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  • 1. Besharat, Zahra
    et al.
    Halldin Stenlid, Joakim
    Soldemo, Markus
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Önsten, Anneli
    Johnson, Magnus
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Weissenrieder, Jonas
    Brinck, Tore
    Göthelid, Mats
    Dehydrogenation of methanol on Cu2O(100) and (111)2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 24, article id 244702Article in journal (Refereed)
    Abstract [en]

    Adsorption and desorption of methanol on the (111) and (100) surfaces of Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (root 3 x root 3)R30 degrees-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surface oxygen.

  • 2.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental femtosecond-laser based investigations of model catalytic surface reactions2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to be able to design novel catalytic processes more efficiently, detailed understanding of the catalyst-reactant interaction and the dynamics of the microscopic reaction steps is needed. The present thesis aims to contribute to the fundamental understanding of catalyst reactant systems by means of experiments using model systems in Ultra High Vacuum (UHV). The main body of work involves femtochemistry/mass spectrometry measurements as well as sum-frequency generation (SFG) measurements, which both make use of a femtosecond laser and a UHV sample environment. The results of two experimental investigations within the field of surface science are presented.

    The first paper concerns CO oxidation on ruthenium (0001) and in particular the energy transfer from substrate to adsorbates upon laser excitation. For these experiments laser-induced desorption was performed. We were able to control the branching ratios of competing mechanisms and understand the role of non-thermal electrons in the mechanisms.

    The second project aims to understand the adsorption and dehydrogenation of methanol on cuprous oxide (Cu2O) which is complicated by the fact that the cuprous oxide surface reconstructs differently under different conditions. The results presented in this part were acquired using mainly X-ray Photoelectron Spectroscopy and SFG. We were able to understand the restructuring of the Cu2O surface and to show that methanol adsorbs molecularly on Cu2O(111) instead of dissociatively as a methoxy and hydrogen species as it does on Cu2O(100).

  • 3.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental investigations of model catalytic surface reactions on metal and metal oxide surfaces2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the development of renewable energies catalysis plays an important role, for example in the production of H2 gas that drives fuel cells, or in the decomposition of annoying by-products of renewable energy production. Most catalysts and catalytic processes currently used in the industry have their roots in macroscopic empirical investigations and trial and error-based optimization. In order to be able to design novel catalytic processes more efficiently, detailed understanding of the catalyst-reactant interaction and the dynamics of the microscopic reaction steps is needed. The present thesis aims to contribute to the fundamental understanding of catalyst reactant systems by means of experiments using model systems in Ultra High Vacuum. For this purpose, several surface science techniques were employed such as vibrational sum-frequency generation (SFG), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and femtochemistry.

    In the present thesis the results of three different projects are presented. The first concerns the adsorption and decomposition of naphthalene on Ni(111). Using scanning tunnelling microscopy (STM) and density functional theory (DFT) we identify the adsorption energy and geometry of the naphthalene molecule. Using SFG and TPD we investigate the temperature dependent breakdown of the naphthalene molecule and identify geometrical changes of the adsorbate as an intermediate step in the decomposition reaction. Additionally, we observe poisoning of the surface due to graphene growth using both STM and XPS and explore the possible effect of co-adsorption with oxygen on the reaction pathway and the poisoning of the catalyst.

    The second section concerns the adsorption and decomposition of ethanol and methanol on cuprous oxide (Cu2O). Using mainly XPS and SFG we show that ethanol adsorbs dissociatively on Cu2O(100) and (111) and that methanol adsorbs dissociatively on the (100) but molecularly on the (111) surface. Furthermore, we identify intermediate surface species and products of the temperature dependent dehydrogenation of both alcohols and show that the (111) surface is the more effective catalyst for decomposition.

    The third section explores the physics of non-thermal excitation methods and discusses CO oxidation on ruthenium (0001) induced by an optical laser and by X-rays from a free electron laser. Based on these femtochemistry experiments we discuss in particular the energy transfer both for direct excitation and for substrate mediated excitations. We show that we were able to control the branching ratios of competing mechanisms and understand the role of non-thermal electrons in the mechanisms of optical laser excitation. Furthermore, we show that it is possible to induce CO oxidation by direct X-ray core hole excitation and can rationalize the relaxation process that leads to CO oxidation.

