| 1. |
- Habermehl-Cwirzen, Karin, et al.
(författare)
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An experimental study on adsorption of benzene on Co(0001)
- 2002
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 507, s. 57-61
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of benzene on Co(0 0 0 1) was studied by X-ray photoelectron spectroscopy, temperature programmed desorption, low energy electron diffraction (LEED) and work function measurements. The adsorption was found to be molecular at room temperature and to saturate at a fractional coverage of 0.125 ML. With LEED a c(2root3 x 4) overlayer structure was seen. Below 220 K at high exposures a p(root7 x root7)R19degrees LEED pattern was observed corresponding to a coverage of 0.143 ML. Temperature programmed desorption measurements stated that benzene starts to decompose around 340 K to hydrogen and a hydrocarbon fragment, most likely C6H5. While the hydrogen desorbed, the hydrocarbon stayed at the surface. The desorption of molecular benzene was negligible. The activation energy for the dehydrogenation was calculated to be about 102 kJ/mol. The work function of Co(0 0 0 1) decreased by 1.3 eV upon saturation with benzene. The induced dipole moment was calculated to be 1.9 Debye/molecule.
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| 2. |
- Habermehl-Cwirzen, Karin, et al.
(författare)
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Coadsorption of CO and C6H6 on Co(0 0 0 1)
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 584:1, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the influence of CO on the adsorption of benzene on the Co(0 0 0 1) surface using LEED, XPS, TDS and work function measurements. CO was found to reduce the benzene adsorption, but even at saturation CO exposure no complete blocking was observed. Thermal desorption of the coadsorbed layer featured CO and H2 peaks indicating partial dehydrogenation of benzene and retaining of the CO bond. Ordered LEED structures were found with all coverages: Pre-adsorption of CO led to patterns already seen for pure carbon monoxide adsorption. Pre-adsorption of benzene showed the known (7×7)R19°structure of pure benzene also with small CO exposures, but higher CO exposures yielded a mixture of (7×7)R19°and (3×3)R30°patterns
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| 3. |
- Habermehl-Cwirzen, Karin, et al.
(författare)
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Hydrogen on cobalt : effects of carbon monoxide and sulphur additives on the D-2/Co(0001) system
- 2004
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Ingår i: Physica scripta. T. - 0281-1847. ; :T108, s. 28-32
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen reaction on catalytic surfaces is an important field of research in fuel cell science. The adsorption of hydrogen (deuterium) on Co(0001) and the influence of carbon monoxide and sulphur on the adsorption were studied by XPS, TDS, WF measurements and LEED. The WF increased due to D2 adsorption, revealing the electronegative character of deuterium. It was found that the deuterium saturation coverage is similar to 0.17 ML at 320K and similar to 0.27ML at 180 K. The activation energy for desorption was estimated to be 33 kJ/mol. The coadsorption measurements with CO indicated a decrease in the deuterium yield by 50%. A downward shift of 50K in the deuterium desorption temperature was observed as a consequence of coadsorbed CO, but changes in the CO desorption were minimal. At small CO exposures the (2 X 2) LEED structure of deuterium was seen, while at exposures of above 5 L the (2 root 3 x 2 root 3)R30... structure was detected by LEED as with pure CO adsorption. Coadsorption with sulphur led also to a decrease in the D2 yield leading to a complete inhibition of hydrogen adsorption at sulphur saturation. The sulphur (2 X 2) LEED structure did not underwent changes due to deuterium adsorption. As assumed, sulphur worked as a strong poison to the adsorption on Co(0001).
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| 4. |
- Habermehl-Cwirzen, Karin, et al.
(författare)
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Methanol on Co(0 0 0 1) : XPS, TDS, WF and LEED results
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 598:1-3, s. 128-135
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and decomposition of methanol on clean Co(0 0 0 1) was studied as a function of temperature and exposure by means of TDS (thermal desorption spectroscopy), XPS (X-ray photoelectron spectroscopy), WF (work function measurements) and LEED (low energy electron diffraction). Methanol was adsorbed by OH-bond scission as methoxide on the cobalt surface. TD and XP spectra revealed that beside a small amount of molecularly desorbing methanol, it decomposed during heating to the final products: CO and H2. Desorption of H2 took place around 356 K and desorption of CO around 390 K. These temperatures are characteristic for desorption of these species on clean cobalt. Work function measurements showed that the adsorption of methanol resulted in a lowering of the WF by 1.1 eV. Heating - and therewith decomposition - led to an increase in the WF of +0.4 eV. After all decomposition products had desorbed, the WF returned to the value for the clean Co(0 0 0 1) surface. LEED exhibited a combination of two ordered structures: p(2 × 2) and (7×7)19.1°. The (7×7)19.1° pattern was formed by methoxide or hydrogen and vanished below 340 K. The p(2 × 2) structure was still found above 380 K and was therefore assigned to CO
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| 5. |
- Habermehl-Cwirzen, Karin, et al.
