Supported bimetallic Pt-Au nanoparticles: Structural features predicted by molecular dynamics simulations

Abstract

We have utilized all-atom molecular dynamics simulations to study bimetallic Pt-Au nanoparticles supported by carbonaceous materials at 700 K. Nanoparticles containing 250 atoms with 25%, 50%, and 75% Pt (${\text{Pt}}_{62}{\text{Au}}_{188}$, ${\text{Pt}}_{125}{\text{Au}}_{125}$, and ${\text{Pt}}_{188}{\text{Au}}_{62}$, respectively) were considered. A single graphite sheet and bundles of seven (10,10), (13,13), and (20,20) single-walled carbon nanotubes were used as supports. It was found that ${\text{Pt}}_{125}{\text{Au}}_{125}$ forms a well-defined Pt core covered by an Au shell, regardless of the support. ${\text{Pt}}_{62}{\text{Au}}_{188}$ exhibits a mixed Pt-Au core with an Au shell. ${\text{Pt}}_{188}{\text{Au}}_{62}$ has a Pt core with a mixed Pt-Au shell. The support affects the atomic distribution. We investigated the percentage of nanoparticle surface atoms that are Pt. Our results show that for ${\text{Pt}}_{62}{\text{Au}}_{188}$ and ${\text{Pt}}_{125}{\text{Pt}}_{125}$, this percentage is lowest when there is no support and highest when carbon nanotubes are supports. We studied the size of clusters of Pt atoms on the nanoparticle surface, finding that the geometry of the support influences the distribution of cluster sizes. Finally, we found that the coordination states of the atoms on the nanoparticle surface are affected by the support structure. These results suggest that it is possible to tailor the distribution of atoms in Pt-Au nanoparticles by controlling the nanoparticle composition and the support geometry. Such level of control is desirable for improving selectivity of catalysts.