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Publications Overview

Scientific publications divided into sections: Papers, Talks, Posters, Theses.




Papers


Molecular understanding of enyne hydrogenation over palladium and copper catalysts
Blaise Bridier, David Karhánek, Javier Pérez-Ramírez, Nuria López

Abstract    Partial hydrogenation of unsaturated hydrocarbons comprises an important family of reactions that are applied in many industrial sectors. Understanding the hydrogenation of polyunsatured and polyunsaturated compounds on heterogeneous catalysts at its molecular level remains a challenging milestone to fine-tune the product distribution. Our study presents a detailed mechanistic analysis of the gas phase hydrogenation of vinylacetylene (1-butene-3-yne) and valylene (2-methyl-1-butene-3-yne) over palladium and copper catalysts. These two metals are selected owing to their pronounced differences in continuous flow catalytic tests at ambient pressure. The chemoselectivity, regioselectivity, isomerization, and oligomerization patterns measured in a broad range of feed hydrogen/ hydrocarbon ratios are rationalized by density functional theory simulations. An extended Brønsted–Evans–Polányi relationship for both substrates and active metals is found for the hydrogenation processes. The identified factors that govern selectivity are similar to those identified for smaller C2 and C3 compounds and, thus, a means of systematization to other polyunsaturated compounds is opened up.

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[ChemCatChem, Volume 4, Issue 9, September 2012, Pages 1420-1427]
[DOI: 10.1002/chem.201200801]


A Journey inside the U28 Nanocapsule
Adrià Gil, David Karhánek, Pere Miró, Mark R. Antonio, May Nyman, Carles Bo

Abstract    Anionic uranyl–peroxide U28 nanocapsules trap cations and other anions inside, whose structures cannot be resolved by X-ray diffraction, owing to crystallographic disorder. DFT calculations enabled the complete characterization of the geometry of these complex systems and also explained the origin of the disorder. The stability of the capsules was strongly influenced by the entrapped cations. Excellent agreement between experiment and theory was also obtained for the electronic character and redox properties.

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[Chemistry - A European Journal, Volume 18, Issue 27, 2 July 2012, Pages 8340-8346]
[DOI: 10.1002/chem.201200801]


A density-functional study of the adsorption of methane-thiol on the (111) surfaces
of the Ni-group metals: I. Molecular and dissociative adsorption

David Karhánek, Tomáš Bučko, Jürgen Hafner

Abstract    The molecular and dissociative adsorption of methane-thiol (CH3SH) in the high-coverage limit on the (111) surfaces of the Ni-group metals has been investigated using ab initio density functional techniques. In molecular form, methane-thiol is bound to the surface only by weak polarization-induced forces in a slightly asymmetric configuration with the C–S axis tilted by 35–60° relative to the surface normal. On Ni and Pd surfaces the S atom occupies a position close to a bridge site; on Pt it is located close to an on-top position. The length of the S–H bond is only slightly stretched relative to its value in the gas phase, indicating only a very modest degree of activation for dehydrogenation. A strong covalent adsorbate/substrate bond is formed upon adsorption of a methane-thiolate (CH3S) radical. On Ni(111) in the energetically most favorable configuration the S atom occupies a position in a threefold hollow, slightly displaced towards a bridge site. The C–S axis is tilted by about 35° across the bridge. On Pd(111) and Pt(111) the S atom of thiolate occupies a position between a hollow and a bridge site, with the C–S axis tilted even more strongly across a neighboring threefold hollow. On all three surfaces our calculations demonstrate the existence of multiple metastable adsorption configurations, including upright CH3S bound in the center of a threefold hollow as reported in some earlier studies. Dehydrogenation of the adsorbed methane-thiol to form co-adsorbed methane-thiolate and atomic hydrogen is an exothermic process, which is not activated on Ni(111) but activated on Pd(111) and Pt(111).

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[Journal of Physics: Condensed Matter, Volume 22, Issue 26, 7 July 2010, Pages 265005 (14pp)]
[DOI: 10.1088/0953-8984/22/26/265005]


A density-functional study of the adsorption of methane-thiol on the (111) surfaces
of the Ni-group metals: II. Vibrational spectroscopy

