Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: CO Oxidation Catalysis.
Rozprawy doktorskie na temat „CO Oxidation Catalysis”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „CO Oxidation Catalysis”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
1
Elias, Joseph Spanjaard. "CO oxidation catalysis with substituted ceria nanoparticles". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105024.
Pełny tekst źródłaStreszczenie:
Thesis: Ph. D. in Inorganic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
The low-temperature and cost-effective oxidation of carbon monoxide to carbon dioxide remains a fundamental challenge in heterogeneous catalysis that would enable a diverse range of technologies for electrochemical storage and respiratory health. The development of new catalysts is often driven by high-throughput screening and many of the resulting compounds are mixed-phase, which obscures a rigorous identification of active sites and mechanisms at play for catalysis. In this thesis, the preparation of substituted ceria nanoparticles is described to bring about a fundamental understanding of the structure of the active sites, mechanism and design descriptors for CO oxidation on ceria-based catalysts. Monodisperse, single-phase nanoparticles of late first-row transition-metal-substituted ceria (MyCe₁.yO₂-x, M = Mn, Fe, Co, Ni and Cu) are prepared from the controlled pyrolysis of heterobimetallic precursors in amine surfactant solutions. By means of kinetic analyses, X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM), the active site for CO oxidation catalysis is identified as atomically-dispersed, square-planar M³+ and M²+ moieties substituted into the surface of the ceria lattice. The introduction of CuO does not contribute to the catalytic activity of CuyCe₁.yO₂-x, lending support to the hypothesis that the substituted ceria itself is responsible for the catalytic rate enhancement in mixed-phased catalysts like CuO/CeO₂ Under oxygen-rich conditions, the kinetic parameters for CO oxidation are consistent with lattice oxygen from the dispersed copper sites contributing directly to the oxidation of CO in the rate-determining step. In-situ X-ray photoelectron spectroscopy (XPS) and FTIR studies indicate that adsorbed CO can be directly oxidized to CO₂ in the absence of gaseous O₂, while in-situ XAS confirms that electron transfer is localized to the copper sites. XAS studies demonstrate that the reversible reducibility of dispersed copper ions is a contributing factor for the special catalytic activity of CuO/CeO₂ catalysts. The oxygen-ion vacancy formation energy is introduced as an activity descriptor to rationalize trends in the catalytic activities measured for MyCe₁-yO₂-x nanoparticles that span over three orders of magnitude. As such, the DFT-calculated vacancy formation energy serves to guide in the rational design of catalysts through computational, rather than experimental, screening of candidate compounds for CO oxidation catalysis.
by Joseph Spanjaard Elias.
Ph. D. in Inorganic Chemistry
2
Lee, Seung-Jae. "Development of supported gold catalysts for low temperature CO oxidation". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270939.
Pełny tekst źródła
3
Lund, Chistopher D. "Patterns and dynamics in heterogeneous catalysis : CO oxidation an plantinum /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9961758.
Pełny tekst źródła
4
Woods, Matthew P. "Activity and Selectivity in Oxidation Catalysis". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228175906.
Pełny tekst źródła
5
Miller, Duane D. "In Situ Infrared Spectroscopy Study of Gold Oxidation Catalysis". University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1152205534.
Pełny tekst źródła
6
Jonsson, Daniel. "Evaluation of Non-Noble Metal Catalysts for CO Oxidation". Thesis, KTH, Skolan för kemivetenskap (CHE), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207363.
Pełny tekst źródłaStreszczenie:
The aim of the study is to evaluate the ability of non-noble metal catalysts to function as the commercially used noble metal catalyst. The exhaust gas that was used in the project is generated from a heater developed by ReformTech AB with diesel as fuel. The compound that was focused on is carbon monoxide that has a concentration of 300-750 ppm. The catalysts that were tested are MnO/CeO2, CuO/CeO2 and a Pt/CeO2 catalyst used to compare the non-noble metal catalyst with. The sensitivity against sulfur poisoning was also analyzed by mixing sulfur into the fuel. Analysis of the exhaust gas was done with a micro-GC and the catalysts were also analyzed with SEM before and after exposure of sulfur. The manganese catalyst with a loading of 7 wt-% did not show any activity against carbon monoxide oxidation. The copper catalysts contained two different loadings of active material, 7 and 14 wt-% and monoliths with 400 and 600 cpsi were used. Both loadings showed good activity against carbon monoxide oxidation. The most prominent catalyst was the 14 wt-% CuO/CeO2 catalyst with a 600 cpsi monolith because of an increase in surface area. The SEM analysis showed that sulfur was present on the surface when the heater was using diesel with 300 ppm sulfur. The sulfur caused complete deactivation of the non-noble metal catalysts and a small decrease in activity was shown on the noble metal Pt catalyst.
7
Wang, Jiamin. "Exploring Strategies to Break Adsorption-Energy Scaling Relations in Catalytic CO Oxidation". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96537.
Pełny tekst źródłaStreszczenie:
An atomistic control of chemical bonds formation and cleavage holds the key to making molecular transformations more energy efficient and product selective. However, inherent scaling relations among binding strengths of adsorbates on various catalytic materials often give rise to volcano-shaped relationships between the catalytic activity and the affinity of critical intermediates to the surface. The optimal catalysts should bind the reactants 'just right', i.e., neither too strong nor too weak, which is the Sabatier's principle. It is extremely useful for searching promising catalysts, but also imposes serious constraints on design flexibility. Therefore, how to circumvent scaling constraints is crucial for advancing catalytic science. It has been shown that hot electrons can selectively activate the chemical bonds that are not responsive to phonon excitation, thus providing a rational approach beyond scaling limitation. Another emerging yet effective way to break the scaling constraint is single atom catalysis. Strong interactions of supported single atoms with supports dramatically affect the electronic structure of active sites, which reroutes mechanistic pathways of surface reactions. In my PhD research, we use CO oxidation reaction on metal-based active sites as a benchmark system to tailor mechanistic pathways through those two strategies 1) ultra-fast laser induced nonadiabatic surface chemistry and 2) oxide-supported single metal catalysis, with the aim to go beyond the Sabatier activity volcano in metal catalysis.Doctor of Philosophy
Catalysis is the process of increasing the chemical reaction rate by lowering down the activation barrier. There are three different types of catalysis including enzyme, homogeneous, and heterogeneous catalysis. Heterogeneous catalytic reactions involve a sequence of elementary steps, e.g., adsorption of reactants onto the solid surface, transformation of adsorbed species, and desorption of the products. However, the existing scaling relations among binding energies of reaction intermediates on various catalytic materials lead to volcano-shaped relationships, which show the reaction activity versus the binding energy of critical intermediates. The optimal catalysts should bind the reaction intermediates neither too strong nor too weak. This is the Sabatier's principle, which provides useful guidance for searching promising catalysts. But it also imposes the constraint on the attainable catalytic performance. How to break the constraint to further improve the catalytic activity is an emerging problem. The recent studies have shown that the hot surface electrons on the metal surfaces induced by the ultra-fast laser can selectively activate the chemical bonds, thus providing a rational approach beyond scaling constraints. Another way to break the scaling constraint is single atom catalysis. The metal oxides are frequently used as the support to stabilize the single metal atoms. The strong interaction between the single metal atoms and the support affects the electronic structure of the catalysts. Thereby catalytic reactions on the single metal atoms catalyst are very different from that on metal surfaces. In my PhD research, we use CO oxidation reaction as a benchmark system, to tailor reaction pathways through those two strategies on 1) Ru(0001) under ultra-fast laser pulse and 2) Ir single metal atoms supported on spinel oxides, to go beyond Sabatier activity volcano in metal catalysis.
8
Atalik, Bora. "Structure Sensitivity Of Selective Co Oxidation Over Precious Metal Catalysts". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12605847/index.pdf.
Pełny tekst źródłaStreszczenie:
In this study, the effect of Pt particle size on the reaction rate and selectivity of preferential oxidation of CO (PROX) reaction was investigated on Pt/Al2O3. 2% Pt/γ
-Al2O3 catalysts were prepared by incipient wetness method
the particle size of the catalysts was modified by calcination temperature and duration. Therefore, the relative amounts of low and high coordination atoms on the metal particle surface can be changed. Over these catalysts, first, the CO oxidation reaction was studied in the absence of hydrogen. The catalyst having the highest dispersion, i.e., lowest metal particle sizes, had the highest activity as indicated by its lowest light-off temperature. On the other hand, the turnover frequencies (TOF) of the catalysts were increasing with decreasing dispersion. The activation energy of the catalysts were also compared and examined: as the particle size increased, the activation energy decreased. In the second part, preferential oxidation of CO reaction in the presence of hydrogen was studied. Both CO conversion and selectivity first increased with increasing reaction temperature, then exhibited a maximum, and finally decreased. Both CO conversion and selectivity did not show any trend for different dispersed catalysts for &
#955
(2PO2/PCO) was 1. In order to reach a definite conclusion about the structure sensitivity of selective CO oxidation, the experiments with different &
#955
&rsquo
s and space times over the same catalysts should be performed.
9
Yung, Matthew Maurice. "Oxidation catalysis in environmental applications nitric oxide and carbon monoxide oxidation for the reduction of combustion emissions and purification of hydrogen streams /". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1187128442.
Pełny tekst źródła
10
Grayson, Benjamin Alan. "Application and modeling of TiO2-supported gold nanoparticles for CO preferential oxidation in excess hydrogen". [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002131.
Pełny tekst źródła
11
Gil, Sepulcre Marcos. "Ru, Co and Ca-based catalysts for artificial photosynthesis". Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/462105.
