Synthesis And Preformance Of A-site Doped LaSrCoO₄ Mixed Oxides

Complex oxides A₂BO₄ with perovskite-like K₂NiF₄-type structure are of specialinterest due to their particular crystal structure, outstanding electromagnetic property,preferable stability at high temperature,planar conductor, transport properties betweensemiconductor and metal as well as their ability to catalyze a large number ofoxidation and reduction reactions.Hence, they have become new-style materialswhich have better foreground than ABO₃ mixed oxides. Catalytic activity of theA₂BO₄ mixed meterials directly relate to the cation composition of A-site and B-site,quantivalence of transition metal B-site and crystal structure. At present, somereferences have reported the Cu-based and Ni-based mixed oxides, a few references inrelation to Co-based mixed oxides has been found, so it's very necessary for us tostudy the Co-based mixed oxides.In the dissertation, the LaSrCoO₄ and La_1-xA_xSrCoO₄ mixed oxides were preparedusing polyacrylamide macromolecule gel method. The catalytic oxidation of CO andCalls used as probe reaction, the experiments were carded out in such a way that allfactors affecting the catalytic activities [the different element doped: rare earths(Nd,Ce) and transition metals (Ni,Fe,Mn), different preparation methods and differentcontent doped of Nd and Ni]. Most of the catalysts were characterized by means ofXRD, IR, BET, H₂-TPR, O₂-TPD, respectively.LaSrCoO₄ catalysts of A-site doped different rare earths (Nd,Ce) and transitionmetals Ni,Fe,Mn) were synthesized by polyacrylamide macromolecule gel method.According to XRD and IR data, most of the catalysts had formed the perovskite-likestructure. With Nd-doping, LaSrCoO₄ catalyst have more content of Co³⁺, quantity ofsurface adsorbed oxygen and lattice oxygen, so enhance catalytic actiities for CO andC₃H₈ oxidation. Unlike, Ce doped reduces the catalytic activities of LaSrCoO₄catalyst.The different preparation methods and Ni (or Nd) doped content seems to bean important factor in structure and catalytic activities of the catalysts..In the paper,polyaerylamide macromolecule gel method, polyglyeol gel method and evaporation-decomposition method were used, and found that the catalyst perpared usingpolyacrylamide macromolecule gel method was shown to be the best active. Becausethe catalyst prepared with this method has bigger surface area, samaller crystal size,more surface adsorbed oxygen and lattice oxygen, and lower activation energybesides, all these seems to be crucial factor in the catalytic activities for oxidation of CO and C₃H₈. In the catalytic process,where the the content of Nd-doped seems to bevery important, suitable content of Nd-doped increase the catalytic activities of theLaSrCoO₄catalyst, since this catalyst reduces crystal size, increases lattice distortionsand lattice oxygen. Fe Doping into LaSrCoO₄ catalyst dosen't change the catalyticactivities greatly. Ni-doped can enhance the catalytic activies, by the reason that it canreduce crystal size, increase the lattice distortions, the content of oxygen vacancy andlattice oxygen, and reduce the activation energy. Ni.(x=0.1-0.7) doped content affectsthe properties of LaSrCoO₄ catalyst. Suitable Ni (x=0.3)doping into LaSrCoO₄catalyst is favorable for the catalytic activity. This can be interpreted that theLa_0.7Ni_0.3SrCoO₄ catalyst has smaller crystal size and bigger lattice distortions.