Structural and chemical properties of Pt-rich PtxZry nanoalloys

Abstract

Density functional theory (DFT) simulations have been performed to study the structure and physico-chemical properties of bimetallic PtxZry nanoclusters, for stoichiometries rich in platinum, and sizes ranging from Pt3Zr to Pt72Zr24. For each cluster, the search for the most stable structural conformations was performed using a mixed approach where a family of stable isomers was first determined by means of a genetic algorithm based on a modified Sutton–Chen semiempirical potential; subsequently, that family of conformations was relaxed by performing DFT calculations. This procedure results in cluster geometries which reproduce reasonably well the ordering and atomic packing present in the bulk Pt–Zr alloys. The binding energies and electronic structures were studied as a function of both stoichiometry and cluster size; as a result, we identified some clusters with enhanced stability, such as Pt5Zr2 or Pt9Zr3. The analysis of the densities of states and local reactivity indicators highlights the strong intermetallic character of the Pt–Zr bonding, with large charge transfer from Zr to Pt atoms. The Pt–Zr interaction also induces a sizable weakening of the ability of Pt sites to bind CO, making these bimetallic clusters less sensitive to poisoning by carbon monoxide.