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| 2. |
- Eriksson, Mats, 1963-, et al.
(author)
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Spillover of hydrogen, oxygen and carbon monoxide in oxidation reactions on SiO2 supported Pd
- 1994
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 311:1-2, s. 139-152
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Journal article (peer-reviewed)abstract
- Oxidation of H2 and CO on large, oxygen preexposed Pd islands supported on SiO2, has been investigated in the temperature range 323 ⩽, T ⩽ 523 K. The results have been compared with the corresponding reactions on a polycrystalline Pd film. A maximum reactive sticking coefficient of 0.9 for H2 and an initial sticking coefficient for O2 of 0.8 on both structures is concluded. The maximum reactive sticking coefficient for CO is 0.85 on the film and apparently larger than unity on the island structure. The results obtained from the island structure can be rationalized if O2 and H2 dissociate on the Pd islands and have the possibility to spillover onto the oxide, while CO adsorbs and reacts both on the Pd islands and on the oxide. Spillover of oxygen occurs in a precursor state and is irreversible with an apparent activation energy of 0.1 eV for the forward reaction.
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| 3. |
- Eriksson, Mats, 1963-, et al.
(author)
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The water-forming reaction on thin, SiO2 supported, palladium films
- 1990
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In: Vacuum. - 0042-207X .- 1879-2715. ; 41:1-3, s. 137-138
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Journal article (peer-reviewed)abstract
- The water-forming reaction has been studied on thin Pd films, evaporated on planar SiO2 substrates. The nominal film thickness varied between 5 and 100 Å. The studies were performed in uhv by means of mass spectrometry, UPS and work function measurements in the temperature range 323–523 K. The film structure was also studied with TEM. The results are compared with previous measurements on 1000 Å, thick, homogeneous Pd films. The structure of the thin Pd films changed dramatically during cyclic H2 and O2 exposures, from that of a continuous film with cracks to that of drop-like metal particles. These structural changes are not observed on the thick (1000 Å) Pd films. Even though there are large structural changes, the water-forming reaction looks qualitatively the same as on a thick Pd film. The total water production however, decreases with decreasing film thickness. We believe that some minor qualitative differences in the water-forming reaction for different nominal Pd film thicknesses, are due to the increasing PdSiO2 boundary as the thickness is reduced.
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| 4. |
- Erlandsson, Ragnar, et al.
(author)
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Gas-induced restructuring of palladium model catalysts studied with atomic force microscopy
- 1991
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In: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 9:2, s. 825-828
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Journal article (peer-reviewed)abstract
- The structure of thin Pd films evaporated onto planar SiO2 substrates changes dramatically during oxygen/hydrogen exposures in ultrahigh vacuum. In this work we have used an atomic force microscope(AFM), operated in the attractive mode, to obtain the three‐dimensional morphology of the Pd surface for different film thicknesses and treatments, and compared the data with transmission electron microscopy(TEM) micrographs. During restructuring, a 100‐Å film changes from being a smooth continuous film with cracks into metal clusters dispersed on the SiO2 support. In the 5‐Å case the metal films are already well dispersed as fabricated. Here the gas exposure instead results in a clustering effect resulting in larger particles. The AFM gives results which are consistent with TEM micrographs but also gives additional information on metal particle shape which can lead to a further understanding of the restructuring process.
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