Study On Catalytic Performance Of Lanthanum Strontium Cobalt Iron Perovskite Composite Catalyst For Soot Oxidation

In recent years,with the increase of diesel vehicle ownership,the exhaust emission problem is becoming more and more serious.Soot particles,as a part of diesel engine exhaust,bring great harm to human health,production and life.At present,soot catalytic oxidation is one of the economical and effective methods to reduce soot particle emissions and improve the performance of diesel engine particulate matter collector（DPF）.Now precious metal catalysts are commonly used.Perovskite catalysts,such as La_0.6Sr_0.4Co_0.2Fe_0.8O₃（LSCF）,show excellent performance in the field of electrocatalysis,low cost and huge market potential.However,there is little research on soot catalytic oxidation,and its performance is poor.In order to further improve its performance,LSCF perovskite materials and a series of composites（such as Ce O₂,Ag,etc.）were prepared independently,and their catalytic performance of soot oxidation was studied by the combination of experiment and simulation.The main contents are as follows:Firstly,LSCF catalysts were prepared by sol-gel method.The catalyst was characterized by X-ray diffraction（XRD）.The results show that the catalyst prepared by this method has high purity and good repeatability.The characteristic temperature value of the catalyst T₁₀（the temperature corresponding to the soot conversion rate of10%,and so on）,T₅₀and T₉₀are 401.1℃,451.3℃and 497.0℃respectively,which is higher than that of the commercial catalyst.The results of scanning electron microscope（SEM）,specific surface area measurement（BET）,X-ray photoelectron spectroscopy（XPS）and oxygen temperature programmed desorption（O₂-TPD）show that the catalyst is flaky,the specific surface area is only 7.44m²/g,the oxygen adsorption capacity of the material surface is weak,and the oxygen vacancy is relatively insufficient.Therefore,the LSCF catalyst needs to be improved.Then,based on the literature research,this paper uses CeO₂and Ag to composite LSCF materials to improve their properties.In this paper,Ce O₂-LSCF,Ag-LSCF and Ag-Ce O₂-LSCF composite catalysts were successfully prepared by impregnation method.The evaluation results of soot activity show that the soot oxidation characteristic temperature of Ag-Ce O₂-LSCF composite catalyst is lower.T₁₀,T₅₀and T₉₀are 344.0℃,394.8℃and 445.1℃respectively,which decreased by 56.9℃,56.5℃and 51.5℃compared with LSCF group.The performance of the four groups of catalysts is arranged from good to poor:Ag-Ce O₂-LSCF>Ag-LSCF>Ce O₂-LSCF>LSCF,indicating that the catalytic performance of LSCF combined with Ag and Ce O₂is significantly improved.SEM and TEM results indicate that the three composites show lamellar overlapping structure,and show the existence of each phase in the micro-morphology and can correspond to their respective crystal planes,indicating that the composite of the materials is better.BET results show that Ag-Ce O₂-LSCF has relatively large specific surface area and pore volume,and relatively strong surface oxygen adsorption capacity and rich surface oxygen species.Then,the effects of Ag content,O₂content,flow rate and heating rate on the catalytic oxidation performance of Ag-Ce O₂-LSCF composites were studied.The catalytic performance is the best when the Ag content is 8wt.%.When the O₂intake ratio,the total inlet rate and the mixed ratio of catalyst and soot are 15%,100ml/min and 10:1respectively,the catalytic soot effect of 8wt.%Ag-Ce O₂-LSCF is the best.When the programmed heating rate is 3℃/min,both the performance and experimental efficiency of soot combustion catalyzed by 8wt.%Ag-Ce O₂-LSCF can be taken into account.Finally,a two-dimensional DPF single-channel model was established by COMSOL Multiphysics 5.6 software,and the model was verified.Combined with the catalytic reaction rate constant and other related data obtained from the experiments,the regeneration process of DPF catalyst containing 8wt.%Ag-Ce O₂-LSCF was simulated.The effects of inlet temperature,average flow rate,catalyst coating and initial soot layer thickness on DPF regeneration were analyzed.The results show that catalyst supported DPF（CDPF）can greatly improve the regeneration efficiency,and the increase of inlet temperature and the decrease of flow rate will increase the reaction rate of soot catalytic oxidation in DPF and shorten the regeneration time.