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Dhanasekaran, Venkatesan. "Oxide supported Au-Pd nanoparticles for CO oxidation reaction." Thesis, Sorbonne Paris Cité, 2017. https://theses.md.univ-paris-diderot.fr/DHANASEKARAN_Venkatesan_1_va_20170629.pdf.
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Les nanoparticules (NPs) bimétalliques Au-Pd ont été étudiées pour leur activité catalytique dans la réaction d'oxydation du CO. La technique de préparation, la taille et la composition des nanoparticules ont un grand impact sur le comportement catalytique du système. Ici, des nanoparticules de 3 et 5nm de diamètre Au1-xPdx (x = 0, 0.25, 0.5, 0.75, 1) ont été utilisées pour étudier l'effet de la taille et de la composition. Les échantillons ont été synthétisés par nano-lithographie à base de micelles, technique bien adaptée pour obtenir des particules ayant une distribution en taille étroite. Afin d’obtenir une répartition homogène des micelles chargées en ions métalliques sur des substrats de SiO2/Si(001), nous avons eu recours à la méthode de « spin-coating » et obtenu une organisation quasi-hexagonales des micelles observable en SEM. Un plasma d'oxygène ou d'hydrogène a été utilisé pour éliminer le polymère, réduire les ions métalliques et permettre la formation de nanoparticules. Nous avons entrepris une approche systématique pour étudier l'effet du plasma sur la structure et la morphologie des NPs à l'aide des techniques de diffusion des rayons X. L'oxydation et l'activité catalytique des NPs Au1-xPdx pour l'oxydation du CO ont été étudiées à 300 °C et 0.5 bar dans le réacteur à flux XCAT disponible sur la ligne de lumière SixS du Synchrotron SOLEIL, France. Les mesures de l'activité d'oxydation du CO ont montré que les NPs préparées en utilisant le plasma d'oxygène présentent un taux de conversion en CO2 plus élevé que les NPs préparées à l'aide de plasma d'hydrogène pour une composition donnée. Les nanoparticules de Pd préparées avec du plasma d'O2 se sont révélées être le catalyseur le plus actif : aucun effet synergique n'a été observé pour les nanoparticules bimétalliques pour la réaction d'oxydation du COAu-Pd bimetallic nanoparticles (NPs) have been studied for their catalytic activity in CO oxidation reaction. The preparation technique, size and composition of the nanoparticles have great impact on the catalytic behaviour of the system. Here, 3 and 5nm diameter Au1-xPdx (x = 0, 0.25, 0.5, 0.75, 1) nanoparticles were employed to study the effect of size and composition. The samples were synthesized by micelle nanolithography, a technique well adapted to yield narrow size distribution of nanoparticles. To achieve monodisperse metal-loaded micelles on SiO2/Si(001) substrates we employed spin-coating and observe quasi-hexagonal ordered micelles in SEM. Oxygen or hydrogen plasma were used to remove the polymer, reduce the metal ions and enable nanoparticle formation. We made a systematic approach to study the effect of plasma on the structure and morphology of the NPs by means of surface x-ray scattering techniques. The oxidation behavior and CO oxidation activity of the Au1-xPdx NPs were studied at 300°C and 0.5 bar in the flow reactor XCAT available at the SixS Beamline, Synchrotron SOLEIL, France. The CO oxidation activity measurements showed that the NPs prepared using the oxygen plasma present higher CO2 conversion rate than the NPs prepared using hydrogen plasma for a given composition. The Pd nanoparticles prepared using O2 plasma were found to be the most active catalyst: no synergetic effects were observed for bimetallic nanoparticles for the CO oxidation reaction
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Balakrishnan, Nianthrini. "Theoretical Studies of Co Based Catalysts on CO Hydrogenation and Oxidation." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4434.
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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.
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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.
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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.
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Kim, Sang Hoon. "Study of reaction mechanisms on single crystal surfaces with scanning tunneling microscopy." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2003. http://dx.doi.org/10.18452/14884.
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Ziel dieser Arbeit war, die Rastertunnelmikroskopie, die bereits zur Aufklärung von einfachen Reaktionsmechanismen eingesetzt wurde, für em kompliziertere Reaktionen anzuwenden. Die Oxidation von CO auf Pd(111) und auf einem RuO2-Film auf Ru(0001) wurde untersucht. Strukturelle Analysen ergeben mikroskopische Verteilungen der Adsorbate in den Überstrukturen von O und CO auf Pd(111) und RuO2. Dynamische und quantitative Analysen der Reaktionen liefern die Kinetik und die Mechanismen der Reaktionen direkt auf der mikroskopischen Ebene. O-Atome auf Pd(111) sind bei mittleren Bedeckungsgraden (0.10< theta mathrm O 135 K beweglich. Die Aktivierungsenergie der Diffusion (E * mathrm diff ) beträgt 0.54 pm 0.08 eV, der präexponentielle Faktor der Sprünge Gamma mathrm o beträgt 10 16 pm 3 s -1. Bei niedrigen Bedeckungen (theta mathrm CO sim 0) sind die CO-Moleküle auf Pd(111) schon bei T mathrm sample = 60 K sehr beweglich. Wenn man einen präexponentiellen Faktor von Gamma mathrm o = 10 13 s -1 annimmt, ergibt sich für E * mathrm diff von CO ein Wert von 0.15 eV. Adsorbiert CO auf der (2 times2) -O-Überstruktur bei T mathrm sample > 130 K, kommt es mit steigendem Bedeckungsgrad von CO zu Phasenübergängen, zunächst in eine ( sqrt 3 times Sqrt 3 ) R30 circ -O-Struktur, dann in eine (2 times1)-Struktur. Während der Phasenübergänge nimmt die Mobilität der O-Atome zu, was sich in einer Abnahme der E* mathrm diff um 10 bis 20 % (unter der Annahme von Gamma mathrm o = 10 16 s -1) im Vergleich zu einer CO-freien Oberfläche niederschlägt. Am Ende der Phasenübergänge entstehen aus einer fast völlig ungeordneten (O+CO)-Phase viele kleine (2 times1)-Inseln, die sich zu grösseren Inseln zusammenlegen. Die (2 times1)-Inseln sind bereits bei T mathrm sample = 136 K sehr reaktiv. Die quantitative Analyse der Abreaktion der (2 times1)-Inseln ergibt, dass die Reaktionsrate proportional zur Inselfläche und nicht zur Randlänge ist. Die Reaktionsordnung bezüglich theta mathrm(2 times1) ist sim 1. Unter der Annahme eines Vorfaktors k mathrm o von 10 13 s -1 wurde für diese Reaktion ein E* mathrm reac von 0.41 eV abgeschätzt. Für eine CO-Adsorption auf der (2 times2)-O-Überstruktur bei T mathrm sample < 130 K kommt es nicht zu einem Phasenübergang, sondern CO adsorbiert auf der (2 times2)-O-Struktur. Der RuO2-Film wurde bei Temperaturen zwischen 650 und 900 K auf der Ru(0001)-Probe aufgewachsen. Die Morphologie des Oxidfilms hängt stark von der Temperatur der Probe während des Wachstums Tprep ab. Bei Tprep sim 650 K ist die Morphologie überwiegend kinetisch bestimmt. Mit steigendener Temperatur bis Tprep = 900 K werden thermodynamische Effekte immer wichtiger. Die Dicke der Oxidschicht hängt nicht von Tprep ab und beträgt 7 AA bis 15 AA, was 2 bis 5 (Ru-O)-Monolagen entspricht. Die thermodynamische Stabilität der Morphologie ergibt sich aus Experimenten, in denen die Oxidschicht durch Heizen auf verschiedene Temperaturen partiell verdampft wurde. Der Film dampft nicht lageweise ab, sondern es entstehen Löcher in der ansonsten unverdampften Oxidschicht. Die Löcher haben eine charakteristische Form. Sie bilden Parallelogramme oder Rechtecke mit einer langen Achse in [001]-Richtung. Die Oberflächenenergie gamma 001 der einen Flanke der Löcher ist 2 bis 5 mal grösser als gamma bar110 der anderen Flanke. Beim Verdampfen des Films verbleiben die freigesetzten Ru-Atome des Oxids auf dem Substrat. Sie bilden dort eine komplizierte Morphologie von hexagonalen und runden Inseln. Die mikroskopischen Beobachtungen der chemischen Prozesse auf dem Film bestätigen die auf den makroskopischen Untersuchungen basierenden Modelle. Ein neuer Befund ist, dass die CO-Moleküle bei Raumtemperatur auf den Rulf -Reihen stabil adsorbieren, sobald die Ruzf -Reihen vollständig mit CO bedeckt sind. Der maximale Bedeckungsgrad theta mathrm CO1f ist 0.5, die COlf-Moleküle bilden lokal geordnete (2times1)-, c(2times2)- und (1times1)-Überstrukturen. Allerdings kommt es bei theta mathrm CO1f sim 0.5 zu einer langsamen Desorption. Wenn man ein k mathrm o von 10 16 s -1 annimmt, lässt sich ein E * mathrm des von 1.00 eV abschätzen. Unter der Annahme von Gamma mathrm o und k mathrm o von 10 13 s -1 lassen sich E* mathrm diff -Werte für O und CO zwischen 0.89 und 0.93 eV abschätzen, und für die Reaktion zwischen COlf und Olf ein Wert von E* mathrm reac sim 0.87 eV. Die Reaktionen zwischen Ozf und COlf, zwischen Olf und COzf sowie zwischen Olf und COlf verlaufen überwiegend statistisch. Manchmal wird eine leicht bevorzugte Reaktion quer zu den Rulf - und Ruzf -Reihen beobachtet. Unter steady-state-Bedingungen kann CO bei genügend grossem Partialdruck auf der Oberfläche adsorbieren. Unter steady-state-Bedingungen werden die gleichen COlf-Überstrukturen beobachtet wie in einer CO-Atmosphäre oder bei der Titration mit CO. Bei massiver Dosierung der Oxidoberfläche mit Oz und CO (sim 100 L) werden weisse Flecken beobachtet, die COlf ähnlich sind. Allerdings reagieren diese weder mit Oz noch mit CO, was auf einen anderen chemischen Zustand der RuO2-Oberfläche als den sauberen Zustand hinweist.Scanning Tunneling Microscopy has already been established as a tool for the investigation of simple reaction mechanisms. The aim of this thesis was to apply this technique to study emmore complicated reactions. The oxidation of CO on Pd(111) and on a RuO2 film grown on Ru(0001) was investigated. Structural analyses of the O, CO and (CO+O) adlayers on Pd(111) and on RuO2 reveal the microscopic distributions of the adsorbates on the surfaces. Dynamic and quantitative analyses of the reactions yield the reaction kinetics and the reaction mechanisms in a direct way at the microscopic level. O atoms on Pd(111) at intermediate coverages (0.10
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Siriwardane, Upali. "Systematic syntheses of iron-triad (Fe,Ru,Os) tetranuclear clusters by redox condensation reactions of [Ru(3);CO(11)) and [Os(3);CO(11)] trinuclear carbonylates; co-crystallization of ruthenium-osmium clusters /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487264603216477.
