PREPARATION AND CHARACTERIZATION OF LAMN1-XCUXO3+LAMBDA PEROVSKITE OXIDES

Compounds of nominal composition LaMn1-xCux03+λ, (0 {precedes above single-line equals sign} × {precedes above single-line equals sign} 1) have been prepared and characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). Substitution of manganese by copper up to x = 0.6 preserves the perovskite structure. For x = 0.8, in addition to the perovskite, La2CuO4 and CuO were formed. For x = 1, the only phases present were La2CuO4 and CuO. The perovskites showed oxidative nonstoichiometry for x {precedes above single-line equals sign} 0.4 and reductive nonstoichiometry for x = 0.6. Stoichiometry was reached for x = 0.5. XPS results for LaMn0.6Cu0.4O3+λ reduced at 473-753 K are indicative of sintering of the copper particles when reduction is effected above 673 K. The TPR curve for LaMnO3+λ showed an inflection point at ca. 0.5 e- per molecule which nearly corresponds to reduction of the estimated oxygen excess in the sample. Samples with substitutions 0 {precedes above single-line equals sign} × {precedes above single-line equals sign} 0.6 showed two reduction steps of Cu2+ to Cu0 and of Mnn+ (n {succeeds above single-line equals sign} 3) to Mn2+. In the fully substituted sample (x = 1) reduction of CuO and reduction of La2CuO4 can be clearly distinguished. Reduction of perovskites of low copper content (x < 0.5) at 673 K or below yielded highly dispersed copper catalysts. © 1990.