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Metal nanoparticles in zeolites
Zhang, Yuyan ; Čejka, Jiří (advisor) ; Zima, Vítězslav (referee) ; Kubička, David (referee)
Zeolites with encapsulated metal nanoparticles have attracted a wide attention in heterogeneous catalysis due to their high catalytic activity, selectivity, and stability. The PhD thesis was focused on design and synthesis of metal@zeolite catalysts with small and uniformly distributed metal nanoparticles. The main interests were encapsulation of metal nanoparticles into zeolites by co-crystallization strategy and 2-dimensional to 3-dimensional zeolite transformation approach. The PhD work was performed at the Department of Synthesis and Catalysis at J. Heyrovský Institute of Physical Chemistry and Department of Physical and Macromolecular Chemistry, Faculty of Science at Charles University under the supervision of Prof. Jiří Čejka. Zeolites are inorganic crystalline aluminosilicates with microporous framework structures. The micropores of zeolites provide the ideal microenvironment to accommodate metal nanoparticles. During metal nanoparticles formation in zeolite micropores, they can be limited by a rigid framework, preventing the aggregation and leaching of metal during the reaction process. Furthermore, the diameters of zeolite micropores are usually in the range of 0.3-1.5 nm, which can be used to discriminate molecules depending on their size and shape, thus endowing the metal@zeolite...
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Stabilization of metal nanoparticles in MWW zeolite for catalytic applications
Molitorisová, Sidónia ; Shamzhy, Mariya (advisor) ; Hronec, Mlan (referee)
Controlling both size of metal nanoparticles (MNPs) and acidobasic characteristics of the zeolite support is highly desirable for preparation of stable and active bifunctional catalysts. 2D-3D transformation of layered zeolite precursor into three-dimensional zeolite coupled with metal encapsulation is one of the most efficient synthetic strategies so far to achieve the appropriate metal dispersion and aggregative stability of MNPs within zeolite matrix. Nevertheless, the effect of support acidic characteristics on the properties of thus prepared metal@zeolite catalyst remained unrevealed, while the synthetic strategy itself requires further optimization to minimize the loss of metal component. This work addresses the influence of chemical composition of zeolite layered precursor on physical-chemical and catalytic properties of metal@zeolite catalysts prepared via 2D-3D transformation strategy, taken Pd@MCM-222D-3D system as a representative example. Both Si/Al ratio of MCM-22P layered precursor (e.g., Si/Al = 15, 20, 30) and Pd loading (e.g., 0.1, 0.3, 0.8 wt.%) were varied resulting in a set of nine Pd@MCM-222D-3D catalysts. In addition, three Pd@MCM-22impreg catalysts with the same metal loading (0.1 wt.%), but different Si/Al ratios of a support were synthesized via conventional impregnation...
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Theoretical Study of Influence of Silanol Nest Defects on Hydrolysis of Zeolite Chabazite
Vacek, Jaroslav ; Grajciar, Lukáš (advisor) ; Fišer, Jiří (referee)
This thesis is focused on theoretical study of influence of the silanol nest defects on the hydrolysis of zeolite Chabazite under harsh steaming conditions. The motivation of the thesis was a recent experiment proving that the silanol nest defect enhances the hydrolysis of a zeolite. The harsh steaming conditions have been chosen as some important technological processes involving zeolites require high temperatures and have water vapour present. The study was performed by using density functional theory calculations. To investigate the influence of the defect two models were used a reference pristine model and a defected model containing the silanol nest defect. The two models were pure siliceous Chabazite periodical models with supercell containing 36 and 35 Si tetrahedra respectively. A multi-step hydrolysis leading to detachment of a Si(OH)4 cluster from the zeolite, known as total desilication, was calculated for the two models. Multiple possible paths of the hydrolysis were discovered, compared and discussed on both models. Both the most favourable hydrolysis paths of the two model as well as their arithmetic means were compared. The experimentally set expectations that a silanol nest defect enhances the hydrolysis of the zeolite have been met.
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Theoretical investigation of water-zeolite interactions under steaming conditions
Benešová, Tereza ; Heard, Christopher James (advisor) ; Fišer, Jiří (referee)
The thesis is focused on theoretical study of hydrolysis and isotopic oxygen exchange in zeolite chabazite under steaming conditions. The theoretical study was performed by the methods of computational chemistry, namely density functional theory. Reactions of water with zeolites were investigated within the periodic model with chabazite supercell consisting of 36 Si/Al tetrahedra. Reactivity was investigated for one or two water molecules corresponding to the conditions relevant to high-temperature steaming. Relevant mechanisms of isotopic oxygen exchange were found and their competitiveness with hydrolysis was discussed.