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Gottfried, Jörg Michael. "CO oxidation over gold adsorption and reaction of oxygen, carbon monoxide, and carbon dioxide on an Au(110)-(1x2) surface /." [S.l. : s.n.], 2003. http://www.diss.fu-berlin.de/2003/133/index.html.
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Freitas, Kênia da Silva. "Eletrocatalisadores de ligas de platina dispersos em substratos de óxidos para a reação de oxidação de hidrogênio puro e na presença de CO." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25082009-164210/.
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Neste trabalho são apresentados resultados dos estudos da reação de oxidação de hidrogênio puro realizados em eletrodos rotatório em camada ultrafina porosa e na presença de CO em células a combustível utilizando catalisadores formados por Pt dispersas em substratos de óxidos, tais como, Pt/RuO 2 -C, Pt/RhO 2 -C, Pt/WO 3 -C e em Pt/WC-C. As reações foram também estudadas em suporte puro, como, RhO 2 /C e WC/C em diferentes proporções atômicas. Este estudo teve como finalidade estudar as propriedades catalíticas destes materiais visando elucidar os mecanismos da reação de oxidação de hidrogênio (ROH) sobre estes catalisadores dispersos, possibilitando a obtenção de parâmetros cinéticos das reações. Em conjunto com as medidas eletroquímicas, foram realizados estudos sobre as propriedades eletrônicas e estruturais destes catalisadores, o que possibilita relacionar suas propriedades eletrônicas e estruturais com a cinética da HOR. Observou-se que a presença dos óxidos de Ru, Rh e WO 3 favorecem a diminuição do grau de recobrimento da Pt por CO, deixando mais sítios disponíveis a ROH, em consequência do esvaziamento da banda 5d da Pt, o que diminui a retro-doação de elétrons da Pt ao CO, diminuindo a força da ligação Pt-CO. Como observado, essas modificação eletrônicas observadas nos espectros de XANES não induziram a nenhuma mudança perceptível na cinética ou no mecanismo reacional. Para quase todos os catalisadores, a tolerância ao CO pode ser explicada tanto em termos do mecanismo eletrônico como do bifuncional evidenciado pela formação de CO 2 nas medidas de EMS.This work shows results of studies of the hydrogen oxidation reaction (HOR) pure in rotation in ultra porous layer and in the presence of CO in the fuel cell to the electrocatalysts of Pt alloy dispersed on oxide substrates such Pt/RuO 2 -C, Pt/RhO 2 -C, Pt/WO 3 -C, Pt/WC-C and pure materials, as RhO 2 /C and WC. The study of the catalytic properties of these materials to elucidate the mechanisms of hydrogen oxidation reaction on these dispersed catalysts, allowing the collection of kinetic parameters of reactions. Together with the electrochemical measurements were carried out studies on the structural and electronic properties of these catalysts, which allow relating their structural and electronic properties with the kinetics of the HOR. It was observed that the presence of oxides of Ru, Rh and WO 3 encourage the reduction of the degree of coating of Pt by CO, leaving more sites available to ROH, as a consequence of emptying of the Pt 5d band, which reduces the backdonation of electrons from Pt to CO by reducing the strength of Pt-CO binding. As noted, these changes observed in electronic spectra of XANES not led to any perceptible change in the kinetics or the reaction mechanism. For almost all catalysts, the CO tolerance can be explained in terms of the electronic effect and the bifunctional mechanism evidenced by the formation of CO 2 in the EMS.
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Herrera, Delgado Karla [Verfasser], and O. [Akademischer Betreuer] Deutschmann. "Surface Reaction Kinetics for Oxidation and Reforming of H2, CO, and CH4 over Nickel-based Catalysts / Karla Herrera Delgado. Betreuer: O. Deutschmann." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1056955864/34.
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Schilling, Christian Michael [Verfasser], Christian [Akademischer Betreuer] Hess, Rolf [Akademischer Betreuer] Schäfer, and Rolf Jürgen [Akademischer Betreuer] Behm. "Operando Spectroscopy and DFT Modeling of Gold/Ceria Catalysts for CO Oxidation and Water-Gas Shift Reaction / Christian Michael Schilling ; Christian Hess, Rolf Schäfer, Rolf Jürgen Behm." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1163013528/34.
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Wang, Tongyu [Verfasser], Karsten [Akademischer Betreuer] Reuter, and Sebastian [Akademischer Betreuer] Günther. "Shape and Catalytic Mechanism of RuO2 Particles at CO Oxidation Reaction Conditions: First-Principles Based Multi-Scale Modeling / Tongyu Wang. Betreuer: Karsten Reuter. Gutachter: Karsten Reuter ; Sebastian Günther." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1079001883/34.
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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.
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Al, Anazi Abdulaziz H. "Synthesis of Recyclable Magnetic Metal-ferrite Nanoparticles for the Removal of Contaminants of Emerging Concern in Water." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1543922143864275.
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Garcia, Amanda Cristina. "Desenvolvimento de eletrocatalisadores a base de paládio dispersos em carbono para a reação de oxidação de hidrogênio na presença de CO." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-07042008-151056/.
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A performance de células a combustível de membrana de troca polimérica (PEMFC) alimentadas com hidrogênio contaminado com CO foi investigada para ânodos com eletrocatalisadores de PdPt/C e PdPtRu/C em diferentes proporções. Os materiais produzidos foram caracterizados por energia dispersiva de raios-X (EDX) e difração de raios-X (DRX). As propriedades eletrônicas da Pt foram analisadas por espectroscopia de absorção de raios-X (XAS) na região de XANES (X-ray absorption near edge structure). As avaliações do desempenho eletroquímico foram feitas através do levantamento sistemático de curvas de polarização de estado estacionário, voltametria cíclica e stripping de CO em células a combustível unitárias. Também foram feitas medidas de espectrometria eletroquímica diferencial de massas para avaliar o monitoramento de CO2 (massa/carga 44). Foi observada uma pequena diminuição da magnitude da linha branca nos espectros para as ligas PdPt/C e PdPtRu/C quando comparados com Pt/C, sendo que este fenômeno foi atribuído a um aumento de ocupação da banda Pt 5d. Melhores resultados com relação a tolerância ao CO da reação de oxidação de hidrogênio foram obtidos para os catalisadores PdPt/C e PdPtRu/C quando comparados com Pt e Pd puros. Nenhum efeito sinérgico favorável foi observado com a adição de Ru. O monitoramento de CO2 nos experimentos de espectrometria de massas (DEMS), enquanto as células eram alimentadas com H2 + 100 ppm CO, mostrou aumento na quantidade de formação deste produto somente para ânodos contendo PdPtRu/C e nenhuma formação de CO2 do início ao final das variações de potenciais nos casos dos eletrodos contendo PdPt/C.The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PdPt/C and PdPtRu/C electrocatalysts at different ratios. The produced materials were characterized by energy dispersive (EDX) and X-ray diffraction (XRD). The electronics properties of Pt were analyzed by X-ray absorption spectroscopy (XAS) X-ray absorption near edge structure (XANES) in the region. Evaluations of the electrochemical performance were carried out by steady state single cell polarization measurements, cyclic voltammetry and the CO-stripping techniques. Measurements of differential electrochemical mass spectrometry (DEMS) were carried out to evaluate the CO2 (mass 44) formation. A small reduction of the white line magnitude was in the XANES spectro for the PdPt/C and PdPtRu/C alloys when compared with Pt/C. This phenomenon was assigned for the increase of occupation of the Pt 5d band. Higher CO-tolerances were obtained for the PdPt/C and PdPtRu/C catalysts when compared with those for pure Pd/C and Pt/C. No favorable synergistic effect occurred with Ru addition in the electrode performance for the PEMFC fed with H2+100 ppm CO. The CO2 (mass 44) monitoring with DEMS experiments with the cells fed with H2+100 ppm CO showed the formation of this product only to PdPtRu/C, while no CO2 formation could be detected from beginning to end potential in the cases of Pd/C and PdPt/C.
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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.
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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).
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Cole, Kieran John. "Copper manganese based mixed oxides for ambient temperature co-oxidation and higher temperature oxidation reactions." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54689/.
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The catalytic oxidation of carbon monoxide is an important reaction in heterogeneous catalysis. Copper manganese mixed oxides in the form of Hopcalite, CuMn2C4, is used as a catalyst for the oxidation at ambient temperature and is important in respiratory protection, particularly in mining industries. These types of catalysts are prepared by a co-precipitation method variables in this preparation procedure are known to control catalytic activity. Previous work has shown that the addition of a cobalt dopant metal to the catalyst structure can have a positive effect on activity towards CO oxidation. This thesis furthers the work of dopant addition by studying the effects of zinc on the copper manganese catalyst. Catalyst testing for CO oxidation showed that the addition of the zinc dopant metal increases the stability of catalytic activity. Temperature Programmed Reduction studies show that the addition of zinc has an effect on the redox properties of the catalyst. Prepared copper manganese oxide catalysts were used as supports for gold catalysts. Gold supported CuMnOx was prepared by a deposition precipitation method. The addition of gold to these active materials leads to a marked increase in the catalytic activity. Scanning Electron Microscopy (SEM) showed that the morphology of the support used, played an important role in producing a highly active catalyst. Also, the ageing time of the catalyst precursor was shown to influence catalytic activity. The most effective catalyst for CO oxidation was found to be a 1 wt% Au supported catalyst. The presence of moisture in the gas feed is known to be detrimental to a Hopcalite catalyst for ambient temperature CO oxidation. The effect of moisture on the copper manganese mixed oxide catalysts highlighted the improvement in moisture tolerance with the addition of gold. The method of depositing gold onto an oxide support was shown to be applicable to a commercially available catalyst. The gold supported CuMnOx catalysts prepared were tested for oxidation reactions at higher temperatures. The reactions investigated were ethylene oxide oxidation and preferential oxidation (PROX) of carbon monoxide. Studies showed the addition of gold to the CuMnOx catalysts, improves activity compared to an undoped catalyst.
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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.
