Coadsorption of Cu and O2 on a Ru(0001) surface

Kalki, K.; Wang, H.; Lohmeier, M.; Schick, M.; Milun, M.; Wandelt, K.

doi:10.1016/0039-6028(92)91266-e

Cited by 18 publications

(5 citation statements)

References 12 publications

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“…11,14) Typical systems, known from the literature, showing a zero-order desorption kinetics are adsorbates of metal atoms from the metal substrates. [14][15][16][17] The maximum temperature of the desorption in the laboratory alloys was 1 100 K, and in the industrial alloys it was 1 220 K and 1 320 K. The shifts in the maximum desorption temperature in the zero-order TDS spectra could be associated with the increasing of the coverage 11,14) or the presence of other atoms on the surface. Namely, the presence of coadsorbed oxygen in the system O/Cu/Ru(0001) caused modified Cu distribution and the shifts in desorption spectra of copper.…”

Section: Discussionmentioning

confidence: 93%

“…Namely, the presence of coadsorbed oxygen in the system O/Cu/Ru(0001) caused modified Cu distribution and the shifts in desorption spectra of copper. 15) We assume therefore that the shifts in TD spectra could be the result of the interactions among the segregated copper and the other elements of the alloying system, both, segregated and in the solid solution.…”

Section: Discussionmentioning

confidence: 99%

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The Surface Segregation of Copper in Non-oriented Electrical Steels

Petrovič

Mandrino

Krajinović³

et al. 2006

ISIJ Int.

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The surface segregation of copper was investigated in laboratory and industrial non-oriented electrical steel sheets containing copper. The cold-rolled samples of Fe-Si-Al alloys were annealed in the temperature range 320-1 120 K in the ultra-high-vacuum chamber of a field-emission Auger electron spectrometer, and subsequently characterized by Auger electron spectroscopy (AES). The Cu segregation rate was estimated based on the surface concentration of Cu after annealing at a given temperature. Not surprisingly, the AES analysis showed that the intensity of the surface segregation of copper increased with increasing annealing temperature. However, thermal desorption spectroscopy (TDS) showed that above 770 K the desorption of Cu started to reduce the surface concentration of Cu, thus making a reliable estimation of the segregation rate impossible. During the annealings, in addition to the surface segregation of copper, the surface segregation of alloying and impurity elements was observed as well. Moreover, it appeared that some of these constituents compete for available surface sites. For example, it could be concluded that the surface segregation of copper hindered the surface segregation of carbon in the Fe-Si-Al alloys.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

The Surface Segregation of Copper in Non-oriented Electrical Steels

Petrovič

Mandrino

Krajinović³

et al. 2006

ISIJ Int.

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“…Samples at higher Cu loading can be modelled as a Ru core covered by 3-D Cu structures. 58,59 At roughly equiatomic composition, the Cu particles only suffice to decorate the Ru, leading to an XPS response that reflects more closely their respective volume fractions, as might be obtained in a physical mixture of nanoparticles. There was a noticeable drop in w Alloying with partially miscible solutes is now recognized as an effective way to stabilize nanocrystallites against sintering.…”

Section: D Xas Spectroscopymentioning

confidence: 99%

“…Thus, the metals appear to act synergistically, and it is tempting to speculate that suppression of H 2 oxidation is linked to partial charge transfer from Cu to Ru 54,55 and/or strain factors that modify both O 2 and H 2 adsorption properties of Cu. 70 Evidence of strain-related reactivity is claimed to be detectable in Cu shells up to 6 monolayers thick 58 although the layers closest to the underlying Ru are influenced to the greatest degree. 38 The finding that Ru 22 Cu 7 , with just a single overlayer of Cu, showed the best performance, is consistent with this viewpoint.…”

Section: E Characterization By Drifts and Catalytic Testing In Co (H ...mentioning

confidence: 99%

Skeletal Ru/Cu catalysts prepared from crystalline and quasicrystalline ternary alloy precursors: characterization by X-ray absorption spectroscopy and CO oxidation

Highfield

Liu

Loo

et al. 2009

Phys. Chem. Chem. Phys.

