"Catalytic growth of Carbon Nanotubes (CNT) provides important advantages of controlling their diameters and possibly chirality. Our work involved growing CNT on model and supported catalyst by catalytic decomposition of carbon source such as benzene, methane and propylene. On supported catalyst, iron nitrate was deposited on alumina and reduced to form metallic iron clusters. These were reacted at 700 - 950 C under varying benzene concentrations. Multi Walled CNT (MWNT) grew below 800 C and Single Wall CNT (SWNT) are observed at 850 C and above as confirmed by TEM and Raman. Model catalysts were studied by producing CNT from ferrocene which acted as the carbon and catalyst source on Silica/Si (100). Large yield of MWNT was observed at 900 C. MWNT grew perpendicular to the model support as seen by SEM. In another model catalyst study, iron salt clusters were deposited on silica/Si (100) by spin coating, controlling their diameters by solution concentration and speed of spinning. Agglomeration of clusters at high temperatures produces only MWNT on silica/Si (100). Cluster agglomeration can be reduced with strong support metal interaction such as with alumina. We deposited alumina on silica/Si (100) by atomic layer deposition, with conformal coatings on surface and low relative roughness. Alumina film was stable under reaction temperatures of 900 C. Cluster deposition on alumina by spin coating was difficult because of different surface acidity compared to silica. Clusters on alumina did not agglomerate at high reaction temperatures. We report effect of parameters such as the temperature of reaction, conditions of pretreatment such as reduction and oxidation of catalyst precursor, type of precursor, type of carbon source, and type of support material on growth of CNT. The role of spin coating in controlling the diameter of salt clusters deposited is discussed. We also report deposition of alumina on top of silica/Si (100) by atomic layer deposition and the effect of deposition and calcination temperatures on the alumina film integrity."

La durabilité des piles à combustible à membrane échangeuse de protons, jugée à l’heure actuelle insuffisante, est principalement liée à la dégradation des supports de catalyseur cathodiques carbonés. Afin d’augmenter cette durabilité, un fin revêtement de dioxyde d’étain est effectué sur différents types de carbone (nanotubes, noirs et aérogel de carbone). L’objectif est d’obtenir un matériau alliant la morphologie et la conductivité électrique des carbones avec la stabilité thermodynamique du dioxyde d’étain. Plusieurs types de carbone avec des propriétés intrinsèques différentes ont été choisis afin d’avoir un large un panel de textures et de structures. Dans ces travaux de thèse, des études expérimentales ont été effectuées dans le but d’obtenir des revêtements d’oxyde d’étain fins, homogènes et couvrants. Ces études ont mis en l’avant l’influence primordiale de la texture et de la structure du carbone, mais aussi de la valeur du pH du milieu réactionnel sur la qualité et la quantité de revêtement. Il a aussi été montré que les mécanismes de transformation du précurseur en dioxyde d’étain dépendent de la valeur de ce pH. En améliorant les interactions entre la surface des carbones et des espèces réactives, il a été possible dans certains cas de diminuer grandement la quantité de précurseur tout en améliorant la qualité du revêtement. Les dépôts de nanoparticules de platine effectués sur des aérogels de carbone bruts et revêtus ont mis en avant un comportement différent du platine qui a tendance à s’agglomérer lorsqu’il est en contact avec le dioxyde d’étain. Les performances initiales ainsi que la durabilité des électrocatalyseurs en fonction de deux tests de vieillissement accéléré (classique ou démarrage/arrêt) ont ensuite été discutées, mettant en avant des résultats mitigés. / The proton exchange membrane fuel cell’s lifespan is insufficient because of the degradation of carbon used as cathodic catalyst supports. In order to reduce this degradation, a thin tin dioxide coating is synthesized on the surface of different carbonaceous materials (nanotubes, carbon blacks and aerogel). The aim is to combine the morphology and the electric conductivity of the carbon with the thermodynamic stability of the tin dioxide. Carbonaceous materials with different intrinsic properties are chosen for this study to test a wide range of textures and structures. Experimental studies were carried out in order to synthesize a thin, homogeneous and covering tin dioxide coating. The major influences of the texture and structure of carbonaceous materials but also the influence of the pH value on the quantity and quality of the coating are highlighted. It turns out that the mechanism of formation of tin dioxide depends on this pH value. Thanks to the improvement of the interactions between the carbon surface and the reactive species, it was possible, in some cases, to reduce drastically the quantity of precursor. Platinum nanoparticles deposition performed on various materials (raw or coated carbon aerogel) highlights a different platinum behavior. In fact, on the tin dioxide surface, nanoparticles tend to agglomerate together instead of making a homogeneous dispersion. Then, the initial performances and the durability of electrocatalysts tested with two accelerated stress tests (load protocol or start/stop protocol) are evaluated, spotlighting mitigate results.

