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| 2. |
- Hägglund, Carl, 1975-, et al.
(författare)
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Growth, intermixing, and surface phase formation for zinc tin oxide nanolaminates produced by atomic layer deposition
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 34:2
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Tidskriftsartikel (refereegranskat)abstract
- A broad and expanding range of materials can be produced by atomic layer deposition at relatively low temperatures, including both oxides and metals. For many applications of interest, however, it is desirable to grow more tailored and complex materials such as semiconductors with a certain doping, mixed oxides, and metallic alloys. How well such mixed materials can be accomplished with ALD requires knowledge of the conditions under which the resulting films will be mixed, solid solutions, or laminated. The growth and lamination of zinc oxide and tin oxide is studied here by means of the extremely surface sensitive technique of low energy ion scattering, combined with bulk composition and thickness determination, and X-ray diffraction. At the low temperatures used for deposition (150 °C) there is little evidence for atomic scale mixing even with the smallest possible bilayer period, and instead a morphology with small ZnO inclusions in a SnOx matrix is deduced. Post-annealing of such laminates above 400 °C however produces a stable surface phase with a 30% increased density. From the surface stoichiometry, this is likely the inverted spinel of zinc stannate, Zn2SnO4. Annealing to 800 °C results in films containing crystalline Zn2SnO4, or multilayered films of crystalline ZnO, Zn2SnO4 and SnO2 phases, depending on the bilayer period.
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| 3. |
- Martin, Natalia Mihaela, 1984, et al.
(författare)
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A LEIS and in situ XAS study of supported Pd-Pt catalysts for CH4 oxidation
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is of vital importance to remove methane (CH4) from the exhausts of natural gas and biogas fueled engines as CH4 is a strong greenhouse gas. So far Pd-based catalysts have been used almost exclusively but their high sensitivity to sulfur and water pushes research to explore other materials. Among these are Pd-Pt catalysts [1-4], which exhibit a slight increase in CH4 oxidation activity with time and higher long-term stability than the Pd-only counterpart [5-7]. Still, however, little is known about the oxidation-reduction behaviour of the Pd-Pt nanoclusters and how this impacts the catalytic activity. This study aims at increase the understanding of the catalytic activity of Al2O3-supported Pd-Pt nanoclusters for low-temperature CH4 oxidation under transient, although generally lean, conditions.
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| 4. |
- Martin, Natalia Mihaela, 1984, et al.
(författare)
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Characterization of Surface Structure and Oxidation/Reduction Behaviour of Pd-Pt/Al2O3 Model Catalysts
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:49, s. 28009-28020
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Tidskriftsartikel (refereegranskat)abstract
- Structural and morphological characterisation of bimetallic Pd-Pt/Al2O3 model cat- alysts are performed using X-ray diffraction, X-ray absorption spectroscopy, transmis- sion electron microscopy and CO chemisorption. Further, the catalysts were studied under oxidising and reducing conditions using both X-ray absorption spectroscopy and low-energy ion scattering spectroscopy. For the as-prepared catalysts, the existence of alloyed bimetallic Pd-Pt particles and of (tetragonal) PdO were found for the samples calcined at 800 C. PdO is present in form of crystals at the surface of the Pd-Pt par- ticles or as isolated PdO crystals on the support oxide. Bimetallic Pd-Pt nanoparticles were only formed on the Pd-Pt catalysts after calcination at 800 C. The results show that the Pd-Pt nanoparticles undergo reversible changes in surface structure composi- tion and chemical state in response to oxidising or reducing conditions. Under oxidising conditions Pd segregates to the shell and oxidises forming PdO, while under reducing conditions regions with metallic Pd and Pd-Pt alloys were observed at the surface. No bimetallic Pd-Pt nanoparticles were observed for the sample initially calcined at 500 C, but instead isolated monometallic particles, where small Pt particles are easily oxidised under O2 treatment. In the monometallic catalysts, the Pd is found to be com- pletely oxidised already after calcination and to consist of metallic Pd after reductive treatment.
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| 7. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Characterization of a Pt-Pd combustion catalyst on an alumina washcoat, with and without prior hydrothermal treatment of the washcoat
- 1992
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Ingår i: Catalysis Letters. - 1572-879X .- 1011-372X. ; 13:1-2, s. 27-38
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Tidskriftsartikel (refereegranskat)abstract
- Two Pt/Pd catalysts on cordierite monoliths were prepared by impregnating two differently treated alumina washcoats with 10/micromol [Pt + Pd] per gram catalyst in the atomic ratio Pt/Pd = 4.0. Both washcoats were first thermally treated, calcined, for 2 h at 550C in air and one of them was additionally treated, hydrothermally, in 100% steam for 2 h at 814C. The hydrothermally treated catalyst was more active for complete oxidation of xylene in air:its light-off temperature was 232C compared to 259C for the sample calcined only. To explain this higher activity, both catalysts were characterized by BET surface area, pore-size distribution, hydrogen chemisorption, X-ray diffraction, TEM/STEM/EDS and low-energy ion scattering spectroscopy (LEIS). The catalyst with a hydrothermally treated washcoat had 30% lower surface area, larger alumina crystal size, higher degree of crystallization ofalumina and larger average catalyst pore size (11 nm vs. 6 nm), than the one with the washcoat, treated only thermally. The LEIS results indicated a surface enrichment of Pd on both catalysts. The Pt signal in LEIS was higher for the hydrothermally treated sample.
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