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In situ soft x-ray spectroscopy of ethylene epoxidation over Ag at 1 atm and 230°C
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
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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: urn:nbn:se:uu:diva-209195OAI: oai:DiVA.org:uu-209195DiVA: diva2:656164
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16Bibliographically approved
In thesis
1. In situ X-Ray Spectroscopy of Ethylene Epoxidation over Ag and studies of Li-ion batteries and Cu sulfidation
Open this publication in new window or tab >>In situ X-Ray Spectroscopy of Ethylene Epoxidation over Ag and studies of Li-ion batteries and Cu sulfidation
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
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:nbn:se:uu:diva-209204 (URN)
Public defence
2013-11-05, Å2005, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Supervisors
Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2013-10-16

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Kristiansen, PawDuda, Laurent C

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