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Couble, Julien. "Développement d’outils et de procédures pour la microcinétique expérimentale : application à la réaction CO/O2 sur des catalyseurs Ir/Al2O3 et bimétalliques Pt-Pd/Al2O3." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10087/document.
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L’objectif de cette thèse est de développer des outils et des procédures pour l’approche par lamicro-cinétique expérimentale, de la réaction CO/O2 appliquée aux catalyseurs à base d’iridium et departicules bimétalliques Pt-Pd supportées sur alumine. La caractérisation de la première étape cléd’adsorption du réactif CO sur différents métaux (type d’adsorption, chaleurs d’adsorption de chaqueespèce) a nécessité le développement d’une méthode initialement adaptée à l’analyse IR en modetransmission dite méthode AEIR (Adsorption Equilibrium InfraRed spectroscopy). Les conditionsexpérimentales permettant une exploitation quantitative des spectres IR en mode réflexion diffuse ontété déterminées pour l’utilisation de la méthode AEIR. Cette méthode a ensuite été développée enétendant son domaine d’application à des catalyseurs reconnus comme dissociant fortement le COd’une part en mode réflexion diffuse pour des catalyseurs ne pouvant être étudiés en modetransmission (Fe/Al2O3) et d’autre part en mode transmission (Co/Al2O3). L’impact des paramètres liésà la préparation du catalyseur (nature du support, dispersion de la phase métallique et formation departicules bimétalliques) sur les chaleurs d’adsorption a ensuite été évalué sur des catalyseurs à based’iridium et des catalyseurs tels que Pt-Pd, Pt-Cu respectivement. Enfin l’approche micro-cinétique dela réaction CO/O2 appliquée aux catalyseurs à base d’iridium et de particules bimétalliques Pt-Pd, viaune étude par oxydation isotherme des espèces CO adsorbées à basses températures, a montré que lesétapes superficielles impliquées étaient similaires à celles sur platine et palladium. Les impacts dedivers paramètres expérimentaux sur l’oxydation des espèces CO adsorbées caractérisée par unepériode d’induction sont qualitativement identiques, seuls les paramètres cinétiques tels que l’énergied’activation apparente de la réaction sont modifiésThe aim of this thesis is to develop tools and procedures to study by the experimentalmicrokinetic approach, in particular for the CO/O2 reaction applied to metal supported catalystcontaining iridium particles and bimetallic Pt-Pd particles. The characterization of the first elementarystep of CO adsorption on different metals (nature of adsorption, heat of adsorption of each species) hasrequired the development of a method initially adapted for the IR analysis in transmission mode:AEIR method (Adsorption Equilibrium InfraRed spectroscopy). The experimental conditions allowinga quantitative exploitation of IR spectra in diffuse reflectance mode has been established allowing theuse of the AEIR method. This method has been developed extending the range of application oncatalysts that dissociate strongly CO firstly using diffuse reflectance mode for catalyst which can notbe study in transmission mode (Fe/Al2O3) and then in transmission mode (Co/Al2O3). The impact ofparameters linked to the preparation of catalyst (nature of the support, dispersion of metallic phase,and formation of bimetallic particles) on the heat of adsorption has been evaluated on Ir catalysts andbimetallic particles like Pt-Pd, Pt-Cu respectively. Then, the microkinetic approach of the CO/O2reaction dedicated to Ir and Pt-Pd catalysts, considering the isothermal oxidation of CO adsorbedspecies at low temperature, has shown that the superficial steps involved were similar to those for Ptand Pd catalysts. The impacts of several experimental parameters on the oxidation of CO adsorbedspecies characterized by an induction period are qualitatively identical, only the kinetic parameterslike the apparent activation energy are modified
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Wesselmark, Maria. "Electrochemical Reactions in Polymer Electrolyte Fuel Cells." Doctoral thesis, KTH, Tillämpad elektrokemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25267.
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The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps. The polymer electrolyte fuel cell converts the chemical energy in a fuel, e.g. hydrogen or methanol, and oxygen into electrical energy. The high efficiency and the possibility to use fuel from renewable sources make them attractive as energy converters in future sustainable energy systems. Great progress has been made in the development of the PEFC during the last decade, but still improved lifetime as well as lowered cost is needed before a broad commercialization can be considered. The electrodes play an important role in this since the cost of platinum used as catalyst constitutes a large part of the total cost for the fuel cell. A large part of the degradation in performance can also be related to the degradation of the porous electrode and a decreased electrochemically active Pt surface. In this thesis, different fuel cell reactions, catalysts and support materials are investigated with the aim to investigate the possibility to improve the activity, stability and utilisation of platinum in the fuel cell electrodes. An exchange current density, i0, of 770 mA cm-2Pt was determined for the hydrogen oxidation reaction in the fuel cell with the model electrodes. This is higher than previously found in literature and implies that the kinetic losses on the anode are very small. The anode loading could therefore be reduced without imposing too high potential losses if good mass transport of hydrogen is ensured. It was also shown that the electrochemically active surface area, activity and stability of the electrode can be affected by the support material. An increased activity was observed at higher potentials for Pt deposited on tungsten oxide, which was related to the postponed oxide formation for Pt on WOx. An improved stability was seen for Pt deposited on tungsten oxide and on iridium oxide. A better Pt stability was also observed for Pt on a low surface non-graphitised support compared to a high surface graphitised support. Pt deposited on titanium and tungsten oxide, displayed an enhanced electrochemically active surface area in the cyclic voltammograms, which was explained by the good proton conductivity of the metal oxides. CO-stripping was shown to provide the most reliable measure of the electrochemically active surface area of the electrode in the fuel cell. It was also shown to be a useful tool in characterization of the degradation of the electrodes. In the study of oxidation of small organic compounds, the reaction was shown to be affected by the off transport of reactants and by the addition of chloride impurities. Pt and PtRu were affected differently, which enabled extraction of information about the reaction mechanisms and rate determining steps.Polymerelektrolytbränslecellen omvandlar den kemiska energin i ett bränsle, exv. vätgas eller metanol, och syrgas till elektrisk energi. Den höga verkningsgraden samt möjligheten att använda bränsle från förnyelsebara källor gör dem attraktiva som energiomvandlare i framtida hållbara energisystem. En enorm utveckling har skett under det senaste årtiondet men för att kunna introducera polymerelektrolytbränslecellen på marknaden i en större skala måste livstiden öka och kostnaden minska. Elektroderna har en central del i detta då den platina som används som katalysator står för en stor del av kostnaden för bränslecellen. En stor del av prestandaförsämringen med tiden hos bränslecellen kan också relateras till en degradering av den porösa elektroden och en minskad elektrokemiskt aktiv platinayta. I denna avhandling studeras olika bränslecellsreaktioner samt olika katalysatorer och supportmaterial med målet att undersöka möjligheten att förbättra platinakatalysatorns aktivitet, stabilitet och utnyttjandegrad i bränslecellselektroder. Utbytesströmtätheten, i0, för vätgasoxidationen i bränslecell bestämdes till 770 mA cm-2Pt genom försök med modellelektroderna. Denna var högre än vad som framkommit tidigare i litteratur, vilket visar att de kinetiska förlusterna på anoden är mycket små. Katalysatormängden på anoden borde därför kunna minskas utan några större potentialförluster så länge masstransporten av vätgas är tillräcklig. Den elektrokemiskt aktiva ytan, aktiviteten och stabiliteten hos elektroden visade sig kunna påverkas av supportmaterialet. Platina deponerad på volfram oxid hade en högre aktivitet vid höga potentialer vilket relaterades till den förskjutna oxidbildningen på ytan. Elektroder med platina på volframoxid och iridiumoxid var mer stabila än elektroder med platina på kol. Det var även platina på ett icke grafitiserat kol med låg yta jämfört med platina på grafitiserade kol med en hög yta. Platina på metalloxidskikt av volfram och titan visade en högre elektrokemiskt aktiv yta i de cykliska voltamogrammen än platina på kol, vilket förklarades med att båda metalloxiderna har en bra protonledningsförmåga. CO-stripping gav det säkraste måttet på den elektrokemiskt aktiva ytan i en elektrod i bränslecell. CO-stripping visade sig även vara användbart för karaktärisering av degraderingen av en elektrod. Oxidationen av små organiska föreningar påverkades av borttransporten av intermediärer samt av kloridföroreningar. Pt aoch PtRu påverkades olika vilket gjorde det möjligt att få fram information om reaktionsmekanismer och hastighetsbestämmande steg.
QC 20101014
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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/.
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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).
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Turner, Joel David. "The performance of a nuclear fuel-matrix material in a sealed CO₂ system." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-performance-of-a-nuclear-fuelmatrix-material-in-a-sealed-co2-system(caaeee7f-9551-485b-b3dc-fe14e75bcc5a).html.
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An advanced concept high temperature reactor (HTR) design has been proposed - The ‘U-Battery’, which utilises a unique sealed coolant loop, and is intended to operate with minimal human oversight. In order to reduce the need for moving parts within the design, CO2 has been selected as a candidate coolant, potentially allowing a naturally circulated system. HTR fuel is held within a semi-graphitic fuel-matrix material, and this has not previously been tested within a CO2 environment. Graphite in CO2 is subject to two oxidation reactions, one thermally driven and one radiolytically. As such, the oxidation performance of fuel-matrix material has been tested within CO2 at both high temperatures and under ionising radiation within a sealed-system. Performance has been compared to that of the Gilsocarbon and NBG-18 nuclear graphite grades. Gilsocarbon is the primary graphite grade used within the currently operating AGR fleet within the UK, and as such is known to have acceptable oxidation performance under reactor conditions. NBG-18 is a modern graphite grade, and is a candidate material for use within the U-Battery. Virgin characterisation of all materials was performed, including measurements of bulk mass and volume, skeletal volumes and surface areas. High-resolution optical microscopy has also been performed and pore size distributions inferred from digital image analysis. All results were seen to agree well with literature values, and the variation between samples has been quanti- fied and found to be < 10% between samples of Gilsocarbon, and < 4% for samples of fuel-matrix and NBG-18. Thermal performance of fuel-matrix material was observed between 600 °C – 1200 °C and seen to be broadly comparable to that of the nuclear graphite grades tested. NBG-18 showed surprisingly poor performance at 600°C, with an oxidation rate of 3×10−4%/min, approximately ten times faster than Gilsocarbon in similar conditions, and three times faster than fuel-matrix material. The radiolytic oxidation performance of fuel-matrix material and NBG-18 has been observed by irradiating sealed quartz ampoules. Ampoules were pressurised with CO2 prior to irradiation, and the pressure after 30 days of irradiation was measured and seen to fall by 50%. Radiolytic oxidation, and the subsequent radiolysis of the reaction product, CO, was seen to cause significant carbonaceous deposition on the internal surfaces of the ampoule and throughout the samples. Due to the short irradiation times available in the present study, an investigation of the microporosity within irradiated samples has been carried out, using nitrogen adsorption and small-angle neutron scattering (SANS). Pore size distributions produced from SANS show the closure of microporosity within NBG-18, most likely as a result of low-temperature neutron irradiation.As a result of this work, CO2 is no longer a candidate coolant for use with the U-Battery design, due to the rapid deposition observed following irradiation.