Pełny tekst źródłaStreszczenie:
La fotosíntesis artificial ofrece una alternativa al panorama energético actual, basado en el consumo de combustibles fósiles. Tratando de emular la fotosíntesis de las plantas, este campo de estudio trata de utilizar la luz solar para producir electrones, protones y oxígeno a partir del agua, para más tarde utilizar los electrones para producir hidrógeno u otros combustibles, y almacenar de esta forma la energía solar en forma de enlaces químicos. Para hacer energéticamente viables estos dos procesos es necesario el uso de catalizadores, comúnmente basados en metales de transición.
En el primer capítulo se introduce brevemente la motivación que ha llevado a la realización de la tesis, discutiéndose también los aspectos mecanísticos más relevantes de la catálisis de oxidación de agua, así como la reducción de protones, dando una visión general de los catalizadores en ambos campos más relevantes hasta la fecha.
El segundo capítulo se centra en los objetivos de este trabajo. El objetivo principal de esta tesis es la síntesis y caracterización estructural y electroquímica de varios catalizadores de Ru, Cu y Co, y el posterior estudio de su reactividad en catálisis de oxidación de agua y/o reducción de protones. El objetivo final es comprender sus mecanismos de reacción y los factores que afectan a su actividad catalítica para ayudar al diseño futuro de catalizadores más eficientes y robustos.
En el tercer capítulo se presenta la síntesis, caracterización y reactividad de una nueva familia de complejos de Ru. Un estudio espectroscópico y cinético detallado ha permitido identificar la formación de nuevas especies tras oxidación de los complejos en soluciones acuosas, las cuales tienen una implicación directa en su comportamiento en catálisis de oxidación de agua. El cuarto capítulo aborda la síntesis y caracterización de una nueva familia de complejos de Cu, estudiándose su reactividad en catálisis de oxidación de agua y comparándose con la de los complejos de cobre más relevantes reportados hasta la fecha en la bibliografía. Finalmente, en el quinto capítulo se presenta la desactivación de un cluster molecular de CoII/CoIII cuando este se somete a potenciales de reducción, dando lugar a la formación de nanopartículas de CoO o CoO(OH) depositadas sobre un electrodo de carbono. Dichas nanopartículas han sido probadas en catálisis de reducción de protones y su reactividad relacionada con su morfología y naturaleza.
En el sexto capítulo se incluyen las conclusiones más relevantes del trabajo realizado. Finalmente, el último capítulo contiene un anexo que incluye otros trabajos realizados y publicados durante esta tesis relacionados con el tema principal de esta tesis.Artificial photosynthesis offers a viable alternative to the actual energetic model based mainly in the consumption of fossil fuels. Trying to emulate the photosynthesis process in higher plants, this area of study attempts to use sunlight in order to produce electrons, protons and oxygen from water, with the aim of using the released electrons for producing hydrogen or other useful fuels. Within this context, the use of catalysts usually based in transition metals is necessary to make these two processes viable. The first chapter contains a brief introduction about the motivation for the research presented in this thesis. The most relevant general mechanistic aspects for water oxidation (WO) as well as proton reduction catalysis are also presented, giving a general view of most relevant catalysts reported to date. The second chapter is focused in the objectives of this work. The main goal of this PhD thesis is the synthesis and the structural and electrochemical characterization of a series of Ru, Co and Cu-based catalysts and the ulterior study of their reactivity towards water oxidation and/or proton reduction catalysis. The final objective is to fully understand the mechanistic pathways and the factors that affect their catalytic performance for helping in the future rational design of more efficient and robust catalysts. In the third chapter, the synthesis, characterization and reactivity of a new family of Ru complexes is presented. A series of detailed electrochemical, spectroscopic and kinetic studies allows the identification of new species formed after oxidation of the complexes in aqueous solution that proved to be key for further understanding their catalytic behavior in water oxidation. The fourth chapter presents the synthesis and characterization of a new family of Cu complexes. Their reactivity towards water oxidation has been studied and compared with that of the most relevant Cu-based WO catalysts reported in the literature. Finally, in the fifth chapter we present the deactivation of a CoII/CoIII molecular cluster after application of reductive potentials, giving rise to the formation of CoO or CoO(OH) nanoparticles deposited onto a glassy carbon electrode. The ability of these nanoparticles for reducing protons has been tested, and their catalytic performance discussed on the basis of the nature of the species obtained and their morphology . In the sixth chapter the most relevant conclusions of this work are discussed. Finally, the last chapter includes an annex containing other works that have been carried out and published during this PhD thesis and that are closely related with the work carried out during the PhD.
12
Hossain, Shaikh Tofazzel Hossain. "Synthesis and Kinetic Study of CeO2 and SiO2 Supported CuO Catalysts for CO Oxidation". Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1526392721561056.
Pełny tekst źródła
13
Ozensoy, Emrah. "Polarization modulation infrared reflection absorption spectroscopy for heterogeneous catalytic applications at elevated pressures". Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2201.
Pełny tekst źródłaStreszczenie:
This dissertation focuses on bridging the pressure and complexity gap between heterogeneous catalysis and surface science by introducing new instrumental tools that can operate under catalytically relevant conditions (i.e. atmospheric pressures and temperatures higher than room temperature). Thus, some of the few detailed examples of the polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) as an in situ vibrational spectroscopic tool for the elevated-pressure investigation of gas/solid interfaces on planar single crystal model catalyst systems were presented in this work. Furthermore, for the first time in the literature, PM-IRAS technique was applied to study complex multi-component model catalyst structures exhibiting three dimensional morphologies such as metal nanoparticles deposited on a metal-oxide thin film. In order to achieve a molecular understanding of the properties of CO+NO catalytic reaction at elevated temperatures and pressures on Pd based catalysts, adsorption trends of each of the reactant molecules were studied separately on Pd (111). The adsorption properties of CO/Pd (111) and NO/Pd (111) systems both under UHV conditions and at elevated pressures were discussed in a comparative manner to highlight the pressure dependent behavioral differences between these two probe molecules by emphasizing the risks of extrapolating UHV trends to elevated pressure regimes. CO+NO reaction mechanism and kinetics was also studied on Pd (111) by in situ PM-IRAS. Factors affecting the conversion and the selectivity of the Pd (111) model catalyst towards CO+NO reaction at elevated pressures were discussed. Formation of isocyanate containing species?? was also observed and the catalytic implications of this observation was elaborated. Finally, design and characterization of a complex model catalyst composed of supported Pd nano-particles was investigated using CO adsorption at elevated pressures. Catalytic activity of the defect sites on the supported Pd nano-particles towards CO dissociation was demonstrated and compared with Pd (111) to elucidate the significance of the surface morphology of the active sites in a catalytic reaction.
14
Ono, Luis. "IN-SITU GAS PHASE CATALYTIC PROPERTIES OF METAL NANOPARTICLES". Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3277.
Pełny tekst źródłaStreszczenie:
Recent advances in surface science technology have opened new opportunities for atomic scale studies in the field of nanoparticle (NP) catalysis. The 2007 Nobel Prize of Chemistry awarded to Prof. G. Ertl, a pioneer in introducing surface science techniques to the field of heterogeneous catalysis, shows the importance of the field and revealed some of the fundamental processes of how chemical reactions take place at extended surfaces. However, after several decades of intense research, fundamental understanding on the factors that dominate the activity, selectivity, and stability (life-time) of nanoscale catalysts are still not well understood. This dissertation aims to explore the basic processes taking place in NP catalyzed chemical reactions by systematically changing their size, shape, oxide support, and composition, one factor at a time. Low temperature oxidation of CO over gold NPs supported on different metal oxides and carbides (SiO2, TiO2, TiC, etc.) has been used as a model reaction. The fabrication of nanocatalysts with a narrow size and shape distribution is essential for the microscopic understanding of reaction kinetics on complex catalyst systems ("real-world" systems). Our NP synthesis tools are based on self-assembly techniques such as diblock-copolymer encapsulation and nanosphere lithography. The morphological, electronic and chemical properties of these nanocatalysts have been investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Chapter 1 describes briefly the basic principles of the instrumentation used within this experimental dissertation. Since most of the state-of-art surface science characterization tools provide ensemble-averaged information, catalyst samples with well defined morphology and structure must be available to be able to extract meaningful information on how size and shape affect the physical and chemical properties of these structures. In chapter 2, the inverse-micelle encapsulation and nanosphere lithography methods used in this dissertation for synthesizing uniformly arranged and narrow size- and shape-selected spherical and triangular NPs are described. Chapter 3 describes morphological changes on individual Au NPs supported on SiO2 as function of the annealing temperature and gaseous environment. In addition, NP mobility is monitored. Chapter 4 explores size-effects on the electronic and catalytic properties of size-selected Au NPs supported on a transition metal carbide, TiC. The effect of interparticle interactions on the reactivity and stability (catalyst lifetime) of Au NPs deposited on TiC is discussed in chapter 5. Size and support effects on the formation and thermal stability of Au2O3, PtO and PtO2 on Au and Pt NPs supported on SiO2, TiO2 and ZrO2 is investigated in chapter 6. Emphasis is given to gaining insight into the role of the NP/support interface and that played by oxygen vacancies on the stability of the above metal oxides. Chapter 7 reports on the formation, thermal stability, and vibrational properties of mono- and bimetallic AuxFe1-x (x = 1, 0.8, 0.5, 0.2, 0) NPs supported on TiO2(110). At the end of the thesis, a brief summary describes the main highlights of this 5-year research program.Ph.D.
Department of Physics
Sciences
Physics PhD
15
Gladh, Jörgen. "Ultrafast Probing of CO Reactions on Metal Surfaces : Changes in the molecular orbitals during the catalysis process". Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-132248.
