Photoemission studies of physisorbed xenon atoms on ruthenium/copper surfaces

Kim, K. S.; Sinfelt, J. H.; Eder, S.; Markert, K.; Wandelt, K.

doi:10.1021/j100293a026

Cited by 29 publications

(7 citation statements)

References 2 publications

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“…The resulting electronic modification can dramatically alter surface chemical (catalytic) properties of the bimetallic system. 1,[13][14][15][16][17][18][19] Strong electronic perturbation between the metal overlayer and the underlying transition metal were observed in X-ray photoelectron spectroscopy (XPS) studies of Cu/Ru(001) 16 as in other bimetallic systems. 15a By use of scanning tunneling spectroscopy (STM), the modified electronic structure was found to induce perturbations, which extend up to 50-100 Å away.…”

Section: Introductionmentioning

confidence: 99%

“…Formation of the bond between the two different metals leads to electron polarization toward the element with the larger fraction of empty states in its valence band and is accompanied by a large perturbation in the electronic properties of the metals. The resulting electronic modification can dramatically alter surface chemical (catalytic) properties of the bimetallic system. ,− Strong electronic perturbation between the metal overlayer and the underlying transition metal were observed in X-ray photoelectron spectroscopy (XPS) studies of Cu/Ru(001) 16 as in other bimetallic systems 15a…”

Section: Introductionmentioning

confidence: 99%

“…They are observed at the step edges or adatoms that may alter adsorbate binding energy and generate new adsorption sites. , Step edges of copper islands on Ru (001) were found to trap H and CO and thus reduce the diffusion coefficient of hydrogen on Ru(001) by 3 orders of magnitude by depositing only 0.2 ML copper . These new adsorption sites are characterized by a substantially different local work function, probed by photoemission of adsorbed xenon (PAX). − …”

Section: Introductionmentioning

confidence: 99%

“…Although adsorption and desorption kinetics of several adsorbates have been studied on the Cu/Ru(001) system, − very few investigations have examined the dependence of the adsorption and dissociation mechanism on the copper coverage. Considerable insight into the catalytic processes can be gained by these investigations, although some discrepancy is found between the “real” polycrystalline Cu/Ru catalyst powder and the smooth Ru(001) deposited by copper atoms . For example, in the C 2 H 4 /Cu/Ru(001) system the copper deposition generated new adsorption sites that have mixed Cu and Ru character.…”

Section: Introductionmentioning

confidence: 99%

“…22 These new adsorption sites are characterized by a substantially different local work function, probed by photoemission of adsorbed xenon (PAX). [17][18][19] Cu is immiscible in Ru, which circumvents the complication of determining the three-dimensional composition. It is known also to grow epitaxially on the clean Ru(001), forming a pseudomorphic film in the first layer.…”

Section: Introductionmentioning

confidence: 99%

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Surface Chemistry of CH₃Br and Methyl Modified by Copper Deposition on Ru(001)

Livneh

Asscher

1999

J. Phys. Chem. B

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The chemistry of methyl bromide on Cu/Ru(001) has been studied utilizing work function change (∆ ) and temperature-programmed desorption (TPD) measurements. The remarkable modification in the methyl fragments dehydrogenation at the completion of a single copper layer and the significant difference in reactivity of the Cu(2 ML)/Ru(001) or Cu(111) surfaces are the focus of this study. A decrease in work function at the completion of 1 ML CH 3 Br of 2.15 ( 0.02 eV and 1.33 ( 0.05 eV was measured, respectively, for Ru (001) and Cu(2 ML)/Ru(001) held at 82 K. Methyl bromide does not dissociate upon adsorption on clean or the copper-covered surfaces, and it is bound with the bromine down. Copper modifies the reactivity of the Ru substrate, gradually decreasing the dissociated fraction of CH 3 Br from 0.55 of the initial one monolayer on clean Ru(001) to 0.06 on Cu(2 ML)/Ru(001), probably because of defects in the copper layer. The methyl fragment dehydrogenation rate slows as the copper coverage increases. At a narrow copper coverage range between 0.8 and 0.95 ML, adsorbed hydrogen and methyl fragments coexist on the surface in the temperature range 230-280 K. Sequential decomposition channels of the parent molecules and the methyl fragment lead to a unique enhancement of methane production rate, this on the account of further hydrocarbon dehydrogenation, as reflected in both ∆p and ∆ TPD measurements. Methane is formed on top of copper terraces as a result of "spill-over" of both methyl and hydrogen atoms, similar to the chemistry over Cu(111) and Cu(110) single-crystal surfaces. The dipole moment of adsorbed methyl is reported here for the first time on metal surfaces, being 0.48 D on top of Cu(2 ML)/Ru(001).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Surface Chemistry of CH₃Br and Methyl Modified by Copper Deposition on Ru(001)

Livneh

Asscher

1999

J. Phys. Chem. B

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Bimetallic Catalysts – Heterogeneous

Sinfelt

2002

Encyclopedia of Catalysis

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Although early attempts to use metal alloys to probe the so‐called electronic factor in catalysis by metals did not meet expectations, investigations of bimetallic catalysts with other objectives have led to major advances. Such investigations have shown that bimetallic catalysts can exhibit selectivities for hydrocarbon transformations that are very different from those observed on monometallic catalysts, favoring the formation of valuable products such as aromatic hydrocarbons at the expense of less valuable ones such as methane. The number of contiguous atoms of a given metal component required in an active catalytic site is an important issue here. Investigations with bimetallic catalysts have also shown that systems of interest are not limited to combinations of metallic elements that are highly miscible in the bulk. For industrial applications of bimetallic catalysts, a crucial advance was the demonstration that highly dispersed bimetallic entities as small as 1 nm in size could be prepared within the pores of materials commonly used as catalyst supports. The term “bimetallic clusters” is used in referring to these entities. A very important industrial application of bimetallic catalysts has occurred on a huge worldwide scale in petroleum reforming processes. This application has played a vital role in making lead‐free gasoline a reality, an accomplishment of enormous environmental significance.

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