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Harding, Theodor. "A prototype dynamic model for the co-treatment of a high strength simple-organic industrial effluent and coal-mine drainage." Doctoral thesis, Faculty of Engineering and the Built Environment, 2020. http://hdl.handle.net/11427/32660.
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This research study's the use of biological sulfate reduction technologies for the treatment of Sasol Secunda's coal-mine drainage (CMD) using Fischer-Tropsch Reaction Water (FTRW) as a cost-efficient carbon source. The research aims to develop a prototype dynamic model that describes this co-treatment of FTRW and CMD in both a continuously stirred tank reactor (CSTR) biological sulfate reduction (BSR) system and a BSR gas-lift (BSR-GL) integrated system. The BSR-GL system recovers elemental sulfur (S0 ) from the H2S produced and stripped from the BSR unit. Furthermore, this study aims to use the prototype model for a quantitative comparison of the CSTR-BSR and BSR-GL systems. Two bench-scale 5-litre CSTR-BSR and a 20-litre BSR-GL system were operated, under varying feed COD concentrations and hydraulic retention times (HRTs), to generate datasets for use in verification and a rudimentary validation of the prototype model. The BSR-GL integrated system includes 1) a 1-litre H2S gas reactive absorption (ABS) unit utilising an aqueous ferric solution for the recovery of elemental sulfur (S0 ) from sulfide and 2) ferrous biological oxidation reactor to regenerate ferric from the ferrous for re-supply to the ABS unit. The datasets generated in the experimental study allowed for the identification, mathematical modelling and reaction verification of 32 components that interact as reactants and products in 23 reactions observed in the two BSR systems. The prototype model is presented in a mass and charge balanced Gujer matrix that includes, i) 5 SRB mediated processes, ii) 2 liquid-gas mass transfer processes, iii) 3 processes describing the ABS and Fe2+ bio-oxidation units, iv) 4 processes describing sulfide and elemental sulfur oxidation and v) the S0 and poly-sulfide aqueous equilibrium and vi) 9 processes describing death regeneration and BPO hydrolysis. This prototype model was implemented in the DHI WEST® software for initial stage simulation trials. The experimental datasets allowed for the first-stage estimation of the best-fit reaction rate equations and the calibration of the kinetic parameters related to the 23 reactions, using MATLAB® curve fitting toolbox. A pre-processor that describe the pH and equilibrium chemistry of the components of the artificially prepared FTRW+CMD feed mixture batches under varying total concentrations have also been developed in this research. This was done to generated influent file to the DHI WEST® simulations that incorporated the dynamics related to the FTRW+CMD feed mixtures. The sulfate utilisation rate (gSO4 -2 .l-1 .d-1 ) of the GL-BSR and CSTR-BSR systems were compared to determine which system had the best sulfate removal. The results were found to be as follows; a. On comparison it was found that the sulfate substrate utilisation rate for the CSTR_BSR system is 39.28% of that of the BSR-GL_N2 system, where both systems were fed at feed mixture of COD of 2500mgCOD/l, where the COD:SO4 2- was 0.7, b. For the same systems fed a feed mixture of COD at 5000mgCOD/l (COD:SO4 2- = 0.7), the sulfate substrate utilisation rate for the CSTR_BSR system was found to be 17.86% less than that of the BSR_GLN2 system. c. Finally, it was also found that the substrate utilisation rate for the CSTR_BSR system was 30.06% less than that of the BSR_GLN2 system at Se of 4gCOD/l, for both systems fed substrate at 5000mgCOD/l. Thus, it can be concluded that the sulfate substrate utilisation rate for the BSR-GL system is higher than that of the CSTR_BSR system, for systems fed COD feed mixtures at 2.5 or 5gCOD/l where both systems have the same effluent substrate concentrations. However, the difference in the comparative substrate utilisation rate is less at higher feed substrate concentrations. This is the influence of substrate inhibition on the active SRB biomass, which increases with higher effluent substrate concentrations. Finally, this research found that the use of gas-lift reactor technologies is superior to CSTR technologies in the treatment of coal-mine drainage utilising biological sulfate reduction (BSR). The CSTR-BSR system, fed sulfate between 1.6 to 14gSO4 2- /l, produced effluent with high dissolved H2S concentrations, on average 285mgS/l and maximum at >600mgS/l. Releasing this effluent to the environment would be hazardous to aquatic and human health and corrosive to infrastructure. As such, the effluent from the CSTR-BSR system requires further treatment to stabilise the water for any use. The BSR-GL technology allows for the conversion of the H2S produced during BSR reactions to form elemental sulfur, which is a resource recovered from this process, thus complying to the circular economy aim of this study.
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Dowey, Una. "Co-contaminant removal of mercury and hydrocarbons from soil using oxidative free radical reactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ28932.pdf.
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Eilers, Gerriet, Anders Persson, Cecilia Gustavsson, Linus Ryderfors, Emad Mukhtar, Göran Possnert, and Mehran Salehpour. "The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala." Uppsala universitet, Tillämpad kärnfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-202651.
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Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for 14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the 14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2 molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect 14CO2, 13CO2, or 12CO2 molecules unambiguously. In ICOGS, the sample is in the form of CO2 gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.
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RAMADAN, DOAA REDA MOHAMED. "PALLADIUM CATALYZED REACTIONS: REDUCTIVE CYCLIZATION OF NITROARENES, AND OXIDATIVE CARBONYLATION OF ANILINE." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/819652.
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Palladium Catalyzed Reactions: Reductive Cyclization of Nitroarenes, and Oxidative Carbonylation of Aniline
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The thesis is divided into two main chapters: reductive cyclization of nitroarenes, and oxidative carbonylation of aniline.
The first chapter involves developing a catalytic system for carbazoles synthesis through reductive cyclization of 2-nitrobiphenyls employing phenyl formate as an in-situ source of CO. Thus, the synthetic chemist can avoid handling pressurized CO lines and perform the reaction in a pressure tube, a cheap and readily available tool for any laboratory. Moreover, the developed protocol can tolerate both air and moisture and can be performed using undried and undistilled commercial DMF. Several carbazoles bearing a wide range of substituents were synthesized in good to excellent yields including some with valuable pharmaceutical or thermo/electrical applications. The reaction could be performed on the grams scale affording carbazole in a very good yield (85%) without the need for chromatographic purification, making our synthetic strategy even more attractive and economically advantageous.
The second chapter deals with the palladium/iodide couple which is the most investigated catalytic system for the oxidative carbonylation of amines to give ureas or carbamates. In reinvestigating it, we found that the most prominent role of iodide is to etch the stainless steel of the autoclave employed in most of previous works, releasing in solution small amounts of iron salts. The latter are much better promoters than iodide itself. Iron and iodide have a complex interplay and, depending on relative ratios, can even deactivate each other. The presence of a halide is beneficial, but chloride is better than iodide in this respect. The ideal Fe/Pd ratio is around 10, but even an equimolar amount of iron with respect to palladium (0.02 mol% with respect to aniline, corresponding to 12 ppm Fe with respect to the whole solution) is sufficient to boost the activity of the catalytic system. Such small amount may also come from Fe(CO)5 impurities present in the CO gas when stored in steel tanks. The role of the solvent has also been investigated. It was found that the reason for the better selectivity in some cases is at least in part due to a hydrolysis of the solvent itself, which removes the coproduced water.
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Lu, Yubing. "Structural and Kinetic Study of Low-temperature Oxidation Reactions on Noble Metal Single Atoms and Subnanometer Clusters." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100586.
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Supported noble metal catalysts make the best utilization of noble metal atoms. Recent advances in nanotechnology have brought many attentions into the rational design of catalysts in the nanometer and subnanometer region. Recent studies showed that catalysts in the subnanometer regime could have extraordinary activity and selectivity. However, the structural performance relationships behind their unique catalytic performances are still unclear. To understand the effect of particle size and shape of noble metals, it is essential to understand the fundamental reaction mechanism. Single atoms catalysts and subnanometer clusters provide a unique opportunity for designing heterogeneous catalysts because of their unique geometric and electronic properties.
CO oxidation is one of the important probe reactions. However, the reaction mechanism of noble single atoms is still unclear. Additionally, there is no agreement on whether the activity of supported single atoms is higher or lower than supported nanoparticles. In this study, we applied different operando techniques including x-ray absorption fine structure (XAFS), diffuse reflectance infrared spectroscopy (DRIFTS), with other characterization techniques including calorimetry and high-resolution scanning transmission electron microscopy (STEM) to investigate the active and stable structure of Ir/MgAl2O4 and Pt/CeO2 single-atom catalysts during CO oxidation. With all these characterization techniques, we also performed a kinetic study and first principle calculations to understand the reaction mechanism of single atoms for CO oxidation. For Ir single atoms catalysts, our results indicate that instead of poisoning by CO on Ir nanoparticles, Ir single atoms could adsorb more than one ligand, and the Ir(CO)(O) structure was identified as the most stable structure under reaction condition. Though one CO was strongly adsorbed during the entire reaction cycle, another CO could react with the surface adsorbed O* through an Eley-Rideal reaction mechanism. Ir single atoms also provide an interfacial site for the facile O2 activation between Ir and Al with a low barrier, and therefore O2 activation step is feasible even at room temperature. For Pt single-atom catalysts, our results showed that Pt(O)3(CO) structure is stable in O2 and N2 at 150 °C. However, when dosing CO at 150 °C, one surface O* in Pt(O)3(CO) could react with CO to form CO2, and the reacted O* can be refilled when flowing O2 again at 150 °C. This suggests that an adsorbed CO is present in the entire reaction cycle as a ligand, and another gas phase CO could react with surface O* to form CO2 during low-temperature CO oxidation.
Supported single atoms synthesized with conventional methods usually consist of a mixture of single atoms and nanoparticles. It is important to quantify the surface site fraction of single atoms and nanoparticles when studying catalytic performances. Because of the unique reaction mechanism of Ir single atoms and Ir nanoparticles, we showed that kinetic measurements could be applied as a simple and direct method of quantifying surface site fractions. Our kinetic methods could also potentially be applied to quantifying other surface species when their kinetic behaviors are significantly different. We also benchmarked other in-situ and ex-situ methods of quantifying surface site fraction of single atoms and nanoparticles.
