Study On Prepration Of Potassium Supported On Cerium Manganese Catalysts And Catalytic Oxidation Characteristics For Diesel Soot

Diesel engines have been widely applied in various vehicles in daily life because of their advantages such as high fuel efficiency,strong power and good reliability.However,the exhaust gas of diesel engines contains a large amount of pollutants,including carbonic oxide（CO）,hydrocarbons（HC）,particulate matter（PM）,and nitrogen oxides（NO_x）,which seriously endanger human health.Therefore,in order to meet the increasingly strict emission regulations,it is significant to reduce pollutants through diesel aftertreatment technology.Among various aftertreatment technologies,the most effective method to remove particulate matter is diesel particulate filter（DPF）.The combustion temperature of soot is around 600℃,the exhaust temperature of diesel engine is generally 150⁴00℃.Therefore,the catalyst needs to be coated on the DPF to reduce the soot ignition temperature.The oxidation catalyst can significantly reduce the ignition temperature of smoke,improve the catalytic oxidation rate,which can realize the passive regeneration of DPF.In this paper,nKOH-Ce_0.5Mn_0.5O₂ and nKNO₃-Ce_0.5Mn_0.5O₂ were prepared by loading different K salt（n=0.05,0.2 and 0.5;n is the molar ratio）.In different mixed gas atmosphere（O₂ and O₂/NO）,the activity of catalysts was investigated by thermogravimetry,and the stability of two kinds catalysts was evaluated by temperature programmed oxidation（TPO）.The greater activity and stability of nKNO₃-Ce_0.5Mn_0.5O₂ catalysts was screened out.The physical and chemical characteristics of nKNO₃-Ce_0.5Mn_0.5O₂ catalysts and the working principles of catalysts were studied by XRD、BET、H₂-TPR and so on.Finally,the nKNO₃-Ce_0.5Mn_0.5O₂catalysts with optimal load ratio were selected for bench test to explore the exhaust soot removal effect in the actual exhaust gas.The specific research contents of this paper are as follows:（1）KOH and KNO₃ were loaded on Ce_0.5Mn_0.5O₂ catalyst respectively,and different loading ratio of nK-Ce_0.5Mn_0.5O₂ catalysts were prepared.In different simulated atmosphere,the activity and stability of the catalysts were evaluated by thermogravimetry and temperature programmed oxidation.The results showed that the performance of the catalyst was improved with the loading of K salt,but the catalytic capacity of the two catalysts was different.Under the atmosphere of O₂/N₂,the catalytic activity of nKNO₃-Ce_0.5Mn_0.5O₂ on soot was superior due to its low melting point.In the O₂/NO atmosphere,the activity of nKOH-Ce_0.5Mn_0.5O₂ was significantly improved due to the presence of NO,which was better than that of nKNO₃-Ce_0.5Mn_0.5O₂.When the soot reacted with the catalyst,nKNO₃-Ce_0.5Mn_0.5O₂ catalysts showed better stability due to the presence of K₂Mn₄O₈ in the catalyst.（2）The nKNO₃-Ce_0.5Mn_0.5O₂ catalysts with good activity and stability were selected for further study.A series of characterization and oxidation kinetics analysis were carried out to explore the effect of KNO₃ loading on the physical and chemical properties of Ce_0.5Mn_0.5O₂ catalyst.The results showed that the loading of KNO₃ can cause a small amount of K⁺to enter the lattice to synergize with the cerium-manganese solid solution,generate different degrees of lattice defects and more oxygen vacancies,and change the contact state between soot and catalyst,which is beneficial to the conversion between different oxygen species and enhance the redox capacity of the catalyst.With the increase loading of KNO₃ on Ce_0.5Mn_0.5O₂ catalyst,the soot oxidation temperature decreases.There was an optimal loading capacity,when n=0.2,the activity of catalysts was optimized,and the activation energy required for the oxidation of soot was 18.37 kJ/mol,and the reaction pre-exponential factor reached a maximum of 98.（3）The Ce_0.5Mn_0.5O₂ and 0.2KNO₃-Ce_0.5Mn_0.5O₂ catalysts were encapsulated and coated on DPF.The ability of the catalyst to remove diesel exhaust was evaluated in an actual exhaust atmosphere.The results showed that the two catalysts have some catalytic effects on the CO,HC,NO_x and PM.Among them,0.2KNO₃-Ce_0.5Mn_0.5O₂showed the best effect on soot removal,and the best removal efficiency was 85.2%.Ce_0.5Mn_0.5O₂ and 0.2KNO₃-Ce_0.5Mn_0.5O₂ catalysts had similar catalytic effects on HC and CO,and the optimal removal efficiency can reach more than 85%.The removal efficiency of NO_x by 0.2KNO₃-Ce_0.5Mn_0.5O₂ catalyst was about 22.1%,which was better than that of Ce_0.5Mn_0.5O₂ catalyst.