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Application of the method of increments to the adsorption of CO on the CeO2(110) surface
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 21, 214701- p.Article in journal (Refereed) Published
Abstract [en]

We have combined an embedded-cluster model with an extension of the method of increments to treat the adsorption of molecules on a surface. In this way we are able to investigate the physisorption of CO on CeO2(110) at the MP2, MP4(SDTQ), and CCSD(T) levels with only moderate computational costs. We find that, at the CCSD(T) level, 25% of the adsorption energy originates from electron correlation. The interactions of the CO molecule with its five nearest cerium and oxygen neighbors in the surface layer make the largest contributions to the electron correlation. Approximately 97% of the adsorption-induced electron correlation energy part of the adsorption energy is recovered by the method of increments (in our chosen expansion), at the MP2 level.

Place, publisher, year, edition, pages
2008. Vol. 128, no 21, 214701- p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-17437DOI: 10.1063/1.2921799ISI: 000256527500034OAI: oai:DiVA.org:uu-17437DiVA: diva2:45208
Available from: 2008-06-24 Created: 2008-06-24 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Physisorption of CO and N2O on ceria surfaces
Open this publication in new window or tab >>Physisorption of CO and N2O on ceria surfaces
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Physisorption of CO and N2O on surfaces of ceria (CeO2) was investigated by means of high-level quantum-mechanical embedded cluster calculations. Both systems have high relevance in the field of environmental chemistry and heterogeneous catalysis. The CO/CeO2 system, has been investigated in a couple of both experimental and theoretical studies, but for the N2O/CeO2 system, this is the first study in the literature, experimental or theoretical.

In physisorption, the interaction relies entirely on classical electrostatic interactions and electron dispersion forces. No covalent bond is formed between the molecule and the surface. A proper description of the dispersion requires some of the most accurate quantum-mechanical methods available, such as MP2 or CCSD(T). Moreover, even the most sophisticated methods cannot heal errors anywhere else in the theoretical treatment. Standard periodic models cannot be used with methods such as CCSD(T), but embedded cluster models can, and have been thoroughly explored in this thesis.

In this thesis, embedded cluster models were constructed for the CeO2(110) and (111) surfaces. Using a range of assessment tests, it was verified that the electronic structure of the central region of a large and fully embedded surface cluster agrees well with the corresponding region in a periodic system. CO physisorption was investigated at the CCSD(T) level. Due to the prohibitively large expenses (in computer time) for standard CCSD(T) calculations, the method of increments, previously used in the literature for bulk systems, was extended to adsorption problems. It was found that, electron correlation contributes by 30 - 80% to the molecule-surface interaction and that the contribution depends on the topology of the surface. The calculated CO-ceria interaction energy is 20 kJ/mol for the (111) surface and 27 kJ/mol for the (110) surface.

In low temperature TPD experiments for the N2O/CeO2(111) system, one surface species was found with an adsorption energy of about 29 kJ/mol. IR measurements showed stretching frequencies that are typically assigned to N2O adsorption with the O-end directed towards surface cations. However, theoretical calculations up to the MP2 level predicted two equally favorable adsorption species. Improvements in the structural model (larger clusters, consideration of molecule-induced relaxation) or the computational method (larger basis sets) did not affect this result. Only at the CCSD(T) level was one dominating surface species found, namely N2O adsorbed over a Ce ion, with the O-end of the molecule directed towards the surface. The calculated stretching vibrational frequency shifts (with respect to the gas phase) for this adsorbed species agree well with the measured IR spectra.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 68 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 644
Series
Keyword
ceria, carbon monoxide, nitrous oxide, embedded cluster, physisorption, method of increments, CCSD(T), vibrational frequencies
National Category
Theoretical Chemistry
Research subject
Quantum Chemistry
Identifiers
urn:nbn:se:uu:diva-101271 (URN)978-91-554-7527-7 (ISBN)
Public defence
2009-06-05, Angström 2001, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-05-14 Created: 2009-04-22 Last updated: 2009-05-14Bibliographically approved

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Müller, CarstenHermansson, Kersti

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