To bridge the gap between single atoms and nanoparticles and have a better understanding of the effect of nuclearity on CO oxidation, we also studied supported Ir subnanometer clusters with the average size less than 0.7 nm (< 13 atoms) prepared by both inorganic precursor and organometallic complex Ir4(CO)12. Low-temperature CO adsorption indicates that CO and O2/O could co-adsorb on Ir subnanometer clusters, however on larger nanoparticle the particle surface is covered by CO only. Additional co-adsorption of CO and O2 was studied by CO and O2 calorimetry at room temperature. CO oxidation results showed that Ir subnanometer clusters are more active than Ir single atoms and Ir nanoparticles at all conditions, and this could be explained by the competitive adsorption of CO and O2 on subnanometer clusters.Doctor of Philosophy
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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.
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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.
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Adcock, Romain. "Synthesis and reactivity of [RhI(CO)2(L)] and [RL][RhI2(CO)2] rhodium complexes where L is a nitrogen-containing ligand for the methanol carbonylation reaction." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0123.
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Ce travail est centré sur la synthèse de complexes du rhodium contenant un ligand azoté et leur mise en œuvre dans la réaction catalytique de carbonylation du méthanol en acide acétique. Dans une première partie, nous nous intéressons à la préparation de complexes neutres de formule générale [RhI2(CO)(L)] (L = amines, imidazoles et pyrazoles) et à quelques homologues chlorés. Ces complexes plans carrés manifestent une réactivité directement liée à l’encombrement stérique du ligand azoté L dans la réaction d’addition oxydante de l’iodomethane suivie de la cis-migration du groupement méthyle pour former l’espèce acétyle. Dans une deuxième partie, les complexes précédents ont été engagés dans des essais catalytiques de carbonylation du méthanol dans les conditions du procédé industriel. Comme il s’est avéré que les complexes neutres se transforment en espèce [RhI2(CO)2]- pour laquelle les contre-cations associés sont constitués du ligand azoté protoné ou methylé, nous avons effectué la préparation et la caractérisation des complexes [HNR3][RhI2(CO)2] ou [MeNR3][RhI2(CO)2]. Par IR, RMN et électrochimie, nous nous sommes intéressés aux phénomènes d’appariement d’ions et nous montrons qu’il s’agit dans le meilleur des cas d’interactions hydrogènes. Celles-ci influent la vitesse de la réaction oxydante de CH3I. Dans la dernière partie, nous avons complété une étude, précédemment initiée au laboratoire, sur le mécanisme, qui dans la dernière étape du cycle catalytique permet de passer de l’espèce acétyle [RhI3(COCH3)(CO)2]- à l’espèce active [RhI2(CO)2]- avec production de l’iodure d’acyle. A l’inverse du concept admis d’élimination réductrice de CH3COI suivie de son hydrolyse immédiate en CH3COOH et HI, nous montrons, avec l’appui de calculs théoriques (DFT) qu’en fait un ligand I- est substitué par un ligand acetate pour conduire à l’espèce [RhI2(OAc)(COCH3)(CO)2]-. L’élimination réductrice produit alors l’anhydride acétique qui est hydrolysé en CH3COOH régénérant [RhI2(CO)2]-. Un tel mécanisme opère en présence d’ions acetate dans les milieux faiblement hydratés visés par l’industrielThis study focuses on the synthesis and reactivity of rhodium complexes bearing N- containing ligands or counter-cations for the [Rh]-catalyzed methanol carbonylation reaction to produce acetic acid under the industrial Celanese Acid Optimization (AO) process conditions. In a first part, full synthesis and characterization of neutral Rh(I) square planar cis- [RhX(CO)2(L)] (X = Cl or I) complexes have been described, for which L is an N-ligand belonging to the amine, imidazole or pyrazole family. For the [RhI(CO)2(L)] complexes, variable-temperature 13C{1H} NMR spectroscopy has put in evidence a fluxional behavior for the different sized L ligands involved. The rate of this fluxional process reveals to be related to both electronic and steric contributions brought by L to the Rh center. These parameters (mainly steric), supported by single-crystal X-ray analyses in the solid state, also influence significantly the kinetics of the methyl iodide oxidative addition reaction followed by rapid CO migratory insertion, the overall being the rate determining step of the [Rh]-catalyzed methanol carbonylation cycle. In absence of CO, this reaction gives rise to the corresponding neutral Rh(III) acetyl complex, which immediately dimerizes to afford [Rh(μ- I)I(COMe)(CO)(L)]2 complex, for which several X-ray crystal structures have been obtained and studied. In addition, the surprising C-H activation in the case of a tBu-pyrazole ligand giving rise to a cyclometalated Rh dimer is reported. In a second part, the reactivity of the latter neutral Rh(I) [RhI(CO)2(L)] complexes as potential precursors has been investigated by batch experiments for the methanol carbonylation reaction. Mechanistic understanding via VT-HP-NMR experiments enabled to detect mainly anionic Rh(I) [RL][RhI2(CO)2] (R = H or CH3 according to the working conditions) complexes formed by decoordination followed by quaternization of the L ligand. Despite this result, the pyrazole family ligands showed better stability under the harsh process conditions. Thus, it cannot be ruled out that equilibrium between neutral and anionic species co-exist in the reaction medium at high temperatures and that [RL]I salt dissociation occurs, restoring the L ligand into the Rh coordination sphere. At this stage we focused on the anionic Rh(I) complex and prepared a series of [XNR3][RhI2(CO)2] (X = H or CH3) species, which have been fully characterized. Infrared, NMR, conductivity experiments and DFT model calculations together put in evidence ion interactions according to the nature of the ammonium counter-cation. Protonated cations significantly impact on the kinetics of the methyl iodide oxidative addition presumably due to H-interactions with the Rh square plane. The final part deals with the mechanism of the reductive elimination reaction, the last step of the [Rh]-catalyzed methanol carbonylation cycle, which from complex [RhI3(COCH3)(CO)2]-, regenerates [RhI2(CO)2]-. In contrast to the classically admitted mechanism of reductive elimination of CH3COI followed by subsequent hydrolysis to form AcOH and HI, we demonstrate from experimental DFT calculation that substitution of an iodo ligand by an acetate ion occurs to give rise to the [RhI2(OAc)(COCH3)(CO)2]- species. Thus, reductive elimination regenerates [RhI2(CO)2]- and produces acetic anhydride, which after hydrolysis affords two molecules of acetic acid. Such a mechanism operates under process conditions at low water content with a significant amount of acetate ions
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Liu, Hang. "In situ investigations of chemical reactions on ZnO-Pt model nanocatalysts for environmentally friendly energy generation sources." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS201.pdf.
Full textAbstract:
Il a été démontré que le catalyseur ZnO/Pt(111) présente des performances catalytiques remarquables dans l'oxydation du CO à basse température. L'identification des sites actifs dans l'oxydation du CO est importante pour une compréhension mécaniste de la relation structure-réactivité. Nous avons d'abord établi une recette pour fabriquer des films minces de ZnO sur Pt(111) par évaporation par faisceau électronique, caractérisée par STM et LEED. Le film se développe en mode couche par couche, à parti rd'une monocouche de type grapheme jusqu'à la surface ZnO(0001)-Zn terminée. Le rôle des limites ZnO/Pt a été révélé par la STM ex situ après exposition à l'O2:CO. Pour mettre en lumière le rôle des limites, une étude comparative systématique du catalyseur ZnO/Pt(111) avec la surface Pt(111) a été entreprise. La spectroscopie de masse et l'analyse NAP-XPS en phase gazeuse étaient pertinentes pour déterminer les régimes dans lesquels la limitation du transfert de masse commence à se produire, ce qui a permis de discuter de la relation entre les fractions molaires à l'état stable des réactifs/produit et la réactivité de surface, et pour étalonner la densité de surface des adsorbats. Les spectres XPS en phase solide nous ont donné accès à la dynamique du film monocouche ZnO ne couvrant que partiellement la surface Pt(111). Le rôle des hydroxyls liés au ZnO a été mis en évidence par l'observation de la signature chimique des produits de réaction associative CO+OH. Le carboxyle formé à basse temperature peut être l'espèce intermédiaire qui conduit à l'évolution du CO2, les OHs à la limite Pt/ZnO étant le co-catalyseur, ce qui explique l'effet synergique du ZnO et du PtThe ZnO/Pt(111) catalyst has been shown to exhibit remarkable catalytic performances in the low temperature CO oxidation. The identification of the active sites in CO oxidation is important for a mechanistic understanding of the structure-reactivity relationship. We first established a recipe to fabricate ZnO thin films on Pt(111) using e-beam evaporation, characterized by STM and LEED. The film grows in layer-by-layer mode, starting from a graphene-like monolayer tothe ZnO(0001)-Zn terminated surface. The role of the ZnO/Pt boundaries was revealed by STM ex situ after exposure to the O2: CO mixture. To shedlight on the role of the boundaries, a systematic comparative study of the ZnO/Pt(111) catalyst with the Pt(111) surface was under taken. The mass spectroscopy and gas phase NAP-XPS analysis were relevant, to determine the regimes where mass transfer limitation starts to occur, allowing a discussion on the relation between steady-state molar fractions of reactants/product and surface reactivity, and to calibrate the surface density of the adsorbates.Solid phase XPS spectra gave us access to the dynamics of the ZnO monolayer film covering only partially the Pt(111) surface. The role of ZnO-bound hydroxyls was highlighted by the observation of the chemical signature of the CO+OH associative reaction products. The carboxyl formed at the low temperature can be the intermediate species that leads to the evolution of CO2, the OHs at the Pt/ZnO boundary being the co-catalyst, which explains the synergistic effect of ZnO and Pt
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Tsai, Meng-Che, and 蔡孟哲. "DFT study of CO oxidation reaction on PtxRu55-x clusters." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/73048154030175415191.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
96
Density functional theory (PAW-GGA) calculations are employed to study CO+OH coadsorption oxidation reaction on Pt-based clusters. In order to get insight into the nano-sized effect toward CO oxidation, adsorption properties of CO, OH group and reaction intermediate have also been investigated. In this study, we adopted two model systems: 55 atoms Pt clusters (Pt55) and Pt(111) 3×3 slab as nanoparticle and bulk properties, respectively. The results show that adsorption energy and reaction barrier of CO oxidation are strongly influenced by the size of Pt nanocatalysts. Recent literature shows that the energy barrier of CO oxidation reaction increases with a decrease in Pt particle size. According to CO+OH coadsorption oxidation mechanism, it occurs through following steps: CO and OH group coadsorb at the most stable sites on the catalyst surface, and CO reacts with OH group, forming cis-COOH then transforms configuration into trans-COOH. At last the H on COOH transfers to surface, leading to CO2 formation. The reaction barrier of CO+OH on Pt55 clusters (111) surface is 0.92 eV, and it is higher than reaction barrier on Pt(111) slab (0.75 eV) which indicates that CO is not easy to react with OH group on the surface of nanoparticles. On the other hand, the presence of second metal (Ru) induces charge transfer from Ru to Pt leading to weaker bond of both CO and OH on the Pt site. By similar CO oxidation mechanism, reaction barrier of CO+OH on Pt-based cluster (shell: Pt, core: Ru) is 0.81 eV.