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The Ru/Cu system is of historical significance in catalysis. The early development and application of X-ray absorption spectroscopy (XAS) led to the original 'bimetallic cluster" concept for highly-immiscible systems. This work explores alkali leaching of Al-based ternary crystalline and quasicrystalline precursors as a potential route to bulk Ru/Cu alloys. Single-phase ternary alloys at 3 trial compositions; Al(71)Ru(22)Cu(7), Al(70.5)Ru(17)Cu(12.5), and Al(70)Ru(10)Cu(20), were prepared by arc melting of the pure metal components. After leaching, the bimetallic residues were characterized principally by transmission XAS, "as-leached" and after annealing in H(2) (and passivation) in a thermobalance. XRD and BET revealed a nanocrystalline product with a native structure of hexagonal Ru. XPS surface analysis of Ru(22)Cu(7) and Ru(17)Cu(12.5) found only slight enrichment by Cu in the as-leached forms, with little change upon annealing. Ru(10)Cu(20) was highly segregated as-leached. XANES data showed preferential oxidation of Cu in Ru(22)Cu(7), implying that it exists as an encapsulating layer. TG data supports this view since it does not show the distinct two-stage O(2) uptake characteristic of skeletal Ru. Cu K-edge EXAFS data for Ru(22)Cu(7) were unique in showing a high proportion of Ru neighbours. The spacing, d(CuRu) = 2.65 A, was that expected from a hypothetical (ideal) solid solution at this composition, but this is unlikely in such a bulk-immiscible system and Ru K-edge EXAFS failed to confirm bulk alloying. Furthermore its invariance under annealing was more indicative of an interfacial bond between bulk components, although partial alloying with retention of local order cannot entirely be ruled out. The XAS and XPS data were reconciled in a model involving surface and bulk segregation, Cu being present at both the grain exterior and in ultra-fine internal pores. This structure can be considered as the 3-dimensional analogue of the classical type. Preliminary studies in CO and H(2) oxidation were made in a DRIFTS flow reactor with on-line MS, and their activities and selectivities were compared against skeletal Ru and Cu controls, Ru/Al(2)O(3), and Au/Fe(2)O(3). All samples were active in CO oxidation above approximately 50 degrees C, showing light-off temperatures in the range 60-70 degrees C. Ru(22)Cu(7) and Ru(17)Cu(12.5) also showed good selectivities (vs. H(2) oxidation), attributed tentatively to Ru-modified Cu surfaces of varying thickness. These compositions are promising candidates to test in a (PROX) fuel processor to supply purified (CO-free) H(2) to a PEM fuel cell.

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“…The Ru(0001) crystal with a miscut of less than 0.5 • was prepared by cycles of Ar ion bombardment followed by heating up to 1300 K. C and S surface contaminations are effectively removed by 20 Langmuir (L) (1 Langmuir = 1.33 × 10 −6 mbar s) of O 2 adsorption, followed by desorption at 1600 K as described in [7,20]. The sample heater was initially calibrated by a Ni/NiCr thermocouple, spot welded to the rim of the crystal.…”

Section: Methodsmentioning

confidence: 99%

O-mediated layer growth of Cu on Ru(0001)

Wolter

Meinel

Ammer

et al. 1999

J. Phys.: Condens. Matter

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The film growth of Cu on clean and O-precovered Ru(0001) at different growth temperatures form 300 K to 450 K was investigated by scanning tunnelling microscopy (STM). Cu films on clean Ru(0001) grow in a multilayer mode at these temperatures. By using an O precoverage in the range of 0.1 monolayers (ML) up to a saturation coverage of 0.5 ML on clean Ru(0001), at 400 K different growth regimes are obtained. For ML a multilayer mode is preserved which changes into an O-induced two-dimensional (2D) growth for higher (0.2-0.5 ML). STM reveals the formation of an O/Cu surfactant structure on the surface due to migration of O initially located at the Ru surface. Its surface coverage rises linearly with O precoverage up to ML where it covers the surface completely. By increasing up to 0.5 ML, a drastic change in the morphology and density of the 2D islands occurs, which is accompanied by a change of the O/Cu surfactant structure. The O/Cu surfactant structure displays some order on a local scale for low , which changes into a disordered structure for ML. Structural similarities to oxidized surfaces of Cu(111) and the structures induced by postadsorption on Cu/Ru(0001) are discussed. Different models of surfactant mechanisms are presented to explain the observations. The locally ordered O/Cu surfactant structure (for ML) together with specific Cu film defects induce a heterogeneous nucleation of Cu with a high island density. Different mobilities of migrating Cu adatoms are established on top of the small islands and on the O/Cu structure resulting in enhanced interlayer diffusion explaining the observed 2D growth. The average island density only slightly changes within the temperatures investigated. In contrast, the saturated and disordered O/Cu surfactant structure (for = 0.4 - 0.5 ML) causes homogeneous nucleation. For this structure, the island density strongly depends on temperature and gives rise to an Arrhenius-like behaviour. The observed 2D growth is attributed to a reduction of the interlayer diffusion barrier. Cu growth on a formerly annealed Cu/O/Ru(0001) film system yields an almost perfect layer-by-layer growth caused by heterogeneous nucleation at periodically arranged Cu film defect sites. The relationship of the O/Cu surfactant structures to the ordered O/Cu bilayer on Ru(0001) - interpreted as a disrupted -like oxidized surface - was revealed.

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Coadsorption of Cu and O2 on a Ru(0001) surface

Cited by 18 publications

References 12 publications

The Surface Segregation of Copper in Non-oriented Electrical Steels

The Surface Segregation of Copper in Non-oriented Electrical Steels

Skeletal Ru/Cu catalysts prepared from crystalline and quasicrystalline ternary alloy precursors: characterization by X-ray absorption spectroscopy and CO oxidation

O-mediated layer growth of Cu on Ru(0001)

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