David Karhánek, Tomáš Bučko, Jürgen Hafner

Abstract    The vibrational eigenstates of methane-thiol (CH3SH) and methane-thiolate (CH3S) in the gas phase and in dense monolayers adsorbed on the (111) surfaces of the Ni-group metals have been investigated within the framework of density-functional theory using generalized response and force-constant techniques. For isolated CH3SH good agreement of eigenfrequencies and intensities with the measured infrared spectra is achieved. For the CH3S radical, experimental information from laser-induced fluorescence spectroscopy is available only for selected eigenmodes. The theoretical predictions show reasonable agreement for the C–H deformation and C–S stretching modes, but predict much higher C–H stretching frequencies in better agreement with estimates based on the vibrational fine structure of the photoemission spectra. For methane-thiol monolayers on Ni(111) and Pt(111) the calculations predict stronger red-shifts of the S–H and C–S stretching modes than reported from high-resolution electron energy loss spectroscopy (HREELS) on condensed multilayers which average over the first layer adsorbed on the metal and further physisorbed molecular layers. For methane-thiolate monolayers the calculations predict modest blue-shifts of the C–H stretching and rocking modes and for the asymmetric C–H deformation modes. Red-shifts are predicted for the symmetric C–H deformation and for the C–S stretching modes. Reasonable agreement with HREELS is achieved. The increased differences between symmetric and asymmetric C–H stretching and deformation modes induced by the adsorption is a consequence of the strongly tilted adsorption geometries.

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[Journal of Physics: Condensed Matter, Volume 22, Issue 26, 7 July 2010, Pages 265006 (9pp)]
[DOI: 10.1088/0953-8984/22/26/265006]


Particle size effect and its influence on the adsorbed complex stability
Jiří Švrček, David Karhánek, Petr Kačer, Eliška Leitmannová, Jana Šplíchalová, Libor Červený

Abstract    The work had engaged in the research area of structural effects and its influences on the course of heterogeneously catalyzed hydrogenation of alkenic substances in the liquid phase on platinum catalysts. The combination of experimental (kinetic method and physical-chemical characterization) and theoretical methods (calculations based on molecular modeling) was utilized in order to efficiently study these effects having impact both on the side of model substrates (alkenic alcohols differing in the location of C=C bond and OH group) and the catalyst active site. This approach allowed comparing the stability of an absorbed complex of all selected model substrates, i.e. the key structure produced during the reactant transformation to a product on the surface of heterogeneous catalysts. The main attention was dedicated to the effect of the particle size of the catalyst active metal that took a significant part in the stability change of the adsorbed complexes of the model substrates as well as the utilization of findings acquired from appositely selected theoretical models to explain this change. The acquired results inferred that it is possible to use the frontier orbitals model to describe the interaction between the active site represented by particles with D > 5-6 nm and C=C bond of the alkenic alcohols. The formed adsorbed complex demonstrated larger stability with hept-1-en-4-ol (b-position of the OH group to the C=C bond) substrate in comparison to pent-1-en-3-ol (α-position of the OH group to the C=C bond). The model of a planar metal complex with the substrate as its ligand appeared to be promising in the case of hydrogenation proceeding on small particles (D < 5-6 nm). The stability of the complexes with α- and β-hydroxyalkenes demonstrated the opposite order of values in comparison with catalysts with larger particles (D > 5-6 nm) - particle size effects.
Keywords   Structure effects   Adsorbed complex   Particle size effect   Molecular modeling

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[Applied Catalysis A: General, Volume 354, Issues 1-2, 15 February 2009, Pages 169-175]
[DOI: 10.1016/j.apcata.2008.11.021]


Application of molecular modelling in heterogeneous catalysis research
Petr Kačer, Marek Kuzma, David Karhánek, Jiří Švrček, Libor Červený

Abstract    Traditionally, heterogeneous catalysis has largely been an experimental field. While this is still true today, it is increasingly recognized that computer modelling and simulation are important tools in the study and development of catalytic systems. Molecular modelling has the potential to provide new insights into reaction pathways, to predict properties of catalysts that have not yet been synthesized, and to bring information for a given system from many different experimental techniques into a coherent picture. A close interaction of modelling and experiment is vital. The most fruit-fully strategy for using modelling in catalysis research is likely to be a dual-feedback mode, where experiments (kinetic studies of reaction rates, thermodynamic information on adsorption, and spectroscopic data on molecular-level structure) are used to validate the modelling and modelling is used to explain experimental results, to suggest new experiments, and perhaps to substitute for experiments in the screening of different catalysts or reaction conditions.