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Chou, Te Ming, and 周德明. "CO oxidation reaction with and without hydrogen over Cu/TiO2 catalysts." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/17855104721240024500.
Full textAbstract:
碩士長庚大學
化工與材料工程學系
100
In this study, the oxidation of CO over Cu/TiO2 catalysts containing different Cu loadings was investigated. The catalysts are characterized by In-situ XRD, ICP/AES, TGA, Raman, XANES and H2-TPR. The Cu/TiO2 catalysts were prepared by impregnating TiO2 with an aqueous solution of Cu(NO3)2. The Cu/TiO2 catalysts were calcined in air and reduced in H2 at 175oC and 300 oC. The Cu/TiO2 shows superior activities in CO oxidation, it may attribute to that presence of different CuO species with distinct catalytic activities, which are isolated Cu atoms, highly dispersed CuO and bulk CuO. When calcination treatment at 225 oC, Cu+ species would formed in the TiO2 lattice, which is the main active phase for the CO oxidation.
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Stiehl, James Daniel. "Model catalyst studies of the CO oxidation reaction on Titania supported gold nanoclusters." Thesis, 2004. http://hdl.handle.net/2152/1416.
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Stiehl, James Daniel Mullins Charles Buddie. "Model catalyst studies of the CO oxidation reaction on Titania supported gold nanoclusters." 2004. http://repositories.lib.utexas.edu/bitstream/handle/2152/1416/stiehlj71428.pdf.
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Yang, Yi-fen, and 楊怡芬. "The Application of Selective Oxidation CO Reaction in Hydrogen Stream over Gold Catalysts." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/16578960110696389734.
Full textAbstract:
碩士國立中央大學
化學工程與材料工程研究所
97
Bulk gold had been known as an inactive catalyst. However, nano gold particles appear to be extremely active. An example of catalytic application is that gold catalysts are able to selectively oxidize carbon monoxide in a hydrogen stream at low temperature, which is important for producing clean hydrogen for fuel cells. When hydrogen-rich fuel is produced from water gas shift reaction, the Pt anodes in fuel cell at low temperatures are poisoned by CO. Highly dispersed gold on suitable metal oxide exhibits high activity to oxidize CO in hydrogen stream to reduce CO concentration less than 50 ppm. In this study, a series of Au catalysts supported on FeOx-TiO2 with various Fe contents were prepared. FeOx-TiO2 support was prepared by incipient-wetness impregnation with aqueous solution of Fe(NO3)3 on TiO2. Gold catalyst with nominal loading of 1 wt. % was prepared by deposition-precipitation at pH 7 and 65°C. Au/TiO2 catalysts were prepared by photo-deposition (PD) method for various preparation parameters, such as pH value, power of UV light and irradiation time. The catalysts were characterized by ICP, XRD, TEM and XPS. The catalytic performance of these catalysts was investigated by preferential oxidation of carbon monoxide in hydrogen stream (PROX). The reaction was carried out in a fixed bed reactor with feed of CO: O2: H2: He = 1.33: 1.33: 65.33: 32.01 (volume ratio). Au/TiO2 catalyst had both high CO oxidation activity and high H2 oxidation activity. Adding suitable amount of Fe2O3 on Au/TiO2 could enhance CO conversion to a higher extent and suppress H2 oxidation conversion. Au/FeOx-TiO2 with molar ratio (10:90) is found to be the best catalyst when compared with other catalysts for PROX and it showed high CO conversion (100%) and selectivity (48%) at 80°C for fuel cell application. Supported gold catalysts, the amorphous nature of iron oxide along with TiO2 not only enhance electronic interaction but also stabilize the nano-size gold particles, thereby enhancing the catalytic activity. Au/TiO2 catalysts prepared by PD method had narrow particle size distribution and the particle size of Au was around 1.5 nm. Among all the catalysts, Au/TiO2 catalyst prepared at pH 10 and irradiated for 10 min showed the highest CO conversion (95%) and CO selectivity (47%) at 80°C for fuel cell operation. When the irradiation time increased from 10 to 60 min, the small gold particles aggregated to form larger gold particles. The catalytic activity of Au/TiO2 decreased with an increase in gold particle size. In long time test, The CO conversion of Au/TiO2 (prepared at pH 10 and 10 min irradiation time) was greater than 90% and CO selectivity also maintained above 42% at 80°C for 60 h. The results clearly demonstrated that the catalyst was stable for a long time. Key words: Au, TiO2, Fe2O3, gold catalyst, preferential oxidation of CO in H2 stream, photo-deposition.
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Liu, Jyong-Yue, and 劉炯岳. "Study of novel catalysts for steam reforming of ethanol and CO oxidation reaction." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/19057989178254329059.
Full textAbstract:
博士國立臺灣科技大學
化學工程系
103
Hydrogen production from ethanol steam reforming has recently attracted increased attention, due to the renewability of bio-ethanol and its potential use in fuel cells. The main strategy being explored to enhance efficiency and reduce the costs associated with ethanol reforming is to design a novel catalyst with improved activity and stability. The main focus of this work is to synthesize novel Ni-base catalysts and investigate the relationship between their structures and their catalytic activities when used for ethanol steam reforming. The CO oxidation reaction is of considerable interest, due to its relevance in many industrial applications, such as H2 purification (PROX) in reforming systems. While reforming systems still have some residual CO that may poison Pt catalysts in fuel cells and CO sensors - it is generally recognized that the noble metal catalysts (Rh, Pd, Pt) are the most effective oxidation catalysts able to eliminate CO; however, the high price of noble metals limits their application. The main target of this study is to develop highly active catalysts that do not contain noble metals for low temperature CO oxidation. The following research topics are addressed in this dissertation: (I) Understanding the metal-support interactions between Ni and La2O3 [derived from perovskite (LaNiO3)], to help us to design an improved catalyst for ethanol steam reforming. Strong metal-support interactions (SMSI) were effectively directed at maximizing the hydrogen yield by suppressing undesired reaction pathways. It was found that Ni, formed as Ni nanoparticles (NPs), was well-dispersed on the La2O3 support’s surface and was additionally partially embedded within it, thereby indicating strong interactions between the two materials. The Ni/La2O3 (derived from perovskite) nanocatalyst, when compared to a Ni/SiO2 catalyst, generated twice the hydrogen yield (3.7 molH2 mol-1EtOH) at 395℃ by inhibiting CO methanation (CO + 3H2 → CH4 + H2O) and promote the WGSR (CO + H2O → H2 + CO2). (II) Cu/Ni nanocatalysts were prepared by thermal reduction of a perovskite LaNixCu1-xO3. In situ XRD measurements and temperature programmed (TPR) results showed that nanosized Ni, decorated with Cu, supported on La2O3 can be produced at 520 ~550˚C. XPS measurements and TPO-TPR results corroborated the hierarchical structure. The hierarchical structure of Cu/Ni/La2O3 catalysts confers synergetic effects which greatly favor the dehydrogenation of ethanol and which break the C-C bond to produce a higher yield of hydrogen at low reaction temperature, while the La2O3 also provides required stability during the reaction. The reaction, at 290˚C, achieved nearly a 100% conversion with the hydrogen yield reaching 2.21, thus indicating that this special structural feature can achieve high activity for ethanol steam reforming at low temperatures. (III) The MnOx catalysts were synthesized by the mesoporous hard template (SBA-15) confined method. The experiment results showed that uniform nanosized rod-like MnO2 catalyst with a high surface area (141.4 m2/g) can be successfully prepared. Prepared samples showed the oxidation state of Mn was lower than 4+, indicating that the rod-like MnO2 surface possesses many oxygen vacancies. The O2-temperature programmed oxidation (TPO) measurement also suggests that oxygen vacancies exist on the surface of rod-like MnO2. Here, we used CO oxidation as a model reaction to demonstrate the catalytic capability of the materials formed. The reaction, at 118℃, achieved 50% CO conversion, due to rod-like MnO2 (MnOx-C3) catalyst with high surface area having many oxygen vacancies, thereby generating more activate oxygen during the reaction. Furthermore, In situ XRD measurements and DFT calculations results helped us confirm the phase transformation during the reaction. The results indicate the (220) plane of MnO2 easily removes oxygen by reacting with the adsorbed CO and then replenishes the oxygen from the gas phase oxygen. This greatly favors the adsorbed CO reacting with the activated oxygen, from the lattice, to produce high a conversion of CO at low reaction temperatures. From this observation, the CO oxidation on rod-like MnO2 catalyst not only follows the Langmuir-Hinshelwood mechanism, but also follows that of Mars-van-Krevelen. After loading 10%Cu on rod-like MnO2 surface, the rod-like manganese oxide-supported CuO catalyst exhibited superior performance. At 110℃ a 100% CO conversion was achieved, indicating that the CuO-MnO2 interface confers synergistic effects for CO oxidation.
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Peng, Yi-Jhen, and 彭怡貞. "Preparation of mixed oxide supported Pt catalysts for CO tolerance in Hydrogen Oxidation Reaction." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/70467915766833858483.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
104
Proton exchange membrane fuel cells (PEMFCs) are expected to have enormous power for both mobile and stationary applications (e.g., automotive, portable, electronics, etc.). Carbon supports are mainly used in electrocatalysts for fuel cells because of good electron conductivity and high surface area that may leads to good dispersion of active Pt particles. However, carbon corrosion under operating conditions of PEMFCs becomes a concern which can cause deterioration in the performance of Pt catalysts. To enhance durability and CO tolerance of anodic catalysts, mixed-oxide supports are examined in this study. A simple hydrothermal process is applied to synthesize supports and the influences of preparation parameters are examined, including pretreatment conditions, dual ion-doping, sequences of Ru inclusion, and changes of M in M0.7Ru0.3O2. Pt loading is prepared by EG method. XRD results show that the prepared 40% Pt/P-Ti0.3Ru0.7O2 contains Pt particle size of 3-4 nm, similar with commercial PtRu/C catalysts. CO stripping and hydrogen oxidation reaction (HOR) under H2 with 100 and 250 pm CO are examined. The results indicate that 40Pt/P-Ti0.7Ru0.3O2-b12 and 40Pt/W0.7Ru0.3O2 catalysts exhibit improved CO tolerance, intrinsic activity and durability comparing to commercial PtRu/C and homemade 40% Pt/Ti0.7Ru0.3O2 catalysts.
