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Theoretical Investigation of Mechanisms of Chemical Reactions Taking Place in Microporous Materials
Položij, Miroslav ; Nachtigall, Petr (advisor) ; Pulido Junquera, María Ángeles (referee)
Mechanisms of three reactions catalyzed by microporous materials were investigated computationally; the reactions investigated include Friedländer and Knoevenagel reactions catalyzed by Cu3BTC2 metal organic framework (MOF) and an intramolecular cyclisation of unsaturated alcohols catalyzed by zeolite H-ZSM-5. It was found that the reaction mechanisms of all three reactions are controlled by a high concentration of active sites in materials. Reaction intermediates interact with more than one active site simultaneously. This novel concept of "multiple-site" interactions is described. The concerted effect of two catalytic sites leads to a decrease of activation barriers on reaction paths of Friedländer and Knoevenagel reactions. On the contrary, a simultaneous interaction of reactants with two active sites has a negative effect on reaction rate in case of alcohol cyclization catalyzed by H-ZSM-5; it was found that the interaction with dual sites results in the increase of activation barriers and diffusion limitations. In case of Knoevenagel reaction catalyzed by CuBTC, the adsorption of reaction precursor to the reaction site allows the creation of a dynamic defect in the MOF framework that subsequently catalyses the reaction. Both, the multiple sites effect and the dynamical defect formation effect...
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First-principles studies of the electronic and structural properties of Lead Zirconate Titanate (PZT)
Planer, Jakub ; Friák, Martin (referee) ; Bartošík, Miroslav (advisor)
This work is focused on Density Functional Theory (DFT) calculations of oxygen vacancy diffusion barriers in mixed perovskite lead zirconate titanate and its pure counterparts. We found out that barrier heights are different in lead titanate and lead zirconate caused by the different localization of the excess electrons due to the oxygen vacancy formation. Diffusion barriers were also determined for titanium-rich mixed phases and compared to experimental values. This work contributes to clarify unusually low experimentally measured diffusion coefficients in PZT. We found out that the induced vacancy states are forming localized bonds to the lead atoms which causes the oxygen vacancies to become immobile due to the increase of the activation energy of the diffusion process.
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"Ab initio" study of Sn-Ce-O mixed oxides
Fečík, Michal ; Szabová, Lucie (advisor) ; Mazur, Daniel (referee)
The present work is focused on a theoretical analysis based on the numerical DFT+U calcula- tions investigating structural and electronic properties of mixed oxide Sn/CeO2. The main reasons for this study are reported improved catalytic properties of this system that are most probably caused by catalytic properties of cerium oxides, which are based on releasing or (re)capturing of oxygen atoms via the process of cerium oxidation and reduction. In this work we study com- pounds of cerium and tin that compose Sn/CeO2 - that is a metal Sn and CeO2 together with other compounds SnO2 and Ce2O3 - especially by means of band structures and densities of states. Furthermore we studied mixed oxide Sn/CeO2 in terms of electronic structure and morphology. In this work we consider two different modifications of the analyzed system - the first one con- tains oxygen vacancy whereas the second one stay unchanged. Our study is focused on analysis of influence of tin defect upon properties of CeO2, mainly its effect on reduction of cerium atoms. 1
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Theoretical calculation of stability and electronic structure of Si surfaces
Krejčí, Ondřej ; Kocán, Pavel (advisor) ; Szabová, Lucie (referee)
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Structure and dynamics of electronic defects in liquid water
Maršálek, Ondřej ; Jungwirth, Pavel (advisor) ; Horáček, Jiří (referee) ; Pittner, Jiří (referee)
Title: Structure and dynamics of electronic defects in liquid water Author: Ondřej Maršálek Institute: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic Supervisor: prof. Mgr. Pavel Jungwirth, DSc. Supervisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: In this thesis we present ab inito molecular dynamics simulations of two different electronic defects in water. Photoionization of liquid water produces a cationic hole, which undergoes ultrafast dynamics and forms the hydrated proton and the hydroxyl radical as its products. We study both the dynamics and spectroscopy of this process. The hydrated electron is a key intermediate in radiation chemistry of aqueous systems. We simulate its equilibrium properties in anionic water clusters as well as the dynamics of vertical electron attachment to cold and warm clusters. The hydrated electron reacts with a hydrated proton to form a hydrogen atom. We examine this reaction at a finite temperature in a larger cluster as well as in more detail in a smaller cluster. Because both of the electronic defects studied here are challenging open-shell species, we put emphasis on benchmarking and testing our computational setup. Six published articles are attached to the thesis. Keywords: density functional theory,...
