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Low temperature behaviour of asphalt mixtures
Štěpanovský, Vlastimil ; Stehlík, Dušan (referee) ; Hýzl, Petr (advisor)
In this thesis it was paid attention to behaviour asphalt mixture of low temperature. The theoretical part deals with the technologies for reducing of mixing temperature and with their comparison. The thesis is notionally divided into two parts. The practical part is focused on the assessment of low temperature features by the test of asphalt mixture resistance against the formation of frost cracks according to ČSN EN 12697-46. Three mixtures were tested. The aim was to find if the low-temperature characteristics get worse compared to the commonly tested mixtures of the same gradation.
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Synthesis of novel zeolite materials and their application in catalysis
Veselý, Ondřej ; Přech, Jan (advisor) ; Zima, Vítězslav (referee) ; Hronec, Mlan (referee)
Zeolites are crystalline microporous tectosilicates with acidic properties. The pore sizes of molecular dimensions restrict molecules from entering/exiting the pores based on the molecule size and geometry, or formation of certain (bulky) transition states within the pores. Accordingly, zeolites have become vital industrial catalysts, adsorbents and ion-exchangers. Zeolites are commonly synthesised by hydrothermal crystallization. However, this method provides only limited control over their crystal structure, morphology, or location of active sites within the framework. Some of these limitations can be overcome using an alternative synthetic method; the Assembly-Disassembly-Organisation- Reassembly (ADOR). The ADOR transforms a parent (germanosilicate) zeolite into a layered precursor and subsequently uses the layers as building blocks for a new zeolite framework. We aimed to develop methodology to control the crystal morphology of germanosilicate zeolite UTL (Assembly), determine the mechanism of the UTL hydrolysis (Disassembly), and to reconstruct the parent UTL zeolite from the ICP-1P layered material (Organisation and Reassembly) since the traditional ADOR yields zeolites of smaller channel size but the parent UTL. We found the UTL crystal morphology progressively varies the Si/Ge molar ratio...
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Synthesis of the violet fragrances on MFI zeolite catalysts
Domenová, Alica ; Mazur, Michal (advisor) ; Kadam, Shashikant Arun (referee)
Zeolites are porous aluminosilicates widely used in acid catalysis due to their properties, such as Brønsted and Lewis acidity, thermal stability, and defined pore structure providing shape selectivity. Zeolites can be synthesized as nanolayered crystals that can be further modified by pillaring. These architectures are more open, thus can lead to novel applications of zeolites in catalysis. One of the acid-catalyzed reactions where 3D standard zeolites were shown to be active catalysts is cyclization of pseudoionone. This reaction is used for the synthesis of α-, β- , and γ-ionones, important organic compounds used in medicine and fragrance industries mainly as violet fragrances. Up to date, there are no reports on the catalytic activity of layered zeolites in ionone synthesis, however, these open structures have a potential to be utilized in such reactions due to the improved reactant diffusion through the catalyst. In this work, catalytic performance of the materials based on MFI zeolite layers was investigated in the conversion of pseudoionone-to-ionones. Catalysts were synthesized using hydrothermal crystallization followed by post-synthesis modification via pillaring. Structure and textural properties of the catalysts were thoroughly characterized using X-ray diffraction and nitrogen...
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Synthesis and characterization of zeolites with controllable location of active sites
Dobiášová, Ivana ; Shamzhy, Mariya (advisor) ; Hulla, Martin (referee)
This bachelor thesis focusses on the synthesis, post-synthesis modification, and comprehensive characterization of two series of zeolites based on IWW and ITH topologies. The investigated zeolite structures were chosen because their frameworks contain d4r units preferentially occupied by Ge atoms, which can be substituted for various catalytically active metal sites such as Al, Ti, and Sn by post-synthesis degermanation/metallation. To study the influence of the chemical composition of the parent germanosilicate on the concentration and accessibility of the incorporated Al-, Ti- and Sn-associated acid sites, IWW and ITH were hydrothermally synthesized with different amounts of germanium in the reaction mixture (Si/Ge = 4 - 10 for IWW and Si/Ge = 10 - 30 for ITH) and used for post-synthesis Ge- for-metal substitution. X-ray diffraction (XRD) was used to verify the structure of the synthesized zeolites; chemical analysis identified their elemental composition; nitrogen physisorption was used to determine their textural characteristics (e.g., micropore volume, total pore volume pore, and external surface area), while scanning electron microscopy (SEM) was applied to visualize the shape and size of the zeolite particles. The coordination state of the incorporated Ti and Sn sites was studied using...
