| 1. |
- Gustafson, Johan, et al.
(författare)
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Catalytic Activity of the Rh Surface Oxide: CO Oxidation over Rh(111) under Realistic Conditions
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:10, s. 4580-4583
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Tidskriftsartikel (refereegranskat)abstract
- Using a combination of surface X-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity of a Rh(111) model catalyst has been studied in conjunction with the surface structure. The measurements show that it specific thin surface oxide is always present in the high activity regime of Rh-based CO oxidation.
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| 2. |
- Gustafson, Johan, et al.
(författare)
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Oxygen-induced step bunching and faceting of Rh(553): Experiment and ab initio calculations
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 74:3
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Tidskriftsartikel (refereegranskat)abstract
- Using a combined experimental and theoretical approach, we show that the initial oxidation of a Rh(553) surface, a surface vicinal to (111), undergoes step bunching when exposed to oxygen, forming lower-index facets. At a pressure of about 10(-6) mbar and a temperature of 380 degrees C this leads to (331) facets with one-dimensional oxide chains along the steps, coexisting with (111) facets. Further increase of the pressure and temperature results in (111) facets only, covered by an O-Rh-O surface oxide. Our density functional theory calculations provide an atomistic understanding of the observed behavior.
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| 3. |
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| 4. |
- Gustafson, Johan, et al.
(författare)
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Self-limited growth of a thin oxide layer on Rh(111)
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 92:12
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.
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| 5. |
- Gustafson, J., et al.
(författare)
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Sensitivity of catalysis to surface structure: The example of CO oxidation on Rh under realistic conditions
- 2008
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 78:4
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Tidskriftsartikel (refereegranskat)abstract
- Using a combination of surface x-ray diffraction and mass spectrometry at realistic pressures, the CO oxidation reactivity of Rh(111) and Rh(100) model catalysts has been studied in conjunction with the surface structure. The measurements show that the presence of a specific thin surface oxide is crucial for the high activity of the Rh based CO oxidation. As this oxide is readily formed on all Rh facets, we conclude that the specific Rh crystal planes exposed during catalysis will not directly influence the reactivity. This is fortified by the very close similarity between the Rh(111) and the Rh(100) results.
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| 6. |
- Gustafson, Johan, et al.
(författare)
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Structure and catalytic reactivity of Rh oxides
- 2009
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 145:3-4, s. 227-235
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Konferensbidrag (refereegranskat)abstract
- Using a combination of experimental and theoretical techniques, we show that a thin RhO2 surface oxide film forms prior to the bulk Rh2O3 corundum oxide on all close-packed single crystal Rh surfaces. Based on previous reports, we argue that the RhO2 surface oxide also forms on vicinal Rh surfaces as well as on Rh nanoparticles. The detailed structure of this film was previously determined using UHV based techniques and density functional theory. In the present paper, we also examine the structure of the bulk Rh2O3 corundum oxide using surface X-ray diffraction. Being armed with this structural information, we have explored the CO oxidation reaction over Rh(1 1 1), Rh(1 0 0) and Pt25Rh75(1 0 0) at realistic pressures using in situ surface X-ray diffraction and online mass spectrometry. In all three cases we find that an increase of the CO2 production coincides with the formation of the thin RhO2 surface oxide film. In the case of Pt25Rh75(1 0 0), our measurements demonstrate that the formation of bulk Rh2O3 corundum oxide poisons the reaction, and argue that this is also valid for all other Rh surfaces. Our study implies that the CO oxidation reaction over Rh surfaces at realistic conditions is insensitive to the exact Rh substrate orientation, but is rather governed by the formation of a specific surface oxide phase. (C) 2008 Elsevier B.V. All rights reserved.
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| 7. |
- Lundgren, Edvin, et al.
(författare)
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Geometry of the valence transition induced surface reconstruction of Sm(0001).
- 2002
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 88:13, s. 136102-136102
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Tidskriftsartikel (refereegranskat)abstract
- We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the 4f electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.
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| 8. |
- Westerström, Rasmus, et al.
(författare)
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Structure and reactivity of a model catalyst alloy under realistic conditions
- 2008
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:18, s. 6-184018
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Tidskriftsartikel (refereegranskat)abstract
- Using a combined experimental and theoretical approach, we show that a thin RhO2 oxide film forms on a Pt25Rh75(100) surface at elevated oxygen pressures and temperatures prior to the bulk oxidation. By the use of in situ surface x-ray diffraction under realistic CO oxidation reaction conditions, we show that the onset of the growth of thin RhO2 oxide film coincides with an increase in CO2 production. During the reaction, the consumed oxide film is continuously re-grown by oxygen in the gas phase. Our theoretical results strongly suggest that the CO adsorbs on the metallic substrate but reacts with the O in the RhO2 oxide film at the border between the RhO2 oxide film and the metallic substrate. This scenario could explain the experimental observations of oxidation reactions on other late transition metal surfaces as well as on their corresponding nanoparticles under realistic conditions.
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