Hamburg 2001 – scientific programme
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O: Oberflächenphysik
O 10: Adsorption an Oberfl
ächen (I)
O 10.11: Talk
Monday, March 26, 2001, 18:45–19:00, C
Ensemble effects and site selective adsorption on bimetallic PdAu surfaces — •P. Liu1, N. Takehiro2, R.J. Behm2, and J.K. Norkov1 — 1Dept. Physics, Techn. Univ. of Denmark, DK-2800 Lyngby — 2Abt. Oberflächenchemie und Katalyse, Univ. Ulm, D-89069 Ulm
Bimetallic catalysts have been investigated extensively because of their often superior performance. Mechanistic aspects and the physical origin for the improved performance, however, are still unclear and under debate. We present results of a combined theoretical and experimental model study on CO and H adsorption on atomic scale defined, bimetallic PdAu surfaces. The surfaces were prepared by Au depositon on Pd(111) and subsequent annealing, and characterized with respect to the concentration and arrangement of the Pd and Au surface atoms by high reolution STM with chemical contrast. Comparitive HREELS and TPD measurements at different Pd surface concentrations allow the experimental determination of vibrational properties and adsorption energies for different ensembles, up to Pd tetramers. Comparison with LDA calculations for CO and H adsorption on model surfaces with different ensembles yields excellent agreement with experimental adsorption energies for a number of different ensembles, and allow a quantitative understanding of the underlying physical effects.