[ES] La presente tesis doctoral ha mostrado la posibilidad de diseñar sitios activos de MOFs y materiales basados en grafeno para ser utilizados como catalizadores con actividad mejorada para reacciones de oxidación y condensación. Específicamente, el desarrollo de una combinación de metales MIL-101(Cr,Fe) ha dado como resultado un catalizador con actividad catalítica mejorada para la reacción de Prins entre ß-pineno y formaldehído con respecto al MIL-101(Cr) o el inestable MIL-101(Fe) en las condiciones de reacción estudiadas. La presencia de iones Fe3+ en los nodos metálicos del MIL-101(Cr, Fe) aumenta la densidad y la fuerza de los sitios ácidos de Lewis del material, mientras que la presencia de Cr+3 en los nodos metálicos proporciona estabilidad al catalizador. Además, esta Tesis ha demostrado que la presencia de grupos NO2 en el ligando orgánico tereftalato de MIL-101(Cr) aumenta la densidad y la fuerza de los sitios ácidos de Lewis del material. Por lo tanto, MIL-101(Cr)-NO2 exhibe una actividad catalítica superior para la síntesis de bencimidazoles a partir de o-fenilendiaminas y derivados de benzaldehído, así como para la oxidación aeróbica del tiofenol y la desulfuración oxidativa aeróbica de dibenzotiofenos. Esta Tesis también ha demostrado que la selección de un agente reductor apropiado como la hidroquinona para la preparación de rGO a partir de GO aumenta la densidad de los sitios activos para promover las oxidaciones aeróbicas de tiofenol e indano. / [CA] La present Tesi doctoral ha mostrat la possibilitat de dissenyar llocs actius de MOFs i materials basats en grafè per ser utilitzats com a catalitzadors amb activitat millorada per a reaccions d'oxidació i condensació. Específicament, el desenvolupament d'una combinació de metalls MIL-101(Cr,Fe) ha donat com a resultat un catalitzador amb activitat catalítica millorada per a la reacció de Prins entre ß-pinè i formaldehíd pel que fa a MIL-101(Cr) o l'inestable MIL-101(Fe) en les condicions de reacció estudiades. La presència de ions Fe3+ en els nodes metàl·lics de MIL-101(Cr,Fe) augmenta la densitat i la força dels llocs àcids de Lewis del material, mentre que la presència de Cr3+ en els nodes metàl·lics proporciona estabilitat al catalitzador. A més a més, aquesta Tesi ha demostrat que la presència de grups NO2 al lligam orgànic tereftalat de MIL-101(Cr) augmenta la densitat i la força dels llocs àcids de Lewis del material. Per tant, MIL 101(Cr)-NO2 exhibeix una activitat catalítica superior per a la síntesis de bencimidazols a partir de o-fenilendiamines i derivats de benzaldehid, així com per a l'oxidació aeròbica del tiofenol i la desulfuració oxidativa aeròbica de dibenzotiofens. Aquesta Tesi també ha demostrat que la sel·lecció d'un agent reductor apropiat com la hidroquinona per a la preparació de rGO a partir de GO augmenta la densitat dels llocs actius per a promoure les oxidacions aeròbiques de tiofenol i indano. / [EN] The present doctoral thesis has shown the possibility of engineering the active sites of MOFs and graphene-based materials as catalysts with enhanced activity for oxidation and condensation reactions. Specifically, the development of a mixed-metal MIL-101(Cr, Fe) has resulted in a catalyst with enhanced catalytic activity for the Prins reaction between ß-pinene and formaldehyde with respect to the use of MIL-101(Cr) or the unstable MIL 101(Fe) under the studied reaction conditions. The presence of Fe3+ ions in the metal nodes of the MIL-101(Cr, Fe) increases the density and strength of the Lewis acid sites of the material and the presence of Cr3+ in the metal nodes provides catalyst stability. Furthermore, this thesis has demonstrated that the presence of NO2 groups in the terephthalate organic ligand of MIL 101(Cr) increases the density and strength of Lewis acid sites of the material. Thus, MIL-101(Cr)-NO2 exhibits a superior catalytic activity for the synthesis of benzimidazoles from o-phenylenediamines and benzaldehyde derivatives, as well as for the aerobic oxidation of thiophenol and the aerobic oxidative desulfuration of dibenzothiophenes. This thesis has also shown that the selection of an appropriate reducing agent (such as hydroquinone) for the preparation of rGO from GO increases the density of active sites and promotes the aerobic oxidations of thiophenol and indane. / Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, CTQ2018-890237-CO2-R1 and Maria de Maeztu, CEX2019-000919-M), is gratefully acknowledged. Generalidad Valenciana is also thanked for funding (Prometeo 2017/083). S.N. thanks financial support by the Ministerio de Ciencia, Innovación y Universidades (RTI 2018-099482-A-100 project), Fundación Ramón Areces (XVIII Concurso Nacional para la Adjudicación de Ayudas a la Investigación en Ciencias de la Vida y de la Materia, 2016), and Generalitat Valenciana grupos de investigación consolidables 2019 (ref: AICO/2019/214) Project. E. G. thanks the ANR-11-LABEX-0039 (LabEx CHARM3AT) for financial support. M.G.