Study On The Effect Of Ca-doped In LaMnO₃Perovskite As Catalyst For NO Oxidation

The perovskite-type oxides have attracted more and more attention as promisingcatalysts for auto exhaust control because of their high catalytic activity, uniquestructure characteristic and low cost. It is well known that oxidation of NO to NO2isan important step in LNT and SCR, and the traditional catalysts for NO oxidation arenoble metal (NM) based ones such as Pt-based catalysts which have showdisadvantages such as high cost and poor thermal durability. The present work isgoing to solve the problems of perovskites, such as low surface area, inferiorlow-temperature catalytic performance and complex compositions, providing for thedevelopment of the application in automotive exhaust control.In this study, a series of La1-xCaxMnO3(x=0-0.5) perovskite-type oxides wereprepared by the sol-gel method. Characterization technologies, for instance, XRD,XRS, EPR and iodometry, moreover, H2-TPR, oxygen storage capacity and NO-TPDexperiments, were taken to investigate the physical and chemical properties of theLa1-xCaxMnO3perovskites. Based on these results, catalytic performance ofLa1-xCaxMnO3perovskites on NO oxidation is considered to connect the physical andchemical properties of materials.According to texture analysis, the phase transition of the structures changing fromrhombohedral into orthorhombic and pseudocubic with the substitution Ca comparedwith pure LaMnO3, also the content of Mn4+increases with the enhanced degree ofsubstitution Ca. It shows that Mn4+contributes to the formation of the stable nitratesspecies, while the Mn3+promotes the active ones. The substitution of Ca2+promotesthe stability of Mn4+and the catalytic activity oxygen in the perovskites, which playan important role to oxidize NO molecules. Compared with the pure LaMnO3sample,La0.9Ca0.1MnO3, La0.5Ca0.5MnO3and La0.6Ca0.4MnO3possessed superior conversionwith the maximum activity point at lower temperature than that of the other samples.For the aged La1-xCaxMnO3perovskite samples, the surface area turns lower andthe crystal size gets bigger. The aged samples show more oxidation effect, while thecapacity of active oxygen decreases on the whole. The substitution of Ca2+canenhance the thermal durability of LaMnO3perovskite catalyst.