Room Temperature Migration of Ag Atoms to Cover Pd Islands on Ag(111)

Gedara, Buddhika S. A.; Muir, Mark; Islam, A. K. M. Maidul; Liu, Dairong; Trenary, Michael

doi:10.1021/acs.jpcc.1c08736

Cited by 6 publications

(17 citation statements)

References 34 publications

(84 reference statements)

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“…These differences in bond distance strongly indicate the presence of heteroatomic bonding in the SD- x : y -Ag:Pd/carbon samples. − Notably, lower CN values are seen for Ag–M than Pd–M for samples with low Pd loadings, which suggests that Pd atoms are predominantly in subsurface locations in these clusters (despite being reduced onto the Ag) and Ag atoms dominate the surface in these samples . This is consistent with the observation made recently by Gedara et al that Ag atoms can migrate to cover Pd islands on Ag(111) in minutes at room temperature . However, this trend reverses at higher Pd loadings, and much lower Pd-M CNs are seen for Pd-rich AgPd clusters which suggests most Pd is on the surface of such clusters (Scheme ).…”

Section: Resultssupporting

confidence: 86%

“…40 This is consistent with the observation made recently by Gedara et al that Ag atoms can migrate to cover Pd islands on Ag(111) in minutes at room temperature. 47 However, this trend reverses at higher Pd loadings, and much lower Pd-M CNs are seen for Pd-rich AgPd clusters which suggests most Pd is on the surface of such clusters (Scheme 1). We note that while the Ag−M CN increases slightly for the SD-1:6-Ag:Pd/carbon sample, there is still a reasonable amount of Ag on the surface of all particles.…”

Section: Resultsmentioning

confidence: 99%

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Atom-Precise Ag Clusters as Precursors for Selective Bimetallic AgPd Heterogeneous Catalysts

et al. 2022

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Bimetallic clusters can have superior catalytic properties compared to those of monometallic clusters due to synergistic interactions between the constituent metals. Here we show that atom-precise Ag clusters can be used as templates for the design of AgPd bimetallic heterogeneous catalysts using a sequential deposition approach. Atom-precise 2,4-dimethylbenzenethiol-protected Ag25(SR)18 clusters were used as precursors for sequential Pd deposition and the eventual structures of the AgPd bimetallic catalysts were revealed by X-ray absorption spectroscopy (XAS) studies. EXAFS data shows that Ag clusters on carbon supports can be thermally activated at low temperatures and then used as templates for the subsequent sequential reduction of Pd ions to form bimetallic clusters. In AgPd bimetallic catalysts with low Pd loadings, Ag atoms are predominately on the catalyst surface while Pd atoms occupy subsurface sites; however at higher Pd loadings most Pd atoms occupy surface sites. These structural changes play a significant role in the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE). Bimetallic AgPd catalysts showed superior activity to monometallic Ag catalysts and higher Ag/Pd ratios led to better MBE selectivity. MBE selectivity of 96.6% was obtained for 12:1-Ag:Pd/carbon catalysts and the selectivity progressively reduced with increased Pd loadings, to 0% for 1:6-Ag:Pd/carbon catalysts, in which only the fully hydrogenated product was formed. This work demonstrates a significant structure–property relationship between the geometry and the catalytic performance of AgPd bimetallic clusters prepared via a sequential deposition strategy.

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Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Atom-Precise Ag Clusters as Precursors for Selective Bimetallic AgPd Heterogeneous Catalysts

et al. 2022

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“…For Ag(111), we reported the height of Ag-encapsulated Pd islands to be 0.420 nm and Patel et al reported 0.459 nm high Ag-capped Pt-rich islands for Pt deposited on Ag(111). 16,47 However, we note that conclusions based on heights alone are not definitive as the Au−Pd interlayer interaction could make the height of a Au-capped Pd island different from what is expected based on assuming that layer heights are simply additive. Because the formation of the Au-capped Pd islands is not accompanied by the formation of vacancy pits, the Au atoms likely detach from step edges and diffuse onto the Pd islands.…”

