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Publications (10 of 32) Show all publications
Hohmann, L., Marks, K., Chien, T.-E., Öström, H., Hansson, T., Muntwiler, M., . . . Harding, D. J. (2024). Effect of Coadsorbed Sulfur on the Dehydrogenation of Naphthalene on Ni(111). The Journal of Physical Chemistry C, 128(1), 67-76
Open this publication in new window or tab >>Effect of Coadsorbed Sulfur on the Dehydrogenation of Naphthalene on Ni(111)
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2024 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 128, no 1, p. 67-76Article in journal (Refereed) Published
Abstract [en]

There are several difficulties when experimentally determined reaction mechanisms are applied from model systems to real catalysis. Besides the infamous pressure and material gaps, it is sometimes necessary to consider impurities in the real reactant feedstock that can act as promoters or catalyst poisons and alter the reaction path. In this study, the effect of sulfur on the dehydrogenation of naphthalene on Ni(111) is investigated by using X-ray photoelectron spectroscopy and scanning tunneling microscopy. Sulfur induces a (5√3 × 2) surface reconstruction, as previously reported in the literature. The sulfur does not have a strong effect on the dehydrogenation temperature of naphthalene. However, the presence of sulfur leads to a preferred formation of carbidic over graphitic carbon and a strong inhibition of carbon diffusion into the nickel bulk, which is one of the steps of destructive whisker carbon formation described in the catalysis literature.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-226125 (URN)10.1021/acs.jpcc.3c04475 (DOI)001141749800001 ()2-s2.0-85180944787 (Scopus ID)
Available from: 2024-02-06 Created: 2024-02-06 Last updated: 2024-02-06Bibliographically approved
Boscolo Bibi, S., El-Zohry, A. M., Davies, B., Grigorev, V., Goodwin, C. M., Lömker, P., . . . Hansson, T. (2024). Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes. Physical Chemistry, Chemical Physics - PCCP, 26(3), 2332-2340
Open this publication in new window or tab >>Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes
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2024 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 26, no 3, p. 2332-2340Article in journal (Refereed) Published
Abstract [en]

Oxide-derived metals are produced by reducing an oxide precursor. These materials, including gold, have shown improved catalytic performance over many native metals. The origin of this improvement for gold is not yet understood. In this study, operando non-resonant sum frequency generation (SFG) and ex situ high-pressure X-ray photoelectron spectroscopy (HP-XPS) have been employed to investigate electrochemically-formed oxide-derived gold (OD-Au) from polycrystalline gold surfaces. A range of different oxidizing conditions were used to form OD-Au in acidic aqueous medium (H3PO4, pH = 1). Our electrochemical data after OD-Au is generated suggest that the surface is metallic gold, however SFG signal variations indicate the presence of subsurface gold oxide remnants between the metallic gold surface layer and bulk gold. The HP-XPS results suggest that this subsurface gold oxide could be in the form of Au2O3 or Au(OH)3. Furthermore, the SFG measurements show that with reducing electrochemical treatments the original gold metallic state can be restored, meaning the subsurface gold oxide is released. This work demonstrates that remnants of gold oxide persist beneath the topmost gold layer when the OD-Au is created, potentially facilitating the understanding of the improved catalytic properties of OD-Au.

National Category
Other Chemistry Topics Materials Chemistry
Identifiers
urn:nbn:se:su:diva-225630 (URN)10.1039/d3cp04009g (DOI)001134636400001 ()38165839 (PubMedID)2-s2.0-85181438734 (Scopus ID)
Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-03-08Bibliographically approved
Marks, K., Erbing, A., Hohmann, L., Chien, T.-E., Yazdi, M. G., Muntwiler, M., . . . Gothelid, M. (2024). Naphthalene Dehydrogenation on Ni(111) in the Presence of Chemisorbed Oxygen and Nickel Oxide. Catalysts, 14(2), Article ID 124.
Open this publication in new window or tab >>Naphthalene Dehydrogenation on Ni(111) in the Presence of Chemisorbed Oxygen and Nickel Oxide
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2024 (English)In: Catalysts, E-ISSN 2073-4344, Vol. 14, no 2, article id 124Article in journal (Refereed) Published
Abstract [en]