L'hydrodynamique et les transferts thermiques dans des réacteurs types lits fixes font l'objet d'études depuis une soixantaine d'années. Les informations fournies par ces travaux sont importantes pour le dimensionnement des réacteurs industriels. En effet, une étroite relation entre les propriétés de transports et le design du procédé (réacteur et support catalytique) est mise en avant dans l'état de l'art. Mais force est de constater que la complexité des phénomènes entraine des divergences entre les observations et les différentes conclusions faites par les auteurs. Deux pilotes à échelle laboratoire ont été conçus et mis en place au cours de cette thèse. L'un est dédié à l'étude hydrodynamique et l'autre à l'étude thermique. La caractérisation hydro-thermique des réacteurs passe également par une étape de développement de modèles mathématiques associés aux pilotes. Ils représentent les transferts opérant au sein d'une colonne garnie. Ils permettent également d'estimer les paramètres effectifs du milieu poreux. Les quatre grandeurs caractéristiques étudiées dans cette thèse sont les pertes de charges, la dispersion axiale, la conductivité effective globale et le coefficient d'échange thermique à la paroi. Les résultats obtenus à partir des modèles sont comparés aux travaux de la littérature. Ceci permet de valider les méthodes d'estimation développées dans cette thèse. Il est remarqué que les corrélations prédictives de la conductivité effective sont peu adaptées aux morphologies de supports les plus complexes. Nous proposons donc aussi de nouvelles corrélations basées sur nos mesures / Hydrodynamics and heat transfers in packed bed reactors have been studied for about sixty years. The information supplied by this work is important for the design of industrial reactors. Indeed, there is a close relationship between the heat and mass transfers and the design of the process (reactor and catalytic support); this is highlighted in the state of the art. It is clear that the complexity of the phenomena is the cause of divergences between the observations and the conclusions made by the authors. Two laboratory-scale pilots were designed and set up during this PhD thesis. One is dedicated to the hydrodynamic studies and the other to the thermal studies. The hydro-thermal characterization of the reactors includes a step of development of mathematical models associated with the pilots. They represent transfers occurring within the bed of particles. Coupling experimental data with the models allows estimating the effective parameters of the porous medium. The four characteristic quantities studied in this PhD thesis are the pressure drop, the axial dispersion, the overall effective conductivity and the heat transfer coefficient at the wall. The results are compared with the data provided by the open literature. This validates the estimation methods developed during this PhD thesis. It is noticed that the predictive correlations of the effective thermal conductivity are not adapted to the morphologies of the most complex supports. Based on our measurements, new correlations were developed

Submitted by Maike Costa (maiksebas@gmail.com) on 2017-06-20T14:18:13Z No. of bitstreams: 1 arquivototal.pdf: 7366953 bytes, checksum: e2858ff3ade34aa9cdf821b90999c936 (MD5) / Made available in DSpace on 2017-06-20T14:18:13Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 7366953 bytes, checksum: e2858ff3ade34aa9cdf821b90999c936 (MD5) Previous issue date: 2017-04-28 / Calcium stannate, CaSnO3, is orthorhombic perovskite-type that presents technological applications as catalysts and photocatalysts. In this work, undoped CaSnO3 and doped with Fe3+, Co2+ or Cu2+ were obtained by the modified Pechini method and applied in photodegradation of the textile dye Remazol Golden Yellow and as catalysts in the reduction reaction of nitrogen monoxide (NO). Furthermore, these materials were deposited on the ZrO2 support or Pd2+-doped or Pd impregnated and evaluated in the reduction of NO with CO and NO with NH3. The catalysts were characterized by thermogravimetric analysis (TG/DTA), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), Raman spectroscopy, analysis of the surface area by the BET method, scanning electron microscopy with field emission (FE-SEM) and transmission electron microscopy (TEM). XRD