(författare)
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Sulfur poisoning of the CO adsorption on Co(0001)
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 573:2, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- CO adsorption on a sulfur covered cobalt surface at 185 K has been studied using XPS, TDS, LEED, and WF measurements. As in the case of CO adsorption on the clean Co(0001) surface, CO adsorbs and desorbs molecularly and no dissociation was observed. The saturation coverage of CO decreases linearly from 0.54 ML to 0.27 ML when the S pre-coverage increases to 0.25 ML. The WF increased during CO adsorption, but did not reach the value obtained for CO adsorption on the clean surface. The smaller work function change is explained by the reduced adsorption of CO on the sulfur-precovered surface. A reduction in the activation energy of desorption for CO from 113 kJ/mol to 88 kJ/mol was observed indicating weaker bonding of the CO molecules to the surface. The behavior of the CO/S/Co(0001) system was explained by a combination of steric and electronic effects.
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| 6. |
- Heikkinen, Olli, et al.
(författare)
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Characterization of a Hexagonal Phosphorus Adlayer on Platinum (111)
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:22, s. 12291-12297
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Tidskriftsartikel (refereegranskat)abstract
- Platinum is a well-known catalytic metal whose efficiency can be degraded by the adsorption of impurities. Using different characterization techniques, such as scanning tunnelling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy, we present a study of phosphorus adsorption on a platinum (111) surface. Under saturation and after annealing at 750 °C, phosphorus was observed to form an ordered hexagonal adlayer with a (4√3 × 4√3)-R30° symmetry. On the basis of density functional theory calculations, we propose a model for the phosphorus adlayer, consisting of either P13 or P14 clusters. In addition, carbon monoxide adsorption as a function of the phosphorus coverage was also investigated. We found that the phosphorus adlayer prevents carbon monoxide adsorption on Pt(111) reducing its catalytic efficiency. (Figure Presented
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| 7. |
- Iurchenkova, Anna A., 1997-, et al.
(författare)
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The effect of the pyrolysis temperature and biomass type on the biocarbons characteristics
- 2023
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Ingår i: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; , s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of biomass and natural wastes into carbon-based materials for various applications such as catalysts and energy-related materials is a fascinating and sustainable approach emerged during recent years. Precursor nature and characteristics are complex, hence, their effect on the properties of resulting materials is still unclear. In this work, we have investigated the effect of different precursors and pyrolysis temperature on the properties of produced carbon materials and their potential application as negative electrode materials in Li-ion batteries. Three biomasses, lignocellulosic brewery spent grain from a local brewery, catechol-rich lignin and tannins, were selected for investigations. We show that such end-product carbon characteristic as functional and elemental composition, porosity, specific surface area, defectiveness level, and morphology strictly depend on the precursor composition, chemical structure, and pyrolysis temperature. The electrochemical characteristics of produced carbon materials are correlate with the characteristics of the produced materials. A higher pyrolysis temperature is shown to be favourable for production of carbon material for the Li-ion battery application in terms of both specific surface area and long-term cycling stability.
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| 8. |
- Pussi, Katariina, et al.
(författare)
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The (√7 × √7)R19.1°-C6H6 adsorption structure on Co{0001} : A combined tensor LEED and DFT study
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 572:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The geometric structure of a Co{0001}-(√7 × √7)R19.1°-C6H6 surface formed by adsorption of benzene to the saturation coverage at 170 K has been determined by low energy electron diffraction (LEED). The favored model consists of a flat laying, nearly undisturbed benzene molecule, with the hydrogen-carbon bonds bent away from the substrate by 0.3 ± 0.2 Å. The carbon ring lies at a hcp-site with the two parallel C-C bonds aligned with [1̄100] direction. Buckling between the inequivalent carbon atoms in the molecular ring is within the experimental uncertainty (0.01 ± 0.11 Å). The experimental results are supported by density functional calculations
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