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Study of Perovskite Type Oxide Catalysts for Partial Oxidation of Methane
Cihlář, Jaroslav ; Hanykýř, Vladimír (referee) ; Čapek,, Libor (referee) ; Čičmanec,, Pavel (advisor)
Research was curried out on the perovskite systems with general formula A1-xA‘xB1-yB‘yO3± (where A=La, Sm, A´=Ca, B´=Al, B=Co,Fe,Mn and Cr). Perovskite oxides were sythesized by polymerisation methods and characterised by RTG analysis, BET method, SEM and EDX. TPD spectra and catalyst testing were measured in high temperature plug flow reactor and products were analysed by mass spectrometry. It was found, that metane oxidation at ratio O2/CH40,5 depended on the temperature. Total oxidation proceeded at the temperature betwen 300-700oC to the carbon dioxide and water, while the partial oxidation of metane (POM) occured at above 700oC to the hydrogen and carbon oxid (syngas). This was ascribed by equilibrium of O2 betwen gas phase and solid perovskite. There was used 12 perovskite systems, which catalysed methane oxidation by the same way. Dry reforming of methane run above temperature 700oC. Cobaltite and ferite type perovskites were found as the most active catalytic systems. On the base of obtained results the Mars van Krevelen mechanism was established for explanation of oxidation and reformation of methane by perovskite systems. It was showed, that POM was running by two steps mechanism. Products of total oxidation was occured in the first step, which were passed over to the syngas (H2+CO) in the second step.
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Study of active centers in zeolite catalysts for cascade Prins-Friedel-Crafts reaction
Golis, Petr ; Shamzhy, Mariya (advisor) ; Pinkas, Jiří (referee)
Conventional zeolites are important shape-selective heterogeneous acid catalysts due to the presence of acid sites accessible through uniform micropores. Recently designed hierarchical zeolites with combined micro-mesoporosity also contain acid sites on the external surface or in mesopores. These highly accessible acid sites are promising active centres for the transformation of bulky molecules, which cannot pass through the micropore openings of conventional zeolites. An example of a reaction that can benefit from the use of zeolites is the one-pot cascade Prins-Friedel-Crafts (PFC) reaction of an aldehyde, homoallylic alcohol, and aromatic compound, which yields valuable heterocyclic compounds containing 4- aryltetrahydropyran moieties. In this work, the acidic characteristics of a series of hierarchical aluminium- and gallium- containing MFI and MWW zeolites were evaluated by FTIR-monitored thermodesorption of probe molecules and further related to the catalytic properties of zeolites in the PFC reaction of butyraldehyde, 3-buten-1-ol, and anisole. The nature, strength, and total concentration of acid sites in the catalysts were evaluated using thermodesorption of pyridine (kinetic diameter 0.54 nm), while the characteristics of the external surface Brønsted acid sites were probed using...
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Development of a heterogeneous catalytic system using multiply charged cyclodextrins and proline-based organocatalysts
Zelený, Jan ; Jindřich, Jindřich (advisor) ; Baszczyňski, Ondřej (referee)
Cyclodextrins are a class of organic molecules consisting of a cyclic system of α(1→4) linked glucose units. These compounds possess a range of interesting properties and can be derivatised to suit various industrial and scientific purposes. Among their derivatives are so- called multiply charged cyclodextrins, the development and application of which is an essential part of our group's research interest. These cyclodextrin derivatives are capable of binding electrostatically to different solid sorbents, such as silicagel or alumina. This electrostatic interaction is mediated by an array of permanently positively charged moieties which are covalently attached to the primary rim of a cyclodextrin unit. The free secondary rim then offers the possibility of further derivatisation and functionalisation of this system. The resultant cyclodextrin derivative represents a modular scaffold which can be used to immobilise different functional components. This project focuses on the application of this system to the immobilisation of a Hayashi- Jørgensen-type catalyst for the purposes of heterogeneous catalysis. The work includes the assembly of the of the chosen catalytic system from its precursors and also the synthesis thereof. Furthermore, the resulting supramolecular system is tested for its catalytic...
