38 research outputs found
Low temperature CO oxidation on bimetallic structures
No full textTitle: Low temperature CO oxidation on bimetallic structures Author: Petr Hanyš Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract: Bimetallic system Sn-Rh in the form of the model Sn/Rh(111) system, supported Rh+Sn/Al2O3 and Rh/SnO2 clusters and Rh/SnO2 and Rh+Sn/Al2O3 powder samples was studied using synchrotron radiation photoelectron spectroscopy (SRPES), X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), molecular beams (MB), transmission and scanning electron microscopy (TEM, SEM), powder X-ray diffraction (XRD) and high pressure reactor within the framework of the study. It was found that formation of Sn-Rh alloy influences catalytic properties of Rh by lowering CO adsorption energy and capacity. It was also found that presence of Rh in this bimetallic system mediates reversible oxidation/reduction of Sn/SnO2, whereas Sn oxide acts as an oxygen reservoir for low temperature CO oxidation. Keywords: bimetallic systems, rhodium, tin, low temperature CO oxidatio
Studium vlivu elektronové struktury na reaktivitu systémů oxid - kov
No full textNázev práce: Studium vlivu elektronové struktury na reaktivitu systémů oxid-kov Autor: Klára Ševčíková Vedoucí práce: doc. RNDr. Václav Nehasil, Dr., Katedra fyziky povrchů a plazmatu Abstrakt Předkládaná práce je zaměřena na studium interakce rhodia a oxidu ceru a její vliv na jejich reaktivitu. Dva druhy systémů, Rh/CeOx a Rh-CeOx, byly charakterizovány pomocí metod fotoelektronové spektroskopie a teplotně programovaných reakcí. Rh/CeOx značí systém složený z rhodiových nanočástic nesených tenkou vrstvou oxidu ceru. V této práci ukazujeme, že dochází k elektronické interakci a přenosu náboje mezi rhodiem a oxidem ceru. Tato interakce závisí na míře redukce oxidu ceru, a přitom značně ovlivňuje reaktivitu celého systému. Rh-CeOx označuje tenké vrstvy oxidu ceru dopované rhodiem. V rámci této práce byly charakterizovány vlastnosti vrstev s různými koncentracemi rhodia. Ukazujeme, že struktura, složení a reaktivita těchto systémů je značně závislá na koncentraci rhodia ve vrstvě oxidu ceru.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.Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Study of dependence of the metal-oxide electron structure on the reactivity of these systems
No full textTitle: 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
Adsorption of gas molecules on bimetallic systems
No full textNazev prace: Adsorpce molekul plynu na bimctalickych systemech Autor: Klara Sevcikova Katedra: Katedra fyziky povrchu a plazmatu Vedouci bakalafske prace: Doc. RNDr. Vaclav Nehasil, Dr. e-mail vcdouciho: nchasif(o)m box.troja.mff.euni.cz Abslrakl: Mctodami termodesorpcnf speklroskopie a rnolekularnich svazku byla studovana adsorpce a desorpcc CO na system u rhodia deponovaneho na polykrystalickem oxidu ceru pro ruzne tloust'ky rhodiove vrstvy. Dale byly na techto systemcch zkoumany reakce molekul CO, zejinena jejich disociace a tvorba CO2. Byly pozorovany dva desorpcni slavy CO i CO2, jejichz dcsorpcni energie klesaji s rostouci tlousfkou deponovane vrstvy Rh. Tvorba CO2 se jevi zavisla na desorpci CO. Nfzkotcplotni desorpcni stav CO odpovida procesu adsorpce - desorpce. Vysokoteplotnf stav by! vysvellen redukci oxidu ceru pfi vysoke teplote, behem niz je z vrstvy uvolnovan kyslik, ktcry reagujc s atomarnim uhlfkem za vzniku CO, v mensf mi'fe i CO2. Z porovnani ploch desorpcm'ch pikti CO a CO2 nizkoteplotm'ho stavu vyplyva, ze nejvetsi procento adsorbovaneho CO disociuje na vzorku s nejvetsim rozhranim Rh/CeO,. Klfcova slova:CeON; Rh; adsorpce a desorpce CO, termodesorpcni spektroskopie Title: Adsorption of gas molecules on bimetallic systems Author: Klara Sevcikova Department: Department of Surface and..
