Reactivity of oxygen of complex cobaltates La1-xSrxCoO3-δ and LaSrCoO4

Complex oxides La1-xSrxCoO3-delta (x = 0.0, 0.3, 0.5) with perovskite-like structure and LaSrCoO4 with layered K2NiF4-type structure have been prepared using freeze-drying technique. The oxygen content of the single-phase samples was determined by iodometric titration. The oxygen mobility and catalytic activity of all cobaltate samples in the reaction of CH4 oxidation were studied under dynamic-thermal O-18-isotope exchange conditions. Catalytic reactions of CH4 and CO oxidation have also been performed under steady flow conditions. The correlations between oxygen mobility and structural features of the catalyst and its initial oxygen deficiency has been established. La0.5Sr0.5CoO2.92 and La0.7Sr0.3CoO2.96 with deficiency in oxygen sublattice were more active in isotope exchange and catalysis, while LaCoO3 and LaSrCoO4 with the stoichiometric oxygen content demonstrated lower activity. The mobility of oxygen in layered LaSrCoO4 is significantly higher than in LaCoO3. Analysis of the methane oxidation using O-18 O-18 allowed to clarify the steps of the catalytic process. It was found also that methane is oxidized by the lattice oxygen of the catalyst. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.