Pełny tekst źródłaStreszczenie:
This thesis presents experimental studies of three different chemical reaction steps relevant for heterogeneous catalysis: dissociation, desorption, and oxidation. CO on single-crystal metal surfaces was chosen as the model systems. X-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) provide information about the electronic structure, and were performed on CO/Fe to measure both a non-dissociative, and a pre-dissociative state. The measurement on the pre-dissociative state showed a π → π* excitation, which implies a partly broken internal π bond in the molecule. Ultrafast laser-induced reactions were used to examine the dynamic properties of desorption and oxidation. Here CO/Ru and CO/O/Ru were used as model systems. Desorption of CO from a Ru surface involve both hot electrons and phonons. In the case of CO oxidation from CO/O/Ru a pronounced wavelength dependence of the branching ratio between desorption and oxidation was observed. Excitation with 400 nm showed a factor of 3-4 higher selectivity towards oxidation than 800 nm. This was attributed to coupling to transiently excited, non-thermalized electrons. Finally, by performing optical pump/x-ray probe XAS and XES changes in the electronic structure during the reaction could be followed, both for desorption and oxidation. In the CO/Ru experiment, two different transient excitation paths were observed, one leading to a precursor state, and one where CO moves into a more highly coordinated site. Using selective excitation in XES, these were shown to coexist on the surface. In the oxidation experiment, probing the reacting species located near the transition state region in an associative catalytic surface reaction was demonstrated for the very first time.
16
Freire, Eleonora Maria Pereira de Luna. "Estudo das propriedades físico-químicas de sistemas Pd, Pd-Fe e Pd-Co suportados em CeO2/Al2O3". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266996.
Pełny tekst źródłaStreszczenie:
Orientadores: Antonio José Gomez Cobo, César Augusto Moraes de AbreuTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-16T13:01:21Z (GMT). No. of bitstreams: 1 Freire_EleonoraMariaPereiradeLuna_D.pdf: 2485469 bytes, checksum: 5c15bdbbb73bd51d623eb4811e9d2248 (MD5) Previous issue date: 2005
Resumo: Os catalisadores à base de paládio apresentam particular interesse para o tratamento de gases de exaustão automotiva, notadamente no caso da combustão do etanol. O presente trabalho tem o objetivo de estudar as propriedades físico- químicas de catalisadores Pd - Fe e Pd - Co suportados em alumina modificada pelo óxido de cério. Para tanto, catalisadores modelo foram preparados através do método de impregnação por via úmida, empregando-se sais precursores à base de nitrato dos metais, e os suportes Al2O3, CeO2 e CeO2/Al2O3. Os catalisadores obtidos tiveram seus teores metálicos determinados por meio de espectrofotometria de absorção atômica, tendo sido caracterizados através de adsorção de nitrogênio (método B.E.T), espectroscopia no infravermelho, difração de raio-X, redução à temperatura programada. Os sistemas preparados foram avaliados pela reação catalítica de oxidação do etanol em fase gasosa em um microreator tubular de leito fixo, operando a pressão atmosférica e a temperatura de 3500 C. Os catalisadores preparados apresentam frações mássicas em torno de 2 % para o Pd, e de 1% para os aditivos Fe ou Co. A adição de Pd, Pd-Fe e Pd-Co aos suportes Al2O3 e CeO2/Al2O3 não levou a modificações, nos volumes dos poros e nas áreas superficiais específicas. Esses resultados mostram que a adição dos metais pouco influenciam nas características texturais. Enquanto para os bimetálicos suportados em céria, há a hipótese da existência de microporos apesar de ter ocorrido diminuições relativas das áreas superficiais específicas os volumes dos poros permanecem constantes. Na reação de oxidação do etanol, os resultados das análises cromatográficas levam a concluir que a introdução dos aditivos cobalto e ferro ao paládio provoca redução de eficiência na conversão do etanol para os sistemas CeO2 e CeO2/Al2O3. A adição do cobalto ao paládio na alumina aumenta a conversão e apresenta alto rendimento para a oxidação do etanol e o catalisador paládio suportado em céria apresenta conversão menor do que o Pd-Co sobre alumina porém rendimentos semelhantes
Abstract: Palladium based catalysts have been, applied at the treatment of the automotive gas exhaustion, particularly in the case of ethanol combustion. In this context, the actual work has the aim to study the physical and chemical properties of the Pd, Pd-Fe and Pd-Co catalysts supported in alumina, ceria and alumina modified by the cerium oxide. The wet impregnation method was used to develop the model catalysts. Precursor salts metal nitrates as well as the supports Al2O3, CeO2 and CeO2/Al2O3, were used for this purpose. The catalysts were characterised by the methods of BET-N2, infrared spectroscopy (I.R), X- ray diffraction (XRD) and reduction at programmed temperature (TPR). The contents of the metal impregnated in the catalysts was quantified by atomic absorption spectrophotometry (A.A.S.). A fixed-bed tubular microreactor was used to evaluate the performance of the catalysts in the oxidation of ethanol in gas phase, at the atmospheric pressure and temperature of 350o C. The mass fractions observed for the palladium catalysts and those that had Fe and Co as additive, were around 2% and 1%, respectively. The addition of the Pd, Pd-Fe and Pd-Co to the alumina support and alumina modified by cerium oxide does not prove modification into they capacity of the porous and surface areas. This results prove that the addition of metals has no power to the textural characteristics. Whereas the supported bimetallic system in ceria has the theory of the existence of micropores despite of a relative decrease of specific surface areas, the capacity of porous remains stable. The ethanol oxidation reaction, and the results of the cromatographicas analysis conclude that the introduction of cobalt and iron into the palladium decreases the efficacy of ethanol conversion into the CeO2 and CeO2/Al2O3 systems. The addition of cobalt into the palladium in alumina increases the conversion and introduces high performance for the ethanol oxidation and the palladium catalyst supported by cerium shows minor , conversion than to the cobalt-palladium upom alumina, but with the same results
Doutorado
Sistemas de Processos Quimicos e Informatica
Doutor em Engenharia Química
17
Ren, Yu. "Applications of ordered mesoporous metal oxides : energy storage, adsorption, and catalysis". Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1705.
Pełny tekst źródłaStreszczenie:
The experimental data and results demonstrated here illustrate the preparation and application of mesoporous metal oxides in energy storage, adsorption, and catalysis. First, a new method of controlling the pore size and wall thickness of mesoporous silica was developed by controlling the calcination temperature. A series of such silica were used as hard templates to prepare the mesoporous metal oxide Co₃O₄. Using other methods, such as varying the silica template hydrothermal treatment temperature, using colloid silica, varying the materials ratio etc., a series of mesoporous β-MnO₂ with different pore size and wall thickness were prepared. By using these materials it has been possible to explore the influence of pore size and wall thickness on the rate of lithium intercalation into mesoporous electrode. There is intense interest in lithium intercalation into titanates due to their potential advantages (safety, rate) replacing graphite for new generation Li-ion battery. After the preparation of an ordered 3D mesoporous anatase the lithium intercalation as anode material has been investigated. To the best of our knowledge, there are no reports of ordered crystalline mesoporous metal oxides with microporous walls. Here, for the first time, the preparation and characterization of three dimensional ordered crystalline mesoporous α-MnO₂ with microporous wall was described, in which K+ and KIT-6 mesoporous silica act to template the micropores and mesopores, respectively. It was used as a cathode material for Li-ion battery. Its adsorption behavior and magnetic property was also surveyed. Following this we described the preparation and characterization of mesoporous CuO and reduced Cu[subscript(x)]O, and demonstrated their application in NO adsorption and delivery. Finally a series of crystalline mesoporous metal oxides were prepared and evaluated as catalysts for the CO oxidation.
18
Wang, Jijin. "Sum frequency generation study of CO adsorbed on palladium single crystal and nanoparticles : adsorption and catalytic oxidation as a function of size". Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00933675.
Pełny tekst źródłaStreszczenie:
The CO reaction on metals is of great interest experimentally and theoretically because it serves as a model system to understand molecular chemisorption and catalyzed reactions on metals. This thesis aims at progressing along the general trends of surface science: bridging the pressure and material gaps in the study of catalysts. Sum Frequency Generation (SFG) is at the heart of this work. It involves a nonlinear optical process with an IR pulse induced coherent first-order polarization up-converted by a visible pulse into a second-order polarization at the sum frequency. In this thesis it is used to record CO vibrational spectra on the Pd nanoparticles (NP)/MgO/Ag(100) to understand the adsorption and oxidation thanks to its specific advantages in surface science: sensitivity and surface selectivity. The questions proposed are the possible roles of the adsorption sites which only exist on the NPs, the effect of the size of NPs and the presence of oxygen on the CO adsorption and catalytic reactivity, the effect of adsorption of oxygen (from 'normal' - dissociative chemisorption to 'sub-surface'), the variation of reactivity of CO in the different sites when pressure and temperature increase. (1) We have studied CO adsorption on Pd(100) as a reference. Below a CO coverage of 0.5 ML SFG results confirm previous IRAS studies. Above 0.5 ML, we have observed in much more details than previously two vibrational bands assigned to CO at compressed and uncompressed bridge sites, of which we have measured the frequency and intensity and the decoherence time T₂ as a function of coverage. (2) Pd NP size effect on CO adsorption is studied (from Pd(100) to particles with about 300 atoms). At pressures below 10⁻³ mbar the CO spectra on a coalesced layer and on large NPs are dominated by the same bridge band as on Pd(100). The CO singleton frequency decreases with coverage, revealing the evolution of chemisorption with size. DFT calculations done at ENS Lyon reveal that the main mechanism is the strain induced by the substrate which increases the Pd-Pd bondlength, favors electron back donation to CO, weakens the CO bond and probably reinforce the CO-metal bond. (3) Because of a limit of our maximal temperature, we have to study the CO catalytic oxidation in an excess of oxygen to avoid self-poisoning by CO. The results strongly suggest that bridge sites are the key sites in catalysis in our experimental condition. However, while a fraction of bridge sites are more reactive on NPs, a large fraction of them seem less reactive with respect to Pd(100). The reactivity of CO on (100) facet decreases at smaller NP size. It emerges the ideal that the reaction proceeds by the most reactive sites, and that the other sites are only reservoir in reactivity, if the diffusion between sites are high enough. Oxygen modifies the adsorption of co-reactants. In the case of CO + O / Pd NPs / MgO, below 10⁻⁴ mbar oxygen does not seem to influence significantly CO adsorption; between 10⁻³ and 10⁻¹ mbar the spectroscopic signature of CO compression disappears, and above 1 mbar a new class of a top sites appears, suggesting that some oxygen species (perhaps "subsurface") favors CO adsorption on linear sites. A pump-probe experiment has been done to compare the effect of pump on different adsorption sites. All this confirms the interest of SFG vibrational spectroscopy for catalysis. An additional contribution of this thesis to SFG is the study of the spectro-temporal aspects of SFG emission. SFG spectra containing several bands are modeled in details based on an ODT/Au system and compared to experimental spectra, showing that in SFG spectra are affected by the spectro-temporal shape of the visible laser. The standard deconvolution method used in the literature is only approximate. Accurate spectro-temporal spectrum modeling is required to evaluate precisely the relative intensities when several bands are present.
