POLARIZED TOTAL-REFLECTION FLUORESCENCE EXAFS STUDY OF ANISOTROPIC STRUCTURE-ANALYSIS FOR CO OXIDES ON ALPHA-AL2O3 (0001) AS MODEL SURFACES FOR ACTIVE OXIDATION CATALYSTS

An in situ Polarized Total-Reflection Fluorescence Extended X-ray Absorption Fine Structure (PTRF-EXAFS) technique was developed to analyze anisotropic structures of metal sites on surfaces. The PTRF-EXAFS can provide structural information in two different directions, separately, parallel (s-polarization) and normal (p-polarization) to the support surface. This technique was used to analyze the anisotropic structures of two kinds of Cooxides on α-A12O3 (0001) which were derived from Co2(CO)8 and α-Al2O3 (0001). The Co-oxides on α-A12O3 (0001) are regarded as model surfaces of Co-oxide catalysts supported on α-A12O3 active for CO oxidation. The s- and p-polarized EXAFS analysis revealed that after contact of Co2(CO)8 with α-Al2O3 (0001), followed by oxidation with O2 at 300K, Co atoms occupied the threefold hollow sites of α-A12O3 (0001) as monomers (CoO = 0.208 nm). By oxidation at 873 K, the Co monomers aggregated to form small spinel-like particles [Co3O4]n with ca. 0.9 nm dimension. The anisotropic structure analysis shows that the particles of seven layers grew with the spinel (001) plane parallel to the α-A12O3 (0001) plane. © 1994 Academic Press, Inc.