Pd Segregation on the Surface of Bimetallic PdAu Nanoparticles Induced by Low Coverage of Adsorbed CO

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For bimetallic Pd–Au/HOPG model catalysts, reversible enrichment of the surface by Pd under CO oxidation conditions was found using a near-ambient pressure X-ray photoelectron spectroscopy technique. Density functional calculations combined with calculations using the topological energy expression method were applied to reveal the mechanism of this phenomenon and to quantify the stability of different arrangements of metal atoms in bimetallic PdAu nanoparticles in the presence of CO adsorbate. According to results of this computational approach, adsorption of CO already at a rather moderate coverage is sufficient to make energetically feasible segregation of Pd at terraces of PdAu nanoparticles similar in size with experimentally studied ones.