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Role of surface defects in ceria-based catalysis
Tovt, Andrii ; Mysliveček, Josef (advisor) ; Čechal, Jan (referee) ; Švec, Martin (referee)
Title: Role of surface defects in ceria-based catalysis Author: Andrii Tovt Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: doc. Mgr. Josef Mysliveček Ph.D., Department of Surface and Plasma Science Abstract: This work concentrates on the analysis of fundamental physicochemical properties of Pt-CeOx, single-atom Pt1 /CeOx, and inverse CeOx/Cu(111) catalysts. Preparation method for stabilized atomically-dispersed Pt2+ ions on ceria was developed and adsorption sites for Pt ions were thoroughly studied using advanced surface science techniques supported by theoretical methods. The mechanism of Pt2+ stabilization on ceria steps was revealed and the step capacity towards Pt2+ ions was estimated. Also, the preparation method for well-ordered cerium oxide ultrathin films with different stoichiometry and ordering of surface oxygen vacancies was developed, and the Ceria/Cu(111) interaction was investigated. Key words: heterogeneous catalysis, model systems, single-atom catalysis, platinum ions, cerium oxide.
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Modeling, Analysis and Computation of heterogeneous catalysis in microchannels
Orava, Vít ; Málek, Josef (advisor) ; Bárta, Tomáš (referee)
We investigate a nonlinear reaction-diffusion system coupled with convection- diffusion system. This combined system corresponds to physical description of heteroge- neous catalysis when the flow of bulk-constituents is driven by a given stationary velocity field; diverse mechanisms between bulk- and surface-parts of the model-domain are de- scribed by Langmuir-Hinshelwood absorption kinetics; and the irreversible reactions on the catalytic walls meets the law of mass action with quadratic rate. The first part of the thesis is focused on analytical results; in Chapter 2 we prove existence and unique- ness of a mild solution for so-called near-by problem using nonlinear semigroup theory; in Chapter 3 we investigate the weak formulation of the problem. We prove an existence of a weak solution for little modified problem which, under an assumption, coincides with the original problem. In the second part of the thesis (Chapter 4) we numerically investigate the evolution of the bio-diesel microreactor. We compute numerical solutions using several methods and we test the results by analytical and physical conditions; with the aim to find the most efficient way to compute precise and physically correct solution. Keywords: heterogeneous catalysis, coupled reaction-diffusion/convection-diffusion system, nonlinear...
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"Ab initio" study of Cu-Ce-O interface
Szabová, Lucie ; Matolín, Vladimír (advisor) ; Chvoj, Zdeněk (referee)
"Ab initio" study of interface Cu-Ce-O Abstract: The present work is a theoretical analysis based on the numerical DFT+U simulations investigating the structural and electronic properties of Cu/CeO2 model systems, which have important applications as heterogeneous catalysts for environment protection and energy sources. We provide a detailed insight into the cohesion of the interface between metal Cu nanoparticles supported on CeO2 substrates. This issue is analyzed both in context of small supported Cu clusters as well as for the extended interface underneath Cu nanoparticles on ceria surfaces. These cases were modelled with a Cu(111)/CeO2(111) interface and with a Cu adatom adsorbed at the oxidized and reduced CeO2(111) surface, respectively. The thesis provides a direct correlation between the cohesive and electronic properties mediated by the charge transfer process. The reduction of surface cerium atoms in the presence of copper either in form of adatom, thin copper layer or a slab of copper is predicted to result from charge transferred from the metal. Since cerium reduction is suggested to play an important role into the catalytic activity of ceria-based catalysts, by predicting the reduction of cerium ions in the presence of copper it can be expected that Cu/CeO2 systems will have important...