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Yu, Chien-hsin, and 余建興. "The additive effect on the activity of CuO/CeO2 catalysts in selective CO oxidation reaction." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/6n9z5v.
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Chung, Yi-Hua, and 鍾宜樺. "Theoretical Investigation on the Mechanism of CO Oxidation Reaction on Ni@Pd Core-Shell Nanoalloy." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/35615142807607702662.
Full textAbstract:
碩士國立中興大學
化學系所
102
We studied the mechanism of the CO oxidation reaction (CO + O2 → CO2 + O) catalyzed by Ni6@Pd32 core-shell nanoalloy using density-functional theory (DFT) calculations to investigate the bimetallic effects on the catalytic activation. The molecular structures and adsorbate/substrate interaction energies were predicted along with the potential energy surface constructed using the nudged elastic band (NEB) method. Our results indicate the CO oxidation prefer processing two step reaction with O2 vertical, and the energetic barriers are lower on the core-shell nanoalloy than those on Pd38. Furthermore all the related chemical species of WGSR can adsorb stably on Ni6@Pd32 to allow the reactions to take place under ambient pressure. To gain insights into the synergy effect in the catalytic activity of the Ni6@Pd32 nanoalloys, the nature of interaction between adsorbate and substrate is also analyzed by the detailed electronic local density of states (LDOS) as well as their molecular structure.
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Chou, Ying-Chieh, and 周映潔. "Gold Nanoparticle Supported on Modified Cerium Oxide in Preferential Oxidation Reaction of CO in H2 stream." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/76859630039360136884.
Full textAbstract:
碩士國立中央大學
化學工程與材料工程研究所
99
Nanoscaled gold particle supported on CeO2 and modified by CuO or Mg(OH)2 were used for preferential oxidation of carbon monoxide in hydrogen-rich stream (PROX). CuO-CeO2 support was prepared by co-precipitaion method, while magnesium was loaded on commercial CeO2 (Nikki) through impregnantion method. Finally, gold was added to these supports by deposition-precipitation method. Different amounts of promoter and different calcination temperatures of the support were changed to develop the best catalyst for PROX reaction. These catalysts were characterized by XRD, TEM, HR-TEM, XPS, and N2-sorption. The PROX reaction was carried out in a fixed bed continuous flow reactor with a feed of CO: O2: H2: He = 1.33: 1.33: 65.33: 32.01 in volume ratios. The results showed that the catalyst with specific Cu content and calcination temperature could reach 100% of CO conversion at the PEM fuel cells operating temperature (65℃-100℃) even as the gold content was reduced from 1 wt. % to 0.5 wt. %. The particle size of gold was around 2-5 nm and Au particles were dispersed well on the support. The incorporation of copper ion into ceria lattice promoted the oxygen storage capacity of ceria support and encouraged the activity of catalysts. The higher calcinations temperature for the support resulted higher crystallinity of CeO2, leading to the higher activity. The CO selectivity increased with increasing copper amount. The promotional effect of magnesium addition was more obvious at higher calcinations temperature (550℃ and 700℃) of support. After deposition-precipitation method, the magnesium presented as phase of Mg(OH)2 rather than MgO as observed by XRD. However, the existed of this hydroxide did not show significant promotion on catalytic activity. These two kinds of catalyst underwent long-term reaction test for 160 hours. The Au/CuO-CeO2 catalyst was more stable than Au/Mg(OH)2-CeO2.
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Huang, Guo-Yan, and 黃國晏. "Preparation of Tungsten Ruthenium mixed oxide supported Pt catalysts for CO tolerance in Hydrogen Oxidation Reaction." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/erd69v.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
106
Proton exchange membrane fuel cells (PEMFCs) are expected to have enormous potential for both mobile and stationary applications. Carbon supports are mainly used in electrocatalysts for fuel cells because of good electron conductivity and high surface area that may leads to good dispersion of active Pt particles. However, carbon corrosion under operating conditions of PEMFCs becomes a concern which can cause deterioration in the performance of Pt catalysts. To enhance the durability and the CO tolerance of anodic catalysts, mixed-oxide supports are examined in this study. A simple hydrothermal process is applied to synthesize mixed W-Ru oxide supports and the influences of preparation parameters are examined, including Tungsten oxide phase, Tungsten Ruthenium ratio, and pretreatment temperature, and subsequently the preparation procedure is optimized. Pt loading is prepared by EG method. XRD results show that the prepared 40wt%Pt/W5Ru5-N12-c300 contains Pt particle size of 3-4 nm. CO stripping and hydrogen oxidation reaction (HOR) with 100 and 250 ppm CO are examined. The results indicate that 40Pt/W5Ru5-N12-c300 and 40Pt/W7Ru3-N12-c300 catalysts exhibit improved CO tolerance, intrinsic activity and durability comparing to the other prepared catalysts. The overall performance is comparable with commercial 20Pt10Ru/C catalysts.
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Su, Yu-cheng, and 蘇育正. "Water Gas Shift Reaction and Preferential Oxidation of CO in H2-rich Stream over Au/TiO2 Catalyst." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/22063494750994230034.
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Schilling, Christian Michael. "Operando Spectroscopy and DFT Modeling of Gold/Ceria Catalysts for CO Oxidation and Water-Gas Shift Reaction." Phd thesis, 2018. https://tuprints.ulb.tu-darmstadt.de/7546/1/Dissertation_Schilling_Christian.pdf.
Full textAbstract:
The aim of this work is to elucidate the reaction mechanism of the CO oxidation and the water-gas shift reaction over gold/ceria as a prototype heterogeneous oxide supported metal catalyst. In this context a combined setup was developed to apply Raman, UV-Vis and infrared spectroscopy under reaction conditions to the active catalyst (operando approach). Along with density functional theory calculations (DFT) of ceria and gold/ceria model systems the experimental results are interpreted on the molecular level.
Employing DFT calculations Raman and infrared active vibrations are calculated and experimental bands are assigned to the vibrational modes properly. With this approach a comprehensive interpretation of the Raman spectra of nanoparticle ceria is possible, while two bands are reassigned to distinct modes of the ceria(111) surface.
At well defined ceria nanocrystals the facet dependent oxygen activation behavior is studied and an overall facilitated oxygen adsorption and peroxide formation at the ceria(100) surface facet is observed. In addition superoxide formation is observed at this surface facet for the first time.
The results on gold/ceria catalysts reveal that the subsurface oxidation state of the ceria support alters the activity of a gold/ceria catalyst for CO oxidation. An oxidized gold species in direct contact with the ceria support is evidenced as the site for CO adsorption and proposed as the active site for oxidation reactions over gold/ceria catalysts.
The results underline the potential of vibrational spectroscopy for operando characterization of catalyst materials. Together with DFT calculations, which allow a proper assignment of the bands in Raman or infrared spectra, this provides an interpretation on the molecular scale and direct conclusions for the reaction mechanism. The results may be directly transferable to other oxide supported metal catalysts highlighting the general relevance of the results presented in this study.
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Lundwall, Matthew James. "Characterization and Reaction Studies of Silica Supported Platinum and Rhodium Model Catalysts." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8839.
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The physical and catalytic properties of silica supported platinum or rhodium model catalysts are studied under both ultra high vacuum (UHV) and elevated pressure reaction conditions (>1torr). Platinum or rhodium nanoparticles are vapor deposited onto a SiO2/Mo(112) surface and characterized using various surface analytical methods. CO chemisorption is utilized as a surface probe to estimate the concentration of various sites on the nanoparticles through thermal desorption spectroscopy (TDS) and infrared reflection absorption spectroscopy (IRAS) along with microscopy techniques to estimate particle size. The results are compared with hard sphere models of face centered cubic metals described as truncated cubo-octahedron. Results demonstrate the excellent agreement between chemisorption and hard sphere models in estimating the concentration of undercoordinated atoms on the nanoparticle surface. Surfaces are then subjected to high pressure reaction conditions to test the efficacy of utilizing the rate of a chemical reaction to obtain structural information about the surface. The surfaces are translated in-situ to a high pressure reaction cell where both structure insensitive and sensitive reactions are performed. Structure insensitive reactions (e.g. CO oxidation) allow a method to calculate the total active area on a per atom basis for silica supported platinum and rhodium model catalysts under reaction conditions. While structure sensitive reactions allow an estimate of the types of reaction sites, such as step sites (≤C7) under reaction conditions (e.g. n-heptane dehydrocyclization). High pressure structure sensitive reactions (e.g. ethylene hydroformylation) are also shown to drastically alter the morphology of the surface by dispersing nanoparticles leading to inhibition of catalytic pathways. Moreover, the relationships between high index single crystals, oxide supported nanoparticles, and high surface area technical catalysts are established. Overall, the results demonstrate the utility of model catalysts in understanding the structure-activity relationships in heterogeneous catalytic reactions and the usefulness of high pressure reactions as an analytical probe of surface morphology.
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Farkas, Attila [Verfasser]. "In situ IR spectroscopic studies of the CO oxidation reaction over a ruthenium model catalyst / von Attila Farkas." 2008. http://d-nb.info/990222527/34.
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Bauer, John C. "Nanoparticles as Reactive Precursors: Synthesis of Alloys, Intermetallic Compounds, and Multi-Metal Oxides Through Low-Temperature Annealing and Conversion Chemistry." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-642.
Full textAbstract:
Alloys, intermetallic compounds and multi-metal oxides are generally made by
traditional solid-state methods that often require melting or grinding/pressing powders
followed by high temperature annealing (> 1000 degrees C) for days or weeks. The research
presented here takes advantage of the fact that nanoparticles have a large fraction of their
atoms on the surface making them highly reactive and their small size virtually
eliminates the solid-solid diffusion process as the rate limiting step. Materials that
normally require high temperatures and long annealing times become more accessible at
relatively low-temperatures because of the increased interfacial contact between the
nanoparticle reactants.