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[Chemistry Central Journal, Volume 2 (Suppl. I) / March 2008, Page P37]
[DOI: 10.1186/1752-153X-2-S1-P37]


The platinum-olefin binding energy in series of (PH3)2Pt(olefin)complexes - a theoretical study
David Karhánek, Petr Kačer, Marek Kuzma, Jana Šplíchalová, Libor Červený

Abstract    Theoretical investigation of Pt(0)-olefin organometallic complexes containing tertiary phosphine ligands was focused on the strength of platinum-olefin electronic interaction. DFT theoretical study of electronic effects in a substantial number of ethylene derivatives was evaluated in terms of the Pt-olefin binding energy using MP2 correlation theory. Organometallics bearing coordinated olefins with general formula (R1R2C=CR3R4)Pt(PH3)2 [R = various substituents] had been selected, including olefins containing both electron-donor substituents as well as electron-withdrawing groups. The stability of the corresponding complexes increases with a strengthening electron-withdrawal ability of the olefin substituents.
Keywords   Binding energy   DFT   Molecular modeling   Platinum complexes

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[Journal of Molecular Modeling, Volume 13, Number 9 / September 2007, Pages 1009-1016]
[DOI: 10.1007/s00894-007-0222-7]




Talks

November 30, 2012
DFT Study of Thiol Adsorption on Metal Surfaces
David Karhánek
Invited lecture,
Philipps-University Marburg, Hans-Meerwein-Straße, DE-35032, Marburg, Germany.

October 19, 2011
Hydrogenation mechanism of ene-yne hydrocarbons over Cu and Pd catalysts
David Karhánek, Núria López
Seminar lecture,
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, ES-43007 Tarragona, Spain.

November 26, 2010
Selective Hydrogenation of Acetylene
David Karhánek, Núria López
INTECAT Annual Meeting 2010,
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, ES-43007 Tarragona, Spain.

May 8, 2009
Thiol SAMs studied by DFT
David Karhánek, Jürgen Hafner
Seminar lecture - Heterogeneous Catalysis Theoretical Research Group,
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, ES-43007 Tarragona, Spain.
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April 18, 2007
Self-Assembled Monolayers on Transition Metal Surfaces
David Karhánek, Jürgen Hafner
New Developments in Surface Science - Seminar
Technical University of Vienna, Gumpendorferstraße 1a, A-1060 Vienna, Austria.
« PDF Direct Download (1615 kB) »        « PDF Announcement (112 kB) »

November 07-08>, 2005
Surface Complexes in Catalysis
David Karhánek, Petr Kačer, Libor Červený
XXXVII Symposium on Catalysis Prague
J. Heyrovsky Institute of Physical Chemistry of Academy of Sciences, Dolejškova 3, CZ-18223 Prague, Czech Republic.
« PDF Download (1823 kB) »          « PDF Talk (78 kB) »        « PDF Abstract (15 kB) »




Posters

June 22-23, 2011
Selective Hydrogenation of Valylene
David Karhánek, Blaise Bridier, Javier Pérez-Ramírez, Nuria López
Summer School »Energy and Materials from the Sun«
Rolduc Abbey Conference Centre, Heyendallaan 82, NL-6464 EP Kerkrade, Netherlands.

May 22-26, 2011
Selective Hydrogenation of Valylene
David Karhánek, Blaise Bridier, Javier Pérez-Ramírez, Nuria López
Psi-k Research Conference: Cat1P (Catalysis from 1st Principles)
Magleås Kursuscenter, Hřsterkøbvej 6, DK-3460 Birkerød, Denmark.

November 28, 2007
Self-Assembled Monolayers Studied by DFT
David Karhánek, Jürgen Hafner
The CMS Science College Evaluation Hearing
Austrian Science Fund (FWF), Haus der Forschung, Sensengasse 1, A-1090 Vienna, Austria.
« PDF Download (1538 kB) »

 October 8-9, 2004
The Platinum-Olefin Binding Energy in (PH3)2Pt(Olefin) Complexes: A Theoretical Study
David Karhánek, Petr Kačer, Marek Kuzma, Libor Červený
XXXVI Symposium on Catalysis Prague.
J. Heyrovský Institute of Physical Chemistry of Academy of Sciences, Dolejškova 3, CZ-18223 Prague, Czech Republic.
« PDF Download (487 kB) »       « PDF Abstract (27 kB) »




Theses

June 2, 2010
Doctoral Thesis: ''Self-assembled monolayers studied by density-functional theory''
David Karhánek
Fakultät für Chemie, Universität Wien, Währinger Str. 42, A-1090 Vienna, Austria.
« Online PDF Download »         « PDF Download (8496 kB) »         « PDF Summary (46 kB) »

June 1, 2005
Master Diploma Thesis: ''Studium povrchových komplexů v heterogenní katalýze''
David Karhánek
Dept. of Organic Technology, ICT Prague, Technická 5, CZ-16628, Prague, Czech Republic.
« PDF Download (1368 kB) »         « PDF Summary (9 kB) »


Veni, vidi, vici.