| 1. |
- Weststrate, C. J., et al.
(författare)
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CO adsorption on Au(310) and Au(321): 6-Fold coordinated gold atoms
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 603:13, s. 2152-2157
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of CO on Au(310) and Au(321) was studied using a combination of thermal desorption spectroscopy and high resolution core level photoemission spectroscopy. These vicinal Au surfaces both have 6-fold coordinated atoms at the step edges but have a different terrace structure. The CO adsorption behavior was found to be very similar for both surfaces. Three different desorption peaks due to chemisorbed CO were identified, which desorb around 100 K(alpha), 120 K(beta) and 180 K(gamma), respectively. The C1s and O1s spectra of the chemisorbed CO show a complex shake-up structure. Our experimental results indicate that CO only adsorbs on the step atoms. The different desorption peaks are explained by substrate-mediated long-range interactions between the adsorbates. Comparison with literature results shows that the CO adsorption energy is not only dependent on the coordination number of the Au atoms, but that the exact geometrical structure of the surface also plays a role. (C) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Westerström, Rasmus, et al.
(författare)
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Stressing Pd atoms: Initial oxidation of the Pd(110) surface
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 602:14, s. 2440-2447
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the oxygen induced structures of the Pd(1 1 0) surface in the pressure range of 10(-5)-10(-3) mbar of oxygen, at a sample temperature of around 300 degrees C. These structures, denoted as "(7 x root 3)" and "(9 x root 3)", are studied in detail by the use of a combination of low-energy electron diffraction, scanning tunneling microscopy, high-resolution core level spectroscopy, and ab-initio simulations. Based on our data a model is proposed for these structures containing segments of Pd atoms in the [1 (1) over bar0] direction, in which the Pd rows are decorated by O atoms in a zig-zag pattern. The segments are periodically separated by displaced Pd atoms. Density functional theory calculations show that the displacements reduce the oxygen induced stress significantly, as compared to a structure with no displacements. The calculations also suggest that the new structures are stabilized by domain formation. (C) 2008 Elsevier B.V. All rights reserved.
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| 3. |
- Zweidinger, S., et al.
(författare)
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Reaction mechanism of the oxidation of HCl over RuO2(110)
- 2008
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:27, s. 9966-9969
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution core-level shift spectroscopy and temperature-programmed reaction experiments together with density functional theory calculations reveal that the oxidation of HCl with oxygen producing Cl-2 and water proceeds on the chlorine-stabilized RuO2(110)surface via a one-dimensional Langmuir-Hinshelwood mechanism. The recombination of two adjacent chlorine atoms on the catalyst's surface constitutes the rate-determining step in this novel Deacon-like process.
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| 4. |
- Westerström, Rasmus, et al.
(författare)
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Lack of surface oxide layers and facile bulk oxide formation on Pd(110)
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 80:12
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of the Pd(110) surface has been studied from ultrahigh vacuum up to atmospherical pressures by combining scanning tunneling microscopy, low-energy electron diffraction and high-resolution core-level spectroscopy with in situ surface x-ray diffraction, and density-functional theory calculations. Under in situ conditions, we observe a c(2x4) structure which transforms via the formation of antiphase domain boundaries to a "complex" structure with increasing partial oxygen pressure. Contrary to other closed packed and vicinal Pd surfaces investigated so far, no surface oxide is formed, which allows for the formation of the PdO bulk oxide closer to the thermodynamic limit at temperatures relevant for catalysis.
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| 5. |
- Weststrate, C J, et al.
(författare)
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CO adsorption on a Au/CeO2 (111) model catalyst
- 2008
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:17, s. 6900-6906
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Tidskriftsartikel (refereegranskat)abstract
- We prepared a Au/CeO2 (111) model catalyst by depositing a thin cerium oxide film on a Ru(0001) surface and subsequently depositing gold. This model system was investigated using high-resolution photoemission spectroscopy. Gold forms metallic nanoparticles on CeO2 with an average particle size that depends on the Au dose. At 80 K adsorption of CO was observed on the supported Au particles, which induces a chemical shift of +0.9 eV in the An 4f level of the An atoms directly involved in the Au-CO bond. CO adsorption also induces an additional, particle-size-dependent shift, which affects all Au atoms in the particle; i.e., the whole Au particle is affected by CO adsorption. The fraction of surface atoms involved in CO bonding decreases with increasing gold particle size, from similar to 60-70% for small particles to 15-20% for large particles. It is concluded that CO only adsorbs on defects (low-coordinated Au atoms). The CO desorption temperature decreases with increasing particle size. This is explained as follows: on small particles the most abundant defects are corner atoms and kinks (6-coordinated), which interact strongly with CO. On large particles the most abundant defects are edges between two planes (7-coordinated), which interact less strongly with CO.
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| 6. |
- Weststrate, C. J., et al.
(författare)
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Influence of Oxygen Vacancies on the Properties of Ceria-Supported Gold
- 2009
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:2, s. 724-728
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of CO on narrosized gold particles deposited on a cerium oxide substrate is strongly influenced by the roughness and concentration of oxygen vacancies of the CeOx substrate surface. Literature showed that Au nucleates at step edges on oxidized samples. For oxidized samples we found that the Au dispersion is dependent on the surface roughness. A rough CeO2 surface has a higher step density, which results in a Au higher particle density with a smaller average diameter. Other studies showed that Au nucleates on oxygen vacancies on reduced CeOx substrates. We found that small Au particles adsorbed on oxygen vacancies exhibit a significantly higher Au 4f binding energy than Au particles on oxidized CeO2. Relatively less CO adsorbs on small Au particles on a reduced substrate, with a significantly lower adsorption energy than on Au on an oxidized substrate. For larger particles the influence of oxygen vacancies in the substrate is negligible.
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