Metal nanoparticles, formed via reduction of metal salts in an aqueous solution
and stabilized by PVP (polyvinylpyrrolidone), were mixed into nanoparticle composites
in stoichometric proportions. The composite mixtures were then annealed at relatively
low temperatures to form alloy and intermetallic compounds at or below 600 degrees C. This
method was further extended to synthesizing multi-metal oxide systems by annealing metal oxide nanoparticle composites hundreds of degrees lower than more traditional
methods.
Nanoparticles of Pt (supported or unsupported) were added to a metal salt
solution of tetraethylene glycol and heated to obtain alloy and intermetallic
nanoparticles. The supported intermetallic nanoparticles were tested as catalysts and
PtPb/Vulcan XC-72 showed enhanced catalytic activity for formic acid oxidation while
Pt3Sn/Vulcan XC-72 and Cu3Pt/y-Al2O3 catalyzed CO oxidiation at lower temperatures
than supported Pt.
Intermetallic nanoparticles of Pd were synthesized by conversion chemistry
methods previously mentioned and were supported on carbon and alumina. These
nanoparticles were tested for Suzuki cross-coupling reactions. However; the
homocoupled product was generally favored. The catalytic activity of Pd3Pb/y-Al2O3
was tested for the Heck reaction and gave results comparable to Pd/y-Al2O3 with a
slightly better selectivity.
Conversion chemistry techniques were used to convert Pt nanocubes into Ptbased
intermetallic nanocrystals in solution. It was discovered that aggregated clusters
of Pt nanoparticles were capable of converting to FePt3; however, when Pt nanocubes
were used the intermetallic phase did not form. Alternatively, it was possible to form
PtSn nanocubes by a conversion reaction with SnCl2.
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Rozé, Emmanuel. "Processus élémentaires associés à la réaction d’oxydation de CO à basses températures sur des catalyseurs à base de Palladium et d’Or supportés sur Al2O3 et SiO2." Thesis, 2010. http://www.theses.fr/2010LYO10290/document.
Full textAbstract:
Dans cette thèse, une approche microcinétique expérimentale est utilisée pour caractériser des étapes élémentaires impliquées dans l’oxydation de CO par O2 sur des catalyseurs à base de Pd et d’Au supportés sur oxydes métalliques et identifier celles qui contrôlent la vitesse de réaction. Sur un catalyseur 1,4%Pd/Al2O3, l’évolution de la production de CO2 (RCO2(t)) par oxydation des espèces CO adsorbées (2 linéaires L et 2 pontées P) a été suivie lors de cycles successifs formation - oxydation des espèces. Une période d’induction est observée, donnant un pic de CO2 caractérisé partm et RCO2m. L’étude de l’impact de différents paramètres expérimentaux sur tm et RCO2m: le tempsde désorption avant oxydation, la pression partielle de O2, la température et le prétraitement ducatalyseur a permis de caractériser les étapes superficielles impliquées. Un modèle cinétique basé surl’oxydation des espèces CO P par une espèce oxygène faiblement adsorbée formée sur des sites libéréspar la désorption et/ou l’oxydation des espèces CO L a permis d’interpréter ces impacts. Ce modèle aégalement permis d’interpréter les différences d’activités du catalyseur vis-à-vis de la réaction CO/O2en fonction de son prétraitement après réduction sous H2 à 713 K : un refroidissement sous hydrogènepermet d’obtenir des conversions de CO proches de 100% à 300 K en excès de O2 alors qu’unedésorption préalable à 713 K donne de faibles conversions (< 4%). Ces différences sont attribuées àune reconstruction de la surface des particules de Pd par désorption de l’hydrogène à 713 K.Sur Au supporté sur Al2O3 et SiO2, l’étude a porté sur la première étape de l’oxydation du CO:l’adsorption du CO. Sous certaines conditions (température et pressions) l’adsorption de CO à 300 Kentraîne une reconstruction progressive des particules d’or modifiant significativement les propriétésdes espèces adsorbées. La cinétique de cette reconstruction à 300 K est étudiée et interprétéeThe aim of this thesis is to use an experimental microkinetic approach to characterize elementary steps involved in the oxidation of CO by O2 over Pd and Au catalysts supported on Al2O3 and SiO2 and to identify those controlling the rate of the reaction. On 1.4% Pd/Al2O3, the evolution of the production of CO2 (RCO2(t)) by oxidation of the adsorbed CO species (2 linear L and 2 bridged B) was followed during successive formationoxidation cycles. An induction period is observed leading to a CO2 peak characterized by tm and RCO2m. The study of the impacts of different experimental parameters on tm and RCO2m such as the duration of a desorption before oxidation, the partial pressure of O2, the temperature and thepretreatment of the catalyst allows us to characterize the different surface elementary steps of thereaction. A kinetic model is proposed which is based on the oxidation of the B CO species by a weaklyadsorbed O species formed on Pd sites liberated by the desorption and the oxidation of the L COspecies. This model allows us to interpret the differences in the catalytic activity of the catalyst for theCO/O2 reaction according to the pretreatment procedure after reduction with H2 at 713 K: cooling thesolid in hydrogen permits obtaining a CO conversion of ��100% in excess O2 whereas a desorption at713 K provides CO conversions < 4%. These differences are ascribed to the reconstruction of thesurface of the Pd particles during the hydrogen desorption at 713 K. On Au/Al2O3 and Au/SiO2, the study concerns the first step of CO oxidation: the adsorption of CO. For a set of experimental conditions (Temperature and partial pressures), the adsorption of CO at 300 K leads to a progressive reconstruction of the Au particles modifying significantly the propertiesof the adsorbed species. The kinetic of this reconstruction is studied
46
Gottfried, Jörg Michael [Verfasser]. "CO oxidation over gold : adsorption and reaction of oxygen, carbon monoxide, and carbon dioxide on an Au(110)-(1x2) surface / von Jörg Michael Gottfried." 2003. http://d-nb.info/967931045/34.
Full text
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Cheng, Ching-hao, and 鄭欽豪. "Nano-sized Cu/Ce catalyst prepared by sol-gel method and its application in water gas shift reaction and CO oxidation under rich hydrogen." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/72544398513363909569.
Full text
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Kim, Sang Hoon [Verfasser]. "Study of reaction mechanisms on single crystal surfaces with scanning tunneling microscopy : atomically resolved CO oxidation on Pd(111) and RuO2(110) / von Sang Hoon Kim." 2003. http://d-nb.info/968530036/34.
Full text
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Chen, Shu-Jhen, and 陳淑禎. "A study of reaction mechanisms and catalytic-activity of Pt-M/C bi-metallic electrodes (M= Ru, Ir and Sn) in the electrocatalytic oxidation of MeOH and CO." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/05964577765003277493.
Full textAbstract:
碩士國立高雄應用科技大學
化學工程與材料工程系
97
The Pt-M/C (M= Ru，Ir and Sn) bi-metallic catalysts with various compositions were prepared by impregnation method for investigation of catalytic-activity of the Pt-M/C bi-metallic catalysts and mechanism of electro-oxidation of methanol on the electrocatalysts. The electrochemical properties of electrodes were studied by cyclic voltammetry (CV), chronoamperometry (CA), CO-stripping voltammetry, and linear sweep voltammetry (LSV) methods. The lattice parameters, composition, particle size-distribution of reduced bi-metallic catalysts were characterized by the means of x-ray diffractometer (XRD), inductively coupled plasma-mass spectrometer (ICP-MS), transmission electron microscope (TEM), and scanning electron microscope (SEM). The results of CV measurements showed the methanol oxidation on-set potential (VMOSP) and CO oxidation on-set potential (VCOSP) at the electrodes measured at various scanning rate are different. There is a significant hysteresis phenomenon, which increases with the increase of the scanning rate, i.e. the VMOSP appears at the forward (backward) scan is more positive (negative) at a higher scanning rate. However, when the scan rate decreases to 1 mV s-1, the VMOSP at the forward scan and backward scan nearly approaches the same value, which indicates the VMOSP at pseudo-steady-state can be obtained at 1 mV s-1. It is also found that the VMOSP at pseudo-steady-state is approximately equal to the average value of VMOSP appears at the forward scan and backward scan at various scanning rate. This result shows that a correct VMOSP can be obtained quickly from the VMOSP appears at the forward scan and backward scan at a higher scanning rate without interference from the occurrence of hysteresis. The VMOSP at Pt/C is 0.368 V (vs. SCE), and the VMOSP at Pt-Ru/C is dependent on the Ru content of the electrocatalysts. When Ru content is higher than 50 atom%, the VMOSP is ca. 0.20 V(vs. SCE) which is equal to the value of VCOSP at the same electrodes and that at a Ru black electrode. However, when Ru content is less than 50 atom%, the VCOSP remains at 0.20 V, but the VMOSP at the electrodes shifts positively with the decrease of Ru content. The VMOSP of Pt80Ru20/C is 0.269 V (vs. SCE). These results shows that the rate determining step (RDS) in the electro-oxidation of methanol at Pt-Ru/C electrodes is dependent on the composition of the electrocatalysts, i.e. the adsorbed CO at Pt active site is able to transfer to the adjacent Ru, and oxidation of the Ru-CO(ads) becomes the RDS when Ru content is higher than 50 atom%. On the other hand, the removal of CO adsorbed at Pt at a more positive potential is the RDS when Ru content is less than 50 atom%. Beisides, the results of chronoamperometry measurement show that the Ru content of the Pt-Ru electrocatalysts for maximum specific current in the electro-oxidation of MeOH is 20~25 atom%. The maximum specific current at the Pt80Ru20/C electrode obtained in 0.5 M H2SO4 + 2.0 M CH3OH electrolyte at 0.35 and 0.40 V are 29.86 and 59.68 mA mg-1Pt, respectively. In addition to the Ru-Pt/C electrocatalyst, the VMOSP at PtIr/C and PtSn/C electrodes, i.e. 0.329 and 0.284 V (vs. SCE), is more negative than that at the Pt/C, and the specific current in the electro-oxidation of MeOH specific is higher than that at Pt/C electrodes. The specific current in the electrooxidation of MeOH at at 0.55 V(vs. SCE) is 1.6 and 1.5 times than that at a Pt/C electrode. Particle size of the electrocatalysts was estimated from TEM and XED graphs. The particle size of Pt/C is ca. 4.03±0.71 nm, and that of the Pt-Ru /C is around 2.8~3.7 nm, which decreases with the increase of the Ru content. Besides, the particle size of PtIr/C containing 50 atom% Ir is ca. 3.02±0.47 nm also showing that a smaller particle electrocatalyst can be obtained in the present of a second metal. In other words, the addition of a second metal for the preparation of Pt-M/C electrodes by impregnation method also favors the dispersion of the electrocatalysts and promotes the utilization Pt.
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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.
Full textAbstract:
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.