19
Seriani, Nicola. "First-principles simulations of the oxidation of methane and CO on platinum oxide surfaces and thin films". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1163174398225-14223.
Pełny tekst źródłaStreszczenie:
The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. The thermodynamic stability of platinum oxide surfaces and thin films was studied, as well as their reactivities towards oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive towards either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favoured at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.
20
Miranda, Aline Rodrigues Lopes. "Oxidação preferencial de CO em catalisadores à base de ouro : estudo do efeito do suporte e do método de síntese do catalisador". Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8770.
Pełny tekst źródłaStreszczenie:
Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-05-19T19:35:37Z
No. of bitstreams: 1
DissARLM.pdf: 2999284 bytes, checksum: cb32a2cd7ed71b40fd67f2b5604ce434 (MD5)Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-23T19:48:47Z (GMT) No. of bitstreams: 1 DissARLM.pdf: 2999284 bytes, checksum: cb32a2cd7ed71b40fd67f2b5604ce434 (MD5)
Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-23T19:48:57Z (GMT) No. of bitstreams: 1 DissARLM.pdf: 2999284 bytes, checksum: cb32a2cd7ed71b40fd67f2b5604ce434 (MD5)
Made available in DSpace on 2017-05-23T19:58:53Z (GMT). No. of bitstreams: 1 DissARLM.pdf: 2999284 bytes, checksum: cb32a2cd7ed71b40fd67f2b5604ce434 (MD5) Previous issue date: 2016-03-29
Outra
The CO preferential oxidation reaction (PROX) is used in the purification of hydrogen streams for various applications. Since the discovery of improved catalytic properties of gold particles, at nanometer range, in the CO oxidation reaction at low temperature, Au catalysts have been the subject of numerous investigations of CO oxidation and PROX. Concerning the heterogeneous catalysis, the catalyst activity is determined by several factors: the nanoparticles size, the metal loading and dispersion, the nature and porosity of the support, and the metal/support interaction. To understand the dependence of the support and the influence of the synthesizing method on the material properties and catalytic performances, gold nanoparticles supported on three different oxides (CeO2, MnO2 and TiO2) were successfully synthesized by the deposition precipitation (DP) method, using urea, and modified polyol (MP) method, using PVP as surfactant and sodium borohydride as reducing agent. Additionally, Au/SiO2 was obtained by the DP method. Characterizations were performed to assess the crystallinity, the metal mass percentage, the reduction temperatures and the respective reducing gas consumptions of pure oxides and supported materials synthesized by both methods. In addition, microscopic pictures were obtained to evaluate the materials morphology and the gold nanoparticles diameter. The Au catalysts synthesized by the DP method presented smaller particle sizes as compared to catalysts obtained by the MP method. Catalytic evaluation of the CO oxidation and PROX reactions were performed using temperature ramp starting at room temperature up to 200 °C. As a comparative parameter, the ratio between the catalyst mass and the gas feed flow remained constant at 1 mg / 1 mL / min for all reactions. The results showed that Au supported on TiO2 prepared by the DP method presented complete CO conversion at room temperature, but with the simultaneous supply of H2, this catalyst tends to oxidize H2, decreasing the CO conversion activity. On the other hand, the Au/CeO2 catalyst prepared by the DP method presented activity up to about 200 °C for PROX and better selectivity towards the CO2 formation.
A reação de oxidação preferencial de CO (PROX) é utilizada na purificação de correntes de hidrogênio para diversas aplicações. Desde a descoberta da melhoria das propriedades catalíticas de partículas de ouro, em escala nanométrica, na reação de oxidação de CO a baixa temperatura, catalisadores de Au têm sido objeto de numerosas investigações em oxidação de CO e de PROX. No que diz respeito a catálise heterogênea, a atividade do catalisador é determinada por vários fatores: o tamanho das nanopartículas, a carga e dispersão metálica, a natureza e a porosidade do suporte, e a interação metal/suporte. Para entender a dependência do suporte e a influência do método de síntese nas propriedades dos materiais e nos desempenhos catalíticos, foram sintetizados com sucesso nanopartículas de ouro suportadas em 3 diferentes óxidos (CeO2, MnO2 e TiO2) pelos métodos de deposição precipitação (DP) com ureia e poliol modificado (PM) utilizando PVP como agente surfactante e borohidreto de sódio como agente redutor. Adionalmente, Au/SiO2 foi obtido pelo método DP. Foram realizadas caracterizações para avaliar a cristalinidade, porcentual mássico de metal, temperaturas de redução e respectivos consumos de gás redutor dos óxidos puros e dos materiais suportados sintetizados por ambos os métodos. Além disso, foram obtidas imagens de microscopia para avaliar a morfologia dos materiais e o diâmetro das nanopartículas de ouro. Os catalisadores de Au sintetizados pelo método DP apresentaram menores tamanhos de partícula, comparados aos catalisadores obtidos pelo método PM. A avaliação catalítica nas reações de oxidação de CO e PROX foram realizadas através de rampa de temperatura, começando pela temperatura ambiente e aquecendo até cerca de 200 ºC. Como parâmetro comparativo, a razão entre a massa de catalisador e a vazão dos gases alimentados manteve-se constante em 1 mg / 1 mL/min em todas as reações. Os resultados mostraram que o catalisador de Au suportado em TiO2 obtido pelo método DP apresentou conversão total de CO em temperatura ambiente, porém com a alimentação simultânea de H2, esse catalisador tende a oxidar o H2, diminuindo a atividade à conversão de CO. Por outro lado, o catalisador de Au/CeO2 preparado pelo método DP apresentou atividade até cerca de 200 ºC na PROX e melhor seletividade à formação de CO2.
PRH-ANP/MCT N° 44
21
Laoufi, Issam. "Structure, morphologie et activité catalytique des nanoparticules d'or supportées sur TiO2(110) : une étude in operando par GIXD et GISAXS au cours de l'oxydation du CO". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00681873.
Pełny tekst źródłaStreszczenie:
Ce travail porte sur l'étude in operando des nanoparticules d'or supportées sur TiO2(110) pendant la réaction d'oxydation du CO. Il s'inscrit dans l'objectif de comprendre les propriétés catalytiques de l'or qui apparaissent à l'échelle nanométrique. Les paramètres géométriques et structuraux des nanoparticules d'or ont été mesurés en présence de 20 mbar d'oxygène ou d'argon, de 0.1-0.2 mbar de CO et en conditions réactionnelles (oxygène + CO à 473 K), par GISAXS et par GIXD en suivant simultanément la composition des gaz par spectrométrie de masse. L'exposition au mélange réactionnel déclenche une évolution instantanée des nanoparticules avec une augmentation de leur taille moyenne qui varie de la même manière que l'activité catalytique. Par contre l'oxygène et le CO ne provoquent pas de changement et seule la température a un effet. Ces évolutions démontrent l'importance des mesures in operando pour déterminer le lien qui existe entre la taille et l'activité des nanoparticules. La variation de l'activité catalytique en fonction du diamètre présente un maximum pour des particules de 2 nm de diamètre et de 1.4 nm de hauteur. Au-dessus de ce maximum, elle suit une loi de puissance du diamètre, d-2.4 ± 0,3, comme attendu pour des sites actifs situés sur les atomes de basse coordinence. La diffraction X montre que, pendant la réaction, les nanoparticules conservent la structure CFC du cristal d'or, mais la distance inter-plan se contracte quand la taille des particules décroit ce qui intervient dans la baisse d'activité au dessous de 2 nm. Cependant d'autres paramètres peuvent aussi avoir un effet négatif sur la réactivité comme la forme des particules et le fait que plus elles sont petites plus elles s'agglomèrent sur les bords de marche du substrat. La similitude des tailles obtenues par GISAXS et par GIXD et de leur comportement sous gaz réactifs indique que les particules mesurées par ces deux techniques sont les mêmes. De plus, la forte corrélation entre la variation de l'activité et les évolutions observées par GISAXS montre que ce sont les particules actives qui sont sondés par les rayons x. La comparaison des résultats avec ceux déjà publiés indique que le comportement que nous avons décrit sur la dépendance de l'activité catalytique des nanoparticules d'or sur TiO2, pour l'oxydation du CO, est représentative des propriétés de ce système. Cependant, il est nécessaire de vérifier expérimentalement comment ces résultats obtenus à 473 K peuvent être extrapolés à température ambiante. L'installation dans notre dispositif d'une nouvelle chambre de réaction doit permettre de gagner un ordre de grandeur en sensibilité et rendre envisageable une telle étude. Mots clés : Catalyse, nanoparticules d'or, GISAXS, diffraction X, in operando, oxydation du CO.
