Characterization of PdCu(110) single crystal surface compositions during CO chemisorption

Mousa,; Loboda‐Čačković, J.; Block, J.H.

doi:10.1016/0042-207x(94)e0002-g

Cited by 20 publications

(14 citation statements)

References 21 publications

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“…Segregation of Pd to the surface without strong electronic perturbation will yield CO desorption temperatures of elemental Pd together with the typical long tail at lower temperatures due to the different adsorption geometries at higher CO coverage. 43 Strong electronic perturbations of a hypothetic Pd segregation layer could indeed lead to much lower CO desorption temperatures. 5 These strong electronic perturbations are usually accompanied by a shift of the Pd 3d core levels to higher binding energy.…”

Section: Resultsmentioning

confidence: 99%

“…A very sensitive tool for surface segregation is CO adsorption followed by TDS. ,− In all of these cases in the literature, the TDS spectra are very sensitive to the amount and ensemble configuration of Pd on the surface. Segregation of Pd to the surface without strong electronic perturbation will yield CO desorption temperatures of elemental Pd together with the typical long tail at lower temperatures due to the different adsorption geometries at higher CO coverage . Strong electronic perturbations of a hypothetic Pd segregation layer could indeed lead to much lower CO desorption temperatures .…”

Section: Discussionmentioning

confidence: 99%

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Surface Investigation of Intermetallic PdGa(1̅ 1̅ 1̅)

et al. 2012

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The intermetallic PdGa is a highly selective and potent catalyst in the semihydrogenation of acetylene, which is attributed to the surface stability and isolated Pd atom ensembles. In this context PdGa single crystals of form B with (111) orientation were investigated by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), X-ray photoelectron diffraction (XPD), and low-energy electron diffraction (LEED) to study the electronic and geometric properties of this surface. UPS and thermal desorption spectroscopy (TDS) were used to probe the chemisorption behavior of CO. The PdGa(111) surface exhibits a (1 × 1) LEED and a pronounced XPD pattern indicating an unreconstructed bulk-truncated surface. Low-temperature STM reveals a smooth surface with a (1 × 1) unit cell. No segregation occurs, and no impurities are detected by XPS. The electronic structure and the CO adsorption properties reveal PdGa(111) to be a bulk-truncated intermetallic compound with Pd-Ga partial covalent bonding.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Surface Investigation of Intermetallic PdGa(1̅ 1̅ 1̅)

et al. 2012

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“…A complete description of surface segregation requires that surface composition be understood as a continuous function of bulk composition. Segregation in most alloys has, however, been examined only at a very limited number of discrete compositions. ,− Surface segregation has been characterized experimentally in a number of binary alloys. − ,,− Cu x Pd 1– x alloys have received significant attention from both experimental and computational research groups because of their importance in the hydrogen purification application. ,,,,, We have reported the experimental characterization of segregation in a polycrystalline Cu 0.30 Pd 0.70 alloy, showing that Cu preferentially segregates to the top-surface of the alloy over a wide temperature range, leaving a Cu-depleted subsurface region . Other researchers have reported similar results for the Cu 0.50 Pd 0.50 (110) , and Cu 0.85 Pd 0.15 (110) , single crystal surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…Segregation in most alloys has, however, been examined only at a very limited number of discrete compositions. ,− Surface segregation has been characterized experimentally in a number of binary alloys. − ,,− Cu x Pd 1– x alloys have received significant attention from both experimental and computational research groups because of their importance in the hydrogen purification application. ,,,,, We have reported the experimental characterization of segregation in a polycrystalline Cu 0.30 Pd 0.70 alloy, showing that Cu preferentially segregates to the top-surface of the alloy over a wide temperature range, leaving a Cu-depleted subsurface region . Other researchers have reported similar results for the Cu 0.50 Pd 0.50 (110) , and Cu 0.85 Pd 0.15 (110) , single crystal surfaces. Theoretical studies of Cu x Pd 1– x alloys suggest that segregation patterns can vary with bulk composition ,, and predict a top layer that is Cu-rich with a second layer that is Cu-depleted with respect to the bulk composition. , We have also shown that adsorption of sulfur onto the Cu 0.30 Pd 0.70 surface causes “segregation reversal”, creating a top-surface that contains only Pd and S atoms .…”

Section: Introductionmentioning

confidence: 99%

High-Throughput Characterization of Surface Segregation in Cu_xPd_1–x Alloys

Priyadarshini

Kondratyuk

Picard³

et al. 2011

J. Phys. Chem. C

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A high throughput methodology for the study of surface segregation in alloys has been developed and applied to the Cu x Pd 1Àx system. A novel offsetfilament deposition tool was used to prepare Cu x Pd 1Àx composition spread alloy films (CSAFs), high throughput sample libraries with continuous lateral composition variation spanning the range x = 0.05À0.95. Spatially resolved low energy ion scattering spectroscopy (LEISS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films' top-surface and near-surface compositions, respectively, as functions of alloy composition, x, and temperature. Electron backscatter diffraction (EBSD) was used to identify the bulk phases in the CSAF as a function of alloy composition, x. Films equilibrated by annealing at temperatures g 700 K displayed preferential segregation of Cu to their top-surfaces at all bulk compositions; segregation patterns did not, however, depend on local structure. The LangmuirÀMcLean thermodynamic model was applied to segregation measurements made in the temperature range 700À900 K in order to estimate the enthalpy (ΔH seg ) and entropy (ΔS seg ) of segregation as a function of bulk Cu x Pd 1Àx composition. Segregation measurements at x = 0.30 on the CSAF compare well with results previously reported for a bulk, polycrystalline Cu 0.30 Pd 0.70 alloy, demonstrating the utility of the CSAF as a high throughput library for study of segregation.

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“…However, the simulated pattern (not shown) clearly demonstrates that Pd and Cu congregate separately upon annealing. Previously Mousa et al [57] concluded that Pd surface can be formed by sputtering the PdeCu alloy surface. Our simulations provide a possible scenario to this conclusion: Cu segregates to the surface of PdeCu alloy, forming a Pd-rich subsurface.…”

Section: Cu In Bulkmentioning

confidence: 99%