Atomistic insights into surface reactivity via density functional theory

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2018
Demirtaş, Merve
In this thesis, three different topics are investigated by using Density Functional Theory. First, an extensive study of the water gas shift reaction on Mo2C surface is carried out. CO is chosen as a probe molecule in order to understand the structural and electronic effects of the metal additives on the surface. We show that preadsorbed K atom enhences the activation and adsorption of CO molecule on the surface when compared to precious metal additives we consider, which are Pt and Au. Additionally, the presence of Pt and K stabilizes the transition state of the C-O bond scission, lowers the activation energy of this reaction. In the fourth part, the oxidation of CH3OH molecule is examined on bare and Ptdoped Au(111) surfaces. With this aim, the adsorption energies of molecules and atoms involved in the reaction of CH3OH dissociation to CH3O and H in order to obtain their stable sites. Having defined them, the activation barrier calculations are carried out on the bare Au(111) surface. Additionally, the same calculations are performed on the Pt-doped Au(111) surface in different concentrations in order to see the effect of them on the activation barrier. We show that the activation barriers are notably decreased when the number of Pt dopant atoms on the surfaces increases. In the fifth part, the interaction between the amorphous SiO2, crystal Si, oxidized crystal Si surfaces and ions of different types of etchants, which are H,F and Cu, is examined. The interaction between ions and amorphous surface is shown to be weaker than the reconstructed bare and oxydized Si surfaces. The adsorption energies are quite high for H and F ions on the reconstructed Si(001) surface. For Cu ions, the adsorption energy is improved with precovered O atom on the Si surface.

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Citation Formats
M. Demirtaş, “Atomistic insights into surface reactivity via density functional theory,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.