22
Neugebohren, Jannis. "Implementing Ion Imaging to Probe Chemical Kinetics and Dynamics at Surfaces". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E43B-1.
Pełny tekst źródła
23
Yan, Zhen. "Model catalytic studies of single crystal, polycrystalline metal, and supported catalysts". [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2455.
Pełny tekst źródła
24
Soares, Jorge Manuel Caramelo. "Low temperature CO oxidation on Au/TiOâ‚‚ catalysts". Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408202.
Pełny tekst źródła
25
Pham, Huu Thien. "Contribution à l'étude de la dépollution de l'air chargé en composés organiques volatils par un procédé associant un plasma de décharge à barrière diélectrique impulsionnelle et des catalyseurs". Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2022/document.
Pełny tekst źródłaStreszczenie:
Cette thèse s’inscrit dans le cadre général de la dépollution d’effluents gazeux faiblement chargés en Composés Organiques Volatils (COV). L’étude concerne l'oxydation de trois COV cibles (méthane, propène, et toluène) dans l'air à la pression atmosphérique dans d'une part un réacteur plasma de décharge à barrière diélectrique (DBD) pulsée et un réacteur catalytique utilisés séparément et d'autre part, dans un réacteur hybride associant le réacteur plasma aux catalyseurs dans deux configurations: le catalyseur au coeur de la décharge et le catalyseur en post-décharge. Les catalyseurs sont à base de Pd, Mn, Cu, et Co supportés sur des billes de Al2O3. Ils ont été caractérisés par ICP-OES, TEM/EDX, XRD, XPS, et DRIFTS. L’efficacité de conversion des COV, la sélectivité en CO/CO2, ainsi que la nature et les concentrations des produits formés pour les trois molécules avec les trois systèmes ont été étudiées en fonction de la température du gaz, de l'énergie injectée, de la concentration des COV, de la taille du support, du type de métal et sa teneur, et de la vitesse volumique horaire. Dans tous les cas, l’activation des catalyseurs à basse température a été démontrée quand ces derniers sont couplés au plasma et les principaux produits de réaction identifiés et quantifiés par spectroscopie infrarouge à transformée de Fourier. Le couplage plasma-catalyseur améliore de façon significative l’efficacité de conversion du méthane, du propène, et du toluène dans l’air ainsi que la sélectivité en sous-produits. L'effet de synergie entre le plasma et les catalyseurs pour la conversion des COV a été démontré dès lors que le plasma est généré directement au sein du réacteur catalytiqueThe focus of this thesis is the application of non-thermal plasma and catalysis in chemical processing, in particular for the removal of Volatile Organic Compounds (VOC) diluted in air. In a first part, the oxidation of three pollutants (methane, propene, and toluene) is studied experimentally in a pulsed dielectric barrier discharge (DBD) reactor and in a catalyst reactor working independently. In a second part, a hybrid plasma-catalyst reactor either in a single-stage or in a two-stages configuration, in which the catalyst is located inside or downstream from the plasma reactor, respectively. Catalyst materials based on Pd, Mn, Cu, and Co supported on alumina beads were tested and characterized by ICP-OES, TEM/EDX, XRD, XPS, and DRIFTS. Products were analyzed and quantified by infrared spectroscopy. Achieved VOCs removal efficiencies and CO/CO2 selectivity, as well as nature and concentrations of the formed products, were evaluated as function of many factors, particularly the specific input energy, the gas temperature, the initial VOCs concentration, the nature of catalyst (size support, metal loading), and the hourly space velocity. It has been successfully demonstrated that the combination of plasma and catalyst in the both configurations has many benefits compared to traditional thermal-catalysis and plasma alone treatment including a lowering of the catalyst operating temperature, an improvement of the conversion of VOCs at similar temperatures, and a better end-products selectivity and energy efficiency. The mutual interaction lead to a synergistic effect in plasma-catalysis especially when the discharge is in direct contact with the catalyst whatever the VOCs studied
26
Balakrishnan, Nianthrini. "Theoretical Studies of Co Based Catalysts on CO Hydrogenation and Oxidation". Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4434.
Pełny tekst źródłaStreszczenie:
CO hydrogenation and CO oxidation are two important processes addressing the energy and environmental issues of great interest. Both processes are carried out using metallic catalysts. The objective of this dissertation is to study the catalytic processes that govern these two reactions from a molecular perspective using quantum mechanical calculations. Density Functional Theory (DFT) has proven to be a valuable tool to study adsorption, dissociation, chain growth, reaction pathways etc., on well-defined surfaces. DFT was used to study the CO reduction reactions on promoted cobalt catalyst surfaces and CO oxidation mechanisms on cobalt surfaces.
CO hydrogenation via Fischer-Tropsch Synthesis (FTS) is a process used to produce liquid fuels from synthesis gas. The economics of the Fischer-Tropsch process strongly depends on the performance of the catalyst used. The desired properties of a catalyst include selectivity towards middle distillate products such as diesel and jet fuel, higher activity and longer catalyst life. Catalysts are often modified by adding promoters to obtain these desirable properties. Promoters can influence the reaction pathways, reducibility, dispersion, activity and selectivity. In FTS, understanding the effect of promoters in the molecular scale would help in tailoring catalysts with higher activity and desired selectivity. Preventing deactivation of catalyst is important in FTS to increase the catalyst life. Deactivation of Co catalyst can occur by reoxidation, C deposition, sintering, formation of cobalt-support compounds etc. Designing catalyst with resistance to deactivation by the use of promoters is explored in this dissertation. The influence of promoters on the initiation pathways of CO hydrogenation is also explored as a first step towards determining the selectivity of promoted catalyst.
The influence of Pt promoter on O removal from the surface of Co catalyst showed that Pt promoter reduced the activation barrier for the removal of O on both flat and stepped Co surfaces. An approximate kinetic model was developed and a volcano plot was established. The turn-over frequency (TOF) calculated based on the activation barriers showed that Pt promoted Co surface had a higher rate than unpromoted Co surface. The effect of Pt and Ru promoters on various pathways of C deposition on Co catalyst was studied to gain a mechanistic understanding. The promoters did not affect the subsurface C formation but they increased the barriers for C-C and C-C-C formation and also decreased the barriers for C-H formation. The promoters also influence the stabilities of C compounds on the Co surface suggesting that Pt and Ru promoters would decrease C deposition on Co catalysts. The effect of Pt promoter on unassisted and H-assisted CO activation pathways on Co catalyst was studied. Pt promoted Co surface followed H-assisted CO activation. Pt promoter decreased the activation barriers for CO activation pathways on Co catalyst thereby increasing the activity of Co catalyst.
CO oxidation is a process used to prevent poisoning of fuel cell catalysts and reduce pollution of the atmosphere through exhaust gases containing CO. Expensive catalysts like Pt are widely used for CO oxidation which significantly increases the cost of the process and hence it is necessary to search for alternative lower cost catalysts. Understanding the mechanism of a reaction is the first step towards designing better and efficient catalyst. DFT is helpful in determining the basic mechanism and intermediates of reactions.
The mechanism of CO oxidation on CoO catalyst was explored. Four possible mechanisms for CO oxidation on CoO catalyst were studied to determine the most likely mechanism. The mechanism was found to be a two-step process with activation barrier for formation of CO2 larger than the barrier for formation of the intermediate species.
27
Moore, Marlene L. "A kinetic study of CO oxidation over a heterogenized wacker catalyst system". Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/11020.
Pełny tekst źródła
28
Iachella, Mathilde. "Nucléation, Croissance et Morphologie de Nanoparticules d'Or et d'Or-Cuivre sur Support Rutile par la Théorie de la Fonctionnelle de la Densité". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEN034/document.
Pełny tekst źródłaStreszczenie:
Dans cette étude, la nucléation, la croissance, la morphologie et la réactivité de nanoparticules Au, Cu et AuCu sont examinées sur support rutile TiO2 (110) stoechiométrique, réduit et hydraté. En premier lieu, la nucléation a été modélisée via l’adsorption et la diffusion d’atomes Au et Cu, à l’aide de calculs de type théorie de la fonctionnelle de la densité (DFT), et de diagrammes d’énergie libre en condition réaliste.Les résultats DFT+U ont montré le rôle promoteur des espèces hydroxyles en surface sur la nucléation, en accord avec les mesures expérimentales de microscopie STM. Ensuite, les propriétés thermodynamiques de croissance et de coalescence de clusters Au et Cu (de 1 à 38 atomes) ont été étudiées par une approche systématique qui a déterminé précisément la stabilité relative d’un grand nombre de structures, tout en soulignant la différence de compétition nucléation/croissance entre les deux métaux. Pour des tailles de particules comprises entre 38 et 201 atomes, et des morphologies variées, la stabilité absolue d’agrégats purs Au et Cu et de nanoalliages AuCu a été évaluée à l’aide de calculs d’énergie de surface. Cette approche a révélé l’existence de relations linéaires entre composition chimique et stabilité. Enfin, la réactivité de nanoparticules Au, Cu et AuCu a été examinée suivant deux aspects : le dépôt de clusters de 38 atomes sur support rutile stoechiométrique, et l’adsorption du monoxyde de carbone à l’interface entre le métal et le support.Cette adsorption est une étape clé pour la réaction d’oxydation du CO ; un procédé important en catalyse hétérogèneIn this study, the nucleation, growth, morphology and reactivity of Au, Cu and AuCu nanoparticles have been examined on rutile TiO2 (110) stoiciometric, reduced and hydrated supports. First, the nucleation has been modeled via the adsorption and diffusion of Au and Cu atoms, thanks to density functional theory (DFT) calculations, and free energy diagrams in realistic conditions. DFT+U results have shown the promotor role of surface hydroxyl species on the nucleation, in agreement with STM experimental measurements.Then, the growth and coalescence thermodynamic properties for Au and Cu clusters (from 1 to 38 atoms) have been investigated with a systematic approach which has determinated precisely the relative stability for a large number of structures, and has underlined the difference for the competition between nucleation and growth between the two metals. For particles in the range 38-201 atoms and varied morphologies, the absolute stability of Au and Cu aggregates and AuCu nanoalloys has been evaluated through surface energy calculations. This approach has revealed the existence of linear relations between the chemical composition and the stability.Finally, the reactivity of Au, Cu and AuCu nanoparticles has been examined following two aspects : the deposition of 38 atoms clustered on the stoichiometric rutile support, and the adsorption of carbon monoxide at the interface between the metal and the support. This adsorption is a key step for the CO oxidation reaction ; an important process in heterogeneous catalysis
29
Zhao, Yanyan. "Dinuclear Heterogeneous Catalysts on Metal Oxide Supports:". Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:109003.
