Regensburg 2016 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 26: Poster session II

MM 26.34: Poster

Dienstag, 8. März 2016, 18:30–20:30, Poster B3

Quantum mechanically based prediction of surface segregation in Ag-Au alloys — •Sandra Hoppe and Stefan Müller — Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany

Nanoporous gold (npAu) offers a high catalytic activity for certain chemical reactions combined with a high selectivity. This phenomenon can theoretically be explained in two ways: First, the rough morphology provides a large number of low-coordinated Au atoms. Second, Ag impurities remaining from the dealloying process may supply reaction sites. Interestingly, Au (111) surfaces roughened by sputtering have been found inactive towards CO-oxidation [1]. Previous density functional theory (DFT) results imply that Ag impurities in the surface dissociate molecular O₂ and supply O atoms [2]. Experimental results show that the catalytic activity of npAu can be tailored via the residual Ag concentration. The aim of this work is to characterize clean Ag-Au surfaces regarding their segregation profile. DFT calculations serve as input for a surface cluster expansion (CE). We find that the resulting surface composition depends strongly on the applied exchange correlation functional. To obtain Ag enrichment in the surface layer, as it has been observed in experimental and theoretical studies [3], it seems necessary that both the lattice parameters and the surface energies of the pure elements are calculated in the correct hierarchy.

[1] J. Gong et al.. J. Phys. Chem. C 112 (2008) 5501.
[2] L. V. Moskaleva et al.. Phys. Chem. Chem. Phys. 13 (2011) 4529.
[3] e.g. T. Déronzier et al.. J. Catal. 311 (2014) 221.