National Repository of Grey Literature 8 records found  Search took 0.00 seconds. 
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...
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...
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...
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...
Nanosponge MFI zeolites functionalized with metal nanoparticles for catalysis
Laštovičková, Anna ; Mazur, Michal (advisor) ; Vyskočilová, Eliška (referee)
Metal nanoparticles immobilized at various supports have outstanding catalytic activity in hydrogenation reactions. Zeolites are used as supports, mainly due to their porous structure. In this work, metal nanoparticles were immobilized on MFI nanosponge zeolites. Zeolite nanosponges (pure silica and degallated) were impregnated with pure platinum and platinum mixed with rare-earth elements (cerium, lanthanum, and yttrium) to form alloys. The main aim of this work was to investigate the activity of bimetallic nanoparticles immobilized on zeolite nanosponges in hydrogenation of cinnamaldehyde. It is a versatile model reaction to investigate catalysts, due to the presence of three different reducible groups (C=C bond, C=O bond and benzene ring) in the cinnamaldehyde molecule. The objective was to focus on selectivity effects of various catalyst towards three possible products of cinnamaldehyde hydrogenation (hydrocinnamaldehyde, cinnamyl alcohol and hydrocinnamyl alcohol). The metal alloys evolution is more feasible on the degallated zeolites due to the defects in the structure called silanol nests. These defects stabilize bimetallic nanoparticles. Moreover, samples prepared with use of degallated support showed larger surface areas. Pure-silica zeolites impregnated with metals were also prepared for...
Shape selectivity of ADOR zeolites in gas-phase m-xylene isomerisation
Remperová, Natália ; Mazur, Michal (advisor) ; Kubička, David (referee)
Zeolites are microporous crystalline aluminosilicates. They are used as catalysts due to their acidity, shape selectivity, high surface area, high thermal, and chemical stability. New types of zeolitic materials are of interests as catalysts for various reactions. Isomerisation of m-xylene is sensitive to shape and dimensionality of pores, thus it is excellent model reaction for zeolites characterisation. The aim of this thesis is to investigate shape selectivity effects of isoreticular zeolites on the catalytic performance in m-xylene isomerisation. Isoreticular zeolites have the same crystalline layers connected in various way resulting in different, tuneable pore systems. The catalytic behaviour of the studied zeolites was compared to commercial ZSM-5 zeolite catalysts. Isoreticular zeolites were prepared via ADOR method. This new method is a top-down approach for zeolite synthesis providing materials with preserved crystalline layers, but different channel systems. Parent Al-UTL (14- and 12-ring channels) zeolite was prepared via hydrothermal synthesis. This material was utilised for the synthesis of daughter zeolites with various channel systems: Al-IPC-7 (14- and 12-ring, as well as 12- and 10-ring channels), Al-IPC-2 (12- and 10-ring channels), Al-IPC-6 (12- and 10-ring, as well as 10- and...
Chemistry of the Interlamellar Space of Two-dimensional Zeolites
Mazur, Michal ; Čejka, Jiří (advisor) ; Zima, Vítězslav (referee) ; Hronec, Mlan (referee)
The presented PhD thesis is focused on the synthesis, characterization, and modifications of zeolites and zeolitic materials. The main interests are two-dimensional (2D) zeolites and modification of their interlamellar space. Presented work was performed at the Department of Synthesis and Catalysis at J. Heyrovský Institute of Physical Chemistry in Prague, Czech Republic under the supervision of Prof. Jiří Čejka. Zeolites are inorganic crystalline solids with a microporous framework structure. They are widely used as catalysts, sorbents, and ion-exchangers. Conventional zeolites have been recognized as three-dimensional (3D) tetrahedrally-connected frameworks. However, some of them are also known to exist in various layered forms (2D zeolites). Recently, the transformation of 3D germanosilicate UTL into layers (IPC-1P) has started a new branch in 2D zeolites chemistry. This chemically selective degradation of UTL framework was performed via acid hydrolysis. In the structure of this germanosilicate, Ge atoms are preferentially located in specific building units, double-four-rings (D4R), which connect dense silica layers. Modifications of the layered precursor IPC-1P led to discovery of the two novel 3D zeolites: IPC-4 (PCR) and IPC-2 (OKO). This novel approach in the zeolite synthesis, called ADOR...

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1 Mazúr, Miroslav
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