Pełny tekst źródłaStreszczenie:
Thesis advisor: Dunwei WangAtomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single atom catalysts (SACs) and nanoparticles (NPs). The study of SACs has brought an attention of understanding the reaction mechanism at the molecular level. SACs is a promising field, however, there are still many challenges and opportunities in developing the next generation of catalysts. Catalysts featuring two atoms with well-defined structures as active sites are poorly studied. It is expected that this class of catalysts will show uniqueness in activity, selectivity, and stability. However, the difficulty in synthesizing such structures has been a critical challenge. I tackled this challenge by using a facile photochemical method to generate active metal centers consisting of two iridium metal atoms bridged by O ligands and bound to a support by stripping the ligands of the organometallic complex. My research also unveiled the structure of this dinuclear heterogeneous catalysts (DHCs) by integrating various characterization resources. Direct evidence unambiguously supporting the dinuclear nature of catalysts anchored on metal oxides is obtained by aberration-corrected scanning transmission electron microscopy. In addition, different binding modes have been achieved on two categories of metal oxides with distinguishable surface oxygen densities and interatomic distances of binding sites. Side-on bound DHCs was demonstrated on iron oxide and ceria where both Ir atoms are affixed to the surface with similar coordination environment. The binding sites on the OH-terminated surface of Fe2O3 and CeO2 anchor the catalysts to provide outstanding stability against detachment, diffusion and aggregation. The competing end-on binding mode, where only one Ir atom is attached to the substrate and the other one is dangling was observed on WO3. Evidence supporting the binding modes was obtained by in situ diffuse reflectance infrared Fourier transform spectroscopy. In addition, the synergistic effect between two adjacent Ir atoms and the uniqueness of different coordinative oxygen atoms around Ir atoms were investigated by a series of operando spectroscopy such as X-ray absorption spectroscopy and microscopy at atomic level under the reaction condition. The resulting catalysts exhibit high activities and stabilities toward H2O photo-oxidation and preferential CO oxidation. Density functional theory calculations provide additional support for atomic structure, binding sites modes on metal oxides, as well as insights into how DHCs may be beneficial for these catalytic reactions. This research has important implications for future studies of highly effective heterogeneous catalysts for complex chemical reactions
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
30
Doory, Layla Kim. "Development of catalytic reactor designs for enhanced CO oxidation". Thesis, University College London (University of London), 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282799.
Pełny tekst źródła
31
Iablokov, Viacheslav. "Manganese and cobalt oxides as highly active catalysts for CO oxidation". Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209847.
Pełny tekst źródłaStreszczenie:
Durant ce travail de thèse, d’importants paramètres concernant la synthèse de matériaux catalytiques nanostructurés à base de manganèse et d’oxydes de cobalt ont été établis. La corrélation entre les propriétés structurales du catalyseur et l’activité catalytique, ainsi que le mécanisme d’oxydation du CO ont été analysé au moyen d’une grande variété de méthodes expérimentales physico-chimiques.De l’oxyde de manganèse non-stœchiométrique (MnOx) a été préparé par décomposition spinodale d’oxalate de manganèse trihydraté en ayant recours à la technique d’oxydation programmée en température (TPO). Tant l’analyse quantitative relatives à ces données TPO que les résultats obtenus par spectroscopie de structure au front d’absorption des rayons X (XANES), ainsi que par spectroscopie des photoélectrons X (XPS) ont permis d’estimer la stœchiométrie de l’oxyde avec un x situé entre 1.61 et 1.67. En accord avec à la fois la surface spécifique élevée et la combinaison d’isothermes d’adsorption/désorption de type I et IV, la microscopie électronique à transmission à haute résolution (HRTEM) démontre la présence de micro-bâtonnets caractéristiques et « imbriqués » les uns dans les autres, accompagné de particules nanocristalline à l’extrémité de ces bâtonnets.
Les découvertes faites par spectroscopie infra-rouge de réflexion diffuse par transformée de Fourier (DRIFTS), par études isotopiques et cinétiques suggère que l’adsorption des deux molécules, CO et O2, est suivie par leur réaction en surface via des intermédiaires de type carbonate/formate, pour finalement produire du CO2. Nous supposons un mécanisme de type Mars-van Krevelen où l’oxygène appartenant à la structure de type MnOx prend part dans l’oxydation catalytique du CO à basse température. Cependant, ces espèces mobiles d’oxygènes ne faisaient pas partie du cœur de phase du réseau d’oxyde, et de ce fait, ont été capables de « sauter » sur la surface et approvisionner les espèces oxygénées nécessaires à l’oxydation du CO déjà adsorbé.
Une structure spinelle d’oxyde de cobalt Co3O4 dans lequel le cobalt présente deux états de valence (+2 et +3) a été choisie pour élucider l’effet de la taille des particules sur l’activité lors de la réaction d’oxydation du CO. Tout d’abord, des nanoparticules monodispersées de cobalt métallique présentant une déviation standard en taille inférieure à 8% ont été synthétisées à partir de carbonyle de cobalt (Co2(CO)8) par une méthode optimisée «d’injection chaude». Un contrôle de la taille des nanoparticules dans la gamme 3 à 11 nm a pu être obtenu en variant la température d’injection du carbonyle de cobalt dans une solution de dichlorobenzène et d’acide oléique. La microscopie électronique à transmission (TEM) nous montre que ces particules de cobalt sont quasiment hémisphériques. Ensuite, de la silice poreuse (de type MCF-17) a été imprégnée par des nanoparticules de cobalt, et ensuite activée par TPO menant à des nanoparticules d’oxyde de cobalt. Des études par diffraction des rayons X (XRD) et spectroscopie des photoélectrons X (XPS) ont démontré la structure spinelle Co3O4. Finalement, l’activité des catalyseurs obtenus vis-à-vis de l’oxydation du monoxyde de carbone fut mesurée à 423 K et ce en fonction de la taille des particules. Les particules de Co3O4 présentant une taille allant de 5 à 8 nm se sont révélées les plus actives. Ceci peut s’expliquer par une plus grande mobilité des atomes d’oxygène en surface des nanoparticules d’oxyde de cobalt.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
32
Hodge, N. A. "A study of supported Au catalysts for low temperature CO oxidation". Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399136.
Pełny tekst źródła
33
Janák, Marcel. "Diagnostika polovodičů a monitorování chemických reakcí metodou SIMS". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443241.
Pełny tekst źródłaStreszczenie:
Hmotnostná spektrometria sekundárnych iónov s analýzou doby letu (TOF-SIMS) patrí vďaka vysokej citlivosti na prvkové zloženie medzi významné metódy analýzy pevných povrchov. Táto práca demonštruje možnosti TOF-SIMS v troch odlišných oblastiach výskumu. Prvá časť práce sa zaoberá lokalizáciou defektov vysokonapäťových polovodičových súčiastok, ktorá je nevyhnutná k ich ďalšiemu skúmaniu metódou TOF-SIMS. Bola navrhnutá experimentálna zostava s riadiacim softvérom umožňujúca automatizované meranie záverného prúdu v rôznych miestach polovodičový súčiastok. Druhá časť práce sa zaoberá kvantifikáciou koncentrácie Mg dopantov v rôznych hĺbkach vzoriek AlGaN. Kvantifikácia je založená na metóde RSF a umožňuje charakterizáciu AlGaN heteroštruktúr určených na výrobu tranzistorov s vysokou elektrónovou mobilitou (HEMT) alebo na výrobu rôznych optoelektronických zariadení. Sada 12 AlGaN kalibračných vzoriek dopovaných Mg, určených na kvantifikáciu hĺbkových profilov, bola pripravená metódou iónovej implantácie. Posledná časť práce demonštruje možnosti metódy TOF-SIMS vo výskume heterogénnej katalýzy. Hlavným objektom nášho výskumu je dynamika oxidácie CO na oxid uhličitý na polykryštalickom povrchu platiny za tlakov vysokého vákua. V tejto práci prezentujem prvé TOF-SIMS pozorovanie časopriestorových vzorov v reálnom čase, ktoré vznikajú v dôsledku rôzneho pokrytia povrchu Pt reaktantmi. Výsledky TOF-SIMS experimentu boli porovnané s výsledkami podobného experiment v rastrovacom elektrónovom mikroskope (SEM).
34
Mankidy, Bijith D. "Design of Colloidal Composite Catalysts for CO2 Photoreduction and for CO Oxidation". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4364.
