Intermetallic Compounds as an Alternative to Single-atom Alloy Catalysts: Geometric and Electronic Structures from Advanced X-ray Spectroscopies and Computational Studies

Pt-Fe intermetallic compound (IMC) catalysts, including Pt3Fe, PtFe and PtFe3, are shown to have advantageous catalytic properties similar to those reported for single-atom alloy catalysts. Suppresion of the Pt ensembles responsible for hydrogenolysis results in high olefin selectivity during propane dehydrogenation. In situ resonant inelastic X-ray scattering (RIXS) results and density functional theory calculations show that these changes are associated with a decrease in the average energy of the filled 5d states of Pt in the Pt-Fe intermetallic compound structures compared to monometallic Pt, accompanied by an increase in the average energy of the unfilled valence bands. The decrease in energy of the filled Pt 5d orbitals increases with increasing Fe content in the IMC, i.e. PtFe3>PtFe>Pt3Fe. These results demonstrate that by altering the stoichiometry of IMC catalysts it is possible to control both the ensemble size and electronic properties of active sites, which affords another mechanism for tuning catalytic properties, in addition to changing promoter metals. The present study demonstrates the potential of ordered intermetallic compounds as an alternative to traditional solid-solution single-atom alloys to serve as catalysts with well-defined and uniform active sites.