| 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. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
- Mazumder, D. N. G., et al.
(författare)
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Bronchiectasis in persons with skin lesions resulting from arsenic in drinking water
- 2005
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Ingår i: Epidemiology. - : Ovid Technologies (Wolters Kluwer Health). - 1044-3983 .- 1531-5487. ; 16:6, s. 760-765
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Tidskriftsartikel (refereegranskat)abstract
- Background: Arsenic is a unique human carcinogen in that it causes lung cancer by exposure through ingestion (in drinking water) as well as through inhalation. Less is known about nonmalignant pulmonary disease after exposure to arsenic in drinking water. Methods: We recruited 108 subjects with arsenic-caused skin lesions and 150 subjects without lesions from a population survey of over 7000 people in an arsenic-exposed region in West Bengal, India. Thirty-eight study participants who reported at least 2 years of chronic cough underwent high-resolution computed tomography (CT); these scans were read by investigators in India and the United States without knowledge of the presence or absence of skin lesions. Results: The mean ( +/- standard deviation) bronchiectasis severity score was 3.4 ( +/- 3.6) in the 27 participants with skin lesions and 0.9 ( +/- 1.6) in the 11 participants without these lesions. In subjects who reported chronic cough, CT evidence of bronchiectasis was found in 18 (67%) participants with skin lesions and 3 (27%) subjects without skin lesions. Overall, subjects with arsenic-caused skin lesions had a 10-fold increased prevalence of bronchiectasis compared with subjects who did not have skin lesions (adjusted odds ratio = 10; 95% confidence interval = 2.7-37). Conclusions: These results suggest that, in addition to being a cause of lung cancer, ingestion of high concentrations of arsenic in drinking water may be a cause of bronchiectasis.
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| 7. |
- McKibbin, Sarah R., et al.
(författare)
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In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering
- 2019
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Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 12:1, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N2 gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 105 particles/cm3) corresponding to a volume fraction below 3 × 10–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions. [Figure not available: see fulltext.].
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| 8. |
- Over, H., et al.
(författare)
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Direct comparison of the reactivity of the non-oxidic phase of Ru(0001) and the RuO2 phase in the Co oxidation reaction
- 2009
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 603:2, s. 298-303
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Tidskriftsartikel (refereegranskat)abstract
- Applying in situ surface X-ray diffraction (SXRD) together with on-line mass spectrometry during the CO oxidation over Ru(0001) allows a direct comparison of the reactivity of the non-oxidic state with that of the RuO2(110) covered surface. This comparison reveals that the RuO2(110) surface is a catalytically active phase at least as active as the non-oxidic phase. At high CO and O-2 pressures of 200 mbar and temperatures above 550 K, the CO oxidation reaction does not proceed isothermally on the RuO2(110) surface. The released reaction heat leads rather to an increase of the sample temperature of up to 130 K accompanied by a self-acceleration of the CO oxidation reaction. (C) 2008 Elsevier B.V. All rights reserved.
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| 9. |
- Over, H., et al.
(författare)
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In situ structure-activity correlation experiments of the ruthenium catalyzed CO oxidation reaction
- 2009
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 145:3-4, s. 236-242
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Konferensbidrag (refereegranskat)abstract
- The complex structure-activity correlation of the CO oxidation on ruthenium has been studied in a batch reactor by using in situ surface X-ray diffraction (SXRD) and on-line mass spectrometry. Two distinct active phases are identified at higher pressures in the mbar range depending on the reaction conditions: a non-oxidic phase and a RuO2(1 1 0) layer of variable thickness ranging from 1.5 nm to 10 nm. For reaction temperatures lower than 520 K the experimental turnover frequency (TOF) numbers are shown to be almost identical for the two types of active phases. Above 520 K the RuO2(1 1 0) layer turned out to be much more active than the non-oxidic phase. Kinetic reaction experiments on the RuO2(1 1 0) phase reveal an activation energy of 78 +/- 10 kJ/mol which is in perfect agreement with corresponding reactivity experiments on supported and powder RuO2 catalyst. Under oxidizing reaction conditions and high concentration of CO2 in the gas mixture, the RuO2(1 1 0) model catalyst shows reversible product-poisoning. (C) 2008 Elsevier B.V. All rights reserved.
