Study On The Modified Ag-based Catalysts For Catalytic Oxidation Of Soot Particulate

With the rapid development of automobile industry,it brings convenience to people,but also leads to the deterioration of the environment and energy crisis.Compared with gasoline vehicles,diesel vehicles are being paid more and more attention because of their advantages of high economy,high power,enough power and low CO2 emissions.However,the soot particles in the tail gas seriously pollute the environment and harm people's health.Especially the haze of large cities,and the emissions of particulate matter in the automobile exhaust are closely related.Therefore,it is necessary to deal with the emission of soot particles.At present,the most effective treatment technology of soot particle removal is the combination of particle capture technology and catalytic combustion technology.According to the reports in literature,Ag-based catalysts have become one of the focuses in soot particle combustion due to their high catalytic activity.However,the thermal stability of Ag-based catalysts is poor,and it is easy to be sintered and thus become deactivation at high temperature.Therefore,the present thesis attempts to modify the supported Ag-based catalysts for the preparation of Ag catalysts with high activity and high stability.Firstly,SBA-15 supported Ag and Cu single metal catalysts and a series of Ag-Cu bimetallic catalysts with different Cu/Ag atomic ratios were prepared by a co-impregnation method.They were then subjected to test the soot particle combustion catalytic activity.The results showed that the introduction of a small amount of Cu in the Ag-based catalyst could effectively improve the activity in the soot particle combustion.Among them,5Ag1-CuO0.1/SBA-15 exhibited the best catalytic activity,the ignition temperature,maximum combustion temperature and final combustion temperature were 225 ?,285 ? and 410 ?,respectively.The physicochemical properties and structure of the catalysts were investigated by TG/DTA,BET,XRD,TEM,H2-TPR,UV-Vis and XPS,and were correlated with the catalytic activity for the soot particles combustion.The results indicated that the introduction of a small amount of Cu could lead to generate a strong interaction between Ag and Cu,which reduces the oxidation-reduction temperature and thus improves the thermal stability of the catalysts.Furthermore,the calculation of kinetic activation energy revealed that the introduction of a small of Cu into Ag/SBA-15 could decrease the apparent activation energy of the reaction,in turn significantly improve the activity of soot particles oxidation the catalysts.Subsequently,due to the advantages of MgAl2O4,such as excellent mechanical strength,good chemical resistance,good hydrothermal stability and so on,it is considered as a suitable catalyst carrier for the removal of soot particles in complex environment.To get a better catalytic performance,Ce-modified MgAl2O4(Ce-MgAl2O4)was prepared by a hydrothermal method.Then the Ag/Ce-MgAl2O4 catalysts with different Ag loadings were prepared by a conventional impregnation method for the soot particles oxidations.The results showed that the catalytic activity was closely related to the loading amount of Ag.Among them,the 10Ag/Ce-MgAl2O4 exhibited the best performance,giving the ignition temperature,maximum combustion temperature and final combustion temperature at 229 ? 358 ? and 396?,respectively.The catalyst displayed negligible deterioration in catalytic performance during recycles for several times.The results of XPS,EPR,Raman and FTIR characterizations revealed that there existed active—redox activity of Ag2+/Ag+,Ag2+/Ag0 and Ag+/Ag0 on the catalyst surfaces and these active rCdox reactions increased the oxidation of soot particles.Moreover,the metal Ag has electron donating ability,to adsorb and activate O2 molecules,and the strong interactions between Ce and Ag increased the number of reactive oxygen species.All these effects promoted the generation of superoxide species(O2)and peroxide species(O22-)on the catalyst surfaces.These surface active oxygen species could spillover to the soot particles and accelerate the oxidation rate.