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Interaction of simple molecules with reducible oxides: model studies of H2O/CeOx and CO/CuOx
Dvořák, Filip ; Mysliveček, Josef (advisor) ; Jirka, Ivan (referee) ; Švec, Martin (referee)
The thesis is focused on the investigation of fundamental catalytic properties of two model catalysts-CeOx/Cu(111) and CuOx/Cu(111)-by means of advanced surface science techniques. The investigations performed on CeOx are devoted to the study of the relationship between the surface structure and the surface activity of ceria. We develop the preparation method leading to growth of epitaxial CeOx(111) thin films with the adjustable morphological parameters-the step density and the ordering of surface oxygen vacancies. By using the CeOx(111) films with precisely controlled structure we identify the role of the step edges and of the oxygen vacancies in the interaction of water with ceria. The investigation performed on CuOx is focused on the microscopic characterization of the reduction process of Cu2O(111) on the molecular level directly under a near ambient pressure of CO. In direct microscopic study we identify the active initiation centers, the intermediate oxide phases, and the kinetics of the reduction reaction of Cu2O(111).
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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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Chemical reactivity of metal-supported ceria thin films: a density functional study
Szabová, Lucie ; Matolín, Vladimír (advisor) ; Balducci, Gabriele (referee) ; Chvoj, Zdeněk (referee)
Title: Chemical reactivity of metal-supported ceria thin films: a density func- tional study Author: Lucie Szabová Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Vladimír Matolín, DrSc., Department of Surface and Plasma Science, FMF, CU Abstract: The present work is a theoretical analysis based on numerical DFT+U simulations investigating the physical and chemical properties of ultrathin ceria films supported by Cu(111). Such materials exhibit high activity towards several important reactions in heterogeneous catalysis such as water-gas shift and CO oxidation, with important applications also for renewable energy technologies such as fuel cells. We provide evidence of the influence of film thickness on the electronic and structural properties as well as on the reactivity of ultrathin ceria films supported by copper. The calculations combined with scanning tunneling microscopy experiments show that one monolayer thin film of ceria on Cu(111) is charged, strained and contains oxygen vacancies due to the limited thickness of the film. The influence of the film thickness on the reactivity of thin ceria films was explored for the case of water adsorption and dissociation. Significant differences were shown for water adsorption and dissociation on one-monolayer ceria compared to thicker films,...
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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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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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