Interaction of CO with Structurally Well-Defined Monolayer PtAu/Pt(111) Surface Alloys

The adsorption properties of structurally well-defined bimetallic PtAu/Pt(111) monolayer surface alloys, with known lateral distribution of the respective surface species and varied Au surface contents, were studied by temperature-programmed desorption (TPD) and infrared reflection–absorption spectroscopy (IRAS), using CO as probe molecule. The surface composition and the lateral distribution of surface atoms in the PtAu/Pt(111) surface alloys were previously determined by high-resolution scanning tunneling microscopy (STM) [Bergbreiter, A.; et al. ChemPhysChem 2010, 11, 1505], showing a tendency for lateral segregation of both metals in the surface layer. CO adsorption on these surfaces is dominated by adsorption on Pt on-top sites; the fraction of bridge-bonded CO ad decays rapidly with increasing Au surface content and is completely absent for surfaces with 35% and more surface Au content. Adsorption on Au sites is negligible at 100 K. The roles of electronic ligand and strain effects and of geometric ensemble effects on the CO adsorption properties, including energetics, maximum CO ad coverage, vibrational properties, and adsorption kinetics, are mapped out and discussed. The results are compared with CO adsorption on comparable surface alloys such as PtAg/Pt(111), PdAu/Pd(111), and PdAg/Pd(111) as well as on the inverse system PtAu/Au(111).