| 1. |
- Degerman, David, 1989-, et al.
(författare)
-
Effect of CO2-Rich Syngas on the Chemical State of Fe(110) during Fischer-Tropsch Synthesis
- 2024
-
Ingår i: The Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:13, s. 5542-5552
-
Tidskriftsartikel (refereegranskat)abstract
- We have used in situ X-ray photoelectron spectroscopy to obtain information about the chemical state of a Fe single-crystal catalyst upon addition of CO2 in the syngas feed during Fischer–Tropsch synthesis (FTS) between 85 and 550 mbar. We found that at certain temperatures, the ternary mixture of CO, CO2, and H2 yields a chemical state which is resemblant of neither the CO hydrogenation nor the CO2 hydrogenation reaction mixtures in isolation. The addition of CO2 to a CO + H2 reaction mixture mostly affects the chemical state at low-temperature FTS conditions (i.e., below 254 °C). In this temperature span, the ternary reaction mixture resulted in a carburized surface, whereas the CO + H2 reaction led to surface oxidation. We propose a hypothesis, where a carbonate intermediate produced by CO2 interaction with Fe oxide aids the reduction of the Fe oxide, paving the way for the carburization of the Fe by dissociated CO. Very small differences in the spectra of the CO + H2 and the CO + CO2 + H2 reaction mixtures were observed above 254 °C, suggesting that the CO2 is a spectator in these conditions. Changing the total pressure of both the CO hydrogenation and ternary reaction mixture causes quantitative changes in the spectra at both low- and high-temperature FTS conditions, the degree of oxidation/carburization was affected in the low-temperature-FTS regime, and the degree of hydrocarbon build-up was affected in the high-temperature-FTS.
|
|
| 2. |
- Gleißner, Robert, et al.
(författare)
-
Role of Oxidation–Reduction Dynamics in the Application of Cu/ZnO-Based Catalysts
- 2023
-
Ingår i: ACS Applied Nano Materials. - 2574-0970. ; 6:9, s. 8004-8016
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated Cu nanoparticles (NPs) on vicinal and basal ZnO supports to obtain an atomistic picture of the catalyst’s structure under in situ oxidizing and reducing conditions. The Cu/ZnO model catalysts were investigated at elevated gas pressures by high energy grazing incidence X-ray diffraction and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We find that the Cu nanoparticles are fully oxidized to Cu2O under atmospheric conditions at room temperature. As the nanoparticles swell during oxidation, they maintain their epitaxy on basal ZnO (000 ± 1) surfaces, whereas on the vicinal ZnO (101̅4) surface, the nanoparticles undergo a coherent tilt. We find that the oxidation process is fully reversible under H2 flow at 500 K, resulting in predominantly well-aligned nanoparticles on the basal surfaces, whereas the orientation of Cu NPs on vicinal ZnO was only partially restored. The analysis of the substrate crystal truncation rods evidences the stability of basal ZnO surfaces under all gas conditions. No Cu–Zn bulk alloy formation is observed. Under CO2 flow, no diffraction signal from the nanoparticles is detected, pointing to their completely disordered state. The AP-XPS results are in line with the formation of CuO. Scanning electron microscopy images show that massive mass transport has set in, leading to the formation of larger agglomerates.
|
|
| 3. |
- Kohantorabi, Mona, et al.
(författare)
-
Light-Induced Transformation of Virus-Like Particles on TiO2
- 2024
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 16:28, s. 37275-37287
-
Tidskriftsartikel (refereegranskat)abstract
- Titanium dioxide (TiO2) shows significant potential as a self-cleaning material to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent virus transmission. This study provides insights into the impact of UV-A light on the photocatalytic inactivation of adsorbed SARS-CoV-2 virus-like particles (VLPs) on a TiO2 surface at the molecular and atomic levels. X-ray photoelectron spectroscopy, combined with density functional theory calculations, reveals that spike proteins can adsorb on TiO2 predominantly via their amine and amide functional groups in their amino acids blocks. We employ atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) to investigate the molecular-scale morphological changes during the inactivation of VLPs on TiO2 under light irradiation. Notably, in situ measurements reveal photoinduced morphological changes of VLPs, resulting in increased particle diameters. These results suggest that the denaturation of structural proteins induced by UV irradiation and oxidation of the virus structure through photocatalytic reactions can take place on the TiO2 surface. The in situ GISAXS measurements under an N2 atmosphere reveal that the virus morphology remains intact under UV light. This provides evidence that the presence of both oxygen and UV light is necessary to initiate photocatalytic reactions on the surface and subsequently inactivate the adsorbed viruses. The chemical insights into the virus inactivation process obtained in this study contribute significantly to the development of solid materials for the inactivation of enveloped viruses.
