Interaction of benzene with protium and deuterium on copper-nickel films with known surface composition*1

Plank, P. Van Der; Sachtler, Wolfgang M.H.

doi:10.1016/0021-9517(68)90071-7

Cited by 107 publications

(4 citation statements)

References 9 publications

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“…The displacement–reduction processes described herein would initially lead to outer and inner Pd regions with an intervening Au shell, a structure previously reported for Pd–Au clusters without mechanistic interpretation or spectroscopic evidence for its formation mechanism . Such structures, however, undergo facile restructuring in response to contact with environments that lead to adsorption of species that bind with different strengths on the two bimetallic components. , The infrared spectra of chemisorbed CO is used here to probe changes in the surface composition of Pd–Au clusters. Clusters were first treated in H 2 (14.3 kPa) at 523 K for 3.6 ks, cooled to 273 K (Section 2.6), and exposed to CO (0.058 kPa CO, 99.942 kPa He).…”

Section: Resultsmentioning

confidence: 84%

“…48 Such structures, however, undergo facile restructuring in response to contact with environments that lead to adsorption of species that bind with different strengths on the two bimetallic components. 49,50 The infrared spectra of chemisorbed CO is used here to probe changes in the surface composition of Pd−Au clusters. Clusters were first treated in H 2 (14.3 kPa) at 523 K for 3.6 ks, cooled to 273 K (Section 2.6), and exposed to CO (0.058 kPa CO, 99.942 kPa He).…”

Section: Resultsmentioning

confidence: 99%

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Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Kunz

Iglesia

2014

J. Phys. Chem. C

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Bimetallic Pd–Au clusters with (Pd/Au)at compositions of 0.5, 1.0, and 2.0 narrowly distributed in size were prepared using colloidal methods with reagents containing only C, H, and O atoms, specifically polyvinyl alcohol (PVA) as protecting species and ethanol as the organic reductant. Synthesis protocols involved contacting a solution of Au precursors with nearly monodisperse Pd clusters. The formation of Pd–Au clusters was inferred from the monotonic growth of clusters with increasing Au content and confirmed by the in situ detection of Au plasmon bands in their UV–visible spectra during synthesis. Specifically, transmission electron microscopy (TEM) showed that growth rates were proportional to the surface area of the clusters, and rigorous deconvolution and background subtraction allowed for determination of the intensity and energy of Au-derived plasmon bands. This feature emerged during initial contact between Au precursors and Pd clusters apparently because Au3+ species deposit as Au0 using Pd0 as the reductant in a fast galvanic displacement process consistent with their respective redox potentials. The plasmon band ultimately disappeared as a result of the subsequent slower reduction of the displaced Pd2+ species by ethanol and of their deposition onto the bimetallic clusters. Such displacement–reduction pathways are consistent with the thermodynamic redox tendencies of Au, Pd, and ethanol and lead to the conclusion that such triads (two metals and an organic reductant) can be chosen from thermodynamic data and applied generally to the synthesis of bimetallic clusters with other compositions. These bimetallic clusters were dispersed on mesoporous γ-Al2O3 supports, and PVA was removed by treatment in ozone at near-ambient temperature without any detectable changes in cluster size. The absence of strongly bound heteroatoms, ubiquitous in many other colloidal synthesis protocols, led to Al2O3-dispersed clusters with chemisorption uptakes consistent with their TEM-derived cluster size, thus demonstrating that cluster surfaces are accessible and free of synthetic debris. The infrared spectra of chemisorbed CO indicated that both Pd and Au were present at such clean surfaces but that any core–shell intracluster structure conferred by synthesis was rapidly destroyed by adsorption of catalytically relevant species, even at ambient temperature; this merely reflects the thermodynamic tendency and kinetic ability of an element to segregate and to decrease surface energies when it binds an adsorbate more strongly than another element in bimetallic particles.

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Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 99%

Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Kunz

Iglesia

2014

J. Phys. Chem. C

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“…͑19͒ since the surface composition of this system is constant independently from the bulk composition, as thermodynamically modeled and proved by hydrogen chemisorption experiments. 41,42 At 200°C the alloy separates into a mixture of a Ni-rich phase with approximately 4 at. % Cu and a Cu-rich phase with approximately 70 at.…”

Section: B Alloy Systems With a Miscibility Gap: Cu-ni Au-ptmentioning

confidence: 99%

Work function calculation of solid solution alloys using the image force model

Rothschild

Eizenberg

2010

Phys. Rev. B

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The electronic work function of polycrystalline solid solution alloys is being analytically calculated using three different approaches. All approaches are derived by assuming that the alloys are in equilibrium and therefore surface segregation causes a difference between the surface composition and the bulk composition. An approach based on the image force, an approach based on the dipole layer formed due to electronegativity differences, and a simple surface concentration approach are compared to published experimental results. The image force model has a good agreement with the experiments, while the dipole-layer approach has a poor agreement, challenging the conventional concept of the double layer.

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“…Copper−nickel has been used a model bimetallic system for numerous catalytic and surface science studies. − One can describe this system in terms of the electron-band theory, in which nickel is distinguished as having an incompletely filled d band, whereas that of copper is filled. When copper atoms are introduced into nickel extra electrons are added to the lattice, which enter the d-band until it is eventually completely filled.…”

Section: Introductionmentioning

confidence: 99%

Growth of Graphite Nanofibers from the Iron−Copper Catalyzed Decomposition of CO/H₂Mixtures

et al. 2003

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We have investigated the formation of graphite nanofibers from the catalytic decomposition of CO/H 2 mixtures over a series of powdered Fe-Cu catalysts at temperatures ranging from 500 to 700 °C. The physical and structural characteristics of the nanofibers have been established from examination of the materials by a variety of techniques including transmission electron microscopy, temperature-programmed oxidation, nitrogen surface area measurements, and X-ray diffraction. It was found that the addition of Cu to Fe did not exert a significant influence on the amount of solid carbon product formed in the reaction. On the other hand, examination of the nanofibers by high-resolution TEM revealed that the materials generated from Fe-rich Cu bimetallics were notably more graphitic in nature than those grown from pure Fe. As the reaction temperature was increased from 600 to 700 °C, the structure of the graphite nanofibers underwent a dramatic change from a "platelet" to "tubular" configuration. It is suggested that this transformation is directly associated with the R-Fe to γ-Fe phase change over this temperature range.

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Interaction of benzene with protium and deuterium on copper-nickel films with known surface composition*1

Cited by 107 publications

References 9 publications

Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Work function calculation of solid solution alloys using the image force model

Growth of Graphite Nanofibers from the Iron−Copper Catalyzed Decomposition of CO/H₂Mixtures

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Interaction of benzene with protium and deuterium on copper-nickel films with known surface composition*1

Cited by 107 publications

References 9 publications

Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Mechanistic Evidence for Sequential Displacement–Reduction Routes in the Synthesis of Pd–Au Clusters with Uniform Size and Clean Surfaces

Work function calculation of solid solution alloys using the image force model

Growth of Graphite Nanofibers from the Iron−Copper Catalyzed Decomposition of CO/H2Mixtures

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Growth of Graphite Nanofibers from the Iron−Copper Catalyzed Decomposition of CO/H₂Mixtures