Preparation and Application of Metallic Oxide Clusters in Zeolite Catalysts

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Catalytically active species of metallic oxide clusters in Cu-Y and Pd-Y zeolite crystals has been studied by means of kinetic and spectroscopic investigations. Active species were formed by R-O treatment consisted of preliminary thermal treatment, reduction with hydrogen and reoxidation with oxygen. Formation of active species in both zeolites was clearly demonstrated by a temperature-programmed reduction (TPR) and strongly depended on the conditions of each step in R-O treatment.With the increase in amount of the active species estimated by the TPR spectra, the catalytic activity of the zeolites in CO oxidation at low temperatures increased proportionally, whereas the activation energies remained unchanged. These observations suggest that the active species are catalytic centers which properties are virtually independent of the density on the surfaces.According to the results in the detailed analysis of extended X-ray absorption fine structure (EXAFS) data for Cu-Y and Pd-Y zeolites, on the other hand, the active species were determined to be CuO and PdO with 4 - 6 A^^ﾟ of diameter, respectively, which were consisted of several atoms. In the catalytic oxidation of CO with O_2 at low temperatures, the active species function as the catalytic centers via the reversible redox mechanism.