Structural and chemical properties of Pt-rich Pt_xZr_y nanoalloys

Density functional theory (DFT) simulations have been performed to study the structure and physico-chemical properties of bimetallic Pt_xZr_y 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.