Active Alloying of Au with Pt in Nanoclusters Supported on a Thin Film of Al₂O₃/NiAl(100)

Abstract

Self-organized alloying of Au with Pt in nanoclusters on a thin film of Al 2 O 3 /NiAl(100) is active at 300 K, toward a preferred bimetallic structure. The photoelectron spectra of Au nanoclusters (diameter 1.0-3.0 nm and height 0.2-1.0 nm) formed from vapor deposition on thin-film Al 2 O 3 /NiAl(100) show that the binding energy (BE) of Au 4f 7/2 decreases from 85.3 ( 0.1 eV upon incorporating subsequently deposited Pt, and saturates near 84.3 ( 0.1 eV with increasing Pt deposition; the line width decreases simultaneously from 1.9 ( 0.1 eV to a minimum near 1.1 eV. The same minimal BE and line width for Au 4f are observed on both deposition of the metals in the reverse order (first Pt and then Au) and with concurrent deposition of Au and Pt. The significant BE shift indicates increased screening, attributed on the basis of the density-functional calculations primarily to the increased coordination number of the alloying Au atom and secondarily to the charge transfer from Pt to Au; the narrowing of the spectral line reflects improved structural order of the clusters, which is corroborated by the diffraction measurements, and enhanced uniformity of the chemical environment around each Au atom. We argue accordingly that the alloying clusters form preferentially either an Au core-Pt shell structure or an Au-Pt intermixed structure with no Au exposed on the cluster surface; the bimetallic clusters have a fcc phase and grow with their facets either (111) or (001) parallel to the θ-Al 2 O 3 (100) surface.

Characterization of Pt–Au and Ni–Au Clusters on TiO2(110)

“…Surprisingly, high resolution XPS investigations of PtAu bimetallic clusters on Al 2 O 3 thin films supported on NiAl(100) [73] reported results different from our Pt-Au clusters on TiO 2 (110). Specifically, there was a large shift in Au(4f) binding energy to lower values after the deposition of Pt.…”

“…The reported absence of Au at the surface of the Pt-Au/ Al 2 O 3 clusters [73] is also in contrast to the Pt core-Au shell structures observed on the TiO 2 support observed here, as well as in other investigations of Pt-Au clusters. From DFT calculations, it was concluded that Pt-Au/Al 2 O 3 clusters consisted of Au core-Pt shell or Pt-Au intermixed structures with Au atoms residing inside the cluster [73].…”

“…From DFT calculations, it was concluded that Pt-Au/Al 2 O 3 clusters consisted of Au core-Pt shell or Pt-Au intermixed structures with Au atoms residing inside the cluster [73]. Notably, the Au(4f) intensity increased with deposition of Pt [73], and this behavior is not consistent with Pt at the surface of the clusters.…”

“…From DFT calculations, it was concluded that Pt-Au/Al 2 O 3 clusters consisted of Au core-Pt shell or Pt-Au intermixed structures with Au atoms residing inside the cluster [73]. Notably, the Au(4f) intensity increased with deposition of Pt [73], and this behavior is not consistent with Pt at the surface of the clusters. In other studies, Pt core-Au shell structures are predicted to be the most stable structures by molecular dynamics simulations of unsupported clusters of 55-561 atoms [74,75] and 250 atom clusters supported on carbon [76].…”

Au as an efficient promoter for electrocatalytic oxidation of formic acid and carbon monoxide: a comparison between Pt-on-Au and PtAu alloy catalysts

“…Additionally, the surface composition of atomic Pt/Au ratio and the preparation method are significantly related to the electrocatalytic activity of bimetallic PtAu catalyst for FA oxidation reaction [13,[34][35][36]. In general, the high electrocatalytic activity of bimetallic PtAu catalyst has been ascribed to the special electronic effect [29,36,37], ensemble effect [11,20,30], and synergistic effect [34,38,39]. Many research findings have revealed that both Pt-onAu and PtAu alloy catalysts exhibited high electrocatalytic activity toward FA oxidation with much less CO ads than that on Pt catalyst surface.…”