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Sulfidation of ceria surfaces from sulfur and sulfur diffusion
College of Physics and Information Engineering, Henan Normal University, Xinxiang, Henan 453007, China.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
College of Physics and Information Engineering, Henan Normal University, Xinxiang, Henan 453007, China.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 15, 8417-8425 p.Article in journal (Refereed) Published
Abstract [en]

Even very low levels of sulfur contaminants can degrade the catalytic performance of cerium oxide. Here, the interaction of atomic sulfur with the ceria (111) and (110) surfaces has been studied using first-principles methods. Two sulfoxy species are identified: oxido-sulfate(2-) species (SO2-) on both the CeO2 (111) and (110) surfaces and hyposulfite (SO22-) on the (110) surface. Sulfide (S2-) is formed when a surface or a subsurface oxygen atoms is replaced by sulfur. These sulfide species are most stable at the surface. Furthermore, sulfite (SO32-) structures are found when sulfur is made to replaces one Ce in the ceria (111) and (110) surfaces. The calculated sulfur diffusion barriers are larger than 1.4 eV for both surfaces and thus sulfur is essentially immobile, providing a possible explanation for the sulfidation phenomena of the ceria-based catalysis. Thus we find three different species from interaction of S with Ceria which are all, due to their strong binding, capable of poisoning the surface, reduced or unreduced. Our results suggest that under reducing conditions, sulfur is likely to be found in the (111) surface (replacing oxygen) but on the (110) surface (as SO22-).

Place, publisher, year, edition, pages
2012. Vol. 116, no 15, 8417-8425 p.
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-167999DOI: 10.1021/jp2092913ISI: 000302924900010OAI: oai:DiVA.org:uu-167999DiVA: diva2:489797
Available from: 2012-02-03 Created: 2012-02-03 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Oxygen Vacancy Chemistry in Ceria
Open this publication in new window or tab >>Oxygen Vacancy Chemistry in Ceria
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cerium(IV) oxide (CeO2), ceria, is an active metal oxide used in solid oxide fuel cells and for the purification of exhaust gases in vehicle emissions control. Behind these technically important applications of ceria lies one overriding feature, namely ceria's exceptional reduction-oxidation properties. These are enabled by the duality of the cerium ion which easily toggles between Ce4+ and Ce3+. Here the cerium 4f electrons and oxygen vacancies (missing oxygen ions in the structure) are key players. In this thesis, the nature of ceria's f electrons and oxygen vacancies are in focus, and examined with theoretical calculations.

It is shown that for single oxygen vacancies at ceria surfaces, the intimate coupling between geometrical structure and electron localisation gives a multitude of almost degenerate local energy mimima. With many vacancies, the situation becomes even more complex, and not even state-of-the-art quantum-mechanical calculations manage to predict the experimentally observed phenomenon of vacancy clustering. Instead, an alternative set of computer experiments managed to produce stable vacancy chains and trimers consistent with experimental findings from the literature and revealed a new general principle for surface vacancy clustering.

The rich surface chemistry of ceria involves not only oxygen vacancies but also other active oxygen species such as superoxide ions (O2). Experiments have shown that nanocrystalline ceria demonstrates an unusually large oxygen storage capacity (OSC) and an appreciable low-temperature redox activity, which have been ascribed to superoxide species. A mechanism explaining these phenomena is presented.

The ceria surface is also known to interact with SOx molecules, which is relevant both in the context of sulfur poisoning of ceria-based catalysts and sulfur recovery from them. In this thesis, the sulfur species and key mechanisms involved are identified.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 896
Keyword
Ceria, Density Functional Theory, Oxygen storage, Nano crystals, Sulfur poisoning
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-167521 (URN)978-91-554-8271-8 (ISBN)
Public defence
2012-03-16, Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-02-24 Created: 2012-01-30 Last updated: 2012-03-01Bibliographically approved

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Kullgren, JollaHermansson, Kersti

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