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Naphthalene on Ni(111): Experimental and Theoretical Insights into Adsorption, Dehydrogenation, and Carbon Passivation
Stockholm University, Faculty of Science, Department of Physics.
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Number of Authors: 92017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 40, p. 22199-22207Article in journal (Refereed) Published
Abstract [en]

An attractive solution to mitigate tars and also to decompose lighter hydrocarbons in biomass gasification is secondary catalytic reforming, converting hydrocarbons to useful permanent gases. Albeit that it has been in use for a long time in fossil feedstock catalytic steam reforming, understanding of the catalytic processes is still limited. Naphthalene is typically present in the biomass gasification gas and to further understand the elementary steps of naphthalene transformation, we investigated the temperature dependent naphthalene adsorption, dehydrogenation and passivation on Ni(111). TPD (temperature-programmed desorption) and STM (scanning tunneling microscopy) in ultrahigh vacuum environment from 110 K up to 780 K, combined with DFT (density functional theory) were used in the study. Room temperature adsorption results in a flat naphthalene monolayer. DFT favors the dibridge[7] geometry but the potential energy surface is rather smooth and other adsorption geometries may coexist. DFT also reveals a pronounced dearomatization and charge transfer from the adsorbed molecule into the nickel surface. Dehydrogenation occurs in two steps, with two desorption peaks at approximately 450 and 600 K. The first step is due to partial dehydrogenation generating active hydrocarbon species that at higher temperatures migrates over the surface forming graphene. The graphene formation is accompanied by desorption of hydrogen in the high temperature TPD peak. The formation of graphene effectively passivates the surface both for hydrogen adsorption and naphthalene dissociation. In conclusion, the obtained results on the model naphthalene and Ni(111) system, provides insight into elementary steps of naphthalene adsorption, dehydrogenation, and carbon passivation, which may serve as a good starting point for rational design, development and optimization of the Ni catalyst surface, as well as process conditions, for the aromatic hydrocarbon reforming process.

Place, publisher, year, edition, pages
2017. Vol. 121, no 40, p. 22199-22207
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-149014DOI: 10.1021/acs.jpcc.7b07757ISI: 000413131700047OAI: oai:DiVA.org:su-149014DiVA, id: diva2:1158353
Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2019-08-19Bibliographically approved
In thesis
1. Experimental investigations of model catalytic surface reactions on metal and metal oxide surfaces
Open this publication in new window or tab >>Experimental investigations of model catalytic surface reactions on metal and metal oxide surfaces
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the development of renewable energies catalysis plays an important role, for example in the production of H2 gas that drives fuel cells, or in the decomposition of annoying by-products of renewable energy production. Most catalysts and catalytic processes currently used in the industry have their roots in macroscopic empirical investigations and trial and error-based optimization. In order to be able to design novel catalytic processes more efficiently, detailed understanding of the catalyst-reactant interaction and the dynamics of the microscopic reaction steps is needed. The present thesis aims to contribute to the fundamental understanding of catalyst reactant systems by means of experiments using model systems in Ultra High Vacuum. For this purpose, several surface science techniques were employed such as vibrational sum-frequency generation (SFG), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and femtochemistry.

In the present thesis the results of three different projects are presented. The first concerns the adsorption and decomposition of naphthalene on Ni(111). Using scanning tunnelling microscopy (STM) and density functional theory (DFT) we identify the adsorption energy and geometry of the naphthalene molecule. Using SFG and TPD we investigate the temperature dependent breakdown of the naphthalene molecule and identify geometrical changes of the adsorbate as an intermediate step in the decomposition reaction. Additionally, we observe poisoning of the surface due to graphene growth using both STM and XPS and explore the possible effect of co-adsorption with oxygen on the reaction pathway and the poisoning of the catalyst.

The second section concerns the adsorption and decomposition of ethanol and methanol on cuprous oxide (Cu2O). Using mainly XPS and SFG we show that ethanol adsorbs dissociatively on Cu2O(100) and (111) and that methanol adsorbs dissociatively on the (100) but molecularly on the (111) surface. Furthermore, we identify intermediate surface species and products of the temperature dependent dehydrogenation of both alcohols and show that the (111) surface is the more effective catalyst for decomposition.

The third section explores the physics of non-thermal excitation methods and discusses CO oxidation on ruthenium (0001) induced by an optical laser and by X-rays from a free electron laser. Based on these femtochemistry experiments we discuss in particular the energy transfer both for direct excitation and for substrate mediated excitations. We show that we were able to control the branching ratios of competing mechanisms and understand the role of non-thermal electrons in the mechanisms of optical laser excitation. Furthermore, we show that it is possible to induce CO oxidation by direct X-ray core hole excitation and can rationalize the relaxation process that leads to CO oxidation.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2019. p. 87
National Category
Other Physics Topics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-171385 (URN)978-91-7797-706-3 (ISBN)978-91-7797-707-0 (ISBN)
Public defence
2019-09-26, FA31 sal, AlbaNova universitetscentrum, Roslagstullbacken 21, Stockholm, 10:00 (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 3: Manuscript.

Available from: 2019-09-03 Created: 2019-08-13 Last updated: 2019-08-30Bibliographically approved

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