| 1. |
- Hagman, Benjamin, et al.
(författare)
-
Steps Control the Dissociation of CO2 on Cu(100)
- 2018
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 140:40, s. 12974-12979
-
Tidskriftsartikel (refereegranskat)abstract
- CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory to obtain an atomistic understanding of the dissociative adsorption of CO2 on Cu(100). We find that the process is dominated by the presence of steps, which promote both a lowering of the dissociation barrier and an efficient separation between adsorbed O and CO, reducing the probability for recombination. The identification of steps as sites for efficient CO2 dissociation provides an understanding that can be used in the design of future CO2 reduction catalysts.
|
|
| 2. |
- Zhang, Chu, et al.
(författare)
-
Steps and catalytic reactions : CO oxidation with preadsorbed O on Rh(553)
- 2022
-
Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 715
-
Tidskriftsartikel (refereegranskat)abstract
- Industrial catalysts are often comprised of nanoparticles supported on high-surface-area oxides, in order to maximise the catalytically active surface area and thereby utilise the active material better. These nanoparticles expose steps and corners that, due to low coordination to neighboring atoms, are more reactive and, as a consequence, are often assumed to have higher catalytic activity. We have investigated the reaction between CO and preadsorbed O on a stepped Rh(553) surface, and show that CO oxidation indeed occurs faster than on the flat Rh(111) surface at the same temperature. However, we do find that this is not a result of reactions at the step sites but rather at the terrace sites close to the steps, due to in-plane relaxation enabled by the step. This insight can provide ways to optimize the shape of the nanoparticles to further improve the activity of certain reactions.
|
|
| 3. |
- Vidal Carulla, Clara, 1985-, et al.
(författare)
-
Development of Preschool Children's Executive Functions throughout a Play-Based Learning Approach That Embeds Science Concepts
- 2021
-
Ingår i: International Journal of Environmental Research and Public Health. - : MDPI. - 1661-7827 .- 1660-4601. ; 18:2
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the development of executive functions in preschool children during a series of science activities. A longitudinal play-based learning intervention was designed and implemented following the design of an educational experiment. Data were collected through visual ethnography in hot situations with adult supervision. Results show how entwined the concepts of inhibitory control and cognitive flexibility are within young children's development. The development of cognitive flexibility or attention shifting readily occurred when there were fictive characters (such as the king and his royal family), but changing perspective toward a nonfictive environment (i.e., taking other children's perspectives) was a more difficult and time-consuming process. This process began in an individual perspective and expanded to acknowledging others' perspectives, then moved toward creating common perspectives or alternative narratives. Results show that science activities can be a bridge for preschool children to transfer their use of executive functions, from fairytales and games toward everyday tasks.
|
|
| 4. |
- Garcia-Martinez, Fernando, et al.
(författare)
-
Catalytic oxidation of CO on a curved Pt(111) surface : simultaneous ignition at all facets through a transient CO-O complex.
- 2020
-
Ingår i: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 59:45, s. 20037-20043
-
Tidskriftsartikel (refereegranskat)abstract
- The catalytic oxidation of carbon monoxide (CO) on transition metals, such as platinum (Pt), is commonly viewed as a sharp transition from the CO-inhibited surface to the active metal, covered with oxygen (O). However, we find that minor amounts of O are present in the CO-poisoned layer that explain why, surprisingly, CO desorbs at stepped and flat Pt crystal planes at once, regardless of the reaction conditions. Using near-ambient pressure X-ray photoemission and a curved Pt(111) crystal we probe the chemical composition at surfaces with variable step density during the CO oxidation reaction. The systematic analysis of carbon and oxygen core levels across the curved crystal reveals that, right before light-off, subsurface O builds up within (111) terraces. This is key to trigger the simultaneous ignition of the catalytic reaction at different Pt surfaces, as indicated by ab-initio theory: a CO-Pt-O complex is formed that equals the CO chemisorption energy at terraces and steps, leading to the abrupt desorption of poisoning CO from all crystal facets at the same temperature.
|
|
| 5. |
- Merte, Lindsay R., et al.
(författare)
-
Structure of two-dimensional Fe3O4
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:11
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface X-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe2+ sandwiched between two close-packed layers of tetrahedrally coordinated Fe3+ and an overall stoichiometry of Fe3O4. As the structure is distinct from bulk iron oxide phases and the coupling with the silver substrate is weak, we propose that the phase should be classified as a metastable two-dimensional oxide. The chemical and physical properties are potentially interesting, thanks to the predicted charge ordering between atomic layers, and analogy with bulk ferrite spinels suggests the possibility of synthesis of a whole class of two-dimensional ternary oxides with varying electronic, optical, and chemical properties.
|
|
| 6. |
- Knudsen, Jan, et al.