Pełny tekst źródłaStreszczenie:
In this doctoral dissertation, novel colloidal routes were used to synthesize nanomaterials with unique features. We have studied the impact of nanoparticle size of catalyst, role of high surface area of a photocatalyst, and the effect of varying elemental composition of co-catalytic nanoparticles in combination with core-shell plasmonic nanoparticles. We have demonstrated how physical and chemical characteristics of nanomaterials with these unique features play a role in catalytic reactions, specifically the oxidation of CO and the photoreduction of CO2. The first objective of this doctoral dissertation involved the preparation of CoO nanoparticles with discrete nanoparticles sizes (1-14 nm) using a colloidal thermal decomposition technique. The impact of size of CoO for CO oxidation reaction was studied using an in-situ FTIR reactor. By analyzing the reaction intermediates observed using in-situ IR, a two-step reaction mechanism was proposed. The average values of activation energies of step-1 and step-2 were ∼15 kJ/mol and ∼90 kJ/mol that showed step-2 was the rate determining step. From activation energy calculations for the catalysts of different CoO sizes, it was found that activation energy increased as nanoparticle size increased. The second objective of this doctoral research involved the development of high surface area TiO2 nanoshells using polymeric templates. The deposition of TiO2 was achieved by surface functionalization procedures. TiO2 was then deposited on colloidal SiO2 after the SiO2 surface was modified by grafting poly(NIPAAM) oligomers. TiO2 nanoshell composites possessed high surface of ∼35 m2/gm. The photocatalytic performances of TiO2 nanoshells and Pt deposited TiO2 nanoshells were evaluated for CO2 photoreduction reaction. Primary products from CO2 photoreduction reactions were carbon monoxide and methane. The product yield and product selectivity of hydrocarbons produced during CO2 photoreduction was measured using a home-built FTIR reactor. When Pt was deposited on TiO2 nanoshells, the overall yield was nearly doubled and the CH4 selectivity nearly quadrupled. The third objective pursued in this research project was to synthesize Ag, Pt and bimetallic Ag-Pt nanoparticles to demonstrate the role of elemental composition of metal co-catalysts for CO2 photoreduction reaction. The novel bimetallic nanoparticles played an important role in improving product selectivity in the photocatalytic reduction of CO2. Bimetallic Ag-Pt nanoparticles synthesized with low Pt content had 4-5 times higher CH4 selectivity compared to native TiO2. The final objective was to prepare Ag(core)/SiO2(shell) nanoparticles with specific core-shell structure to enhance photoactivity of TiO2 during catalytic reactions. Ag@SiO2 core-shell nanoparticles have plasmonic character that helped to improve product yield by increasing the number of electron-hole pair generations. When bimetallic Ag-Pt nanoparticles were used in combination with core-shell Ag@SiO2 plasmonic nanoparticles, the overall yield increased ∼8-fold compared to native TiO2.
35
Davó-Quiñonero, Arantxa. "Copper-based catalysts for the Preferential Oxidation of CO in H2-rich streams (CO-PROX reaction)". Doctoral thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10045/98737.
Pełny tekst źródłaStreszczenie:
The Preferential CO Oxidation (CO-PROX) is a promising catalytic strategy to remove CO residual content from H2-rich streams. Mixed copper and cerium oxide catalysts are materials that display an excellent performance towards COPROX reaction by means of synergistic interaction the copper and cerium-rich phases. Alternatively, mixed manganese oxides are proposed as active supports with very positive catalytic features when these are loaded with copper species. This Project Thesis comprises a detailed study on the implementation of copper oxide – manganese oxide catalysts in CO-PROX reaction and the establishment of a critical comparison with regards to the consolidated cerium-based catalysts.
36
Euesden, Claire. "Comparison of sol-gel prepared catalysts for CO oxidation and N2O decomposition reactions". Thesis, University of Surrey, 2002. http://epubs.surrey.ac.uk/813159/.
Pełny tekst źródłaStreszczenie:
This thesis comprises analysis for two types of catalysis: CO oxidation and N2O decomposition; related by their research in sol-gel catalysis. The CO oxidation work was undertaken on behalf of Servomex plc in order to understand how their catalyst-based sensor (Tfx 1750) worked and why it failed when exposed to coal power station flue streams within its two-year guarantee period. This research will show, by means of many analytical techniques and catalytic tests: 1. A comparison of the Servomex catalyst powder and a sol-gel prepared material containing the same components: 10 % Pt on 10 % Zr02 doped Al2O3. 2. The mechanism of CO oxidation observed on the surface of these catalysts. 3. What effect sulphur oxides (SO2 and SO3) have on both catalysts, and the mechanisms that give rise to S build up on their surfaces. In contrast, the catalysed N2O decomposition research was sponsored by Dytech in order to determine which metal oxides and multimetal oxide systems are suitable for N2O decomposition in satellite propulsion systems. This research will allow: 1. A comparison of a wide range of metal oxide systems during thermal treatment in an N2O atmosphere. 2. Further analysis into the best systems with respect to their suitability as catalysts; such as selectivity, activation temperatures, longevity and reliability. 3. A comparison of different preparation techniques; precipitation and sol-gel, by using various analytical techniques and catalytic testing. 4. A comparison of the in-house rig system designed for the comparison of catalysts by thermal treatment, and a rig system built by the Surrey Space Group as a realistic comparison for actual satellite propulsion systems. This comparison will justify the results shown in part (1).
37
Al-Sayari, Saleh Abdullah. "Synthesis of active supported gold catalysts for CO oxidation and light alkane activation". Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/56051/.
Pełny tekst źródłaStreszczenie:
The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine important factors, such as selection of support material and preparation method, and preparation parameters, such as preparation temperature, pH, and ageing process. These factors control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. The two preparation methods differ in the manner in which the pH is controlled during coprecipitation, either constant pH throughout or variable pH in which the pH is raised from an initial low value to a defined end point. Non- calcined Au/ZnO catalysts prepared using both methods are very sensitive to pH and ageing time. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short indication period during which the oxidation activity increases. In contrast, the calcined catalysts are not sensitive to preparation conditions. Non-calcined Au/Fe203 catalysts exhibit high activity when prepared at pH > 5. Active calcined Au/Fe2O3 catalysts can be prepared when the pH is controlled at pH 6-7, 8, whereas calcined catalysts prepared using the variable pH method are inactive. The study demonstrates the immense sensitivity of catalyst preparation methods on the performance. Catalysts exhibited excellent catalytic activity and stability compared with the pure supports, ZnO and Fe2O3, and the best preparation temperature was 80 C. Use of temperatures > 80 C led to inactive catalysts. The deposition-precipitation (DP) method was also employed using four different supports in this study (ZnO, Fe2O3, MgO, and MnO2). A comparison between these catalysts was taken rather than an investigation of the effect of the preparation parameters on catalysts prepared by DP method because they have been well studied previously. Several characterization techniques including AAS, BET surface area, XRD, TPR, and XPS, were utilised to investigate the physical and chemical properties of the prepared supported gold catalysts. Characterization results were combined with catalytic results for the low temperature CO oxidation reaction of catalysts in order to study the aforementioned factors that can affect either the properties of catalysts or their activities. Subsequently, several experiments at high GHSV were conducted to study the catalytic activities of these catalysts in-depth and to correlate data with alkane activation reactions. CH4 activation reaction using supported gold catalysts at light temperatures and the effect of the preparation parameters, types of supports on catalysts activities were investigated. The Au/Fe2O3 catalyst prepared by coprecipitation method B at pH 8 showed the highest catalytic activity for CO oxidation and CH4 activation reactions. The most active catalysts were also evaluated for C2H6 and C3H8 activation at low temperature. After this, a comparison between CO oxidation and alkane activation over supported gold catalysts was undertaken to investigate the relationship between the behaviour of supported gold catalysts for these two types of reactions. Activation energies and pre-exponential factors of many catalysts were calculated based on the Arrhenius equation either for CO oxidation or for alkane activation. The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine the important factors that control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. (Abstract shortened by UMI.)
38
Ngameni, Emmanuel. "Comportement électrochimique de biporphyrines adsorbées ou en solutions aqueuses acides : Etude du pouvoir catalytique de la biporphyrine de cobalt, CO::(2) FTF4, à l'égard de la réduction de l'oxygène". Brest, 1988. http://www.theses.fr/1988BRES2021.
Pełny tekst źródła
39
Aoyama, Yoshimasa. "Hybridization of 4d Metal Nanoparticles with Metal-Organic Framework and the Investigation of the Catalytic Property". Kyoto University, 2020. http://hdl.handle.net/2433/254504.
Pełny tekst źródła
40
Cerasari, Stefano. "Kinetic and nonlinear effects associated with the catalytic CO oxidation on Pt surfaces". [S.l. : s.n.], 2000. http://www.diss.fu-berlin.de/2000/61/index.html.
Pełny tekst źródła
41
Zell, Elizabeth Theresa. "Synthesis and Support Shape Effects on the Catalytic Activities of CuOx/CeO2 Nanomaterials". Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1525699148756394.
Pełny tekst źródła
42
Petrolekas, Panagiotis. "Solid electrolyte potentiometric study of La(Sr)MnOâ†3 catalyst during CO oxidation". Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264135.
Pełny tekst źródła
43
Berends, Hans-Martin [Verfasser]. "Manganese compounds as catalysts for water oxidation and as CO releasing molecules / Hans-Martin Berends". Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/1020244836/34.
Pełny tekst źródła
44
Yang, Kai-Yu, i 楊鎧輿. "Synergistic catalysis of reversed micelles-synthesized Cu/samaria-doped ceria catalyst in selective CO oxidation". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/04620927597093590816.
Pełny tekst źródłaStreszczenie:
碩士義守大學
生物技術與化學工程研究所碩士班
99
Copper oxide impregnated on samaria-doped ceria (SDC) prepared by reverse microemulsion was empolyed as catalyst for the selective CO oxidation in a hydrogen-rich environment. Activity tests, as well as H2-temperature programmed reduction (H2-TPR), were carried out to investigate the behavior of the catalysts thus prepared, and compared with those made by co-precipitation. It has been found that the best performance can be obtained with 2 mol% of Sm doping. Activity results showed that for Cu/2SDC, CO oxidation picked up considerably at 60℃ and reached almost 100% conversion at 100℃ due to higher reactivity of CO toward interfacial oxygen ions, while at the latter temperature the hydrogen consumption increased to some extent, which related well with the occurrence of α peak temperature in H2-TPR. In addition, the competitive oxidation of CO and H2 were carried out at 120℃, showing that CO exhibits a higher oxidation activity and the active sites of the catalyst are apt to be occupied by CO thus limiting the accessibility of hydrogen to oxygen. These results demonstrate that the catalysts studied in this work exhibit superior selectivity in CO oxidation in rich hydrogen, without appreciable hydrogen consumption at 150℃.