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Role of surface defects in ceria-based catalysis
Tovt, Andrii ; Mysliveček, Josef (advisor)
Title: Role of surface defects in ceria-based catalysis Author: Andrii Tovt Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: doc. Mgr. Josef Mysliveček Ph.D., Department of Surface and Plasma Science Abstract: This work concentrates on the analysis of fundamental physicochemical properties of Pt-CeOx, single-atom Pt1 /CeOx, and inverse CeOx/Cu(111) catalysts. Preparation method for stabilized atomically-dispersed Pt2+ ions on ceria was developed and adsorption sites for Pt ions were thoroughly studied using advanced surface science techniques supported by theoretical methods. The mechanism of Pt2+ stabilization on ceria steps was revealed and the step capacity towards Pt2+ ions was estimated. Also, the preparation method for well-ordered cerium oxide ultrathin films with different stoichiometry and ordering of surface oxygen vacancies was developed, and the Ceria/Cu(111) interaction was investigated. Key words: heterogeneous catalysis, model systems, single-atom catalysis, platinum ions, cerium oxide.
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Role of surface defects in ceria-based catalysis
Tovt, Andrii ; Mysliveček, Josef (advisor)
Title: Role of surface defects in ceria-based catalysis Author: Andrii Tovt Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: doc. Mgr. Josef Mysliveček Ph.D., Department of Surface and Plasma Science Abstract: This work concentrates on the analysis of fundamental physicochemical properties of Pt-CeOx, single-atom Pt1 /CeOx, and inverse CeOx/Cu(111) catalysts. Preparation method for stabilized atomically-dispersed Pt2+ ions on ceria was developed and adsorption sites for Pt ions were thoroughly studied using advanced surface science techniques supported by theoretical methods. The mechanism of Pt2+ stabilization on ceria steps was revealed and the step capacity towards Pt2+ ions was estimated. Also, the preparation method for well-ordered cerium oxide ultrathin films with different stoichiometry and ordering of surface oxygen vacancies was developed, and the Ceria/Cu(111) interaction was investigated. Key words: heterogeneous catalysis, model systems, single-atom catalysis, platinum ions, cerium oxide.
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Role of surface defects in ceria-based catalysis
Tovt, Andrii ; Mysliveček, Josef (advisor) ; Čechal, Jan (referee) ; Švec, Martin (referee)
Title: Role of surface defects in ceria-based catalysis Author: Andrii Tovt Department: Department of Surface and Plasma Science Supervisor of the doctoral thesis: doc. Mgr. Josef Mysliveček Ph.D., Department of Surface and Plasma Science Abstract: This work concentrates on the analysis of fundamental physicochemical properties of Pt-CeOx, single-atom Pt1 /CeOx, and inverse CeOx/Cu(111) catalysts. Preparation method for stabilized atomically-dispersed Pt2+ ions on ceria was developed and adsorption sites for Pt ions were thoroughly studied using advanced surface science techniques supported by theoretical methods. The mechanism of Pt2+ stabilization on ceria steps was revealed and the step capacity towards Pt2+ ions was estimated. Also, the preparation method for well-ordered cerium oxide ultrathin films with different stoichiometry and ordering of surface oxygen vacancies was developed, and the Ceria/Cu(111) interaction was investigated. Key words: heterogeneous catalysis, model systems, single-atom catalysis, platinum ions, cerium oxide.
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Electronic and structural properties of model catalysts based on cerium oxide
Duchoň, Tomáš ; Veltruská, Kateřina (advisor) ; Bartoš, Igor (referee) ; Kullgren, Jolla (referee)
Catalysts based on cerium oxide are ubiquitous in industrial-scale chemical conversion. Here, a thorough study of their fundamental properties is undertaken via a model system ap- proach with the goal of furthering rational design in heterogeneous catalysis. A focus is put on understanding the behavior of oxygen vacancies in cerium oxide with respect to atomic co-ordination and electronic structure perturbations. Utilizing state-of-the-art probing tech- niques, a scalable model system framework is developed that allows for control over both the oxygen vacancy concentration and local co-ordination. High precision of the innova- tive approach facilitated observation of new phases of substoichiometric cerium oxide and lead to a first-of-a-kind investigation of the electronic structure of cerium oxide throughout isostructural transition from CeO2 to Ce2O3. The acquired results advance fundamental understanding of essential properties of cerium oxide that are relevant to its utilization in heterogeneous catalysis and open new pathways for functionalization of cerium oxide-based materials. Furthermore, the methodology developed in the thesis is transferable to other important reducible oxides. 1
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