Synthesis and catalytic properties of perovskite-related phases in the La–Sr–Co–Cu–Ru–O system
1996; Royal Society of Chemistry; Volume: 6; Issue: 1 Linguagem: Inglês
10.1039/jm9960600097
ISSN1364-5501
AutoresYasutake Teraoka, H. Nii, Shuichi Kagawa, Kjell Jansson, Mats Nygren,
Tópico(s)Catalytic Processes in Materials Science
ResumoA series of oxides of the composition La0.8Sr0.2Co1–2yCuyRuyO3 with the perovskite structure were synthesized and characterized by their X-ray diffraction (XRD) patterns and by element analysis in a transmission electron microscope (TEM) equipped with an energy-dispersive spectrometer (EDS). The XRD and TEM–EDS studies confirmed that almost monophasic samples with the perovskite structure having rhombohedral (hexagonal) symmetry were obtained for 0 ⩽y⩽ 0.20, although the simultaneous formation of a by product with the K2NiF4-type structure was observed for high y values. The lattice parameters and rhombohedral distortion increased monotonically with increasing y value due to the fact that the average ionic radius of the substituting Cu/Ru pair is larger than that of the host Co ion. Temperature-programmed desorption (TPD) studies showed that the substitution of the Cu/Ru pair for Co caused a decrease in the amount of oxygen desorbed from the bulk of the oxide, and the catalytic activity for CO oxidation and CO–NO reactions decreased. The Cu/Ru substitution did, however, selectivity increase the N2 formation and decreased that of N2O in the CO–NO reactions. Synthesis of K2NiF4-type oxides with the overall compositions (La0.8Sr0.2)2Co0.50Cu0.50–zRuzO4 with z= 0.05 and 0.10 was also attempted. In both cases, tetragonal K2NiF4-type oxides having a composition close to (La0.8Sr0.2)2(Co,Cu)0.97Ru0.03O4 were obtained, implying that the solubility of Ru into the given K2NiF4-type framework is very low.
Referência(s)