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  • 4.
    Marks, Kess
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Besharat, Zahra
    Soldemo, Markus
    Önsten, Anneli
    Weissenrieder, Jonas
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Göthelid, Mats
    Adsorption and decoposition of ethanol on Cu2O(111) and (100)2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 33, p. 20384-20392Article in journal (Refereed)
    Abstract [en]

    Ethanol dehydrogenation on metal oxides such as Cu2O is an important reaction for the production of renewable energy by fuel cells both via the production of H2 fuel and applied in direct alcohol fuel cells. To better understand this reaction we studied the adsorption, dissociation and desorption of ethanol on Cu2O(111) and (100) surfaces using high-resolution photoelectron spectroscopy (PES), vibrational sum frequency generation spectroscopy (SFG), and temperature programmed desorption (TPD) accompanied by density functional theory (DFT) calculations. On Cu2O(100) the first layer consists primarily of dissociatively adsorbed ethoxy. Second and third layers of ethanol physisorb at low temperature and desorb below 200 K. On the Cu2O(111) surface, adsorption is mixed as ethoxy, ethanol and the products following C-C cleavage, CHx and OCHx, are found in the first layer. Upon heating, products following both C-C and C-O bond breaking are observed on both surfaces and continued heating accentuates the molecular cracking. C-O cleavage occurs more on the (100) surface, whereas on the Cu2O(111) C-C cleavage dominates and occurs at lower temperatures than on the (100) surface. The increased ability of Cu2O(111) to crack ethanol is explained by the varied surface structure including both surface oxygen, electron rich O-vacancies and Cu.

  • 5.
    Marks, Kess
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Yazdi, Milad Ghadami
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Engvall, Klas
    Harding, Dan J.
    Göthelid, Mats
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Adsorption and decomposition of naphthalene on oxygen pre-covered Ni(111)Manuscript (preprint) (Other academic)
  • 6.
    Marks, Kess
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Yazdi, Milad Ghadami
    Piskorz, Witold
    Simonov, Konstantin
    Stefanuik, Robert
    Sostina, Daria
    Guarnaccio, Ambra
    Ovsyannikov, Ruslan
    Giangrisostomi, Erika
    Sassa, Yasmine
    Bachellier, Nicolas
    Muntwiler, Matthias
    Johansson, Fredrik O. L.
    Lindblad, Andreas
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Kotarba, Andrzej
    Engvall, Klas
    Göthelid, Mats
    Harding, Dan J.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Investigation of the surface species during temperature dependent dehydrogenation of naphthalene on Ni(111)2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 24, article id 244704Article in journal (Refereed)
    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.

  • 7.
    Schreck, Simon
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Diesen, Elias
    Stockholm University, Faculty of Science, Department of Physics.
    LaRue, Jerry
    Ogasawara, Hirohito
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Nordlund, Dennis
    Weston, Matthew
    Stockholm University, Faculty of Science, Department of Physics.
    Beye, Martin
    Cavalca, Filippo
    Stockholm University, Faculty of Science, Department of Physics.
    Perakis, Fivos
    Stockholm University, Faculty of Science, Department of Physics.
    Sellberg, Jonas
    Eilert, André
    Stockholm University, Faculty of Science, Department of Physics.
    Kim, Kyung Hwan
    Stockholm University, Faculty of Science, Department of Physics.
    Coslovich, Giacomo
    Coffee, Ryan
    Krzywinski, Jacek
    Reid, Alex
    Moeller, Stefan
    Lutman, Alberto
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Atom-specific activation in CO oxidation2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 23, article id 234707Article in journal (Refereed)
    Abstract [en]

    We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft X-ray pulses and discuss the prospects of femtosecond X-ray pump X-ray spectroscopy probe, as well as X-ray two-pulse correlation measurements for fundamental investigations of chemical reactions via selective X-ray excitation.

  • 8. Yazdi, Milad Ghadami
    et al.
    Moud, Pouya. H.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Piskorz, Witold
    Östrom, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Kotarba, Andrzej
    Engvall, Klas
    Göthelid, Mats
    Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 40, p. 22199-22207Article in journal (Refereed)
    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.

  • 9.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Östrom, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Indication of non-thermal contribution to visible femtosecond laser-induced CO oxidation on Ru(0001)2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, no 7, article id 074701Article in journal (Refereed)
    Abstract [en]

    We studied CO oxidation on Ru(0001) induced by 400 nm and 800 nm femtosecond laser pulses where we find a branching ratio between CO oxidation and desorption of 1: 9 and 1: 31, respectively, showing higher selectivity towards CO oxidation for the shorter wavelength excitation. Activation energies computed with density functional theory show discrepancies with values extracted from the experiments, indicating both a mixture between different adsorbed phases and importance of non-adiabatic effects on the effective barrier for oxidation. We simulated the reactions using kinetic modeling based on the two-temperature model of laser-induced energy transfer in the substrate combined with a friction model for the coupling to adsorbate vibrations. This model gives an overall good agreement with experiment except for the substantial difference in yield ratio between CO oxidation and desorption at 400 nm and 800 nm. However, including also the initial, non-thermal effect of electrons transiently excited into antibonding states of the O-Ru bond yielded good agreement with all experimental results.

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