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Preparation of hierarchical zeolites for fine chemical synthesis
Veselý, Ondřej ; Eliášová, Pavla (advisor) ; Přech, Jan (referee)
Preparation of hierarchical zeolites for fine chemical synthesis Author: Bc. Ondřej Veselý Supervisor: Mgr. Pavla Eliášová, Ph.D. Prague, 2019 Abstract (in english): The thesis is focused on synthesis of hierarchical (micro-mesoporous) zeolites by several different methods and their application in catalytic reactions. Performance of hierarchical materials prepared by different approaches has been investigated, as well as the effect of framework topology and type of acidity on the outcome of the reactions. The work was elaborated in the Department of Physical and Macromolecular Chemistry of Charles University under the supervision of Mgr. Pavla Eliášová, Ph. D. The work is divided into three parts. In the first part several methods of preparation of hierarchical zeolites have been investigated and compared in catalytic reactions. Desilication, selective removal of silicon from the framework, is a post-synthetic method that can be used to introduce additional mesoporosity into a zeolite. The process leads to formation of mesopores by introducing defects into the zeolite structure. The resulting mesopore size is very broad. To partially control the pore size, alkylammonium cations may be added to the solution to protect the crystal surface. The desilication was performed on MTW zeolite which contains...
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Theoretical Investigation of Properties of 3D and 2D Zeolites
Ho, Viet Thang ; Nachtigall, Petr (advisor) ; Fišer, Jiří (referee) ; Cwiklik, Lukasz (referee)
Zeolites have been widely used in many different fields including catalysis, adsorption and separation, ion exchange, or gas storage. Conventional zeolites have three- dimensional (3D) structures with microporous channel system; typical pore sizes are well below 1 nanometer, therefore, diffusion limitation plays important role in many process and bulkier reactants (or products) cannot enter (or leave) the zeolite channel system. Two-dimensional (2D) zeolites prepared in last years can lift all diffusion limitation and they thus offer a very attractive alternative to conventional 3D zeolites. 2D zeolites attracted considerable attention on the experimental side; however, understanding of 2D zeolites based on computational investigation or on a combination of experimental and computational investigation is limited. A motivation for the computational work presented here is to improve our understanding of properties of 2D zeolites based on computational investigation. The originality of the research presented herein is in the strategy: we carried out systematic investigation of properties of corresponding 2D and 3D zeolites and we focus on the identification of similarities and differences. The most important zeolite properties, i.e., presence of Brønsted and Lewis acid sites, are investigated. A number of...
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Theoretical Investigation of silver clusters in zeolites
Hermann, Jan ; Nachtigall, Petr (advisor) ; Fišer, Jiří (referee)
The structure and stability of Agn+ 3 clusters (n = 1, 2, 3) in zeolite Y and their photochemical properties are investigated. Silver-exchanged zeolites have potential technological applications as UV-to-visible light converters. The structure and stability of silver clusters were examined using the periodic den- sity functional theory (DFT), and employing a developed and programmed geometry optimization driver. Non-reduced silver cations are preferably lo- cated in 6-member rings, far from each other. Upon a partial reduction, trigonal clusters are formed in the sodalite cages. The photochemical prop- erties are examined by various methods including the EOM-CCSD, MRPT2 and TD-DFT. No charge transfer transitions from ligands to silver clusters are found. Instead, transitions involving d and s electrons on silver clusters fall in the visible spectral range. Our results contradict the previous sugges- tion proposing existence of linear silver clusters through a double-6-member ring unit. Both parts of our investigations (structural and photochemical) disprove this previous proposition. A new interpretation of experimental spectra is proposed-the reduced trigonal silver cluster is responsible for photoactivity of Ag-doped zeolites with a low silver loading. Theoretical in- vestigation reported in this...
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Possibilities of using of energy by-products as raw materials for hydrothermal reaction
Galvánková, Lucie ; Koplík, Jan (referee) ; Opravil, Tomáš (advisor)
The aim of this master thesis is study of possibilities of processing energy by-products, especially coal fly ash and fluidized bed ash, by hydrothermal treatment. Thanks to hydrothermal conditions and proper alkali activation of ashes we can obtain zeolites. Zeolites are microporous crystalline aluminosilicates which are use in many industrial sectors as catalysts, adsorbents and very good ion exchangers. The results of hydrothermal synthesis are influenced by many variable factors. This thesis mainly focused on influence of chosen alkali activator and the concentration of the activator together with a temperature of hydrothermal process. Other factor that is studied is choice of starting materials and solution/ash ratio. Phase composition of prepared samples was characterized by XRD and scanning electron microscopy (SEM). Also cation exchange capacity of prepared samples was determined.
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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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