Theoretical mo delling of nanoparticles with applications to catalysis and sustainable energy

Simon Hedegaard Brodersen

Research output: Book/ReportPh.D. thesisResearch

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Abstract

The aim of this thesis is to gain a better understanding of the shape and structure of nanoparticles. Nanoparticles are important in heterogeneous catalysis, where the chemical reaction happens at the surface, since they maximise the available surface area for a given amount of catalyst. Studies of the catalytic activity on single surfaces have shown that the reaction rates depends strongly on the geometry of the adsorbing and active site on the surface, and the structure of nanoparticles therefore plays and important role in understanding their catalytic capabilities.
Different simulation methods are in this thesis used to model the shape and structure of nanoparticles with different levels of detail. Molecular dynamics and Monte Carlo methods are used to elucidate the surface structure of Pt5Y core-shell and gold nanoparticles respectively. The Pt5Y nanoparticles are modelled with focus on the oxygen reduction reaction, where the flat (111)-surface atoms are believed to constitute the active site. It is found that the surface layer of the Pt5Y particles is compressed and that it contains significantly more atoms resembling the flat (111)-surface compared to pure platinum particles. The gold nanoparticles are modelled with focus on the oxidation of carbon monoxide (CO), where low-coordinated atoms are believed to constitute the active site. It is here found that the activity solely steams form low-coordinated corner atoms. Further more is a continuous Wulff construction applied together with microkinetic modelling to model the shape of late transition metal particles under reaction conditions with focus on the direct decomposition of nitrogen monoxide (NO). It is found that the gas-environment has a considerable influence on the shape of the particles, even in this simple model.
Interatomic potentials have been used to describe the potential energy of the nanoparticles in the molecular dynamics and Monte Carlo simulations. These potentials are based on empirical grounds, and the thesis therefore includes a method to fit the potentials to different material properties. This method has been used to fit different potentials.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages194
Publication statusPublished - 2014

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