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Tracking the evolution and stability of metal nanoparticles in zeolites by in-situ heating electron microscopy
Krakl, František ; Mazur, Michal (advisor) ; Knotková, Kateřina (referee)
Zeolites, with their unique characteristics, such as microporosity, thermal stability, and shape selectivity, are used as a support for metal nanoparticles to enhance their catalytic properties. Metal nanoparticles have a large attainable surface in relation to their mass, thus volume. There are several ways of supporting metal on zeolites, such as ion-exchange, impregnation, or direct encapsulation during synthesis. The latter method provides the stability of metal, however, even the zeolite-encapsulated nanoparticles are not fully sinter-resistant, especially at high temperatures. Insights into the sintering mechanism is crucial for improvement of stability of supported metal catalysts. In this work platinum nanoparticles were directly introduced into chabazite (CHA) zeolite during hydrothermal synthesis. The goal of this thesis was to understand metal nanoparticle sintering mechanisms. the role of aluminium content in zeolite framework in the stabilisation of metal nanoparticles was described. The structure of prepared materials was confirmed by powder X-ray diffraction. Inductively coupled plasma mass spectrometry was used to determine the elemental composition of the materials and their distribution in crystals was mapped by energy dispersive X-ray spectroscopy in a scanning transmission...
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Theoretical investigation of 27Al chemical shifts dependence on water amount and temperature in zeolite MFI
Willimetz, Daniel ; Grajciar, Lukáš (advisor) ; Blahut, Jan (referee)
Title: Theoretical investigation of 27 Al chemical shifts dependence on water amount and temperature in zeolite MFI Abstract: This bachelor thesis explores 27 Al NMR spectra in zeolite MFI and investigates the impact of several factors on the chemical shielding values, including water loading, temperature, and the relative positions of aluminum pairs. Various machine learning-based methods for calculating chemical shift are evaluated. Molecular dynamics simulations with neural network potentials are used to simulate experimental conditions. Neural network potentials offer a highly efficient means of calculating energy with a significant speed-up of approximately 1000 times faster than density functional theory, while maintaining a high level of accuracy. This study is the first to examine 27 Al NMR under operando conditions, with a focus on the experimentally relevant amount of water. Keywords: 27 Al NMR, machine learning, zeolites, MFI, operando conditions, neural network potentials
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The role of topology and chemical composition of zeolites on their biomedical characteristics
Nováková, Denisa ; Grajciar, Lukáš (advisor) ; Rubeš, Miroslav (referee)
7 Abstract Zeolites are traditionally used materials in the petrochemical and chemical industry that have recently drawn attention for their possible utilization in biomedicine as drug and gene carriers, materials in bone tissue engineering, or adsorbents for detoxifying human organisms. Zeolites offer a possible solution for removing protein-binding uremic toxins, such as p-cresol, that are unremovable during classical hemodialysis. This bachelor's thesis focuses on analyzing the motion of water within zeolite with CAN framework topology using molecular dynamics simulations with neural network potentials. The obtained data is used to calculate the self-diffusion coefficients and analyze the effect of water loading, aluminum content, and the distribution of aluminum atoms on water diffusion and degree of deprotonation of Brønsted acid sites (BASs). In addition, the thoroughly tested water-loaded CAN models are used for evaluation of the interaction between the zeolite framework and water molecules and p-cresol in the context of potential application of zeolites for dialysis. Key words zeolites, machine learning, biomedicine, p-cresol, CAN
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The effect of substituents, structure of the reactant and type of active sites on the reaction rate and selectivity of cyclization reactions
Živný, Marek ; Veselý, Ondřej (advisor) ; Bulánek, Roman (referee)
