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In situ X-Ray Spectroscopy of Ethylene Epoxidation over Ag and studies of Li-ion batteries and Cu sulfidation
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on experiments applying synchrotron based X-ray Absorption Spectroscopy(XAS) and Resonant Inelastic X-ray Scattering (RIXS) in the soft X-ray region to energy related systems. The main work of this thesis has been to develop a reaction cell that allowed for in situ XAS and RIXS investigations of the partial epoxidation of ethylene over a Ag catalyst at 1 atm and up to 250C. The developed in situ cell can be used in two sample modes: 1) the Ag catalyst is deposited directly onto the vacuum separating membrane with the reaction gases flowing beneath it or 2) a slightly compressed Ag powder sample is at a distance to the vacuum membrane with the reaction gases flowing between the Ag powder sample and the membrane.Both sample modes offers the total florescence yield, TFY, and the total electron yield, TEY, to be recorded simultaneously. By means of the developed in situ cell a number of oxygen species, residing in/on the Ag surface or in the Ag bulk, have been detected. We claim to detect adsorbed O2 under epoxidation conditions, as well as Ag–O–H groups. We are also able to monitor changes of the absorbed oxygen as we change the composition of the reaction gas feed. The first charging cycle of Li-ion batteries have been investigate by ex situ measurements on the cathode Li2-xMnSiO4 and the anode composite LixNi0:5TiOPO4/C . The initial crystalline material becomes amorphous due to lithiation during the first first charging. We find that the redox behaviors of these two states are significantly different. Sulfidation of natural copper oxides are is found to be strongly promoted when it is grown on the host metal by a disproportionation.

Place, publisher, year, edition, pages
Uppsala: Arkitektkopia, Uppsala , 2013. , 64 p.
Keyword [en]
In situ, XAS, RIXS, heterogeneous catalysis
National Category
Atom and Molecular Physics and Optics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-209204OAI: oai:DiVA.org:uu-209204DiVA: diva2:656219
Public defence
2013-11-05, Å2005, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16
List of papers
1. Reaction cell for in situ soft x-ray absorption spectroscopy and resonant inelastic x-ray scattering measurements of heterogeneous catalysis up to 1 atm and 250 °C
Open this publication in new window or tab >>Reaction cell for in situ soft x-ray absorption spectroscopy and resonant inelastic x-ray scattering measurements of heterogeneous catalysis up to 1 atm and 250 °C
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2013 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 11, 113107- p.Article in journal (Refereed) Published
Abstract [en]

We present a novel in situ reaction cell for heterogeneous catalysis monitored in situ by x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS). The reaction can be carried out at a total pressure up to 1 atm, a regime that has not been accessible to comparable in situ techniques and thus closes the pressure gap to many industrial standard conditions. Two alternate catalyst geometries were tested: A) a thin film evaporated directly onto a x-ray transparent membrane with a flowing reaction gas mixture behind it or B) a powder placed behind both the membrane and a gap of flowing reaction gas mixture. To illustrate the working principle and feasibility of our reaction cell setup we have chosen ethylene epoxidation over a silver catalyst as a test case. The evolution of incorporated oxygen species was monitored by total electron/fluorescence yield O K-XAS as well as O K-RIXS, which is a powerful method to separate contributions from inequivalent sites. We find that our method can reliably detect transient species that exist during catalytic reaction conditions that are hardly accessible using other spectroscopic methods.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209192 (URN)10.1063/1.4829630 (DOI)000329982000008 ()
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved
2. In situ soft x-ray spectroscopy of ethylene epoxidation over Ag at 1 atm and 230°C
Open this publication in new window or tab >>In situ soft x-ray spectroscopy of ethylene epoxidation over Ag at 1 atm and 230°C
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We perform in situ soft x-ray XAS and RIXS of ethylene epoxidation over Ag. We find that several oxygen species are loaded into the Ag when it is heated to 230C and exposed to oxygen containing mixtures. Candidate fingerprints of the intensively debated electrophilic oxygen species, Oelec, that is necessary for the epoxidation process, are reached in this work.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209195 (URN)
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16Bibliographically approved
3. X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery cathodeLi(2-x)MnSiO4
Open this publication in new window or tab >>X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery cathodeLi(2-x)MnSiO4
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2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 8, 3846-3852 p.Article in journal (Refereed) Published
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209196 (URN)10.1039/C3CP54103G (DOI)000330779700057 ()
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved
4. X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery anode material Li(x)Ni(0.5)TiOPO4/C
Open this publication in new window or tab >>X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery anode material Li(x)Ni(0.5)TiOPO4/C
(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209198 (URN)
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16
5. Combined Experimental and ab initio Multi Reference Configuration Interaction study of the Resonant Inelastic X-RayScattering spectrum of CO2
Open this publication in new window or tab >>Combined Experimental and ab initio Multi Reference Configuration Interaction study of the Resonant Inelastic X-RayScattering spectrum of CO2
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2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 35, 20163-20175 p.Article in journal (Refereed) Published
Abstract [en]

