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O: Fachverband Oberflächenphysik

O 100: Metal Substrates: Adsorption and Reactivity

O 100.2: Vortrag

Freitag, 20. März 2015, 10:45–11:00, MA 043

Oxygen dissociation and recombination on Au/Ag(110) thin film alloys — •Martin Schmid¹, Joshua E. Klobas², and Cynthia M. Friend² — ¹Fachbereich Chemie, Philipps Universität Marburg — ²Dpt. of Chemistry and Chemical Biology, Harvard University, Cambridge MA, USA

In order to gain insight into the fundamental processes on complex bimetallic catalysts, such as nanoporous gold or bimetallic AuAg nanoparticles, O₂ dissociation and recombination on Au/Ag(110) thin film alloys of various compositions were studied with Temperature-Programmed Desorption (TPD). An increasing gold content of the thin film alloys is associated with a linear decrease of the maximum oxygen uptake of the surfaces; the oxygen uptake is completely quenched at gold concentrations higher than 50%. A closer analysis of the TPD signals shows that there is no transfer of oxygen adatoms between Au and Ag sites and that the oxygen chemistry is, in general, dominated by the Ag sites on the alloy surfaces. Apart from passivating the surface against oxygen uptake, gold also leads to a reduction of the recombination temperature of oxygen adatoms by   20 K. These results indicate that there are at least two neighboring Ag atoms required to dissociate oxygen and demonstrate that gold efficiently lowers the amount of adsorbed oxygen and facilitates recombination and release of the remaining oxygen adatoms. The results provide a lower limit for the size of active groups of Ag atoms and show that the bond strength between surface and oxygen adatoms is influenced by the local Au:Ag stoichiometry.