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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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Study of CeOx / Rh inverse catalyst
Kettner, Miroslav ; Nehasil, Václav (advisor) ; Johánek, Viktor (referee)
Title: Study of CeOX / Rh inverse catalyst Author: Bc. Miroslav Kettner Department: Department of Surface and Plasma Science Supervisor: doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract: Inverse catalysts of cerium oxide deposited on polycrystalline and monocrystalline (111) rhodium substrates were studied by means of surface science experimental methods. Growth characteristics of cerium oxide were investigated in dependence on deposition conditions and different thickness determination methods were compared. Acording to oxidizing or reducing exposition conditions changes in degree of oxidation of CeOX were observed. Further spectra analysis showed additional Ce-Rh alloy formation. Adsorption positions CO on-top and CO hollow on Rh (111) surface were differentiated by spectra fitting procedures. Oxygen absorption and reverse desorption in CeOX was confirmed. Performed experiments indicate that this process occurs through oxide-metal interface. CO oxidation reaction mechanisms at room temperature were proposed. Cerium oxide presence is necessary for reaction occurrence. Significant influence of deposited CeOX on proposed CO oxidation reaction mechanisms was proved by this way. Keywords: Rhodium, cerium oxide, alloy, inverse catalyst, CO oxidation.
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Model catalysts based on cerium oxide
Aulická, Marie ; Veltruská, Kateřina (advisor) ; Nemšák, Slavomír (referee) ; Švec, Martin (referee)
This work deals with the preparation of thin cerium oxide films on the Cu(110) single crystal. Physico-chemical properties of this system were studied by surface science techniques (XPS, UPS, ARUPS, LEED, LEEM and STM). The first part of the work concerns interaction of Cu(110) single crystal with oxygen. Condi- tions for formation of O(2x1) and Oc(6x2) oxygen reconstructions were found. Various methods of preparation of CeOx films were discussed. A novel method for continuous control of ceria stoichiometry from CeO2 to Ce2O3 through variation of oxygen vacancy concentration has been developed. Ceria facilitated oxygen spill-over was observed on copper substrate. It was found that a restructuring of copper substrate occurs at the copper-ceria interface with subsequent formation of Cu(13 13 1) facets, which support a Carpet-like ceria overlayer. Interaction of this system with platinum was studied. Finally, high temperature growth of CeOx films was studied and creation of ceria islands exposing the (110) plane was observed. 1
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Physically chemical properties of epitaxial films CeO2/Cu(110)
Aulická, Marie ; Veltruská, Kateřina (advisor) ; Nehasil, Václav (referee)
In this work ways of preparation of thin epitaxial cerium oxide film on Cu(110) surface were studied. X-ray photoelectron spectroscopy (XPS), X-ray photoelectron difraction (XPD), low energy electron difraction (LEED), ion scattering spectroscopy (ISS) and scanning tunneling microscopy (STM) were used for the characterization of prepared systems. The island structure of CeO2 was prepared by the method of reactive evaporation in oxygen atmosphere. The influence of temperature on the electronic structure and morphology was studied. At the temperature above 550 ˚C partial reduction to Ce2O3 and reordering of the islands to the CeO2(331) structure was observed. The ceria promoted oxidation of copper surface was approved, since the clean c(6x2) reconstruction of the surface was observed at the oxygen exposure 1,5 order of magnitude lower then on Cu(110) alone. The other model system was prepared by cerium evaporation to the oxygen precovered Cu(110) surface. The mix of (2x1) and c(6x2) surface reconstruction was formed by oxygen exposition at 300 ˚C. Cerium was deposited on this surface, also at 300 ˚C. During the following heating to 500 ˚C the formation of epitaxial film Ce2O3(0001) was observed, accompanied by the formation of large hundreds nm long smooth band structures in the [11̄0] direction.
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Reactivity of transition metals - influence of the degree of oxidation of active substrate
Kettner, Miroslav ; Nehasil, Václav (advisor) ; Jiříček, Petr (referee) ; Lykhach, Yaroslava (referee)
The impacts of fluorine doping of ceria are studied by means of surface science experimental methods. Fluorine-doped and fluorine-free ceria layers are epitaxially grown on rhodium single crystals and their properties are compared in regular and inverse catalyst configurations. A procedure for epitaxial growth of CeO2(110) and CeOxFy(110) layers on Rh(110) single crystal is developed and described in detail. Shape alterations of Ce 3d spectrum brought about by fluorine doping are explained and a suitable deconvolution method is proposed. Special attention is focused towards stability of fluorine in ceria. Presented data show that fluorine incorporation in ceria lattice causes stable reduction of ceria, which withstands up to 200řC in near-ambient pressure conditions. Morphological changes are observed due to elongation of surface lattice constant of reduced ceria. Oxygen storage capacities and hydrogen oxidation reaction rates of four different studied systems are compared and discussed. The twofold nature of oxygen exposure of fluorinated ceria is discovered and explained. Oxygen repels fluorine from the surface, while the remaining part of fluorine is expelled to adsorbate positions, where its electronic state is altered. Moreover, such fluorine is prone to interact with atomic hydrogen. This reaction is...