45
Mokoena, Lebohang Vivacious. "Effect of gold nanoparticles on the activity of perovskites for CO oxidation". Thesis, 2011. http://hdl.handle.net/10539/10809.
Pełny tekst źródłaStreszczenie:
MSc., Faculty of Science, University of the Witwatersrand, 2011Gold has for many years been regarded as being inert and catalytically inactive compared to the PGMs (platinum group metals). However, in the past decade it has attracted a lot of interest as both a heterogeneous and a homogenous catalyst and has been shown to catalyse a wide range of reactions e.g. oxidation, hydrogenation and reduction among others. Highly dispersed gold nanoparticles on metal oxides, like titanium oxide (Degussa, P25) have predominantly been studied because they yield some of the most active and stable catalysts. Modification of the catalysts and/or supports has been shown to affect their catalytic properties. Likewise, perovskites, which can be manipulated by partial substitution, are reported to be active supports for CO oxidation, but only at high temperatures with no activity shown for temperatures below 200°C. In this study, these perovskites were investigated at low temperatures (below 100°C) with improved activity found upon gold deposition. The presence of gold nanoparticles therefore significantly enhanced the catalytic activity, while the support itself was suspected to be involved in the reaction mechanism. A series of perovskites of the type ABO3 (LaMnO3, LaFeO3, LaCoO3 and LaCuO3) were prepared using the citrate method, while the gold was deposited on them using the deposition-precipitation method. The supports were calcined at different temperatures for optimisation. The catalysts were tested for carbon monoxide oxidation and the active catalysts characterised by XRF, XPS, XRD, Raman spectroscopy and BET surface area measurements. With the support calcined at 800ºC, the best catalyst was then modified and compared with the unmodified catalyst. The 1-wt%Au supported on LaFeO3 was found to give the best catalytic performance. This support was then modified with various weight loadings of calcium to determine the effect of calcium on the catalytic activity. Calcium-doped materials showed decreased surface area, poorer crystallinity and a drop in catalytic activity relative to the Au-LaFeO3 which indicated the best results for CO oxidation. In addition, Au-LaFeO3 showed online stability over 21 hours. Calcining the support improved the incorporation of gold nanoparticles into the perovskite lattice, resulting in superior catalytic activity. Nevertheless, at higher calcination temperatures, the catalytic activity of Au-CaTiO3 was depressed while that of Au-LaFeO3 was enhanced. The activity of perovskites increased upon gold deposition. XPS, revealed that in the active catalysts, both cationic and metallic gold co-existed, whilst in the inactive catalysts the gold existed predominantly either as cationic or metallic gold.
46
Pineda, Rodriguez Miguel Arnaldo [Verfasser]. "Fluctuations in heterogeneous catalysis : CO oxidation as a case study / von Miguel Arnaldo Pineda Rodriguez". 2008. http://d-nb.info/989034631/34.
Pełny tekst źródła
47
"Development and Application of Operando TEM to a Ruthenium Catalyst for CO Oxidation". Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.38801.
Pełny tekst źródłaStreszczenie:
abstract: Operando transmission electron microscopy (TEM) is an extension of in-situ TEM in which the performance of the material being observed is measured simultaneously. This is of great value, since structure-performance relationships lie at the heart of materials science. For catalyst materials, like the SiO2-supported Ru nanoparticles studied, the important performance metric, catalyst activity, is measured inside the microscope by determining the gas composition during imaging. This is accomplished by acquisition of electron energy loss spectra (EELS) of the gas in the environmental TEM while catalysis is taking place. In this work, automated methods for rapidly quantifying low-loss and core-loss EELS of gases were developed. A new sample preparation method was also established to increase catalytic conversion inside a differentially-pumped environmental TEM, and the maximum CO conversion observed was about 80%. A system for mixing gases and delivering them to the environmental TEM was designed and built, and a method for locating and imaging nanoparticles in zone axis orientations while minimizing electron dose rate was determined.
After atomic resolution images of Ru nanoparticles observed during CO oxidation were obtained, the shape and surface structures of these particles was investigated. A Wulff model structure for Ru particles was compared to experimental images both by manually rotating the model, and by automatically determining a matching orientation using cross-correlation of shape signatures. From this analysis, it was determined that most Ru particles are close to Wulff-shaped during CO oxidation. While thick oxide layers were not observed to form on Ru during CO oxidation, thin RuO2 layers on the surface of Ru nanoparticles were imaged with atomic resolution for the first time. The activity of these layers is discussed in the context of the literature on the subject, which has thus far been inconclusive. We conclude that disordered oxidized ruthenium, rather than crystalline RuO2 is the most active species.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2016
48
Chiang, Chia-Wen, i 江嘉雯. "Preparation of Gold nanoparticles on Modified SBA-15 Mesoporous Thin Film and Catalysis Research for CO Oxidation". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/26470897129269810546.
Pełny tekst źródła
49
Cai, Yun. "In Situ Polarization Modulation Infrared Reflection Absorption Spectroscopic and Kinetic Investigations of Heterogeneous Catalytic Reactions". 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2008-12-162.
Pełny tekst źródłaStreszczenie:
A molecular-level understanding of a heterogeneous catalytic reaction is the key
goal of heterogeneous catalysis. A surface science approach enables the realization of
this goal. However, the working conditions (ultrahigh vacuum (UHV) conditions) of
traditional surface science techniques restrict the investigations of heterogeneous
catalysis system under industrial working conditions (atmospheric pressures).
Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRAS) can
be operated in both UHV and atmospheric pressure conditions with a wide temperature
span while providing high resolution (4 cm-1 is used in this dissertation) spectra. In this
dissertation, PM-IRAS has been employed as a major technique to: 1) obtain both
electronic and chemical information of catalysts from UHV to elevated pressure
conditions; 2) explore reaction mechanisms by in situ monitoring surface species with
concurrent kinetic measurements.
In this dissertation, NO adsorption and dissociation on Rh(111) have been
studied. Our PM-IRAS spectra show a transition of NO adsorption on three-fold hollow
sites to atop sites occurs at low temperatures (<275 K). NO dissociation is found to account for this transition. The results indicated the dissociation of NO occurs well
below the temperature previously reported.
Characterizations of highly catalytically active Au films have also been carried
out. Electronic and chemical properties of (1 x 1)- and (1 x 3)-Au/TiOx/Mo(112) films
are investigated by PM-IRAS using CO as a probe molecule. The Au overlayers are
found to be electron-rich and to have significantly different electronic properties
compared with bulk Au. The exceptionally high catalytic activity of the Au bilayer
structure is related to its unique electronic properties.
CO oxidation reactions on Rh, Pd, and Pt single crystals are explored from low
CO pressures under steady-state conditions (less than 1 x 10-4 Torr) to high pressures
(0.01-10 Torr) at various gaseous reactant compositions. Surface CO species are probed
with in situ PM-IRAS to elucidate the surface phases under reaction conditions. These
experimental results are used to correlate reaction kinetics and surface reactant species.
It is evident that there is a continuum over the pressure range studied with respect to the
reaction mechanism. The most active phase has been shown to be an oxygen-dominant
surface. The formation of a subsurface oxygen layer is found to deactivate the reaction.
50
Liao, Wei-ting, i 廖瑋婷. "Low Temperature CO oxidation over supported gold catalysts". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/48171907066060780252.
Pełny tekst źródłaStreszczenie:
碩士國立中央大學
化學工程與材料工程研究所
98
Massive gold was a stable and precious metal; it is not an active catalyst. In nanosize scale,the nano-gold supported on the metal oxide could oxidize CO at low temperature and produced carbon dioxide. CO was a toxic, colorless and tasteless gas; it is produced by the fuel without complete oxidation. The most extensively studied reaction in the history of heterogeneous catalysis is becoming increasingly important in the context of cleaning air and lower automotive emissions. The reaction is important for environment protection. When gold is deposited as nanoparticles on metal oxides by impregnation, co-precipitation and deposition-precipitation (DP) techniques, it exhibits surprisingly high catalytic activity for CO oxidation at a temperature as low as 200 K. The activity of gold catalysts also depends on support, preparation method and condition. The promoters were added in Au/TiO2 to change the support properties, including electronic effect and geometric effect. In this study, the effects of promoter such as Cu and Co were investigated. The support was prepared by incipient-wetness impregnation with aqueous solution of nitrate salt. TiO2 was supplied by Evonik-Degussa Company (P-25). A series of Au catalysts was prepared by deposition-precipitation (DP) method and the pH value was 7. The catalysts were characterized by inductively-coupled plasma-mass spectrometry (ICP-MS), temperature programming reduction (TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The reaction was carried out in a fixed bed reactor with a feed containing 1% CO in air at WHSV=120,000 ml/h g and WHSV=180,000 ml/h g. High gold dispersion and narrow size distribution was obtained by DP method. Two different promoters were added in Au/TiO2, which were also enhanced the activity on CO oxidation. Cu and Co have different promotive effect. Au/5% CuOx-TiO2 was the best catalyst in a series of Au/CuOx-TiO2 and the Au/3% CoOx-TiO2 was the best catalysts in a series of Au/CoOx-TiO2. Au/3% CoOx-TiO2 had better stability than Au/5% CuOx-TiO2 catalyst. In this study, we have successfully prepared the catalysts at suitable content with very high activity on CO oxidation.