Reactivity of oxygen of complex cobaltates La 1− xSr xCoO 3− δ and LaSrCoO 4

Abstract

Complex oxides La 1− x Sr x CoO 3− δ ( x=0.0, 0.3, 0.5) with perovskite-like structure and LaSrCoO 4 with layered K 2NiF 4-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 CH 4 oxidation were studied under dynamic-thermal 18O-isotope exchange conditions. Catalytic reactions of CH 4 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. La 0.5Sr 0.5CoO 2.92 and La 0.7Sr 0.3CoO 2.96 with deficiency in oxygen sublattice were more active in isotope exchange and catalysis, while LaCoO 3 and LaSrCoO 4 with the stoichiometric oxygen content demonstrated lower activity. The mobility of oxygen in layered LaSrCoO 4 is significantly higher than in LaCoO 3. Analysis of the methane oxidation using 18O 18O allowed to clarify the steps of the catalytic process. It was found also that methane is oxidized by the lattice oxygen of the catalyst.