An amorphous approach to the structure of a Pt–Fe/γ-Al2O3catalyst characterized by XAFS

Abstract

A Pt–Fe/γ-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 Å, respectively, are found for each Pt atom on Pt/γ-Al₂O₃. However, only one type of Pt neighbor, at 2.75 Å 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 γ-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.