patterns showed a small change in the long range-order for the doped samples due to partial substitution of cations. The Raman spectra indicated that the incorporation of Fe3+, Co2+ and Cu2+ in the CaSnO3 lattice promoted a symmetry breaking, which was confirmed by the change of the band gap values of the samples. The photocatalytic tests of RNL dye were performed in the reactor using a UVC lamp (λ = 254 nm). The catalytic tests were carried out in a reactor containing a gaseous mixture with stoichiometric amounts of nitrogen monoxide (NO) and carbon monoxide (CO) in helium in the temperature range of 300 °C to 700 °C or in a reactor containing a mixture of NO and ammonia (NH3) in helium in the temperature range of 250 °C to 500 °C. The results of the photocatalytic evaluation showed that CaSnO3 doping with transition metals increased the photocatalytic efficiency of the material, especially for the Cu2+ (76% of discoloration), which was related to the while the decrease in the intensity of the photoluminescence spectrum as a function of doping. The catalytic tests of NO with CO showed that Co2+ and Cu2+-doped perovskites showed 100% of conversion, at temperatures above 500ºC. The palladium impregnation promoted the conversion of NO with CO throughout the evaluated temperature range, but it did not favor the reaction of NO with NH3, probably due to the oxidation of NH3 by Pd. The perovskite deposited on the ZrO2 support showed the best catalytic conversion values. The results of FEG and TEM confirmed the deposition of the active phase on the ZrO2 support and indicated the formation of core@shell systems. / Estanato de cálcio, CaSnO3, é uma perovskita do tipo ortorrômbica que apresenta aplicações tecnológicas como catalisadores e fotocatalisadores. Neste trabalho, CaSnO3 não dopado e dopado com Fe3+, Co2+ ou Cu2+ foram obtidos pelo método Pechini-modificado e aplicados na fotodegradação do corante têxtil remazol amarelo ouro (RNL), e como catalisadores na reação de redução de monóxido de nitrogênio (NO). Além disso, esses materiais foram depositados sobre o suporte catalítico ZrO2 ou impregnados ou dopados com paládio e avaliados na redução de NO com CO e NO com NH3. Os catalisadores foram caracterizados por análise termogravimétrica (TG/DTA), difração de raios-X (DRX), espectroscopia de absorção na região do ultravioleta e do visível (UV-Vis), espectroscopia vibracional na região do infravermelho (IV), espectroscopia Raman, análise da área superficial (SBET), microscopia eletrônica de varredura com emissão de campo (MEV-EC) e microscopia eletrônica de transmissão (MET). Os resultados de DRX mostraram uma pequena mudança na ordem a longo alcance das amostras dopadas devido à substituição parcial dos cátions. Os espectros Raman indicaram que a incorporação dos metais Fe3+, Co2+ e Cu2+ na rede do CaSnO3 promoveu quebra de simetria, o que foi confirmado pela mudança nos valores do band gap das amostras. Os ensaios fotocatalíticos do corante RNL foram realizados em reator utilizando uma lâmpada UVC (λ= 254 nm). Por sua vez, os testes catalíticos foram realizados em um reator contendo uma mistura gasosa, com quantidades estequiométricas de monóxido de nitrogênio (NO) e monóxido de carbono (CO), em hélio, na faixa de temperatura de 300°C a 700°C ou em um reator contendo mistura de NO e amônia (NH3), em hélio, na faixa de temperatura de 250°C a 500°C. Os resultados da avaliação fotocatalítica mostraram que a dopagem do CaSnO3 com os metais de transição aumentou a eficiência fotocatalítica do material, sendo mais expressiva para o material dopado com Cu2+ (76% de descoloração), o que foi relacionado à diminuição na intensidade dos espectros de fotoluminescência em função da dopagem. Os testes catalíticos de NO com CO mostraram que as perovskitas mássicas dopadas com Co2+ e Cu2+ apresentaram 100% de conversão, em temperaturas superiores a 500ºC. A impregnação com paládio favoreceu a conversão de NO com CO em toda a faixa de temperatura avaliada, no entanto, desfavoreceu a reação de NO com NH3, provavelmente devido à oxidação de NH3 pelo Pd. As perovskitas depositadas sobre o suporte ZrO2 mostraram os melhores valores de conversão catalítica. Os resultados de MEV-EC e MET confirmaram a deposição da fase ativa sobre o suporte ZrO2 e indicaram a formação de sistemas core@shell.

