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Advanced electron diffraction methods for structural description of zeolites
Laštovičková, Anna ; Mazur, Michal (advisor) ; Tyrpekl, Václav (referee)
Electron diffraction (ED) is a powerful tool for the structure determination of crystalline materials. It offers an alternative to single crystal X-ray diffraction (SCXRD) that is often limited by the size of synthesized crystals. Electron diffraction allows analysis of materials at the nanoscale, thus it is particularly useful for samples which crystals are too small for other methods. ED utilizes electrons for collection of diffraction patterns that can be performed in a transmission electron microscope (TEM). Collected ED patterns are further analyzed allowing for the determination of unit cell parameters, lattice type, and even the crystal structure itself. Nevertheless, the effective structure determination from standard ED patterns requires in-depth expertise and data collection is time consuming. Current development of ED methods focuses on the facilitation and automatization of data collection and processing. Notably, highly advanced, continuous rotation electron diffraction (cRED) data collection takes only a few minutes enabling structure determination within a single day. In this work, I present the utilization of cRED method for the structural characterization of zeolites. These materials are often synthesized as polycrystalline samples with crystals of nanometer in size. This makes...
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Rational synthesis of zeolitic materials and their characterization by advanced electron microscopy methods
Li, Ang ; Mazur, Michal (advisor) ; Chmielarz, Lucjan (referee) ; Zima, Vítězslav (referee)
Supported metal nanoparticles are a prominent class of catalysts due to their high activity in redox reactions and wide applications in numerous industrial processes. They often suffer from deactivation by sintering. One of the recognized and effective strategies to prevent sintering is to confine them into a zeolite matrix thus improving the stability of metal nanoparticles. The aim of my Ph. D. thesis was the rational design and synthesis of zeolite-supported metal nanoparticles (metal@zeolite materials). I have put my main focus on the interactions of nanoparticles with the zeolite supports. The essential experimental tool utilized in this work was advanced electron microscopy. I used this method for the investigation of the structure, location, and stability of supported metal species. Synthesized novel metal@zeolite materials were used as model systems for detailed investigation of metal-zeolite interactions. Prepared materials were investigated as heterogeneous catalysts in the hydrogenation of benzonitrile and dry reforming of methane. My thesis covered the following aspects: i) Rh nanoparticles were incorporated into hierarchical zeolitic materials (Rh@IPCs) via swelling of layered zeolite precursor IPC-1P. The final morphology and porosity of prepared materials were tuned by differing the...
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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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