Pt80fe20 surface from first principles: Electronic structure and adsorption of CO and atomic H

The electronic structure and the local adsorption properties of the Pt80Fe20 (111) alloy surface have been theoretically studied in comparison to a pure Pt (111) surface in the framework of spin-density-functional theory. Pt-based alloys are important catalysts for the production of unsaturated alcohols. According to several experimental determinations of the surface composition, the surface is modeled by a Pt3Fe bulk alloy terminated by a single layer of pure Pt. Test adsorbates are CO and atomic hydrogen. Iron atoms bond strongly to neighboring Pt atoms, thereby shifting their d bands toward higher binding energies and reducing their chemical reactivity. The site dependence of those effects could be resolved by evaluating the partial densities of states of individual d-band orbitals. Though only iron atoms carry a magnetic moment, spin polarization is qualitatively important. In a second step we investigated the influence of iron atoms in the surface layer, using Pt3Fe (111) as a test surface. Here an additional effect of local strain adds to the electronic changes through heteroatomic bonds.