selected polyethylene glycol 20000,the amount of deionized water was 20ml,the citric acid/M^x+ratio was 1.5?Cu/Ce?and 2?Mn/Ce?,the drying temperature was 80?.Because the thermal stability is very important for the industrialization of the catalyst,the thermal stability test of the catalyst was carried out,and it was found that the MnCe composite oxide catalyst had relatively good thermal stability.When the soot combustion reaction is carried out,the adsorbed species on the surface of the catalyst,especially the high-valent nitrogen species,can effectively promote the combustion of soot.In order to explore the specific effect of the nitrogen species on the combustion activity of soot,the adsorption and oxidation behavior of NO on manganese-cerium catalyst were characterized by NO-TPO,NO₂-TPD,FT-IR and in-situ DRIFTS.It was found that at low temperature?100-200??the nitric acid species were mainly nitrite and monodentate nitrate,and gradually changed to the better thermostable bidentate and ionic nitrots with the increase of temperature.The in-situ DRIFTS was used to observe the oxidation of soot particles by manganese-cerium composite oxide in 1000ppm NO/10%O₂/N₂ atmosphere,it was found that the bidentate nitrate and ionic nitrate stored in the catalyst may react directly with the soot particles to produce C?O?or CO₂,C?O?was further oxidized to CO₂.