Molecular dynamics simulations are used to study CO adsorption on Ag nanoclusters ranging from 38 to 500 Ag atoms, supported on carbon nanotube. Each nanocluster was simulated under various pressures of CO gas at different temperatures. The absolute value of enthalpy of adsorption was calculated for all of the nanoclusters in constant coverage which is increased sharply by decreasing cluster size. This increasing trend with coverage reaches a maximum around 0.75 ML for Ag 108 . Also, the structural changes are irreversible in such a way that by gradually decreasing the pressure to zero, the nanocluster geometry is not reversed to its initial structure in vacuum conditions. It was found that structural irreversibility increases with the size. Also, the difference between diffusivity of Ag nanoclusters in vacuum and CO atmosphere increases with the size.
The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a first-principles atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the Pt/vacancy interaction or destabilizing close to a perfect Pt(core)/Ag(shell) arrangement. It is found that alloying with Pt appreciably increases the barriers for homotops transformations, thus rationalizing the issues encountered at the experimental level in producing Ag-Pt equilibrated nanoparticles and bulk phase diagram.
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