Adsorption of gas molecules on bimetallic systems
No full textNazev prace: Adsorpce molekul plynu na bimctalickych systemech Autor: Klara Sevcikova Katedra: Katedra fyziky povrchu a plazmatu Vedouci bakalafske prace: Doc. RNDr. Vaclav Nehasil, Dr. e-mail vcdouciho: nchasif(o)m box.troja.mff.euni.cz Abslrakl: Mctodami termodesorpcnf speklroskopie a rnolekularnich svazku byla studovana adsorpce a desorpcc CO na system u rhodia deponovaneho na polykrystalickem oxidu ceru pro ruzne tloust'ky rhodiove vrstvy. Dale byly na techto systemcch zkoumany reakce molekul CO, zejinena jejich disociace a tvorba CO2. Byly pozorovany dva desorpcni slavy CO i CO2, jejichz dcsorpcni energie klesaji s rostouci tlousfkou deponovane vrstvy Rh. Tvorba CO2 se jevi zavisla na desorpci CO. Nfzkotcplotni desorpcni stav CO odpovida procesu adsorpce - desorpce. Vysokoteplotnf stav by! vysvellen redukci oxidu ceru pfi vysoke teplote, behem niz je z vrstvy uvolnovan kyslik, ktcry reagujc s atomarnim uhlfkem za vzniku CO, v mensf mi'fe i CO2. Z porovnani ploch desorpcm'ch pikti CO a CO2 nizkoteplotm'ho stavu vyplyva, ze nejvetsi procento adsorbovaneho CO disociuje na vzorku s nejvetsim rozhranim Rh/CeO,. Klfcova slova:CeON; Rh; adsorpce a desorpce CO, termodesorpcni spektroskopie Title: Adsorption of gas molecules on bimetallic systems Author: Klara Sevcikova Department: Department of Surface and..
Study of gas molecule - surface interaction
No full textTitle: Study of gas molecule - surface interaction Author: Miroslav Kettner Department: Department of surface and plasma science Supervisor: doc. RNDr. Václav Nehasil, Dr., Department of surface and plasma science Abstract: In this work, we examined the suitability of rhodium deposited on a plasma sprayed substrate of titanium dioxide for catalysis reactions. With X-ray photoelectron spectroscopy method, the thermal stability of TiO2 prepared with plasma spray technology on aluminum plate was tested at first. Then, rhodium was evaporated on substrate and thermal stability of the whole system Rh/TiO2 was determined. Further methods of thermal desorption spectroscopy and molecular beam were used to study adsorption and desorption of CO and reaction of CO with oxygen. It was verified that the system Rh/TiO2 ceases to adsorbing CO after heating above 620 K, also the CO reaction with oxygen exhibits considerably lower intensity after heating above 620 K. After calibrating on rhodium plate, it was determined that the intensity of CO2 creation on Rh/TiO2 is four times lower than intensity on the rhodium plate. Unprompted adsorption and desorption passivation of the system, however, seems to be the most significant problem. Therefore, the system was assessed as unsuitable for further research. Keywords: Rh, TiO2,..
Study of CeOx / Rh inverse catalyst
No full textTitle: 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
Study of cerium oxide-metal interaction with gases - carbon monoxide oxidation and methanol decomposition
No full textTitle: Study of cerium oxide-metal intraction with gases - carbon monoxide oxidation and methanol decomposition Author: Tatiana Kolářová Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract: Dissertation thesis is focused on the study of two catalytic systems on the basis of cerium oxide-metal. The systems were characterized by various methods of surface analysis. The first part of the work concerns influence of the preparation parameters on the character of gold nanoparticles deposited onto the sputtered cerium oxide layers from a solution. Catalytic activity of prepared Au/CeOx/(C)/Si systems, containing particles with the mean sizes of 4- 10 nm, was tested toward CO oxidation at atmospheric pressure. The results show that with increasing amount of gold present on the samples, also the productivity of CO2 during the reactions grows. The work is further focused on the preparation of an inverse model CeOx/Pt(111) system. On this system, adsorption of methanol at low temeperatures and its decomposition during a heating was studied. It is apparent from presented results that the decomposition of methanol on the inverse CeOx/Pt(111) systems behaves in a different way than on a clean platinum sample or a thick..
