| 1. |
- Boscolo Bibi, Sara, 1993-, et al.
(författare)
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Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:3, s. 2332-2340
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Hohmann, Lea, et al.
(författare)
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Effect of Coadsorbed Sulfur on the Dehydrogenation of Naphthalene on Ni(111)
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 128:1, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- 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 root 3 x 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.
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| 3. |
- Marks, Kess, 1987-, et al.
(författare)
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Naphthalene Dehydrogenation on Ni(111) in the Presence of Chemisorbed Oxygen and Nickel Oxide
- 2024
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 14:2
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Wang, Dong, et al.
(författare)
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Molecular quantum wave-packet splitting and revivals in shared phase space
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79:2, s. 23402-
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of a molecular wave packet created by an ultrashort laser pulse in a system of two coupled bound states is investigated by quantum dynamics calculations and semiclassical theory. Under suitable dynamical quantum interference conditions, the wave packet may be split into two separable fractions that move in different but partially overlapping regions of the energetically available phase space. Each wave-packet part can be individually addressed in the divided parts of the molecular phase space, and they are shown to go through separate long-term collapse-revival cycles analogous to those of wave packets moving in single anharmonic potentials. In a pump-probe scheme, the dynamics of the system would look very different depending on what internuclear distances are probed. The regular dynamics observable in the separated parts of the phase space takes on a quite irregular appearance in the regions that are shared by the wave-packet components. The wave-packet regularity is shown to depend sensitively on the pump pulse wavelength, which is a reflection of the energy range over which the quantum interference conditions are maintained. These conditions, as well as the wave-packet fraction revival times, are well reproduced by semiclassical theory.
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| 5. |
- Wang, Dong, et al.
(författare)
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Molecular quantum wavepacket revivals in coupled electronic states
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 449:4-6, s. 266-271
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Tidskriftsartikel (refereegranskat)abstract
- Large-amplitude revivals of molecular wavepackets in two coupled electronic states were obtained in quantum dynamical calculations. The revivals occurred in both bound and predissociative systems with a pattern analogous to that of wavepackets in single anharmonic potentials. Essential for their appearance was dynamical interference of wavepacket fractions moving along diabatic and adiabatic paths. The full revival period of the coupled system was shown to be given by an average of those of the diabatic and adiabatic states weighted in proportion to the wavepacket splitting ratio at the potential curve crossing.
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