The Study On Preparation And Properties Of The Rare Earth Double Perovskite Catalytists La₂NiBO₆(B=Mn, Fe, V)

The perovskite-type composite oxides La₂NiBO₆(B=Mn,Fe,V) were synthesized by the sol-gel method and characterized by means of XRD,TPR,BET, FT-IR,TEM,SEM,Electrical conductivity Test and magnetic properties.Meanwhile, we investigated catalytic activity of catalysts in methane catalytic combustion.The double perovskite catalysts La₂NiBO₆(B=Mn,Fe,V) were prepared by using sol-gel method,followed by annealing under air atmosphere(air flow,at 1100℃for 3 hours).For La₂NiMnO₆ and La₂NiFeO₆,single-phase double perovskite catalysts can be formed.La₂NiMnO₆ showed a better catalytic activity for methane combustion than La₂NiFeO₆ and La₂NiVO₆,its T₁₀(methane conversion of 10%)and T₉₀(methane conversion of 90%) were 440℃and 666℃respectively.Under room temperature conductivity testing indicated electrical conductivity of La₂NiMnO₆ was better than La₂NiVO₆.Then phase's variation of La₂NiMnO₆ was investigated in different calcination temperature,we can deduce that the formation temperature of single-phase double perovskite La₂NiMnO₆ oxides is between 900℃and 1100℃.The rare earth double perovskite catalyst La₂NiFeO₆ was prepared by the sol-gel method using citric acid as complexing agent,followed by annealing under air atmosphere at 800℃,900℃,1000℃and 1100℃for 3 hours,then we can study effect of calcination temperature on the physicochemical properties and catalytic activity.With increasing the calcination temperature,single perovskite oxide changed into double perovskite oxide gradually,it formed double perovskite La₂NiFeO₆ at 900℃.Because of perfect structure of double perovskite,catalytic activity in methane combustion of La₂NiFeO₆ improves with the calcination temperature increasing in the range of 800℃-1000℃.On the basis of the samples La₂NiMnO₆ modified with Sr,then finding there is no improvement on catalytic activity,so Sr doped double perovskite oxides La_2-xSr_xNiFeO₆(x=0.02,0.08,0.1,0.5) were prepared by the sol-gel method,the different modification of strontium could affect catalytic activity of double perovskite La₂NiFeO₆.The result showed that catalytic activity of La_1.9Sr_0.1NiFeO₆ was the best, T₁₀and T₉₀were 378℃and 528℃respectively.When doping content increased to 0.5, catalytic activity of double perovskite oxides decreased.Therefore appropriate doping content is beneficial to enhance catalytic activity.