The fundamental problem of the symmetry breaking in the resonant inelastic X-ray scattering (RIXS) of the CO2 gas molecule is studied. The measurements were performed under catalytically relevant conditions within an in-house constructed reaction cell. The experimental RIXS plane is constructed from a sequence of resonances, covering the near-edge X-ray absorption fine structure (NEXAFS) spectrum up to 539 eV. The spectra show significant sensitivity with respect to the excitation frequency. The NEXAFS absorption spectrum, as well as the corresponding RIXS spectra, is interpreted with the aid of multireference configuration interaction (MRCI) theory. In this framework, the configuration interaction space spans the space of the intermediate and final states with single and single-double excitations. The dynamic character of the RIXS spectra is investigated by considering the electronic-nuclear vibrational coupling with the bending and antisymmetric stretching vibrations in the important intermediate excited states. In addition, the vibronic coupling mechanism involving the Renner-Teller effect and the core-hole localization pseudo-Jahn-Teller effect of the intermediate states is fully considered. The physical origin of the observed spectral features is discussed qualitatively and quantitatively in terms of individual core-to-valence excitations and valence-to-core decays, respectively. The computational protocol presented here, based on multireference wave function ab initio theory, serves as an important reference for future theoretical and experimental applications of RIXS spectroscopy.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209199 (URN)10.1021/jp505628y (DOI)000341337700013 ()
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2017-12-06Bibliographically approved
6. X-ray spectroscopic studies of selected Cu(II) compounds exposed to dilute sulfide solutions
Open this publication in new window or tab >>X-ray spectroscopic studies of selected Cu(II) compounds exposed to dilute sulfide solutions
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(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209200 (URN)
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16Bibliographically approved
7. Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
Open this publication in new window or tab >>Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
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2011 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 158, no 1, C1-C5 p.Article in journal (Refereed) Published
Abstract [en]

We present results from X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) of oxidized polycrystalline copper surfaces [Cu(I) and Cu(II), respectively] exposed to a 1.0 mM aqueous solution of Na2S (sodium sulfide) for several hours. Scanning electron microscopy reveals that the Cu oxide surfaces attain a much rougher texture upon sodium sulfide exposure, and that the exposed Cu(II) oxide sample exhibits areas with crystallites. The XAS spectra show that sodium sulfide effectively reduces Cu(II) oxide to Cu(I) compounds. The RIXS spectra of the exposed surfaces closely resemble those of the Cu2O reference sample with the notable exception of their Cu LIII,II-RIXS spectra. We conclude that copper evidently forms a Cu(I) compound with oxygen but with a Cu 3d-band of much reduced width, pointing to the possibility of a more complex compound containing both oxygen and sulfur.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-139392 (URN)10.1149/1.3504891 (DOI)000284697900020 ()
Available from: 2010-12-27 Created: 2010-12-23 Last updated: 2017-12-11Bibliographically approved
8. Sub-band gap electronic states in nanocrystalline WO3 thin films studied by soft x-ray spectroscopy, optical absorption spectroscopy and density functional calculations
Open this publication in new window or tab >>Sub-band gap electronic states in nanocrystalline WO3 thin films studied by soft x-ray spectroscopy, optical absorption spectroscopy and density functional calculations
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(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-209201 (URN)
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2015-06-24Bibliographically approved

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