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Theoretical Investigation of Friedlander Reaction catalyzed by CuBTC
Položij, Miroslav ; Nachtigall, Petr (advisor) ; Čejka, Jiří (referee)
The mechanism of Friedlander reaction was investigated theoretically. The main objective was to find a reaction path of Friedlander reaction catalyzed by Cu3(BTC)2 (BTC = benzene-1,3,5-tricarboxylic acid), a microporous metal organic framework. In addition, possible mechanisms of non-catalyzed and acid-catalyzed reaction were investigated in the gas phase and in the solution. The suitability of Cu3(BTC)2 as catalyst for Friedlander reaction is discussed based on the computational results obtained.
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Modelling of Chemical Processes
Al Mahmoud Alsheikh, Amer ; Bártlová,, Milada (referee) ; Urban,, Ján (referee) ; Žídek, Jan (advisor)
V této práci je prezentována studie fragmentačního procesu zvolené molekuly a jeho vztah ke složení fragmentačních produktů. Práce je zaměřená na výpočet fragmentační energie molekuly pomocí ab initio kvantově chemických metod, metodou „density functional theory (DFT)“ a také srovnáním s experimentem. Je prezentován vliv výpočetní metody, bázového setu, a geometrie molekuly na simulaci. Byla porovnána fragmentace methylfenylsilanu (MPS), dimethylfenylsilanu (DMPS), a trimetylfenylsilanu (TMPS). Fragmentace byla iniciována monochromatickým elektronovým svazkem (EII). Hmotnostní spektrometrie byla využita ke studiu složení fragmentačních produktů MPS a TMPS. Fragmentační produkty MPS a TMPS měřené v rámci této práce byly doplněny o experimentální studii DMPS, která byla prezentována v literatuře. Takto byla získána řada molekul, které jsou strukturně podobné, ale mají výrazně rozdílné chování během fragmentace. Pomocí měření účinného průřezu byly měřeny disociační energie vazeb a tyto disociační energie byly vypočteny pomocí metody DFT. Kombinací teoretického výpočtu metodou DFT a experimentálního měření jsme poukázali na společné rysy a na rozdíly ve fragmentačním schématu všech tří molekul. Navrhli jsme odštěpení dvou vodíkových atomů během plazmově indukovaného fragmentačního procesu. Vodíky mohou být odštěpeny pomocí dvou mechanismů: i. odštěpení dvou vodíků jeden po druhém a ii. odštěpení molekuly H2 v jednom kroku. Z profilů energie dokážeme určit, který mechanismus bude v tom konkrétním případě pravděpodobnější. Předpokládaný mechanismus je v korelaci s experimentálními výsledky fragmentace zjištěnými z hmotnostních spekter.
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Interpretation of the C=O band of modified diamond nanoparticles by means of DFT theory
Jirásek, Vít ; Kozak, Halyna ; Remeš, Zdeněk ; Kromka, Alexander
Diamond nanoparticles (DNPs) are an interesting class of nanomaterials, which has many unique properties. Their applications in medicine and molecular biology have been mentioned. The DNPs were reviewed in sense of their surface chemistry and a range of analytic techniques was pointed out. The experimental analysis can be enhanced by theoretical models based on the first principles. An approach to theoretical analysis of infrared spectra was introduced. As an example, a part of FTIR spectra of the oxidized DNPs was interpreted by means of the DFT theory. The calculation of the C=O stretch vibrational frequencies of carboxylic and anhydride groups on certain model clusters enabled to explain the shift and splitting of the measured spectral bands.
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Modelování spektrálních a fotochemických vlastností diiminových karbonylových komplexů přechodových kovů s diiminy
Šebera, Jakub ; Záliš, Stanislav ; Vlček, Antonín
The felxibility pf the coordination sphere of mixed valence carbonyl complexes enables to tune spectral and protochemical properties. The variety of excited states in ilustrated on Ru, Re and W mixed ligand carbonyl complexed. The lowest excited states of [W(CO)4L] and [W(CO)5L’] (L=N,N'-di-methyl-1,4-diazabutadiene, ethylenediamine, 2,2’-bipyridine, phenantroline; L’= pyridine, 4-CN-pyridine, piperidine) ckomplexes were found to be either W -> pi*(L) or W -> pi*(CO) in charakter, depending on the type of the heteroligands.
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