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Adsorption and Cyclotrimerization Kinetics of C2H2 at a Cu(110) Surface
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 17, 9550-9560 p.Article in journal (Refereed) Published
Abstract [en]

The kinetics of acetylene adsorption and cyclotrimerization was studied by vibrational sum-frequency generation spectroscopy (SFG) and density functional theory (DFT) calculations. At low temperature, SFG shows two resonances corresponding to acetylene adsorbed in two different sites. Upon heating, two new vibrational resonances appear. We interpret these resonances as being due to C2H2 island formation and adsorbed C4H4, which is the intermediate in the subsequent cyclotrimerization reaction to form benzene. A kinetic model is applied, which allows determination of the relevant activation barriers. The barrier for C2H2 diffusion is determined to be 43 +/- 1 kJ/mol. The activation barrier for formation of the C4H4 intermediate is found to be 84 +/- 6 kJ/mol and the barrier for benzene formation 5 +/- 3 kJ/mol lower. Barriers to diffusion and formation of C4H4 and C6H6 obtained from DFT calculations are in quantitative agreement with the experiments once the locally high coverage in C2H2 islands is included.

Place, publisher, year, edition, pages
2012. Vol. 116, no 17, 9550-9560 p.
National Category
Physical Sciences Physical Chemistry Materials Engineering
Identifiers
URN: urn:nbn:se:su:diva-80097DOI: 10.1021/jp300514fISI: 000303426500053OAI: oai:DiVA.org:su-80097DiVA: diva2:555271
Note

AuthorCount:7;

Available from: 2012-09-19 Created: 2012-09-12 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Surface reactions and chemical bonding in heterogeneous catalysis
Open this publication in new window or tab >>Surface reactions and chemical bonding in heterogeneous catalysis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis summarizes studies which focus on addressing, using both theoretical and experimental methods, fundamental questions about surface phenomena, such as chemical reactions and bonding, related to processes in heterogeneous catalysis. The main focus is on the theoretical approach and this aspect of the results. The included articles are collected into three categories of which the first contains detailed studies of model systems in heterogeneous catalysis. For example, the trimerization of acetylene adsorbed on Cu(110) is measured using vibrational spectroscopy and modeled within the framework of Density Functional Theory (DFT) and quantitative agreement of the reaction barriers is obtained. In the second category, aspects of fuel cell catalysis are discussed. O2 dissociation is rate-limiting for the reduction of oxygen (ORR) under certain conditions and we find that adsorbate-adsorbate interactions are decisive when modeling this reaction step. Oxidation of Pt(111) (Pt is the electrocatalyst), which may alter the overall activity of the catalyst, is found to start via a PtO-like surface oxide while formation of α-PtO2 trilayers precedes bulk oxidation. When considering alternative catalyst materials for the ORR, their stability needs to be investigated in detail under realistic conditions. The Pt/Cu(111) skin alloy offers a promising candidate but segregation of Cu atoms to the surface is induced by O adsorption. This is confirmed by modeling oxygen x-ray emission (XES) and absorption spectra of the segregated system and near-perfect agreement with experiment is obtained when vibrational interference effects are included in the computed XES. The last category shows results from femtosecond laser measurements of processes involving CO on Ru(0001). Using free-electron x-ray laser experiments a precursor state to desorption is detected and also found in simulations if van der Waals effects are included. Resonant XES can be used to distinguish two different species of CO on the surface; vibrationally hot, chemisorbed CO and CO in the precursor state. Laser-induced CO oxidation on Ru(0001) is modeled and three competing mechanisms are found. Kinetic modeling reproduces the experiment qualitatively.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2014. 66 p.
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-102323 (URN)978-91-7447-893-8 (ISBN)
Public defence
2014-05-12, sal FP41, AlbaNova universitetscentrum, Roslagstullsbacken 33, Stockholm, 13:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 8: Manuscript.

Available from: 2014-04-16 Created: 2014-04-01 Last updated: 2014-04-22Bibliographically approved

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Öberg, HenrikNestsiarenka, YuliyaGladh, JörgenHansson, TonyPettersson, Lars G.M.Öström, Henrik
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