Study On Catalytic Decomperzation Of N₂O By Transition Metal Composite Oxides

N2O is a harmful greenhouse gas,causing serious greenhouse effect on the natural environment.The emission of chemical production is one of the main sources of N2O,which contains low concentration NO,O2 and other impurities.In this thesis,we prepared the iron-based spinel oxides and supported cobalt metal oxides by co-precipitation and impregnation.XRD,BET,XPS and H2-TPR were used to characterize the texture properties of catalysts.The activity evaluation of N2O catalytic decomposition was carried out in a fixed-bed reactor.The high temperature stability and resistence of catalysts to impurity gases were also investigated.Firstly,a series of AxFe1-xFe2O4(A=Co,Mg,Zn,Mn,Ni,Fe.x=0,0.2,0.4,0.6,0.8,1.0)spinel oxides were prepared,and screened out the most active catalyst.Under the certain conditions,Co0.8Fe0.2Fe2O4 prepared by co-precipitation shows the highest activity.N2O conversion over Co0.8Fe0.2Fe2O4 is 99.98%at 495?.Co doping reduces the crystal size of the catalyst and increases the specific surface area of the catalyst.The interaction between Co ion and Fe ion improves the oxidation-reduction ability of the catalyst,accelerating the renewal speed of the surface active sites,and improving the catalytic performance.The addition of ?-Al2O3 in the catalyst reduces the crystallinity of Co0.8Fe0.2Fe2O4 and keeps the catalytic performance at high temperature environment.However,Co0.8Fe0.2Fe2O4 performed low catalytic activity over impurity gas(NO,O2),weaken the resistence of catalysts to impurity gases.To enhance the catalytic activity and strengthen the resistence to impurity gases,a series of MxCo0.8Fe0.2Fe2O4 catalysts were prepared(M=Ce,La,Ni,Mg,Sr),and investigated the improvement of catalyst performance by the amount of M doped.Under the certain conditions,La0.3Co0.8Fe0.2Fe2O4 shows the best catalytic activity,completely decompose N2O at 450?.La doping produces tiny grains of perovskite oxide Co0.4Fe0.6LaO3,which increases the specific surface area of the catalyst.The bond energy of Fe-O and Co-O were reduced,which promotes the decomposition of N2O and enhances the resistence to impurity gases.To enhance the high temperature stability,La0.3Co0.8Fe0.2Fe2O4/40%?-Al2O3 catalyst was prepared.The addition of?-Al2O3 in the catalyst reduces the crystallinity of La0.3Co0.8Fe0.2Fe2O4 and keeps the catalytic performance at high temperature environment.To reduce the preparation cost,a series of supported cobalt metal oxides NyCo5-?/?-Al2O3/ZrO2(N=Ni,Cu,Fe)with a metal loading of 5%were prepared by the impregnation and investigated the effect of supports type and metal loading on the catalytic performance.Ni2.5Co2.5/ZrO2 shows the best activity.Ni,Cu,and Fe improve the oxidation-reduction capacity of the catalyst and promote the activity of the catalyst(Ni>Cu>Fe).Compared with ?-Al2O3,ZrO2 has a certain catalytic activity.The catalyst keeps high metal dispersion after high-temperature calcination because of the lower metal loading which reduces the preparation cost of the catalyst.So that the catalyst has excellent high-temperature stability and strong resistance to impurity gases.