|
|
| 4. |
- Shipilin, Mikhail, et al.
(författare)
-
In Situ Surface-Sensitive Investigation of Multiple Carbon Phases on Fe(110) in the Fischer-Tropsch Synthesis
- 2022
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:13, s. 7609-7621
-
Tidskriftsartikel (refereegranskat)abstract
- Carbide formation on iron-based catalysts is an integral and, arguably, the most important part of the Fischer–Tropsch synthesis process, converting CO and H2 into synthetic fuels and numerous valuable chemicals. Here, we report an in situ surface-sensitive study of the effect of pressure, temperature, time, and gas feed composition on the growth dynamics of two distinct iron–carbon phases with the octahedral and trigonal prismatic coordination of carbon sites on an Fe(110) single crystal acting as a model catalyst. Using a combination of state-of-the-art X-ray photoelectron spectroscopy at an unprecedentedly high pressure, high-energy surface X-ray diffraction, mass spectrometry, and theoretical calculations, we reveal the details of iron surface carburization and product formation under semirealistic conditions. We provide a detailed insight into the state of the catalyst’s surface in relation to the reaction.
|
|
| 5. |
- Thomas, Andrew G., et al.
(författare)
-
Adsorption Studies of p-Aminobenzoic Acid on the Anatase TiO2(101) Surface
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:41, s. 12306-12314
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of p-aminobenzoic acid (pABA) on the anatase TiO2(101) surface has been investigated using synchrotron radiation photoelectron spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). Photoelectron spectroscopy indicates that the molecule is adsorbed in a bidentate mode through the carboxyl group following deprotonation. NEXAFS spectroscopy and DFT calculations of the adsorption structures indicate the ordering of a monolayer of the amino acid on the surface with the plane of the ring in an almost upright orientation. The adsorption of pABA on nanoparticulate TiO2 leads to a red shift of the optical absorption relative to bare TiO2 nanoparticles. DFT and valence band photoelectron spectroscopy suggest that the shift is attributed to the presence of the highest occupied molecular orbitals in the TiO2 band gap region and the presence of new molecularly derived states near the foot of the TiO2 conduction band.
|
|
| 6. |
- Wagstaffe, Michael, et al.
(författare)
-
An Experimental Investigation of the Adsorption of a Phosphonic Acid on the Anatase TiO2(101) Surface
- 2016
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:3, s. 1693-1700
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to study the adsorption of phenylphosphonic acid (PPA) on anatase TiO2(101) single crystal at coverages of 0.15 monolayer (ML) and 0.85 ML. The photoelectron spectroscopy data suggest that at 0.15 ML coverage PPA adsorbs in a bidentate geometry following deprotonation of both phosphonate hydroxyl groups, leaving the P-O group unbound. At 0.85 ML there is a shift to a mixed bidentate/monodentate binding mode. The carbon K-edge NEXAFS spectra were recorded at two azimuths. Our calculations show that for PPA on anatase TiO2(101) the phenyl ring is oriented 65 +/- 4 degrees away from the surface plane with an azimuthal twist of 57 +/- 11 degrees away from the [101] azimuth.
|
|
| 7. |
- Wagstaffe, Michael, et al.
(författare)
-
Ionic Liquid Ordering at an Oxide Surface
- 2016
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-4235. ; 17:21, s. 3430-3434
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyte–electrode and dye-sensitized solar cells. The initial interaction involves degradation of the [BF4]− anion, resulting in incorporation of F into O vacancies in the anatase surface. At low coverages, [C4C1Im][BF4] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO2 surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost.
|
|
