The Investigation Of No Oxidation Performance Of Lanthanum-based Perovskite Oxide Catalysts

Lean combustion technology with high efficiency and energy saving have drawattention of many people. Lean burn engine exhaust aftertreatment technology hasbeen rapidly developed. Therefore, the new method applied to control the lean-burnengine exhaust is required, including NSR, SCR and DPF technology. NO oxidationis always play key role in those technologies. Perovskite materials with manyadvantages, such as the crystal structure, excellent stability and low cost advantage,are considered to be the potential catalysts applied to the motor vehicle exhaust aftertreatment.Lanthanum based perovskite-type catalyst LaMeO3(Me=Mn, Fe, Co) wasprepared by sol-gel method. The single crystal perovskite phase was obtained for allthe samples. The NO oxidation activity of LaCoO3is the highest, and the activity ofLaFeO3was the worst. The activity and structure stability of LaMnO3are middle ofthem. The surface adsorption ability and the reducibility of the catalyst is the keyfactor to control the NO oxidation reaction. At the same time, after hydrothermalaging, catalyst particle growed and the specific surface area decreased. The catalyticactivity decreased obviously, but LaCoO3perovskite still maintained a relatively highcatalytic performance.The effects of Co doping on the catalytic activity of LaFeO3perovskite andstructural stability were studied. The results show that, the doping of Co did notchange the crystal structure of LaFeO3, and improves the NO oxidation activity of thecatalyst. With the increased amount of Co doping, NO oxidation activity of thecatalyst increases. The doping of Co increased the content of active oxygen LaFeO3perovskite, also makes the catalyst surface adsorption ability enhancement NO.Study on the stoichiometric La0.95Fe1-yCoyO3(x=0.1,0.2,0.3) the catalyticperformance of perovskite. Experimental results show that, the nonstoichiometrysignificantly increases the NO oxidation activity of LaFeCoO3perovskite, especiallylow temperature activity. With the increase of the doping amount of Co, the activityof the catalyst increases first and then decreases, the La0.95Fe0.8Co0.2O3catalyst in NOoxidation activity was the highest, higher activity in250oC above2wt.%Pt/Al2O3catalyst. Non-stoichiometric makes LaFeCoO3perovskite surface low amount of Co doping Co ion concentration, enhance the oxidation catalyst surface reducing power,A La ion deficiency reduced stability of perovskite structure, while increasing theactivity of the catalyst. After hydrothermal aging catalyst particles were aggregatedsintering and specific surface area decreased.Finally, the catalytic properties of nonstoichiometric LaMnO3perovskite wereinvestigated. The experimental results show that, the non-stoichiometry significantlyimproved the catalytic activity of LaMnO3perovskite, and with the X value increases,catalyst activity decreases gradually. A La make LaMnO3Mn4+defect perovskite ionmore to maintain the price balance by B. More Mn4+ions content reduces thestructure stability of the catalyst, valence of Mn4+/Mn3+ion instability is the innerreason of catalyst with NO oxidation capacity. From the kinetic experiments ofLaxMnO3(x=0.9,0.95,1,1.05,1.11) perovskite for NO oxidation reaction, theactivation energy was44.8±2.7kJ/mol. After hydrothermal aging, the catalystsintering, grain growth phenomenon, the catalytic activity decreased.