An amorphous approach to the structure of a Pt-Fe/gamma-Al2O3 catalyst characterized by XAFS

A Pt-Fe/gamma -Al2O3 catalyst has been investigated by means of Pt L-III-an d Fe K-edge X-ray absorption fine structure (XAFS). X-Ray absorption near-e dge structure (XANES) clearly indicates the formation of highly dispersed z erovalent Pt atoms on the surface after reduction. The iron precursor Fe2O3 is reduced to well-dispersed FeO. Six Pt neighbors at 2.72, 3.14 and 3.83 Angstrom, respectively, are found for each Pt atom on Pt/gamma -Al2O3. Howe ver, only one type of Pt neighbor, at 2.75 Angstrom with a low coordination number of 0.8, is detected for the Pt sites on Pt-Fe/Al2O3. An amorphous a pproach to rationalizing a possible structure of Pt-Fe/Al2O3 has been discu ssed at the atomic level by consideration of the surface coordinate geometr y. The XAFS-derived parameters are highly commensurate with a sandwich mode l. An iron oxide phase with the stoichiometry Fe17O19 is present as an inte rface between Pt and gamma -Al2O3 while zerovalent Pt atoms are randomly di stributed on the iron oxide surface as a mixture of monomers, dimers and tr imers, well separated from each other.