By Pechini (class) Preparation Of Perovskite Oxides And Characterized

Perovskite(-like) mixed oxides as catalysts for three-way catalysts has attracted much interest. In the paper, Pechini method is used for the synthesis of a series of such mixed oxides. Mainly, the work has been divided into four parts:(1) Pechini method is used to prepare perovskite-like mixed oxides La1.8Sr0.2CuO4.(2) PEG is used as dispersant in order to obtain products with a higher specific surface area in a better compositional homogeneity compared with the sample prepared without PEG. (3) La2-xSrxCuO4 samples with x=0,0.1,0.2,0.3,0.4 are prepared by Pechini method.(4) Perovskite mixed oxides La0.8Sr0.2O3 is prepared by Pechini method. XRD, FT-IR, SEM, TEM, BET and H2-TPR are used to characterize the samples obtained.Under the system that La1.8Sr0.2CuO4 is prepared by Pechini method, the effects of concentration of total metal nitrates, water-bath heat temperature, the amount of citric acid and calcination temperature on the quality of gel formed and phase formation of the samples obtained are discussed. The experiment shows that when the water-bath heat temperature is 70℃and the concentration of metal nitrates is 2mol/L, the gel obtained is transparent and homogenous. XRD results show that the calcinations temperature and the amount of citric acid have great influence on the phase formation. The optimized calcination temperature and citric acid to metal nitrates molar ratio are 800℃and 4 respectively. The results of FT-IR is in accordance with that of XRD, indicating a characteristic K2NiF4 structure.SEM results show that the sample obtained is porous, and some particle agglomeration can be found in the photograph.PEG is used as dispersant in the synthesis of La1.8Sr0.2CuO4. XRD results show that the samples obtained are single mixed oxides without the presence of impure phase. The polemerization degree and amount of PEG have no effects on the phase formation of the samples, but play a significant role in the catalytic capability as well as specific surface area. With the increase in molecular weight of PEG, the specific surface area and oxidizing capacity of the sample decrease. TEM results show that the particle agglomeration of samples prepared in the presence of PEG is less seen compared with samples prepared without the dispersant. H2-TPR results demonstrate that the samples prepared in the presence of PEG have a better oxidizing capacity under low temperature than those without the dispersant.La2-xSrxCuO4(x=0-0.4) are prepared by Pechini method. The effects of the substitution amount "x" on the phase formation, specific surface area and catalytic capability are studied. XRD results show that when x>0, all the samples obtained is single-phase perovskite-like mixed oxides. Taking FT-IR analysis into consideration, it can be concluded that the crystal structure of the samples shift from orthorhombic to tetragonal. With the increase of x, the specific surface area of the samples increase and the catalytic performance of samples at low temperature have been improved, as shown in BET results and H2-TPR results respectively.La0.8Sr0.2O3 is synthesized by Pechini method. XRD patterns show that mixed oxides without impure phase can not be obtained under ambient conditions. It can also be seen from the XRD results and SEM photographs that the calcination temperature not only has great effects on the phase formation, but also influences the particle aggregation. H2-TPR results show that La1.8Sr0.2CuO4 has a better catalytic performance at low temperature when the structure of La0.8Sr0.2O3 has a higher stability at high temperature.