Catalyst passivation through carbon poisoning is a common and costly problem as it reduces the lifetime and performance of the catalyst. Adding oxygen to the feed stream could reduce poisoning but may also affect the activity negatively. We have studied the dehydrogenation, decomposition, and desorption of naphthalene co-adsorbed with oxygen on Ni(111) by combining temperature-programmed desorption (TPD), sum frequency generation spectroscopy (SFG), photoelectron spectroscopy (PES), and density functional theory (DFT). Chemisorbed oxygen reduces the sticking of naphthalene and shifts H2 production and desorption to higher temperatures by blocking active Ni sites. Oxygen increases the production of CO and reduces carbon residues on the surface. Chemisorbed oxygen is readily removed when naphthalene is decomposed. Oxide passivates the surface and reduces the sticking coefficient. But it also increases the production of CO dramatically and reduces the carbon residues. Ni2O3 is more active than NiO.

Keywords
dehydrogenation, decomposition, naphthalene, nickel, oxygen, nickel oxide
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:su:diva-227740 (URN)10.3390/catal14020124 (DOI)001172450400001 ()2-s2.0-85187295000 (Scopus ID)
Available from: 2024-03-26 Created: 2024-03-26 Last updated: 2024-03-26Bibliographically approved
Koroidov, S., Winiwarter, A., Diaz-Morales, O., Görlin, M., Halldin Stenlid, J., Wang, H.-Y., . . . Nilsson, A. (2021). Chemisorbed oxygen or surface oxides steer the selectivity in Pd electrocatalytic propene oxidation observed by operando Pd L-edge X-ray absorption spectroscopy. Catalysis Science & Technology, 11(10), 3347-3352
Open this publication in new window or tab >>Chemisorbed oxygen or surface oxides steer the selectivity in Pd electrocatalytic propene oxidation observed by operando Pd L-edge X-ray absorption spectroscopy
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2021 (English)In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 11, no 10, p. 3347-3352Article in journal (Refereed) Published
Abstract [en]

Controlled electrochemical oxidation of hydrocarbons to desired products is an attractive approach in catalysis. Here we study the electrochemical propene oxidation under operando conditions using Pd L-edge X-ray absorption spectroscopy (XAS) as a sensitive probe to elucidate surface processes occurring during catalysis. Together with ab initio multiple-scattering calculations, our XAS results enable assignment of characteristic changes of the Pd L-edge intensity and energy position in terms of a mechanistic understanding of the selective oxidation of propene. The results, supported by electrochemical density functional theory DFT simulations, show that in the potential range of 0.8–1.0 V vs. the reversible hydrogen electrode (RHE), selective oxidation of propene to acrolein and acrylic acid occurs on the metallic Pd surface. These reactions are proposed to proceed via the Langmuir–Hinshelwood mechanism. In contrast, for the potential range of 1.1–1.3 V vs. RHE, selective oxidation of propene to propylene glycol takes place on a Pd oxide surface.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-195892 (URN)10.1039/d0cy02134b (DOI)000653964500028 ()
Funder
Swedish Research Council, 2019-05114Knut and Alice Wallenberg Foundation
Available from: 2021-08-26 Created: 2021-08-26 Last updated: 2024-04-08Bibliographically approved
Schalk, O., Galiana, J., Geng, T., Larsson, T. L., Thomas, R. D., Galvan, I. F., . . . Vacher, M. (2020). Competition between ring-puckering and ring-opening excited state reactions exemplified on 5H-furan-2-one and derivatives. Journal of Chemical Physics, 152(6), Article ID 064301.
Open this publication in new window or tab >>Competition between ring-puckering and ring-opening excited state reactions exemplified on 5H-furan-2-one and derivatives
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2020 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 152, no 6, article id 064301Article in journal (Refereed) Published
Abstract [en]

