Study On Oxidation Characteristics Of Diesel Particulate Matter With Cerium Manganese Potassium Composite Metal Oxides

Diesel engine has good economy and high reliability.It is more widely used in commercial vehicles and agricultural vehicles than gasoline engines,but its main pollutants are harmful to the environment and human health.It is difficult to completely remove the pollutants emitted by diesel engines by relying on internal purification.Therefore,more effective post-processing technology research is of great significance to meet more stringent emission regulations.The catalytic oxidation of particulate matter by catalysts has the advantages of low cost and effective and many researchers focus on it due to its wide application.After forming solid solution,cerium and manganese can better promote the flow of oxygen species,and the number of oxygen vacancies also increases sharply,because of the excellent oxygen storage/release ability of CeO₂ and the strong oxidation ability of MnO_x,which has attracted many researchers.In this paper,the preparation and characterization of cerium-manganese catalyst and potassium-doped cerium-manganese catalyst were studied.The activity and thermodynamic analysis of the catalyst for soot were studied.In addition,this article also examined the link between the physicochemical properties and activity of the catalyst.The coating of the blank DPF was carried out on the basis of analyzing the performance of the catalyst,and the performance under the steady state condition of the diesel engine was evaluated with the coated DPF.The specific research contents are as follows.?1?Ce_xMn_1-xO₂ solid solution was prepared by sol-gel method.Catalytic activity of Ce_xMn_1-xO₂ on soot was investigated,and the activation energy and Pre-exponential factor analysis were calculated by thermodynamics.Prepared catalyst was also characterized by XRD,BET,H₂-TPR,Raman and XPS,etc.The results showed that the weight loss curve of particulate matter is obviously shifted to the low temperature range under Ce_xMn_1-xO₂,and the soot ignition temperature and maximum peak combustion temperature decreased sharply.Thermodynamic analysis results showed that the increasing of Mn content reduced the activation energy and increased the pre-exponential factor of catalysts.Mn didn't change the cubic fluorite structure of CeO₂,Mn also inhibit cell growth,and increased the specific surface area.During the reaction,the lattice oxygen in the catalyst was converted into surface-adsorbed oxygen and participates in the reaction due to the increase of surface oxygen vacancies.?2?K element was doped with Ce_0.5Mn_0.5O₂,and the doped K_z-Ce_0.5Mn_0.5O₂catalyst was characterized and the oxidation of diesel particulate matter was evaluated.The results showed that after doping K element,the oxidation temperature of SOF in particulate matter was significantly decreased,and the ignition temperature of soot precursor and dry soot was also decreased to some extent.K_0.2-Ce_0.5Mn_0.5O₂ has excellent performance,which make soot ignition temperature dropped by 28°C and maximum peak combustion temperature dropped by 61°C.The electron orbitals of Ce and Mn ions are active after K doping,and its atomic adsorption O^-species increases with the changing of oxygen species.?3?Ce_0.5Mn_0.5O₂ and K_0.2-Ce_0.5Mn_0.5O₂ were coated to a blank DPF and packaged,and the after-treatment device was installed in the diesel engine test bench to analyze the purification effect under the actual exhaust atmosphere.The results showed that K_0.2-Ce_0.5Mn_0.5O₂ has the most obvious catalystic effect on particulate matter emission under all loads at 2400 r·min^-1.The soot specific emission was 0.011g/?kW·h?under 100%load,78.1%lower than 0.049 g/?kW·h?of original emission.NO_x emission purification effect of the two catalysts on diesel engine was not significant.Only at high load,NO₂ participated in the oxidative combustion of soot.For HC emission,The HC of K_0.2-Ce_0.5Mn_0.5O₂ is 55.2%lower than the original emission under 100%load,and 91.1%lower under 10%load with the highest HC emission,which catalystic effect is better than Ce_0.5Mn_0.5O₂.The catalytic oxidation of CO by Ce_0.5Mn_0.5O₂ and K_0.2-Ce_0.5Mn_0.5O₂ catalysts was similar when the exhaust gas temperature was high,and their average catalytic efficiencies under four loads were 98.3%and 98.9%respectively.