Figure 7.

Conditions for existence of Pd surface species on the surface of PdAu truncated-octahedral NPs with a given Pd:Au ratio and diameter D, nm (the upper scale shows also the NP nuclearity, n). The solid line (circles) corresponds to Pd concentration ${\rho }_{core}^{Pd}=0.6$ in the core covered with Au shell (${\theta }_{terrace}^{Pd}=0$). With the increase of ${\rho }_{core}^{Pd}$ above this line, Pd1 monomers and ensembles become stable on the surface of NPs (${\theta }_{terrace}^{Pd}>0$); below is the region with Pd fraction residing inside the core surrounded by the purely Au shell. The dashed line (diamonds) corresponds to ${\rho }_{core}^{Pd}=0.25$, where a bulk-like PdAu₃ ordering is expected. Below this line, $0<{\rho }_{core}^{Pd}<0.25$, Pd fraction is distributed in the form of single Pd atoms in the core of NPs.