[ES] Las zeolitas han destacado por sus aplicaciones en procesos catalíticos y de adsorción/separación de gases de alto impacto industrial. Esto es debido a que presentan propiedades de tamiz molecular como consecuencia de sus estructuras microporosas y, además es posible ajustar sus propiedades catalíticas variando su composición química, presencia de defectos estructurales, tamaño promedio de cristal, etc. Hasta el momento se han reconocido 255 estructuras zeolíticas diferentes, pero la obtención de zeolitas con nuevas estructuras es un aspecto muy relevante dentro de la ciencia de materiales ya que permite ampliar el rango de aplicaciones de estos materiales. Por ello, el objetivo fundamental de esta tesis doctoral es la obtención de nuevos materiales zeolíticos, empleándose para ello, cationes orgánicos que actuarán como agentes directores de estructura (ADEs) en la cristalización de zeolitas. Así, se ha estudiado el empleo cationes derivados de biciclopirrolidina como ADEs sintetizados mediante reacciones orgánicas de cicloadición [3+2]. Estos ADEs han sido efectivos en la síntesis de zeolitas, obteniéndose diversos sólidos microporosos cuya preparación había sido descrita anteriormente con otros cationes orgánicos. Sin embargo, uno de los cationes empleados ha dado lugar a la cristalización de una nueva zeolita, denominada ITQ-69, que presenta un sistema tridireccional de canales rectos, de poro pequeño (8 x 8 x 8 R) y ausencia de cavidades. Este material ha sido efectivo en la separación selectiva de propileno de propano en su forma de germanosilicato. La síntesis de zeolitas quirales, es sin duda el objetivo más ambicioso propuesto. En esta tesis se ha explorado el empleo de derivados de azúcares como parte fundamental en la síntesis de ADEs. En concreto, se ha explorado la isomanida como unidad sintética quiral en la preparación de dicationes quirales. Cuando la isomanida se combina con la presencia de imidazolios (altamente selectivos hacía la estructura STW) se ha obtenido un material STW en forma de germanosilicato. Este sólido cristaliza formando cristales de tamaño suficientemente grande como para realizar estudios de difracción de Rayos X en monocristal, y determinar el exceso enantiomérico de distintas preparaciones. En todos los casos, se obtiene cristales S-STW homoquirales enantimórficamente puros, constituyendo el primer ejemplo de obtención selectiva quiral de una zeolita reportado hasta la fecha. En esta parte de la tesis, también se obtuvieron zeolitas con topología STW empleando ADEs no quirales. Algunos de estos sólidos, se evaluaron en la separación de hidrocarburos con diferentes grados de ramificación (zeolita STW puramente silícea) y en la reducción selectiva de NO con propano (zeolita Al-STW intercambiadas con Cu). Finalmente, se han estudiado diferentes cationes organofosforados como ADEs. La elevada estabilidad de estos cationes en el medio de síntesis, ha permitido la obtención de una nueva zeolita, ITQ-70, que presenta un elevado grado de defectos de conectividad y una muy baja densidad de red. La estructura de la zeolita ITQ-70 presenta un sistema de supercavidades con ventanas interconectadas de acceso a las mismas (20 x 20 x 18 R) y cristaliza con un grupo de simetría proquiral. / [CAT] Zeolites are well-known for their industrial applications. The presence of pores of molecular dimensions forming a structured channels system confers them the property of performing as a molecular sieve. This characteristic of zeolites, combined with the possibility of modifying their chemical composition, structural defects, average crystal size, etc., provides them with exceptional properties for catalytic and separation processes. Up to now, 255 different zeolitic structures have been compiled. However, obtaining zeolites with new structures remains an important challenge in materials science and broadening their applications. Therefore, the main objective of this doctoral thesis is the obtention of new zeolitic materials using organic cations as structure-directing agents (SDAs) in the crystallization process. Thus, the use of bicyclopyrrolidine-derived cations as ADEs, synthesized by organic cycloaddition reactions [3+2], has been studied. Several microporous solids whose preparation had been previously described using other organic cations have been obtained by utilizing these bicyclopyrrolidine-derived cations as ADEs. In addition, the crystallization of a new zeolite, ITQ-69, has been reached. This structure presents a tridirectional system of straight small pore size channels (8 x 8 x 8 R) and the absence of cavities. ITQ-69, in its germanosilicate form, has been proved to be significantly effective for the separation of propylene from propane. Obtaining chiral zeolite is undoubtedly one of the most ambitious objectives proposed in the field of zeolite synthesis. In this thesis, sugar derivatives have been specifically considered as starting molecules for the synthesis of chiral ADEs. Particularly, the synthesis of dicationic ADEs starting from isomannide as a chiral synthetic unit has been explored. When isomannide was combined with imidazole (highly selective towards the STW structure), a STW-structure material in the form of germanosilicate was