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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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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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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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Design of zeolite materials with tailored interlayer structure and tunable textural properties
Kasneryk, Valeryia ; Opanasenko, Maksym (advisor) ; Zima, Vítězslav (referee) ; Shvets, Oleksiy (referee)
Germanosilicate zeolites attracted a lot of attention during the last decade. The reason for such interest is related to the unique structural properties of germanosilicates, which include zeolites of UTL, UOV, ITH, IWR, IWW, and CIT-13 types. The frameworks of these materials can be described as Si-rich layers connected by double four ring (D4R) units preferentially occupied by Ge atoms. Hydrolytic instability of Ge-O bonds in mentioned frameworks compared with Si-O bonds in conventional zeolites gives the opportunity for controllable chemically selective transformation of the germanosilicate frameworks towards novel types of zeolites including their 2D analogues. This PhD thesis focuses on modification of the structure and textural properties of germanosilicates using different ways of post-synthesis treatment: the ADOR (Assembly - Disassembly - Organization - Reassembly) transformation and post-synthesis degermanation and alumination. Presented work was carried out in the Department of Synthesis and Catalysis at J. Heyrovský Institute of Physical Chemistry in Prague under the supervision of Dr. Maksym Opanasenko and advising of Prof. Jiři Čejka. First way of post-synthesis treatment applied in this work was the recently developed method of zeolite synthesis - the ADOR transformation....
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Theoretical Investigation of ethanol dehydration catalyzed by acid sites in zeolites
Vacek, Jaroslav ; Nachtigall, Petr (advisor) ; Uhlík, Filip (referee)
Zeolites are a group of aluminosilicate minerals with catalytic properties. They may be used for many industrial applications such as catalytic cracking of oil. Zeolites are also capable of converting ethanol to diethylether and ethylen. This reaction is known as dehydration of ethanol. The reaction is potentially interesting as a way of converting ethanol to more valuable molecules. An experimental study (Shashikant A. Kadam, Mariya V. Shamzhy, 2018) has proven that diethylether is the preferred product when the temperatures are low and the partial pressure of ethanol is high. Ethylen is more significant product with higher temperature and lower partial pressure of ethanol. Aim of this thesis is to determine the mechanism of dehydration of ethanol. Furthermore it was attempted to explain the behavior of the reaction under different circumstances. The research was done in silico using the methods of computational chemistry. Such methods give information on the geometry and the energy of systems of molecules. Thus computational chemistry can be used to investigate the relational path and activation energy of the studied reaction. This thesis is a theoretical study of dehydration of ethanol catalysed by a zeolite.
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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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