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| 10. |
- van Rijn, R., et al.
(författare)
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Surface structure and reactivity of Pd(100) during CO oxidation near ambient pressures
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 13:29, s. 13167-13171
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Tidskriftsartikel (refereegranskat)abstract
- The surface structure of Pd(100) during CO oxidation was measured using a combination of a flow reactor and in situ surface X-ray diffraction coupled to a large-area 2-dimensional detector. The surface structure was measured for P-O2/P-CO ratios between 0.6 and 10 at a fixed total gas pressure of 200 mbar and a fixed CO pressure of 10 +/- 1 mbar. In conjunction with the surface structure the reactivity of the surface was also determined. For all P-O2/P-CO ratios the surface was found to oxidize above a certain temperature. Three different types of oxides were observed: the (root 5 x root 5)R27 degrees surface oxide, an epitaxial layer of bulk-like PdO, and a non-epitaxial layer of bulk-like PdO. As soon as an oxide was present the reactivity of the surface was found to be mass transfer limited by the flux of CO molecules reaching the surface.
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| 11. |
- von Fieant, Kristina, et al.
(författare)
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In Situ Formation of Ge Nanoparticles by Annealing of Al-Ge‑N ThinFilms Followed by HAXPES and XRD
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:16, s. 11100-11109
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Tidskriftsartikel (refereegranskat)abstract
- Ge nanoparticles embedded in thin films have attracted a lot of attention due to their promising optical and electronic properties that can be tuned by varying the particle size and choice of matrix material. In this study, Ge nanoparticle formation was investigated for Al-Ge-N based thin films by simultaneous measurements of HAXPES and grazing incidence XRD during in situ annealing in vacuum conditions. As-deposited Al-Ge-N thin films, synthesized by reactive dc magnetron sputtering, consisted of a nanocrystalline (Al1–xGex)Ny solid solution and an amorphous tissue phase of Ge3Ny. Upon annealing to 750 °C, elemental Ge was formed shown by both HAXPES and XRD measurements, and N2 gas was released as measured by a mass spectrometer. Postannealed ex situ analysis by SEM and TEM showed that the elemental Ge phase formed spherical nanoparticles on the surface of the film, with an average size of 210 nm. As the annealing temperature increased further to 850 °C, the Ge particles on the film surface evaporated, while the phase segregation of Ge still could be observed within the film. Thus, these results show the possibility for a controlled synthesis of Ge nanoparticles through annealing of Al-Ge-N thin films to produce materials suitable for use in electronic or optoelectronic devices.
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| 12. |
- 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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| 13. |
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| 14. |
- 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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| 15. |
- Zweidinger, S., et al.
(författare)
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In situ studies of the oxidation of HCl over RuO2 model catalysts: Stability and reactivity
- 2010
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 272:1, s. 169-175
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Tidskriftsartikel (refereegranskat)abstract
- Structure-activity experiments were performed for the HCl oxidation reaction (Deacon-like process) over RuO2 model catalysts - RuO2(1 1 0) and RuO2(1 0 0) - applying in situ surface X-ray diffraction (SXRD) combined with on-line mass spectrometry. The studied model catalysts turned out to be long-term stable under reaction conditions with gas feed ratios p(HCl):p(O-2) ranging from 1:4 to 4:1 in the mbar pressure regime and temperatures as high as 685 K. Even pure HCl exposure in the mbar regime was not able to reduce RuO2 below 600 K; above 650 K chemical reduction of the oxide sets in. Under strongly oxidizing reaction conditions, the (surface) oxides grow slowly in thickness. On-line reactivity experiments of both types of model catalysts in a batch reactor yield a mean turn-over frequency (TOP) of 0.6 Cl-2 molecules per second and active site for the HCl oxidation at 650 K and initial partial pressures of p(HCl) = 2 mbar and p(O-2) = 0.5 mbar. The HCl oxidation over RuO2 is therefore considered to be structure insensitive. (C) 2010 Elsevier Inc. All rights reserved.
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