| 1. |
- Tafoya, D., et al.
(författare)
-
Detection of HCO+ emission toward the planetary nebula K3-35
- 2007
-
Ingår i: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 133:2, s. 364-369
-
Tidskriftsartikel (refereegranskat)abstract
- We report the detection, for the first time, of HCO+(J = 1 -> 0) emission, as well as marginal CO(J = 1 -> 0) emission, toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO( J 2 ! 1) and water maser emission, as well as upper limits for the emission of the SiO, (HCO+)-C-13, HNC, HCN, HC3OH, HC5N, CS, HC3N, (CO)-C-13, CN, and NH3 molecules. From the ratio of CO(J = 2 -> 1) to CO(J = 1 -> 0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of similar or equal to 20 K. Using this result we have estimated a molecular mass for the envelope of similar or equal to 0.017M(circle dot) and an HCO+ abundance relative to H-2 of 6 x 10(-7), similar to the abundances found in other PNe. K3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region, as well as at a distance of similar or equal to 5000 AU from the center. The presence of molecular emission provides some clues that could help in understanding the persistence of water molecules in the envelope of K3-35. The HCO+ emission could be arising in dense molecular clumps, which may provide the shielding mechanism that protects water molecules in this source.
|
|
| 2. |
- Westerström, Rasmus, et al.
(författare)
-
Structure and reactivity of a model catalyst alloy under realistic conditions
- 2008
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:18, s. 6-184018
-
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.
|
|
| 3. |
- Gustafson, Johan, et al.
(författare)
-
Structure and catalytic reactivity of Rh oxides
- 2009
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 145:3-4, s. 227-235
-
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.
|
|