Studium interakce systémů oxid ceru-kov s plyny - oxidace oxidu uhelnatého a dekompozice metanolu
No full textNázev práce: Studium interakce systémů oxid ceru-kov s plyny - oxidace oxidu uhelnatého a dekompozice metanolu Autor: Tatiana Kolářová Katedra/Ústav: Katedra fyziky povrchů a plazmatu Vedoucí disertační práce: Doc. RNDr. Václav Nehasil, Dr., Katedra fyziky povrchů a plazmatu Abstrakt: Dizertačná práca je venovaná štúdiu dvoch typov katalytických systémov na báze oxid céru-kov. Systémy boli charakterizované rôznymi metódami analýzy povrchov. Prvá časť sa zaoberá vplyvom parametrov prípravy na charakter zlatých nanočastíc deponovaných z roztoku na naprašovanú vrstvu oxidu céru. Katalytická aktivita pripravených systémov Au/CeOx/(C)/Si, obsahujúcich častice s priemernou veľkosťou 4-10 nm, bola testovaná pri CO oxidácii za atmosférického tlaku. Výsledky ukazujú, že so zvyšujúcim sa množstvom zlata na povrchu vzoriek zaznamenávame počas reakcií rastúcu produkciu CO2. Práca sa ďalej zaoberá prípravou inverzného modelového systému CeOx/Pt(111). Na tomto systéme bola sledovaná adsorpcia metanolu za nízkych teplôt a jeho rozklad pri následnom ohreve. Z prezentovaných výsledkov je zrejmé, že rozklad metanolu na inverzných systémoch CeOx/Pt(111) prebieha odlišným spôsobom ako v prípade čistej platiny a hrubej vrstvy CeO2/Pt(111). Vplyv na priebeh rozkladu metanolu a prítomnosť konkrétnych fragmentov má stupeň oxidácie...Title: Study of cerium oxide-metal intraction with gases - carbon monoxide oxidation and methanol decomposition Author: Tatiana Kolářová Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Václav Nehasil, Dr., Department of Surface and Plasma Science Abstract: Dissertation thesis is focused on the study of two catalytic systems on the basis of cerium oxide-metal. The systems were characterized by various methods of surface analysis. The first part of the work concerns influence of the preparation parameters on the character of gold nanoparticles deposited onto the sputtered cerium oxide layers from a solution. Catalytic activity of prepared Au/CeOx/(C)/Si systems, containing particles with the mean sizes of 4- 10 nm, was tested toward CO oxidation at atmospheric pressure. The results show that with increasing amount of gold present on the samples, also the productivity of CO2 during the reactions grows. The work is further focused on the preparation of an inverse model CeOx/Pt(111) system. On this system, adsorption of methanol at low temeperatures and its decomposition during a heating was studied. It is apparent from presented results that the decomposition of methanol on the inverse CeOx/Pt(111) systems behaves in a different way than on a clean platinum sample or a thick...Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Charakterizace technických povrchů elektronovým svazkem za kryogenních teplot
No full textThis dissertation presents applied research on the electron irradiation-induced emission of electrons and molecules and thermally controlled gas adsorption and desorption at cryogenic temperatures. Various technical-grade metal surfaces and functional surface coatings and treatments are studied under conditions relevant to many technical applications. A particular focus is on understanding the electron cloud and dynamic vacuum phenomena in CERN’s Large Hadron Collider (LHC), which operates at cryogenic temperatures below 20 K. Its electron cloud is characterised by low energies in 0–1 keV range but high doses up to 10 mC.mm−2 . Such conditions are controllably reproduced in a newly developed cryogenic laboratory setup designed for collector-based measurements of Secondary electron emission (SEY), electron stimulated desorption (ESD), and temperature programmed desorption (TPD) at high sensitivity, precision, and accuracy. The experimental results are acquired, analysed and systematically discussed in detail. Finally, semiempirical parametric models of the SEY and ESD yields are developed to capture the energy, dose, angle, temperature and composition dependencies, allowing further use in the field. While emphasising the LHC’s electron cloud-induced dynamic vacuum effect and related phenomena, the research findings are interpreted in a generalist manner, making them relevant to other accelerators and technical applications.Tato disertační práce se zabývá aplikovaným výzkumem emise elektronů a molekul vyvolané elektronovým zářením a tepelně řízenou adsorpci a desorpci plynů za kryogenních teplot. Studovány jsou různé technické kovové povrchy a funkční povlaky a povrchové úpravy za podmínek relevantních pro mnoho technických aplikací. Zvláštní pozornost se věnuje jevům elektronového oblaku a dynamického vakua ve Velkém hadronovém urychlovači (LHC), který pracuje za kryogenních teplot pod 20 K, a jehož elektronový oblak má nízké energie v rozmezí 0–1 keV ale vysoké dávky až po 10 mC.mm−2 . Takové podmínky lze řízeně reprodukovat v nově vyvinutém kryogenním laboratorním systému určeném pro vysoce citlivé a přesné kolektorové měření sekundární elektronové emise (SEY), elektronově stimulované desorpce (ESD) a teplotně programované desorpce (TPD). Získané experimentální výsledky jsou podrobně analyzovány a systematicky diskutovány. Nakonec jsou vyvinuty semiempirické parametrické modely pro jevy SEY a ESD, které zachycují závislosti na energii, dávce, úhlu, teplotě a složení a umožňují další využití výsledků v této oblasti. Přestože je kladen důraz na efekt dynamického vakua vyvolaný elektronovým mrakem na urychlovači LHC a související jevy, jsou výsledky výzkumu interpretovány obecně, takže jsou relevantní i pro jiné urychlovače a technické aplikace
