Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.