Structural and electronic properties of PtPd and PtNi nanoalloys

The lowest-energy structures of binary (PtPd) n , (PtNi) m , (PtNi 3 ) s , and (Pt 3 Ni) s nanoclusters, with n=2–28, m=2–20, and s=4–6, modeled by the many-body Gupta potential, were obtained by using a genetic-symbiotic algorithm. These structures were further relaxed within the density functional theory framework in order to obtain the most stable structures for each composition. Segregation is confirmed in all the (PtPd) n clusters, where the Pt atoms occupy the cluster core and the Pd atoms are situated on the cluster surface. In contrast, for the (PtNi) m nanoalloys, the Ni atoms are mainly found in the cluster core and the Pt atoms are segregated to the cluster surface. Likewise, for the (PtNi 3 ) s nanoalloys, Ni atoms mainly compose the cluster core but there is no clear segregation of the Pt atoms to the surface. Furthermore, for the (Pt 3 Ni) s bimetallic clusters the Pt atoms concentrate in the cluster core and the Ni atoms are segregated to the surface. On the other hand, it has been experimentally found that the Pt 0.75 Ni 0.25 supported nanoparticles present a higher catalytic activity for the selective oxidation of CO in the presence of hydrogen than the Pt 0.5 Ni 0.5 and Pt 0.25 Ni 0.75 nanoparticles. In order to understand this tendency in the catalytic activity, we also performed density functional calculations of the molecular CO adsorption on bimetallic Pt-Ni nanoclusters with the mentioned compositions.