Formation of a Surface–Sandwich Structure in Pd-Ni Nanoparticles by Interdiffusion: Atomistic Modelling

1. Introduction Bimetallic Pd-Ni nanoparticles are currently attracting a great deal of interest due to their physical and chemical properties, which are determined by their size, shape, structure and composition. In particular, it is well-known that Pd is a metal with important existing and potential applications as a catalyst in heterogeneous catalysis. The use of Pd as a single active metal component in catalysis has received considerable attention on the basis of its remarkable activity for oxidation reactions and the availability of cleaner fuels, but at the same time it has negative economical aspects due to its high cost [1]. An interesting approach in these respects consists of alloying Pd with lower cost and higher surface energy metals, since it would be economically attractive to design bimetallic catalyst nanoparticles in which the precious and catalytic Pd atoms segregate to the surface. Promising results in this sense have been obtained by using Ni [1-3]. Understanding and controlling of the atomic structure of alloy nanoparticles are important in both fundamental science and technological applications. Atomistic simulation techniques such as molecular dynamics (MD) have become a powerful tool in the field of nanotechnology by providing physical insight in understanding phenomena on an atomic scale and predicting many of the properties of nanomaterials. In the present study, long–time scale molecular dynamics simulation in combination with the embedded atom method is used to investigate the effect of surface segregation phenomena on the atomic structure of Pd alloy nanoparticles (of diameter of ∼ 4.5 nm) containing ∼ 30 at. % Ni.