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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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TPD spectraof Au/R(15 × 3)C/W(110) after exposure to 10 langmuirsof CO. A deposition time of 1 min corresponds to a coverage of 0.1–0.2ML.
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fig4: TPD spectraof Au/R(15 × 3)C/W(110) after exposure to 10 langmuirsof CO. A deposition time of 1 min corresponds to a coverage of 0.1–0.2ML.

Mentions: Depositionof Au on R(15 × 3) essentially quenches the low-temperature“molecular” CO desorption features located at T ≲ 400 K (see Figure 4).This can be understood as a site-blocking effect. Surprisingly, athigh temperatures (ca. 850–900 K) a new CO desorption featureevolves with increasing gold coverage. It is tempting to attributethis observation to CO molecules adsorbed at the periphery or on topof the deposited gold particles. However, in view of the weak CO–goldinteraction,52−56 such a high desorption temperature seems to be impossible for molecularlyadsorbed CO. It appears to be more reasonable to assign this desorptionfeature to recombinatively desorbing CO. This implies the presenceof atomic oxygen which can only arise from CO dissociation. The microscopicorigin for this surprising Au-induced CO dissociation is unclear atpresent.


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)

TPD spectraof Au/R(15 × 3)C/W(110) after exposure to 10 langmuirsof CO. A deposition time of 1 min corresponds to a coverage of 0.1–0.2ML.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: TPD spectraof Au/R(15 × 3)C/W(110) after exposure to 10 langmuirsof CO. A deposition time of 1 min corresponds to a coverage of 0.1–0.2ML.
Mentions: Depositionof Au on R(15 × 3) essentially quenches the low-temperature“molecular” CO desorption features located at T ≲ 400 K (see Figure 4).This can be understood as a site-blocking effect. Surprisingly, athigh temperatures (ca. 850–900 K) a new CO desorption featureevolves with increasing gold coverage. It is tempting to attributethis observation to CO molecules adsorbed at the periphery or on topof the deposited gold particles. However, in view of the weak CO–goldinteraction,52−56 such a high desorption temperature seems to be impossible for molecularlyadsorbed CO. It appears to be more reasonable to assign this desorptionfeature to recombinatively desorbing CO. This implies the presenceof atomic oxygen which can only arise from CO dissociation. The microscopicorigin for this surprising Au-induced CO dissociation is unclear atpresent.

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