| 1. |
- Blomberg, Sara, et al.
(författare)
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A high pressure X-ray photoelectron spectroscopy study of oxidation and reduction of Rh(100) and Rh nanoparticles
- 2014
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 628, s. 153-158
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the oxidation and reduction of Rh(100) and SiO2 supported Rh particles using high pressure X-ray photoelectron spectroscopy. We show that the formation and reduction of Rh bulk oxide can be followed in situ in O-2 and CO pressures in the range of 0.1 Torr. In general, the oxidation/reduction processes are similar on Rh(100) and the nanoparticles, but there are significant differences in temperature dependence. Already at a sample temperature of 140 degrees C, the particles show clear signs of a thin bulk oxide, while an ultra-thin so-called surface oxide covers the single crystal at the same temperature. Both of these oxide films, however, hinder further oxidation, and a thick oxide is only found at a temperature of at least 300 degrees C, for both samples. The reduction, in contrast, starts at a higher temperature on the particles as compared to the single crystal, but once started the particles are completely reduced at lower temperatures. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
- Blomberg, Sara, et al.
(författare)
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Generation and oxidation of aerosol deposited PdAg nanoparticles
- 2013
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 616, s. 186-191
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Tidskriftsartikel (refereegranskat)abstract
- PdAg nanoparticles with a diameter of 10 nm have been generated by an aerosol particle method, and supported on a silica substrate. By using a combination of X-ray Energy Dispersive Spectroscopy and X-ray Photoelectron Spectroscopy it is shown that the size distribution of the particles is narrow and that the two metals form an alloy with a mixture of 75% Pd and 25% Ag. Under oxidizing conditions, Pd is found to segregate to the surface and a thin PdO like oxide is formed similar to the surface oxide previously reported on extended PdAg and pure Pd surfaces. (C) 2013 Elsevier B.V. All rights reserved.
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| 3. |
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| 4. |
- Westerström, Rasmus, et al.
(författare)
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Oxidation and reduction of Pd(100) and aerosol-deposited Pd nanoparticles
- 2011
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 83:11
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Tidskriftsartikel (refereegranskat)abstract
- Using in situ high-pressure x-ray photoelectron spectroscopy, we have followed the oxidation and the reduction of Pd model catalysts in oxygen and CO pressures in the millibar range. The study includes a Pd(100) single crystal as well as SiOx-supported Pd nanoparticles of 15 or 35 nm diameter, respectively. We demonstrate that nanoparticles also form ultrathin surface oxides prior to the onset of the bulk PdO. The Pd nanoparticles are observed to bulk oxidize at sample temperatures 40 degrees lower than the single-crystal surface. In the Pd 3d(5/2) and the O 1s spectrum, we identify a component corresponding to undercoordinated atoms at the surface of the PdO oxide. The experimentally observed PdO core-level shift is supported by density functional theory calculations. In a CO atmosphere, the Pd 3d(5/2) component corresponding to undercoordinated PdO atoms is shifted by + 0.55 eV with respect to PdO bulk, demonstrating that CO molecules preferably adsorb at these sites. CO coordinated to Pd atoms in the metallic and the oxidized phases can also be distinguished in the C 1s spectrum. The initial reduction by CO is similar for the single-crystal and the nanoparticle samples, but after the complete removal of the oxide we detect a significant deviation between the two systems, namely that the nanoparticles incorporate carbon to form a Pd carbide. Our results indicate that CO can dissociate on the nanoparticle samples, whereas no such behavior is observed for the Pd(100) single crystal. These results demonstrate the similarities, as well as the important differences, between the single crystals used as model systems for catalysis and nm-sized particles on oxide supports.
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