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Electron correlation contribution to the N2O/ceria(111) interaction
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.
Freie Universität Berlin, Physikalische und Theoretische Chemie.
2009 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 362, no 3, p. 91-96Article in journal (Refereed) Published
##### Abstract [en]

We have investigated the electron correlation contribution to the interaction energy of the N2O/ceria(111) system at the CCSD(T) level. N2O binds either with the N-end towards the surface with an interaction energy $E_{int}$ = -0.23 eV or with the O-end with $E_{int}$ = -0.27 eV. In the former case almost the entire binding energy is due to electron correlation effects, in the latter these effects contribute with about 60%. Analyses of the interaction energy contributions show that mostof the electron correlation part originates from the interaction of N2O with the O ions in the topmost surface layer.

##### Place, publisher, year, edition, pages
2009. Vol. 362, no 3, p. 91-96
##### Keyword [en]
Ab initio quantum-chemical methods and calculations, Physical adsorption, Cerium dioxide, Nitrous monoxide, Electron correlation calculations
##### National Category
Chemical Sciences
##### Research subject
Quantum Chemistry
##### Identifiers
ISI: 000270123300002OAI: oai:DiVA.org:uu-101213DiVA, id: diva2:212080
Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2017-12-13Bibliographically 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. p. 68
##### Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 644
##### 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)
##### Supervisors
Available from: 2009-05-14 Created: 2009-04-22 Last updated: 2009-05-14Bibliographically approved

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Müller, Carsten

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