The influence of ring-puckering on the light-induced ring-opening dynamics of heterocyclic compounds was studied on the sample 5-membered ring molecules gamma-valerolactone and 5H-furan-2-one using time-resolved photoelectron spectroscopy and ab initio molecular dynamics simulations. In gamma-valerolactone, ring-puckering is not a viable relaxation channel and the only available reaction pathway is ring-opening, which occurs within one vibrational period along the C-O bond. In 5H-furan-2-one, the C = C double bond in the ring allows for ring-puckering which slows down the ring-opening process by about 150 fs while only marginally reducing its quantum yield. This demonstrates that ring-puckering is an ultrafast process, which is directly accessible upon excitation and which spreads the excited state wave packet quickly enough to influence even the outcome of an otherwise expectedly direct ring-opening reaction.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-181087 (URN)10.1063/1.5129366 (DOI)000522040400014 ()32061211 (PubMedID)2-s2.0-85079405406 (Scopus ID)
Available from: 2020-04-29 Created: 2020-04-29 Last updated: 2022-11-07Bibliographically approved
Geng, T., Ehrmaier, J., Schalk, O., Richings, G. W., Hansson, T., Worth, G. & Thomas, R. D. (2020). Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole. Journal of Physical Chemistry A, 124(20), 3984-3992
Open this publication in new window or tab >>Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole
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2020 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 124, no 20, p. 3984-3992Article in journal (Refereed) Published
Abstract [en]

The excited state relaxation pathways of isoxazole and oxazole upon excitation with UV-light were investigated by nonadiabatic ab initio dynamics simulations and time-resolved photoelectron spectroscopy. Excitation of the bright ππ*-state of isoxazole predominantly leads to ring-opening dynamics. Both the initially excited ππ*-state and the dissociative πσ*-state offer a combined barrier-free reaction pathway, such that ring-opening, defined as a distance of more than 2 Å between two neighboring atoms, occurs within 45 fs. For oxazole, in contrast, the excited state dynamics is about twice as slow (85 fs) and the quantum yield for ring-opening is lower. This is caused by a small barrier between the ππ*-state and the πσ*-state along the reaction path, which suppresses direct ring-opening. Theoretical findings are consistent with the measured time-resolved photoelectron spectra, confirming the timescales and the quantum yields for the ring-opening channel. The results indicate that a combination of time-resolved photoelectron spectroscopy and excited state dynamics simulations can explain the dominant reaction pathways for this class of molecules. As a general rule, we suggest that the antibonding σ*-orbital located between the oxygen atom and a neighboring atom of a five-membered heterocyclic system provides a driving force for ring-opening reactions, which is modified by the presence and position of additional nitrogen atoms.

National Category
Atom and Molecular Physics and Optics Physical Chemistry
Identifiers
urn:nbn:se:su:diva-182120 (URN)10.1021/acs.jpca.9b11788 (DOI)000537424600003 ()
Available from: 2020-05-30 Created: 2020-05-30 Last updated: 2022-03-23Bibliographically approved
Marks, K., Yazdi, M. G., Piskorz, W., Simonov, K., Stefanuik, R., Sostina, D., . . . Öström, H. (2019). Investigation of the surface species during temperature dependent dehydrogenation of naphthalene on Ni(111). Journal of Chemical Physics, 150(24), Article ID 244704.
Open this publication in new window or tab >>Investigation of the surface species during temperature dependent dehydrogenation of naphthalene on Ni(111)
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2019 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 24, article id 244704Article in journal (Refereed) Published
Abstract [en]

The temperature dependent dehydrogenation of naphthalene on Ni(111) has been investigated using vibrational sum-frequency generation spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory with the aim of discerning the reaction mechanism and the intermediates on the surface. At 110 K, multiple layers of naphthalene adsorb on Ni(111); the first layer is a flat lying chemisorbed monolayer, whereas the next layer(s) consist of physisorbed naphthalene. The aromaticity of the carbon rings in the first layer is reduced due to bonding to the surface Ni-atoms. Heating at 200 K causes desorption of the multilayers. At 360 K, the chemisorbed naphthalene monolayer starts dehydrogenating and the geometry of the molecules changes as the dehydrogenated carbon atoms coordinate to the nickel surface; thus, the molecule tilts with respect to the surface, recovering some of its original aromaticity. This effect peaks at 400 K and coincides with hydrogen desorption. Increasing the temperature leads to further dehydrogenation and production of H-2 gas, as well as the formation of carbidic and graphitic surface carbon. Published under license by AIP Publishing.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-170840 (URN)10.1063/1.5098533 (DOI)000473303200040 ()31255092 (PubMedID)2-s2.0-85068220749 (Scopus ID)
Available from: 2019-07-29 Created: 2019-07-29 Last updated: 2022-11-02Bibliographically approved
Schalk, O., Geng, T., Hansson, T. & Thomas, R. D. (2018). The ring-opening channel and the influence of Rydberg states on the excited state dynamics of furan and its derivatives. Journal of Chemical Physics, 149(8), Article ID 084303.
Open this publication in new window or tab >>The ring-opening channel and the influence of Rydberg states on the excited state dynamics of furan and its derivatives
2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 8, article id 084303Article in journal (Refereed) Published
Abstract [en]

