One of the goals of nanoscience is the fundamental understanding of the catalytic properties of materials. Accordingly, a wealth of experimental and theoretical studies has been dedicated to the investigation of the interaction of adsorbates with well-defined low-indexed metal surfaces. However, the catalytic particles used in industrial processes are often applied as small clusters, which have unique electronic properties. Therefore the knowledge of the morphology of the particles is a crucial prerequisite for a realistic description. Furthermore, the shape of the particles will be changed by the interaction with the surrounding gas, especially for reactive adsorbates such as oxygen. Although the typical size of these particles is too large to allow for atomistic modelling, their equilibrium shape can be estimated from the respective Gibbs free surface energies.
Therefore the adsorption of oxygen has been studied on the low-indexed (111), (100), (110) and the stepped (331), (311) and (211) surfaces of selected late transition metals, that is rhodium, palladium and silver. The calculations have been performed with the Vienna ab-initio simulation package (VASP), using PAW potentials and the gradient corrected PBE functional. The adsorption energies at various oxygen coverages give access to the minimal Gibbs free surface energy for each surface orientation. This quantity in turn can be used for the construction of the equilibrium shape of the nanoparticle depending on the chemical potential of oxygen. Common trends in the morphological changes of the different metals will be presented. |