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Adsorption and Reactions of Carbon Monoxide and Oxygen on Bare and Au-Decorated Carburized W(110).

Bachmann M, Bikaljevic D, Memmel N, Bertel E - J Phys Chem C Nanomater Interfaces (2013)

Bottom Line: Probably the latter is associated with the existence of double-layer gold clusters and islands.Deposition of gold enhances the desorption rate of the formed CO at the low-temperature end of the recombinative CO desorption range, indicating a promoting effect of gold for oxidation of surface carbon.Two reasons could be identified: (1) weakly bound CO with desorption temperatures between 100 and 200 K (as reported for other related systems) is not observed, and (2) oxygen atoms are bonded too strongly to the templates.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 52a, A-6020 Innsbruck, Austria.

ABSTRACT
Adsorption and coadsorption of carbon monoxide and oxygen on different types of Au clusters on R(15 × 3)C/W(110) and R(15 × 12)C/W(110), respectively, are studied with respect to the catalytic behavior for oxidation of CO as well as of surface carbon. Carburization of the W(110) surface results in a weakening of the adsorption bond for molecularly adsorbed CO. Dissociation of carbon monoxide, which occurs on W(110), is reduced on the low-carbon coverage R(15 × 12) surface and completely suppressed on the carbon-saturated R(15 × 3) phase. Deposition of gold results in a blocking of adsorption sites for molecularly adsorbed CO and reopening of the dissociation channel. Probably the latter is associated with the existence of double-layer gold clusters and islands. At room temperature the gold clusters on both carburized templates are stable in CO atmosphere as shown by in-situ STM measurements. In contrast, exposure to oxygen alters the clusters on the R(15 × 12) surface, implying dissociation of oxygen not only on the substrate but also on or in immediate vicinity of the gold clusters. On the Au-free carburized templates oxygen adsorbs dissociatively and is released as CO at temperatures beyond 800 K due to reaction with carbon atoms from the templates. Deposition of gold enhances the desorption rate of the formed CO at the low-temperature end of the recombinative CO desorption range, indicating a promoting effect of gold for oxidation of surface carbon. In contrast, low-temperature CO oxidation catalyzed by the deposited Au clusters is not observed. Two reasons could be identified: (1) weakly bound CO with desorption temperatures between 100 and 200 K (as reported for other related systems) is not observed, and (2) oxygen atoms are bonded too strongly to the templates.

No MeSH data available.


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CO uptake curves(at 90 K) on W(110), R(15 × 12)C/W(110),and R(15 × 3)/C/W(110) as obtained from the integrated TPD curves.
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fig2: CO uptake curves(at 90 K) on W(110), R(15 × 12)C/W(110),and R(15 × 3)/C/W(110) as obtained from the integrated TPD curves.

Mentions: The uptake curves(at 90 K) for CO on the three templates as derivedfrom the integrated TDS intensities are summarized in Figure 2. All curves are quite similar, showing a precursor-mediatedadsorption behavior with a linear coverage increase for exposuresup to 3.4 langmuirs and an almost constant coverage for larger exposures.The achievable saturation coverages on both carburized surfaces areroughly equal to that on clean W(110), for which saturation valuesbetween 0.7 and 1.1 ML were derived in the literature.44−46 In good agreement with these values, we calculate a saturation coverageof 0.9 ML from the required saturation exposure of 3.4 langmuirs underthe assumption of a constant unity sticking coefficient.


Adsorption and Reactions of Carbon Monoxide and Oxygen on Bare and Au-Decorated Carburized W(110).

Bachmann M, Bikaljevic D, Memmel N, Bertel E - J Phys Chem C Nanomater Interfaces (2013)

CO uptake curves(at 90 K) on W(110), R(15 × 12)C/W(110),and R(15 × 3)/C/W(110) as obtained from the integrated TPD curves.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3753032&req=5

fig2: CO uptake curves(at 90 K) on W(110), R(15 × 12)C/W(110),and R(15 × 3)/C/W(110) as obtained from the integrated TPD curves.
Mentions: The uptake curves(at 90 K) for CO on the three templates as derivedfrom the integrated TDS intensities are summarized in Figure 2. All curves are quite similar, showing a precursor-mediatedadsorption behavior with a linear coverage increase for exposuresup to 3.4 langmuirs and an almost constant coverage for larger exposures.The achievable saturation coverages on both carburized surfaces areroughly equal to that on clean W(110), for which saturation valuesbetween 0.7 and 1.1 ML were derived in the literature.44−46 In good agreement with these values, we calculate a saturation coverageof 0.9 ML from the required saturation exposure of 3.4 langmuirs underthe assumption of a constant unity sticking coefficient.

Bottom Line: Probably the latter is associated with the existence of double-layer gold clusters and islands.Deposition of gold enhances the desorption rate of the formed CO at the low-temperature end of the recombinative CO desorption range, indicating a promoting effect of gold for oxidation of surface carbon.Two reasons could be identified: (1) weakly bound CO with desorption temperatures between 100 and 200 K (as reported for other related systems) is not observed, and (2) oxygen atoms are bonded too strongly to the templates.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 52a, A-6020 Innsbruck, Austria.

ABSTRACT
Adsorption and coadsorption of carbon monoxide and oxygen on different types of Au clusters on R(15 × 3)C/W(110) and R(15 × 12)C/W(110), respectively, are studied with respect to the catalytic behavior for oxidation of CO as well as of surface carbon. Carburization of the W(110) surface results in a weakening of the adsorption bond for molecularly adsorbed CO. Dissociation of carbon monoxide, which occurs on W(110), is reduced on the low-carbon coverage R(15 × 12) surface and completely suppressed on the carbon-saturated R(15 × 3) phase. Deposition of gold results in a blocking of adsorption sites for molecularly adsorbed CO and reopening of the dissociation channel. Probably the latter is associated with the existence of double-layer gold clusters and islands. At room temperature the gold clusters on both carburized templates are stable in CO atmosphere as shown by in-situ STM measurements. In contrast, exposure to oxygen alters the clusters on the R(15 × 12) surface, implying dissociation of oxygen not only on the substrate but also on or in immediate vicinity of the gold clusters. On the Au-free carburized templates oxygen adsorbs dissociatively and is released as CO at temperatures beyond 800 K due to reaction with carbon atoms from the templates. Deposition of gold enhances the desorption rate of the formed CO at the low-temperature end of the recombinative CO desorption range, indicating a promoting effect of gold for oxidation of surface carbon. In contrast, low-temperature CO oxidation catalyzed by the deposited Au clusters is not observed. Two reasons could be identified: (1) weakly bound CO with desorption temperatures between 100 and 200 K (as reported for other related systems) is not observed, and (2) oxygen atoms are bonded too strongly to the templates.

No MeSH data available.


Related in: MedlinePlus