Study On The Structure Regulation Of Perovskite Type Mn-based Catalysts And Their Catalytic Performance On Carbon Soot Combustion

Diesel exhaust particulate matter?PM?is one of the main pollutants which mainly constituted of soot and caused serious health and environmental problems.Now the diesel particulate filter?Diesel Particulate,DPF?was installed in the engine exhaust pipe for the purpose of particle filtering and trapping filter off the exhaust PM.Introducing effective catalysts into the DFP would reduce the ignition temperature of carbon black particles and benefit soot removal.Therefore,the development of oxidation catalyst appeared to be a challenge issue for controlling emission pollution.Perovskite type composite oxide catalyst attracted much attention because of its low cost,high thermal stability,flexible components and also could used be as catalyst support.Perovskite MnO₃ composite oxides possess excellent activity,and show great potential in the application of DPF.In this paper,alkaline earth metal elements?Ca,Sr,and La?used to replace the La on the A-site of perovskite structure,and the influence of different elements and the amounts of substitution on the structure and redox properties of perovskite catalysts were investigated.On the other hand,Cu and Fe was used to replace Mn on the B-site in the perovskite structure The following conclusions could be obtained.?1?The alkaline earth metal modified La1-xMx MnO3?M =Ba,Sr,and Ca?catalyst was prepared and characterized.The results indicated that the substitution amount of x ? 0.5,Sr and Ca elements could arbitrarily occupy A-site by replacing La in the MnO₃ perovskite structure without changing the structure of perovskite.For Ba substituted catalysts,as the substitution amount x ? 0.3,Ba element also could arbitrarily occupy A-site in the MnO₃,but a new crystalline BaMnO₃ was found in the catalyst when the substitution amount x > 0.3.Compared to Ba and Ca substituted catalysts,the Sr substituted catalysts had better structural symmetry.The redox properties and surface oxygen species of the prepared catalysts were characterized by the H_2-TPR and O_2-TPD.The facts showed that the surface of Sr substituted catalysts had more chemical adsorption oxygen.Among them,La_0.6Sr_0.4MnO₃ catalyst had the best catalytic activity and the ignition temperature?Ti?of soot combustion was only 356 oC.?2?Based on La_0.6Sr_0.4MnO₃ perovskite catalyst,a series of Fe substituted catalysts were prepared by citric acid sol-gel method.The structures of the catalysts were characterized by XRD,BET,FT-IR and SEM.It could be found that the Fe element could be well into the structure of perovskite catalyst.Introducing Fe ions into the catalyst would decrease the symmetry of BO₆ octahedral,which was not benefitted the adsorption of chemical oxygen,but it could increase the oxygen vacancies on the surface of the catalyst and also increased chemical adsorption oxygen.The La_0.6Sr_0.4Mn_0.9Fe_0.1O₃ catalyst showed the best catalytic activity,and the ignition temperature?Ti?of soot was only 343 oC.?3?The same method was used to investigate the influence of lower valence Cu element on the structure,composition and activity of catalysts.A series of Cu substituted catalysts were prepared by citric acid sol-gel method.The structure of the catalyst was characterized by XRD,BET,FT-IR and SEM.It was found that the Cu element could be well into the structure of the perovskite catalyst,which lead to different degrees of distortion on the structure of catalyst.In addition,the low valence of Cu would result in the valence changing of Mn in B-site and also reducing the amount of active component Mn⁴⁺/Mn³⁺.At the same time,Mn ions in high valence occupied more coordination oxygen,which lead to the decrease of oxygen adsorption on the surface of the catalyst.These factors lead to the decrease of the catalytic activity of the Cu substituted catalysts in the catalytic oxidation of soot.