Tetrahydropyrans (THPs) are valuable compounds in the synthesis of pharmaceuticals and fragrances. Currently, THPs are most commonly synthesized using the Prins cyclisation, hetero-Diels-Alder reaction and oxy-Michael reaction. These reactions are undesirable because they use catalysts based on heavy metals and strong acids, which are harmful to the environment. In this thesis, we investigated the synthesis of THPs with the aim of replacing toxic heavy metals and strong acids with more benign catalysts, such as zeolites. Zeolites are microporous crystalline metallosilicates, which are commonly used as catalysts due to their high acidity, selectivity and stability. Previous research has successfully shown that zeolites can catalyse THP synthesis through cyclisation of unsaturated alcohols and determined the effect of pore size on catalytic activity. In contrast, this work aimed to examine zeolites with different framework elements, which introduce diverse types of acid sites. Additionally, we aimed to investigate the impact of functional groups present in the structure of the reactants, specifically functional groups with either electron-donating (EDG) or electron-withdrawing (EWG) effects and with different aromatic cycle systems. We chose (E)5-phenyl-4-pentenol as the primary reactant for the cyclisation....
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The effect of reaction conditions and type of active sites on the kinetics of heterogeneously catalysed formylation of amines
Olšovská, Adéla ; Veselý, Ondřej (advisor) ; Kubička, David (referee)
Formamides are valuable compounds in pharmaceutical production and organic synthesis; however, their common synthesis methods suffer from number of drawbacks including low reaction rate and contamination with heavy metals leached from a catalyst. According to several articles, these problems could be overcome by using zeolite-based catalysts. Nevertheless, the mentioned articles provide somewhat conflicting results and also lack a clear description of which centres in zeolites are catalytic active. Therefore, we prepared a set of zeolite-based catalysts commonly described in the literature (zeolite Beta ion exchanged to H+ and Cu2+ form) in order to test them as catalysts and clarify their catalytic behaviour and nature of the active sites. We chose formylation of N-methylaniline by formic acid as the model reaction for our research and performed a series of experiments under varying conditions (solvents, concentration of reactants, temperature). In contrast to the published articles, none of the investigated materials demonstrated significant catalytic activity in our experiments. Moreover, we found that the often pronounced catalyst: zeolite Beta ion-exchanged into the copper form, is unstable in the presence of formic acid, which causes leaching of copper into the reaction mixture. At the same...
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Dynamic Processes in Porous Nanomaterials: Adsorption and Diffusion
Trachta, Michal ; Bludský, Ota (advisor) ; Heard, Christopher James (referee) ; Čičmanec, Pavel (referee)
Dynamical processes in porous nanomaterials (adsorption, diffusion, separation) play a significant role in many industrial applications. Modeling of these applications theoretically provides atomistic details of adsorption and diffusion phenomena - information that is often difficult to obtain using contemporary experimental methods. Theory may thus provide a deeper insight into these processes, e.g., explaining the mechanisms and assisting in the search for new materials suited for a specific application through material screening. In this work, the dynamical processes in porous materials were investigated by means of force field and ab initio modeling. On a set of relevant simulation data, two particular problems related to the modeling of such processes are thoroughly addressed: (i) the sensitivity of the results to material geometry, and (ii) the accuracy of the potential energy surface description. Regarding the structure description, the reliability of theoretically-predicted structures is still limited, despite the significant increase in computational power and algorithm development. The drawbacks of individual methods are identified; even state-of-the-art density functional theory approaches suffer from inaccuracies, e.g., due to an imbalance between the semi-local (GGA) functional and...
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