CATION/ANION MODIFIED CERIA-ZIRCONIA SOLID SOLUTIONS PROMOTED BY Pt AS CATALYSTS OF METHANE OXIDATION INTO SYNGAS BY WATER IN REVERSIBLE REDOX CYCLES

Ca and/or F-modified fluorite-like Ce-Zr-mixed oxides have been prepared by Pechinis method. The bulk structure of samples was characterized by XRD, EXAFS and FTIRS of the lattice modes. The surface properties were studied by SIMS and FTIRS of adsorbed CO and surface hydroxyls. The specific reactivity of the surface oxygen, its amount, coefficients of bulk and near-surface diffusion, as dependent upon the sample composition and temperature, were estimated using sample reduction by CO in the pulse/flow mode. Insertion of fluorine into the lattice results in decreasing the degree of oxygen polyhedra distortion, thus decreasing the amount of reactive oxygen and diffusion coefficients. Calcium and Pt addition counteracts this effect. At 500^oC for Pt-supported Ce-Zr-O samples including those modified by Ca and F, the lattice oxygen is easily removed by methane generating CO and hydrogen with high selectivity. Reoxidation of reduced samples by water or carbon dioxide at the same temperature restores the oxygen capacity producing more hydrogen or carbon monoxide.