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Extending the σ-Hole Concept to Metals: An Electrostatic Interpretation of the Nanostructural Effects in Gold and Platinum Catalysis
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. (Brinck group)ORCID iD: 0000-0003-3832-2331
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-2673-075X
2017 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed) Published
Abstract [en]

Crystalline surfaces of gold are chemically inert, whereas nanoparticles of gold are excellent catalysts for many reactions. The catalytic properties of nanostructured gold have been connected to increased binding affinities of reactant molecules to low-coordinated Au atoms. Here we show that the high reactivity at these sites is a consequence of the formation of σ-holes, i.e. maxima in the surface electrostatic potential (Vs,max) due to the overlap of mainly the valence s-orbitals when forming the bonding σ-orbitals. The σ-holes are binding sites for Lewis bases, and binding energies correlate with magnitudes of the Vs,max. For symmetrical Au clusters, of varying size, the most positive Vs,max are found at corners, edges, and surfaces (facets) and decreasing in that order. This is in agreement with the experimentally and theoretically observed dependence of catalytic activity on local structure. The density of σ-holes can explain the increasing catalytic activity with decreasing particle size also for other transition metal catalysts, such as platinum.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017.
National Category
Physical Chemistry Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-211788DOI: 10.1021/jacs.7b05987ISI: 000408074800019Scopus ID: 2-s2.0-85026319771OAI: oai:DiVA.org:kth-211788DiVA, id: diva2:1131180
Note

QC 20170816

Available from: 2017-08-13 Created: 2017-08-13 Last updated: 2017-09-26Bibliographically approved
In thesis
1. Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
Open this publication in new window or tab >>Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The chemical bond – a corner stone in science and a prerequisite for life – is the focus of this thesis. Fundamental and applied aspects of chemical bonding are covered including the development of new computational methods for the characterization and rationalization of chemical interactions. The thesis also covers the study of corrosion of copper-based materials. The latter is motivated by the proposed use of copper as encapsulating material for spent nuclear fuel in Sweden.

In close collaboration with experimental groups, state-of-the-art computational methods were employed for the study of chemistry at the atomic scale. First, oxidation of nanoparticulate copper was examined in anoxic aqueous media in order to better understand the copper-water thermodynamics in relation to the corrosion of copper material under oxygen free conditions. With a similar ambition, the water-cuprite interface was investigated with regards to its chemical composition and reactivity. This was compared to the behavior of methanol and hydrogen sulfide at the cuprite surface.

An overall ambition during the development of computational methods for the analysis of chemical bonding was to bridge the gap between molecular and materials chemistry. Theory and results are thus presented and applied in both a molecular and a solid-state framework. A new property, the local electron attachment energy, for the characterization of a compound’s local electrophilicity was introduced. Together with the surface electrostatic potential, the new property predicts and rationalizes regioselectivity and trends of molecular reactions, and interactions on metal and oxide nanoparticles and extended surfaces.

Detailed atomistic understanding of chemical processes is a prerequisite for the efficient development of chemistry. We therefore envisage that the results of this thesis will find widespread use in areas such as heterogeneous catalysis, drug discovery, and nanotechnology.

Abstract [sv]

Den kemiska bindningen – en hörnsten inom naturvetenskapen och oumbärlig för allt liv – är det centrala temat i den här avhandlingen. Både grundläggande och tillämpade aspekter behandlas. Detta inkluderar utvecklingen av nya beräkningsmetoder för förståelse och karaktärisering av kemiska interaktioner. Dessutom behandlas korrosion av kopparbaserade material. Det sistnämnda är motiverat av förslaget att använda koppar som inkapslingsmaterial för hanteringen av kärnavfall i Sverige.

Kvantkemiska beräkningsmetoder enligt state-of-the-art har använts för att studera kemi på atomnivå, detta i nära sammabete med experimentella grupper. Initialt studerades oxidation av kopparnanopartiklar under syrgasfria och vattenrika förhållanden. Detta för att bättre kartlägga koppar-vattensystemets termodynamik. Av samma orsak detaljstuderades även gränsskiktet mellan vatten och kuprit med fokus på dess kemiska sammansättning och reaktivitet. Resultaten har jämförts med metanols och vätesulfids kemiska beteende på ytan av kuprit.

En övergripande målsättningen under arbetet med att utveckla nya beräkningsbaserade analysverktyg för kemiska bindningar har varit att överbrygga gapet mellan molekylär- och materialkemi. Därför presenteras teoretiska aspekter samt tillämpningar från både ett molekylärt samt ett fast-fas perspektiv. En ny deskriptor för karaktärisering av föreningars lokala elektrofilicitet har introducerats – den lokala elektronadditionsenergin. Tillsammans med den elektrostatiska potentialen uppvisar den nya deskriptorn förmåga att förutsäga samt förklara regioselektivitet och trender för molekylära reaktioner, och för interaktioner på metal- och oxidbaserade nanopartiklar och ytor.

En detaljerad förståelse av kemiska processer på atomnivå är en nödvändighet för ett effektivt utvecklande av kemivetenskapen. Vi förutspår därför att resultaten från den här avhandlingen kommer att få omfattande användning inom områden som heterogen katalys, läkemedelsdesign och nanoteknologi.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 143
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:35
Keywords
computational chemistry, density functional theory, chemical interactions, reactivity descriptors, copper corrosion, surface and materials science, nucleophilic substitution reactions, heterogeneous catalysis, transition metal oxides, nanotechnology, beräkningskemi, täthetsfunktionalteori, kemiska interaktioner, reaktivitetsdeskriptorer, kopparkorrosion, yt- och materialvetenskap, nukleofila substitutionsreaktioner, heterogen katalys, överångsmetalloxider, nanoteknologi
National Category
Chemical Sciences Materials Chemistry Organic Chemistry Physical Chemistry Theoretical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-213028 (URN)978-91-7729-506-8 (ISBN)
Public defence
2017-09-29, F3 (rumsnr: 132), Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170829

Available from: 2017-08-29 Created: 2017-08-28 Last updated: 2017-08-29Bibliographically approved

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Publisher's full textScopushttp://dx.doi.org/10.1021/jacs.7b05987

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