Pd Single-Atom Sites on the Surface of PdAu Nanoparticles: A DFT-Based Topological Search for Suitable Compositions

Abstract

Structure of model bimetallic PdAu nanoparticles is analyzed aiming to find Pd:Au ratios optimal for existence of Pd1 single-atom surface sites inside outer Au atomic shell. The analysis is performed using density-functional theory (DFT) calculations and topological approach based on DFT-parameterized topological energy expression. The number of the surface Pd1 sites in the absence of adsorbates is calculated as a function of Pd concentration inside the particles. At low Pd contents none of the Pd atoms emerge on the surface in the lowest-energy chemical orderings. However, surface Pd1 sites become stable, when Pd content inside a Pd-Au particle reaches ca. 60%. Further Pd content increase up to almost pure Pd core is accompanied by increased concentration of surface Pd atoms, mostly as Pd1 sites, although larger Pd ensembles as dimers and linear trimers are formed as well. Analysis of the chemical orderings inside PdAu nanoparticles at different Pd contents revealed that enrichment of the subsurface shell by Pd with predominant occupation of its edge positions precedes emergence of Pd surface species.

Chemical ordering in Pt–Au, Pt–Ag and Pt–Cu nanoparticles from density functional calculations using a topological approach

“…Pd-Au, [13][14][15]17 Pd-Ag, 14 Pd-Cu, 14 Pd-Zn, 14 Pd-Rh, 16 Pt-Ag, 18 Pt-Co, 19,20 Pt-Ni, 21 Pt-Sn, 22 and Ni-Cu, 23 revealed efficiency and broad applicability of the TOP method. This study deals with bimetallic nanoalloys of essential for catalysis metal Pt with quite inert coinage metals Au, Ag, and Cu.…”

“…Such emergence of surface Pd atoms is triggered by stabilizing Pd-Au bonds reflected in negative energies for Pd-Au NPs. [13][14][15]17 Pd -Au BOND According to (Table 1), heterometallic bonds of Pt are stabilizing neither in Pt-Au, nor…”

Hydrogen-Driven Surface Segregation in Pd Alloys from Atomic-Scale Simulations

“…Understanding the segregation behavior in different atmospheres is thus crucial to obtain sensors that are not only functional but also sustain long-term operation. Surface segregation in binary systems has been studied extensively with experimental and computational methods for the past decades, in particular under vacuum conditions, and it is known that adsorbates can have a substantial impact on the segregation behavior. ,− Generally, it is found that Au segregates to the surface relative to Pd in vacuum − and that Pd segregates to the surface relative to Au and Cu in a hydrogen environment . There is less of a consensus regarding CuPd in vacuum, and different segregation behaviors have been suggested. ,,,− …”

AgPd, AuPd, and AuPt Nanoalloys with Ag- or Au-Rich Compositions: Modeling Chemical Ordering and Optical Properties

“… 4 , 11 , 33 , 34 Very recently, critical compositions of AuPd NPs have been established, at which single-surface Pd atoms are stabilized inside the monatomic Au skin. 35 Interestingly, a variety of different structures have been observed experimentally. 36 − 38 …”

“…The miscibility of the two components was evidenced by calorimetric measures of the enthalpy of mixing, which assumes negative values for all compositions. Theoretical studies predicted the Au-shell/Pd-core structure as the most thermodynamically stable in NPs of various sizes and compositions. ,,, Very recently, critical compositions of AuPd NPs have been established, at which single-surface Pd atoms are stabilized inside the monatomic Au skin . Interestingly, a variety of different structures have been observed experimentally. − …”