THE OXYGEN MOBILITY AND CATALYTIC ACTIVITY OF LaMO 3 ±• (M=Cr, Mn, Co) PHASES. I.A. KOUDRIASHOV*, L.V. BOROVSKIKH*, G.N. MAZO*, S. SCHEURELL**, E. KEMNITZ** *Moscow State University, Chemistry Department, Moscow, Russia "Humboldt University, Institute of Inorganic Chemistry, Berlin, Germany ABSTRACT The activity of LaMO 3 , where M=Cr, Mn, Co, perovskite-type complex oxides in oxygen diffusion and catalytic processes was investigated. For sample preparation freeze-drying technique was used and dynamic thermal isotope exchange method was used to study exchange reaction between 180 from the gas phase and 160 from the samples synthesized, and to investigate the methane catalytic oxidation reaction. The results obtained allowed to indicate temperature intervals of different types of reaction taking place and that LaCrO 3 is far less active in mentioned reactions than LaCoO 3 and LaMnO 3 . INTRODUCTION Highly defective nonstoichiometric perovskite-like complex oxides of 3d-transition elements are promising objects for elaboration of multi-functional materials. The compounds of the general formula Lal.xSrxM0 3 , where M=Mn, Co, Cr, are interesting because of their unusual physical properties (e.g. CMR-effect for manganites [1,2], metal-insulator transition for cobaltates [3-6], etc.). These compounds are of interest as catalysts of different redox reactions [7-9], as the activation energies of oxygen diffusion are rather low, but the question about the role of solid phase oxygen in catalytic processes is not completely solved yet. The results of studies of catalytic properties are not in good agreement with each other, as in a number of works concerning the problem amorphous [10] or containing impurities [9] samples were investigated. The reaction of isotope exchange between oxygen molecules 3202 and 3602 occurring in the presence of a solid oxide phase can be considered the simplest catalytic reaction with oxygen participation [11]. From the course of the oxygen exchange reaction, conclusions can be drawn about the way in which oxygen takes part in the catalytic process [12]. In this work, the mobility of oxygen in multicomponent oxides was studied by the dynamic-thermal isotope exchange method, which made it possible to determine the temperature intervals of the occurrence and the characteristics of various processes in the oxygen-solid system. The purpose of this work was to investigate oxygen mobility in the LaCrO 3 , LaMnO 3 , and LaCoO 3 , phases and its correlation with the catalytic activity of these phases in the oxidation of CH4. EXPERIMENT In order to obtain samples with a high surface area, the freeze-drying method was used. The method allows preparing substances with a high level of homogeneity in cation distribution at rather low temperatures [8,13]. The freeze-drying precursors obtained from solutions of nitrates of the appropriate cations were heated up to 773K at 0,5 K/min and annealed for 20h at that temperature. Then the powders synthesized were fired at 873K, 973K, 1073K with intermediate grindings. The whole firing time was 80h. When preparing LaCrO 3 , we also used additional sintering at 1173K and 1273K, for this sample, the time of synthesis was 120h. 377 Mat. Res. Soc. Symp. Proc. Vol. 602 0 2000 Materials Research Society