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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.


Related in: MedlinePlus

In-situ STMstudy of the influence of oxygen (p = 5 × 10–8 mbar) on the R(15 × 3) andR(15 × 12) templates covered with Au clusters: (a) R(15 ×3), before gas exposure, (b) R(15 × 3) after 55 langmuirs ofO2, (c) R(15 × 12), before gas exposure, (d) R(15× 12) after 86 langmuirs of O2. Image sizes: 40 nm× 40 nm (a, b) and 80 × 80 nm (c, d).
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fig6: In-situ STMstudy of the influence of oxygen (p = 5 × 10–8 mbar) on the R(15 × 3) andR(15 × 12) templates covered with Au clusters: (a) R(15 ×3), before gas exposure, (b) R(15 × 3) after 55 langmuirs ofO2, (c) R(15 × 12), before gas exposure, (d) R(15× 12) after 86 langmuirs of O2. Image sizes: 40 nm× 40 nm (a, b) and 80 × 80 nm (c, d).

Mentions: The evolution of the Au-covered R(15 × 3)C/W(110)surfaceupon O2 exposure is shown in Figure 6a,b. (More images are shown in the SupportingInformation, Figures S4 and S5.) Apart from very occasionalmodifications (such as the disappearing cluster in the center of thewhite marker) the bilayer gold particles obviously are quite stableto O2. By contrast, pronounced oxygen-induced changes occurfor the Au clusters on the R(15 × 12) template (see Figure 6c,d). With increasing oxygen exposure the originallywell-aligned nanodots show strong modifications: Increasing oxygenexposure leads to less perfect ordering, the size distribution isbroadened significantly, and some bilayer clusters are formed. Afteran exposure of ≈90 langmuirs a quite stable state is reached;the clusters are hardly altered anymore. Agglomeration to larger islands,supposedly exhibiting a negative effect on the reactivity of Au clusters,is not observed. Note that the rather strong oxygen-induced alterationsof the gold nanoparticles indicate dissociation of the oxygen moleculeson or at least in close vicinity of the Au clusters on the R(15 ×12) substrate.


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)

In-situ STMstudy of the influence of oxygen (p = 5 × 10–8 mbar) on the R(15 × 3) andR(15 × 12) templates covered with Au clusters: (a) R(15 ×3), before gas exposure, (b) R(15 × 3) after 55 langmuirs ofO2, (c) R(15 × 12), before gas exposure, (d) R(15× 12) after 86 langmuirs of O2. Image sizes: 40 nm× 40 nm (a, b) and 80 × 80 nm (c, d).
© Copyright Policy
Related In: Results  -  Collection

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

fig6: In-situ STMstudy of the influence of oxygen (p = 5 × 10–8 mbar) on the R(15 × 3) andR(15 × 12) templates covered with Au clusters: (a) R(15 ×3), before gas exposure, (b) R(15 × 3) after 55 langmuirs ofO2, (c) R(15 × 12), before gas exposure, (d) R(15× 12) after 86 langmuirs of O2. Image sizes: 40 nm× 40 nm (a, b) and 80 × 80 nm (c, d).
Mentions: The evolution of the Au-covered R(15 × 3)C/W(110)surfaceupon O2 exposure is shown in Figure 6a,b. (More images are shown in the SupportingInformation, Figures S4 and S5.) Apart from very occasionalmodifications (such as the disappearing cluster in the center of thewhite marker) the bilayer gold particles obviously are quite stableto O2. By contrast, pronounced oxygen-induced changes occurfor the Au clusters on the R(15 × 12) template (see Figure 6c,d). With increasing oxygen exposure the originallywell-aligned nanodots show strong modifications: Increasing oxygenexposure leads to less perfect ordering, the size distribution isbroadened significantly, and some bilayer clusters are formed. Afteran exposure of ≈90 langmuirs a quite stable state is reached;the clusters are hardly altered anymore. Agglomeration to larger islands,supposedly exhibiting a negative effect on the reactivity of Au clusters,is not observed. Note that the rather strong oxygen-induced alterationsof the gold nanoparticles indicate dissociation of the oxygen moleculeson or at least in close vicinity of the Au clusters on the R(15 ×12) substrate.

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