Section: ■ Experimental Sectionmentioning

confidence: 62%

“…15 Previously, we reported a scanning tunneling microscopy (STM) study of the evolution of the structure of Pd islands on Ag(111) with time and upon annealing to different temperatures. 16 In this study, we compare and contrast the behavior of Pd on the Au(111) and Ag(111) surfaces. The thermodynamics of Pd on Ag(111) and Au(111) favors diffusion of Pd into the bulk of the substrate because of the higher surface free energy of Pd (2.0 J m −2 ) than that of Ag (1.3 J m −2 ) and Au (1.6 J m −2 ).…”

Section: ■ Introductionmentioning

confidence: 99%

Stability of Pd Islands on Ag(111) and Au(111)

Gedara

Trenary

2022

J. Phys. Chem. C

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Scanning tunneling microscopy was used to compare the evolution with time and annealing temperature of the structure of Pd islands formed after room-temperature (RT) deposition of Pd on Ag(111) and Au(111). Although silver and gold share many properties, their clean (111) surfaces have distinctly different structures, and this leads to distinctly different behavior following Pd deposition. On Ag(111), large Pd islands form and become capped by Ag atoms with the simultaneous formation of vacancy pits on the Ag(111) surface. On Au(111), smaller Pd islands form for comparable Pd coverages. In contrast to Ag(111), much less capping of Pd by Au atoms occurs on the Au(111) surface at RT and no vacancy pits were observed. Upon annealing to 340 K, 98% of the Pd islands were capped by Ag atoms on Ag(111), whereas less than 4% of Pd islands on Au(111) were covered by surface Au atoms, but again without forming vacancy pits. Upon further annealing to 470 K, Pd diffuses into the subsurface of both Ag(111) and Au(111). The contrasting behavior is attributed to the herringbone reconstruction on Au(111), which provides sites with higher binding energies for Pd atoms, whereas such sites are not present on Ag(111).

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“…CO causes Pd segregation into the topmost surface layer [ 32 ]. The strong effects of reactive gases such as CO or O 2 on the alloy structure and composition were investigated by scanning tunneling microscope (STM) and Fourier transform infrared spectroscopy (FTIR) to illustrate the correlation of chemical properties with structural aspects of bimetallic surfaces of a given composition at ambient pressure [ 33 , 34 , 35 ]. Theoretical calculations show that the driving force for the structural reconstruction is the strong interaction of the surface Pd sites with the adsorbed CO molecules, which changes the surface energy and leads to surface segregation of Pd [ 36 , 37 ].…”

Section: Introductionmentioning

confidence: 99%

PdAg/Ag(111) Surface Alloys: A Highly Efficient Catalyst of Oxygen Reduction Reaction

Hua

Tian

et al. 2022

Nanomaterials

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In this article, the behavior of various Pd ensembles on the PdAg(111) surfaces was systematically investigated for oxygen reduction reaction (ORR) intermediates using density functional theory (DFT) simulation. The Pd monomer on the PdAg(111) surface (with a Pd subsurface layer) has the best predicted performance, with a higher limiting potential (0.82 V) than Pt(111) (0.80 V). It could be explained by the subsurface coordination, which was also proven by the analysis of electronic properties. In this case, it is necessary to consider the influence of the near-surface layers when modeling the single-atom alloy (SAA) catalyst processes. Another important advantage of PdAg SAA is that atomic-dispersed Pd as adsorption sites can significantly improve the resistance to CO poisoning. Furthermore, by adjusting the Pd ensembles on the catalyst surface, an exciting ORR catalyst combination with predicted activity and high tolerance to CO poisoning can be designed.

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Room Temperature Migration of Ag Atoms to Cover Pd Islands on Ag(111)

Cited by 6 publications

References 34 publications

Atom-Precise Ag Clusters as Precursors for Selective Bimetallic AgPd Heterogeneous Catalysts

Atom-Precise Ag Clusters as Precursors for Selective Bimetallic AgPd Heterogeneous Catalysts

Stability of Pd Islands on Ag(111) and Au(111)

PdAg/Ag(111) Surface Alloys: A Highly Efficient Catalyst of Oxygen Reduction Reaction

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