One important relaxation pathway for photo-excited five-membered heterocyclic organic molecules is ring-opening via a dissociative pi sigma* state. In this study, we investigate the influence of this pathway in furan and several hydrogenated and methylated derivatives by combining time-resolved photoelectron spectroscopy with time-dependent density functional theory and coupled cluster calculations. We find strong experimental evidence that the ring-opening channel is the major relaxation channel in furan, 2,3-dihydrofuran, and 2-methylfuran (2-MF). In 2,5-dimethylfuran (25-DMF), however, we observe that the molecules relax either via a pi 3s Rydberg state or through a direct return to the ground state by undergoing ring-puckering motions. From the supporting calculations, for 2-MF and 25-DMF, we predict that there is strong mixing between the pi sigma* state and the pi 3s Rydberg state along the ring opening pathway. However, in 25-DMF, no crossing between the pi sigma*/pi 3s state and the initially excited pi pi* state can be found along the ring opening coordinate, effectively blocking this channel.

Keywords
Time-resolved photoemission spectroscopy, Photoelectron spectra, Coupled-cluster methods, Time dependent density functional theory, Chemical compounds and components, Chemical bonding, Chemical elements, Rydberg states, Correlation-consistent basis sets, Potential energy surfaces
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-161137 (URN)10.1063/1.5024655 (DOI)000444035800027 ()30193494 (PubMedID)2-s2.0-85052830649 (Scopus ID)
Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2022-10-26Bibliographically approved
Geng, T., Schalk, O., Neville, S. P., Hansson, T. & Thomas, R. D. (2017). Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivatives. Journal of Chemical Physics, 146(14), Article ID 144307.
Open this publication in new window or tab >>Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivatives
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2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 14, article id 144307Article in journal (Refereed) Published
Abstract [en]

The involvement of intermediate Rydberg states in the relaxation dynamics of small organic molecules which, after excitation to the valence manifold, also return to the valence manifold is rarely observed. We report here that such a transiently populated Rydberg state may offer the possibility to modify the outcome of a photochemical reaction. In a time resolved photoelectron study on pyrrole and its methylated derivatives, N-methyl pyrrole and 2,5-dimethyl pyrrole, 6.2 eV photons (200 nm) are used to excite these molecules into a bright pi pi* state. In each case, a pi 3p-Rydberg state, either the B-1(pi 3p(y)) or the A(2)(pi 3p(z)) state, is populated within 20-50 fs after excitation. The wavepacket then proceeds to the lower lying A(2)(pi sigma*) state within a further 20 fs, at which point two competing reaction channels can be accessed: prompt N-H (N-CH3) bond cleavage or return to the ground state via a conical intersection accessed after ring puckering, the latter of which is predicted to require an additional 100-160 fs depending on the molecule.

National Category
Chemical Sciences Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-143588 (URN)10.1063/1.4979681 (DOI)000399078700017 ()28411588 (PubMedID)2-s2.0-85017597283 (Scopus ID)
Available from: 2017-05-31 Created: 2017-05-31 Last updated: 2022-10-19Bibliographically approved
Yazdi, M. G., Moud, P. H. H., Marks, K., Piskorz, W., Östrom, H., Hansson, T., . . . Göthelid, M. (2017). Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation. The Journal of Physical Chemistry C, 121(40), 22199-22207
Open this publication in new window or tab >>Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 40, p. 22199-22207Article in journal (Refereed) Published
Abstract [en]

An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit that it has been in use for a long time in fossil feedstock catalytic steam reforming, understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature-programmed desorption) and STM (scanning tunneling microscopy) in ultrahigh vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the dibridge[7] geometry but the potential energy surface is rather smooth and other adsorption geometries may coexist. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation, and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-149014 (URN)10.1021/acs.jpcc.7b07757 (DOI)000413131700047 ()2-s2.0-85031329487 (Scopus ID)
Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2022-10-20Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8051-0582

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