Molecular Beam Study of the CO Adsorption on a Regular Array of PdAu Clusters on Alumina

Sitja, Georges; Henry, Claude R.

doi:10.1021/acs.jpcc.8b07350

Cited by 7 publications

(5 citation statements)

References 75 publications

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“…The activity and selectivity of bimetallic catalysts are often discussed using the concept of the ensemble (geometric) and ligand (electronic) effects [ 13 , 48 , 49 , 50 , 51 ]. These effects originate from the formation of contiguous palladium domains, when diluting Pd with Au, and charge transfer between Au and Pd or orbital re-hybridization of metal atoms involved in heteronuclear metal-metal bonds.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2021

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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.

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Section: Resultsmentioning

confidence: 99%

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

et al. 2021

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“…The high stability of the cluster organization is certainly due to the particular surface structure of these films and probably also to their small thickness (0.5 nm). In summary, regular arrays of metal clusters on alumina/Ni 3 Al(111) appear to be the best candidates to study accurately the size effect in catalysis with surface science techniques, as it has been already shown for Pd and PdAu clusters. ,− It is rather astonishing that no attempt of Pt deposition on this alumina film has been reported yet, despite the great interest of Pt in heterogeneous catalysis. Here, we present the first attempt to prepare regular arrays of Pt clusters on alumina ultrathin films on Ni 3 Al(111) used as a template.…”

Section: Introductionmentioning

confidence: 87%

Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al₂O₃/Ni₃Al(111)

et al. 2019

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Alumina ultrathin films obtained by high temperature oxidation of a Ni3Al (111) surface are a good template to grow regular arrays of metal clusters. Up to now two hexagonal organizations called 'dot' and 'network' structures have been observed with distances between clusters of 4.1 and 2.4 nm, respectively. In the present article we report on an investigation by in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS), showing that Pt deposited at room temperature (RT) and for a low coverage forms a new hexagonal structure with a distance between clusters of 1.38 nm. For the first time, an assembly of tiny Pt clusters (1-6 atoms) with a very high density (5.85x10 13 cm-2) and presenting a good organization on an alumina surface, is obtained. This system could be used to investigate by surface science techniques the new emerging field of Single Atom Catalysis (SAC). By deposition at 573 K small Pt clusters are organized on the network structure. By deposition of Pt at 573 K on pre-formed Pd seeds, large Pt (Pd) clusters containing a hundred of atoms are organized on the dot structure and they remain organized up to 733 K. We show that the three structures are interrelated. The different organizations of the Pt clusters on the alumina surface are explained by the presence of 3 types of sites corresponding to different adsorption energy for Pt atoms.

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“…The difference in the proneness of Pd atoms to segregation for those two samples could be explained by the initial Pd/Au ratios of the metals deposited onto the HOPG surface. Sitja et al [33] recently reported on a molecular beam study of the CO adsorption on a regular array of PdAu clusters supported on alumina. They showed that an increase in the Au surface concentration leads to a decrease in the CO adsorption energy on PdAu clusters.…”

Section: Sample Au/c Pd/c Pd/aumentioning

confidence: 99%

“…The activity and selectivity of bimetallic catalysts are often discussed within the context of the ensemble (geometric) and ligand (electronic) effects [13,18,[32][33][34][45][46][47][48]. The former addresses the formation of a contiguous palladium domain when diluting the Pd lattice with Au.…”

Section: Sample Au/c Pd/c Pd/aumentioning

confidence: 99%

Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio

et al. 2021

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In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite (HOPG)-supported bimetallic Pd-Au catalysts towards the CO oxidation based on the Pd/Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd/Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu-2 sample with a lower Pd/Au surface ratio (~0.75) was already active at temperatures less than 150 °C, while the PdAu-1 sample with a higher Pd/Au surface ratio (~1.0) became active only at temperatures above 200 °C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near-surface regions of the two-component Pd-Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd/Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near-surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmosphere.

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Molecular Beam Study of the CO Adsorption on a Regular Array of PdAu Clusters on Alumina

Cited by 7 publications

References 75 publications

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

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

Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al₂O₃/Ni₃Al(111)

Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio

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Molecular Beam Study of the CO Adsorption on a Regular Array of PdAu Clusters on Alumina

Cited by 7 publications

References 75 publications

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

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

Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al2O3/Ni3Al(111)

Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio

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Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al₂O₃/Ni₃Al(111)