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Epitaxial films of ceria for opto- electronics
Kubát, Jan ; Mysliveček, Josef (advisor) ; Antoš, Roman (referee)
This diploma thesis studies magneto-optical (MO) response of epitaxial thin films of Co-doped ceria. Thin films were characterized by XPS, LEED, STM, spectroscopic ellipsometry and measurement of MO activity. The work focuses on studying MO response of the films depending on film thickness, cobalt concentration, oxidation state of cerium and chemical state of cobalt. Spectra of MO response consist of low energy region where the MO activity is mediated by transitions from defect induced states to conduction band and high energy region where a peak of MO activity appears which we attribute to transitions from valence band to conduction band. In this work we qualitatively explain the effects of the physico- chemical states of the thin films on the structure of the obtained MO spectra, mainly on the appearance of the MO activity in the low energy region, and on the changes of the position of the MO peak. Compared to other preparation methods the epitaxial thin films allow achieving a shift of the MO peak in the direction of higher photon energy.
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Study of dependence of the metal-oxide electron structure on the reactivity of these systems
Ševčíková, Klára
Title: Study of dependence of the metal-oxide electron structure on the reactivity of these systems Author: Klára Ševčíková Supervisor: doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract The presented thesis focuses on studying the interaction between rhodium and cerium oxide and its impact on the reactivity. We investigated two different systems, Rh/CeOx and Rh- CeOx, by means of the photoelectron spectroscopy and the temperature programmed reactions. Rh/CeOx stands for rhodium nanoparticles supported by cerium oxide thin film. We show that there is an electronic metal-substrate interaction between rhodium and cerium oxide. The type of the interaction depends on a degree of cerium oxide reduction and it has a tremendous impact on the reactivity of the system. On the other hand, Rh-CeOx represents cerium oxide thin films doped by rhodium. We characterized the properties of the films with various concentration of rhodium. We show that the morphology, chemical composition and reactivity of the samples strongly depend on the concentration of the rhodium dopant.
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Study of the structural properties of model ceria based catalysts
Beran, Jan
This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)
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Reactivity of transition metals - influence of the degree of oxidation of active substrate
Kettner, Miroslav ; Nehasil, Václav (advisor)
The impacts of fluorine doping of ceria are studied by means of surface science experimental methods. Fluorine-doped and fluorine-free ceria layers are epitaxially grown on rhodium single crystals and their properties are compared in regular and inverse catalyst configurations. A procedure for epitaxial growth of CeO2(110) and CeOxFy(110) layers on Rh(110) single crystal is developed and described in detail. Shape alterations of Ce 3d spectrum brought about by fluorine doping are explained and a suitable deconvolution method is proposed. Special attention is focused towards stability of fluorine in ceria. Presented data show that fluorine incorporation in ceria lattice causes stable reduction of ceria, which withstands up to 200řC in near-ambient pressure conditions. Morphological changes are observed due to elongation of surface lattice constant of reduced ceria. Oxygen storage capacities and hydrogen oxidation reaction rates of four different studied systems are compared and discussed. The twofold nature of oxygen exposure of fluorinated ceria is discovered and explained. Oxygen repels fluorine from the surface, while the remaining part of fluorine is expelled to adsorbate positions, where its electronic state is altered. Moreover, such fluorine is prone to interact with atomic hydrogen. This reaction is...
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Model catalysts based on cerium oxide
Aulická, Marie ; Veltruská, Kateřina (advisor)
This work deals with the preparation of thin cerium oxide films on the Cu(110) single crystal. Physico-chemical properties of this system were studied by surface science techniques (XPS, UPS, ARUPS, LEED, LEEM and STM). The first part of the work concerns interaction of Cu(110) single crystal with oxygen. Condi- tions for formation of O(2x1) and Oc(6x2) oxygen reconstructions were found. Various methods of preparation of CeOx films were discussed. A novel method for continuous control of ceria stoichiometry from CeO2 to Ce2O3 through variation of oxygen vacancy concentration has been developed. Ceria facilitated oxygen spill-over was observed on copper substrate. It was found that a restructuring of copper substrate occurs at the copper-ceria interface with subsequent formation of Cu(13 13 1) facets, which support a Carpet-like ceria overlayer. Interaction of this system with platinum was studied. Finally, high temperature growth of CeOx films was studied and creation of ceria islands exposing the (110) plane was observed. 1
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