obtained. This solid crystallizes forming sufficiently large crystals to perform single-crystal X-ray diffraction studies and determine the enantiomeric excess of different preparations. In all cases, enantiomorphically pure homochiral S-STW crystals are obtained, constituting the first reported example of chiral selective synthesis of a zeolite. Zeolites with STW structure were also obtained using non-chiral ADEs. The properties of these microporous solids were evaluated in the separation of hydrocarbons with different branching, in the form of purely siliceous STW, and in the selective reduction of NO with propane using Cu-exchanged Al-STW zeolites. Finally, different organophosphorus cations have been studied as ADEs. The high stability of these cations in the zeolites crystallization medium has allowed the isolation of a new zeolite, ITQ-70, which presents a high number of connectivity defects and a very low lattice density. The structure of the ITQ-70 zeolite possesses a super-cavity system with interconnected access windows (20 x 20 x 18) and crystallized with a prochiral symmetry group. / [EN] Les zeolites han destacat per les seues aplicacions en processos catalítics i processos d'adsorció/separació de gasos d'alt impacte industrial. Açò és degut al fet que presenten propietats de tamís molecular a conseqüència de les seues estructures microporoses i, a més és possible ajustar les seues propietats catalítiques variant la seua composició química, presència de defectes estructutals, grandària del cristall, etc. Fins al moment es reconeixen 255 estructures zeolítiques diferents, però l'obtenció de zeolites amb noves estructures és un aspecte molt rellevant dins de la ciència de materials, ja que permet ampliar el rang d'aplicacions d'aquests materials. Per tant, l'aspecte fonamental d'aquesta tesi doctoral és l'obtenció de nous materials zeolítics empleant cations orgànics que actuaran com a agents directors d'estructura (ADEs) en la cristal·lització de zeolites. Així, s'ha explorat l'us de cations derivats de biciclopirrolidina com ADEs sintetitzats mitjançant reaccions orgàniques de cicloadició [3+2]. Aquests ADEs han sigut efectius en la síntesis de zeolites, obtenint-se diversos sòlids microporosos, la preparació dels quals havia sigut descrita anteriorment amb altres cations orgànics. No obstant, un dels cations empleats ha donat lloc a la cristal·lització d'una nova zeolita, denominada ITQ-69, que presenta un sistema tridireccional de canals rectes, porus xicotets (8 x 8 x 8 R) i absència de cavitats. Aquest material ha sigut efectiu en la separació selectiva de propilé de propà en la seua forma de germanosilicat. Dins de la síntesi de zeolites, la síntesi de zeolites quirals, és sens dubte un dels objectius més ambiciosos proposats. En aquesta tesi s'ha explorat l'ús de derivats de sucres com a part fonamental en la síntesi de ADEs. En concret, s'ha explorat la isomanida com a unitat sintètica quiral en la preparació de dications quirals. Quan la isomanida es combina amb la presència de imidazolios (altament selectius feia l'estructura STW) s'ha obtingut un material STW en forma de germanosilicato. Aquest sòlid cristal·litza formant cristalls de grandària prou gran com per a realitzar estudis de difracció de Raigs X en monocristall, i determinar l'excés enantioméric de diferents preparacions. En tots els casos, s'obté cristalls S-STW homoquirals enantimórficament purs, constituint el primer exemple d'obtenció selectiva quiral d'una zeolita reportat fins a la data. En aquesta part de la tesi, també es van obtindre zeolites amb topologia STW empleant ADEs no quirals. Alguns dels materials STW es van avaluar les propietats d'aquests sòlids microporosos en la separació d'hidrocarburs amb diferents graus de ramificació amb STW purament silici i en la reducció selectiva de NO amb propà empleant zeolites Al-STW intercanviades amb Cu. Finalment, s'han estudiat diferents cations organofosforats com ADEs. L'elevada estabilitat d'aquests cations en el mitjà de cristal·lització de zeolites ha permés aïllar una nova zeolita, ITQ-70, que presenta un elevat grau de defectes de connectivitat i una molt baixa densitat de xarxa. L'estructura de la zeolita ITQ-70 té un sistema compost per supercavitats amb finestres interconnectades d'accés a les mateixes (20 x 20 x 18) i cristal·litza amb un grup de simetria proquiral. / Al Ministerio de Economía, Industria y Competitividad por concederme la Beca BES-2016-078684 que ha permitido la realización de esta tesis doctoral, junto a la ayuda económica proporcionada en los proyectos MAT2015-71842 y RTI2018-101784-B-100. A la Generalitat Valenciana su financiación a través del proyecto PROMETEO/2021/07 y por último a la Universidad Politécnica de Valencia (UPV), al Consejo Superior de Investigaciones Científicas (CSIC) y al Instituto de Tecnología Química (ITQ) por proporcionar las instalaciones y equipamiento necesarios para llevar a cabo el trabajo de investigación. / Sala Gascón, A. (2022). Síntesis y caracterización avanzada de materiales zeolíticos mediante el empleo de nuevos agentes orgánicos directores de estructura [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/186873 / TESIS

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