H. Falcon et al., Defect LaCuO3-delta (delta=0.05-0.45) perovskites - Bulk and surface structures and their relevance in CO oxidation, APP CATAL B, 26(2), 2000, pp. 131-142
Citations number
31
Categorie Soggetti
Physical Chemistry/Chemical Physics","Environmental Engineering & Energy
Polycrystalline LaCuO3-delta (delta=0.45, 0.35, 0.17 and 0.05) powders have
been prepared by a citrate technique followed by annealing under 200 bar O
-2 pressure at temperatures 1073-1273 K. The crystal structure of three sel
ected samples was refined by the Rietveld method from room temperature neut
ron powder diffraction data. Thermogravimetric analysis of the samples in a
H-2/N-2 Row allowed the determination of the oxygen nonstoichiometry. Thes
e TG profiles showed two clear reduction processes: the first one correspon
ds to a partial reduction to give intermediate perovskites and in the secon
d step the sample is completely reduced to Cu-0 and La2O3. However, surface
analysis of a representative sample (LaCuO2.55) revealed that at intermedi
ate reduction temperatures, a fraction of copper is already reduced to meta
llic state while the other fraction still contains Cu-III stabilized in the
lattice. These samples were tested in the catalytic oxidation of CO under
flow condition, and the intrinsic activity was found to depend strongly on
the oxygen nonstoichiometry. The increasing structural instability observed
in LaCuO3-delta phases as delta increases appears to be responsible for th
e enhancement of the catalytic properties of this perovskite based system.
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