(författare)
-
Stroboscopic operando spectroscopy of the dynamics in heterogeneous catalysis by event-averaging
- 2021
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous catalyst surfaces are dynamic entities that respond rapidly to changes in their local gas environment, and the dynamics of the response is a decisive factor for the catalysts’ action and activity. Few probes are able to map catalyst structure and local gas environment simultaneously under reaction conditions at the timescales of the dynamic changes. Here we use the CO oxidation reaction and a Pd(100) model catalyst to demonstrate how such studies can be performed by time-resolved ambient pressure photoelectron spectroscopy. Central elements of the method are cyclic gas pulsing and software-based event-averaging by image recognition of spectral features. A key finding is that at 3.2 mbar total pressure a metallic, predominantly CO-covered metallic surface turns highly active for a few seconds once the O2:CO ratio becomes high enough to lift the CO poisoning effect before mass transport limitations triggers formation of a √5 oxide.
|
|
| 7. |
- Isaksson, Simon, 1988, et al.
(författare)
-
Protein-Containing Lipid Bilayers Intercalated with Size-Matched Mesoporous Silica Thin Films
- 2017
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 17:1, s. 476-485
-
Tidskriftsartikel (refereegranskat)abstract
- Proteins are key components in a multitude of biological processes, of which the functions carried out by transmembrane (membrane-spanning) proteins are especially demanding for investigations. This is because this class of protein needs to be incorporated into a lipid bilayer representing its native environment, and in addition, many experimental conditions also require a solid support for stabilization and analytical purposes. The solid support substrate may, however, limit the protein functionality due to protein material interactions and a lack of physical space. We have in this work tailored the pore size and pore ordering of a mesoporous silica thin film to match the native cell-membrane arrangement of the transmembrane protein human aquaporin 4 (hAQP4). Using neutron reflectivity (NR), we provide evidence of how substrate pores host the bulky water-soluble domain of hAQP4, which is shown to extend 7.2 nm into the pores of the substrate. Complementary surface analytical tools, including quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence microscopy, revealed successful protein-containing supported lipid bilayer (pSLB) formation on mesoporous silica substrates, whereas pSLB formation was hampered on nonporous silica. Additionally, electron microscopy (TEM and SEM), light scattering (DLS and stopped-flow), and small-angle X-ray scattering (SAXS) were employed to provide a comprehensive characterization of this novel hybrid organic-inorganic interface, the tailoring of which is likely to be generally applicable to improve the function and stability of a broad range of membrane proteins containing water-soluble domains.
|
|
| 8. |
- Garcia-Martinez, Fernando, et al.
(författare)
-
Reduced Carbon Monoxide Saturation Coverage on Vicinal Palladium Surfaces: The Importance of the Adsorption Site
- 2021
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:39, s. 9508-9515
-
Tidskriftsartikel (refereegranskat)abstract
- Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces.
|
|
| 9. |
- Gajdek, Dorotea, et al.
(författare)
-
Structural Changes in Monolayer Cobalt Oxides under Ambient Pressure CO and O 2 Studied by In Situ Grazing-Incidence X-ray Absorption Fine Structure Spectroscopy
- 2022
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:7, s. 3411-3418
-
Tidskriftsartikel (refereegranskat)abstract
- We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.
|
|
| 10. |
- Adbo, Karina
(författare)
-
Relationships between models used for teaching chemistry and those expressed by students
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused upon chemistry as a school subject and students' interpretations and use of formally introduced teaching models. To explore students' developing repertoire of chemical models, a longitudinal interview study was undertaken spanning the first year of upper secondary school chemistry. Matter in its different states was selected as the target framework for this study. The results presented are derived from both generalisations of groups of students as well as a case study describing an individual learner's interpretation of formal content. The results obtained demonstrated that the formal teaching models provided to the students included in this study were not sufficient to afford them a coherent framework of matter in its different states or for chemical bonding. Instead, students' expressed models of matter and phase change were to a high degree dependent on electron movement (Paper I), anthropomorphism (Paper II) and, for one student, a mechanistic approach based on small particles and gravitation (Paper III). The results from this study place focus on the importance of learners' prior learning (previous experiences) and the need to develop a coherent framework of formal teaching models for the nature of matter and phase change.
|
|
