Adsorption of Rh, Pd, Ir, and Pt on the Au(111) and Cu(111) Surfaces: A Density Functional Theory Investigation

作者：Freire Rafael L H^*; Kiejna Adam; Da Silva Juarez L F

来源：Journal of Physical Chemistry C, 2014, 118(33): 19051-19061.

DOI：10.1021/jp5033228

Several experimental and theoretical studies have suggested that the formation of surface alloys or the deposition of strained transition metal (TM) monolayers (ML) on TM supports can be considered as a route for the designing of new catalysts. In this work, we report an extensive first-principles investigation based on density functional theory of the adsorption of TM (Rh, Pd, Ir, Pt) on the Cu(111) and Au(111) surfaces considering TM coverages ranging from 1/9, 2/9, up to 1 ML. Although there are clear differences in the atomic radii of the Cu, Rh, Pd, Ir, Pt, and Au atoms, at low TM coverages, both systems exhibit similar behavior, namely, the lowest energy adsorption site for a single TM adatom is not in the hollow sites on the surface, but in the lattice sites located in the topmost layer. For TM/Au(111), this trend follows adatom by adatom up to the limit in which all the substrate Au atoms are exposed to the vacuum region, with the underlying TM adatoms, and it is also valid for Rh/Cu(111). For Pd, Ir, and Pt on Cu( iii), the same trend is observed up to 4/9, 8/9, and 6/9 TM coverages, and the adatoms are exposed to the vacuum region for higher coverages. For TM/Au(111), our analyses indicate a tensile strain built-in due to the mixture of adatoms with smaller radii with Au with a larger radius in the same first (topmost) surface layer, while a compressive strain can be seen for TM/Cu(111), in particular for Pd, Ir, and Pt at high coverages, which favors the location of the TM adatoms on Cu(111). Judging by the Pauling electronegativity scale, we would expect a different behavior for the substrate work function change upon TM adsorption on Cu(111) and Au(111). However, a similar behavior was obtained for the lowest energy configurations on both substrates. This is rationalized in terms of the electronegativity differences, geometrical effect of atomic smoothing, the insertion of the adatoms in the first (topmost) surface layer, and the exposed layer to the vacuum region.

• 出版日期2014-8-21