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-and Fe K-edge X-ray absorption fine structure (XAFS). X-Ray absorption near-edge structure (XANES) clearly indicates the formation of highly dispersed zerovalent 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. However, 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 approach to rationalizing a possible structure of Pt-Fe/Al2O3 has been discussed at the atomic level by consideration of the surface coordinate geometry. The XAFS-derived parameters are highly commensurate with a sandwich model. An iron oxide phase with the stoichiometry Fe17O19 is present as an interface between Pt and gamma -Al2O3 while zerovalent Pt atoms are randomly distributed on the iron oxide surface as a mixture of monomers, dimers and trimers, well separated from each other