Correlation of Oxidation States in LaFexNi1-xO3+δ Oxides with Catalytic Activity for H2O2 Decomposition

• Published in: Journal of catalysis Vol. 203; no. 2; pp. 264 - 272
• Main Authors: Falcón, H, Carbonio, R.E, Fierro, J.L.G
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 25.10.2001; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; compensation effect; Exact sciences and technology; General and physical chemistry; H2O2 decomposition; LaFexNi1−xO3 perovskites; oxygen nonstoichiometry; temperature-programmed reduction; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; compensation effect; temperature-programmed reduction; LaFexNi1−xO3 perovskites; H2O2 decomposition; oxygen nonstoichiometry; Scanning electron microscopy; Catalytic reaction; Perovskite type compound; Nickel Oxides; Lanthanum Oxides; Hydrogen Peroxides; Chemical reduction; Programmed temperature; Heterogeneous catalysis; Iron Oxides; Quaternary compound; Valence; Non stoichiometric compound; Chemical decomposition; Catalyst activity
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.2001.3351

Mixed oxides of the type LaFexNi1−xO3 with a perovskite structure were prepared by thermal decomposition of citrate mixtures at temperatures ranging from 773 to 1373 K. Temperature-programmed reduction profiles showed a low temperature step (450–500 K) due to the reduction of Ni3+ to Ni2+ and a high temperature step (650–1170 K) associated with the reduction of Ni2+ to Ni0 and Fe3+ to Fe0. From the microgravimetric reduction profiles it was established that the samples exhibit oxidative nonstoichiometry LaFexNi1−xO3+δ with δ=0.00–0.08. All the catalysts were tested in the heterogeneous decomposition of hydrogen peroxide (H2O2→H2O+1/2 O2) in alkaline medium. It was found that the active sites for the reaction are the highly oxidized transition metals (NiIII and FeIV). The concentration of these sites, as determined by iodometric titration, varied with catalyst composition and also with the calcination temperature of the precursors. The compensation effect was observed in all the catalysts investigated for hydrogen peroxide decomposition. The appearance of this effect was interpreted in terms of the catalytic reaction occurring on a heterogeneous catalytic surface, that is, a surface with active sites bearing different activation energies.