OP-II-3

PP-I-44HIGH TEMPERATURE OXYGEN TRANSPORT IN MIXED OXIDESWITH STRUCTURE OF FLUORITE AND PEROVSKITE. EFFECT OFOXYGEN MOBILITY ON CATALYTIC PROPERTIES IN THEREACTIONS WITH OXYGEN PARTICIPATIONPinaeva L.G., Sadovskaya E.M., Ivanov D.V., Isupova L.A.Boreskov Institute of Catalysis SB RAS, pr. Lavrentieva, 5, 630090, Novosibirsk,Russia, e-mail: pinaeva@catalysis.ruMixed oxides with structure of fluorite or perovskite constitute a broad class of thecatalysts for high temperature processes with oxygen participation. It is commonlyconsidered that their activity in the reactions of hydrocarbons oxidation is due to highlattice oxygen mobility. Nevertheless, until now no direct correlation between the reactionrate and the coefficient of oxygen diffusion as measured in the close conditions wasreported. As to other reactions, the nature of the factors determining their activity is stillopen. Present study was focused on elucidation of the mechanism of oxygen transportin the La-Sr-(Mn,Fe)-O and Ce-Zr-(La)O mixed oxides and possible relationshipsbetween oxygen mobility and catalytic activity in the reactions of methane and ammoniaoxidation, nitrous oxide decomposition and CO water gas shift.Transient experiments on the interaction of the reaction mixture with the catalystsunambiguously showed that it is the lattice oxygen that is included into reactionproducts at methane oxidation and CO water gas shift. The same conclusion for thereaction of N 2 O decomposition followed from the dynamics of labeled oxygen ( 18 O)transfer from the catalyst to gas phase products.Investigation of the kinetics of isotope exchange between 18 O 2 and mixed oxidesin the temperature range 600÷900°C showed that the sharp increase of both the rateof oxygen exchange on the surface and the oxygen diffusion in the bulk can be dueto appearance of fast pathway of oxygen transfer through defects (Fig.1). Forperovskites, these defects include both isolated and ordered in the lanthanide planesoxygen vacancies that are formed in the lattice to compensate the reduced cationcharge at Sr substitution for La. Developed network of domain boundariesdetermines high rate of oxygen exchange in the fluorites. Supporting of Pt clustersadditionally increases the oxygen mobility due to fast oxygen transfer from Pt tosupport (characteristic time < 10 –2 s) and formation of oxygen vacancies originatedfrom the incorporation of highly dispersed Pt atoms into the mixed oxide latticethrough the domain boundaries.299