-M thanks support from “la Caixa” Fundation (LCF/BQ/PI19/11690022) and Generalitat Valenciana (SEJI/2020/036). Financial support by the Spanish Ministry of Science and Innovation (Severo Ochoa and RTI2018-098237-CO21) and Generalitat Valenciana (Prometeo 2017/083) is gratefully acknowledged. / Vallés García, C. (2021). Engineering catalytic sites for oxidation and condensation reactions using metal-organic frameworks or graphene-based materials [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/175802 / TESIS

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Dans une thématique de plus en plus importante qui est celle du développement durable, il est aujourd’hui nécessaire d’adapter les réactions chimiques aux contraintes écologiques. Le développement de catalyseurs existe depuis le début de la chimie. Cependant, la compréhension des mécanismes mis en jeu lors des réactions chimiques est beaucoup plus récente, et ce, grâce à l’apparition de techniques d’analyse qui permettent de sonder les systèmes à différentes étapes des réactions. De nombreux catalyseurs moléculaires ont été développés, avec de très bons résultats au niveau des nombres de cycles catalytiques et de la sélectivité des réactions. Toutefois, ces catalyseurs sont souvent constitués d’un centre métallique de type iridium, ruthénium, palladium, rhodium ou platine, qui sont des métaux chers non biocompatibles. D’autre part, les oxydations sont des transformations chimiques très importantes. Des conditions de réactions dures, avec des oxydants stœchiométriques, souvent toxiques ou nocifs, sont généralement utilisées. Au contraire, des systèmes biologiques sont capables d’effectuer l’oxydation de molécules organiques en utilisant le dioxygène de l’air, en présence uniquement de protons, d’électrons, dans des conditions physiologiques. Quel grand défi pour les chimistes que d’arriver à développer des systèmes capables de mimer les systèmes biologiques, avec des catalyseurs composés de métaux biocompatibles tels que le cuivre, le manganèse et le fer. Le développement de ces catalyseurs biomimétiques demande une très bonne compréhension des systèmes biologiques, où les première et seconde sphères de coordination sont primordiales pour l'efficacité et la sélectivité des réactions. De nombreux complexes de fer(II) ont été développés comme catalyseurs dans notre équipe lors de thèses précédentes. L’interaction d’oxydants chimiques avec ces complexes a été étudiée, et une partie de mon projet a été de modifier les ligands pour augmenter la stabilité des catalyseurs, permettant l’augmentation de la sélectivité et les rendements de l’oxydation du cyclohexane et de l’anisole. Deux autres projets ont nécessité la fonctionnalisation d’un ligand utilisé communément au laboratoire pour son greffage covalent sur une électrode d’or ou dans une protéine. Afin de contrôler l’apport d’électrons au centre métallique pour réaliser l'activation réductrice du dioxygène, le complexe fonctionnalisé a été greffé sur des électrodes d’or. Le greffage sur électrode d’or a permis de mettre en avant la formation d’une monocouche homogène. Les premiers tests de réactivité de la SAM avec le dioxygène ont été également effectués. D’autre part, dans le but d’améliorer les rendements ainsi que la sélectivité des réactions en catalyse d’oxydation, un autre complexe fonctionnalisé a été greffé covalemment dans une protéine. Le greffage du complexe dans la β-lactoglobuline a permis de développer une nouvelle méthode de dosage du complexe de fer au sein de la protéine. Il a été possible de générer un intermédiaire réactionnel Feᴵᴵᴵ-peroxo, et les premiers tests en catalyse d’oxydation du thioanisole ont montré que la métalloenzyme artificielle permet d’observer une énantiosélectivité intéressante par rapport au complexe en solution. / According to sustainable development it is necessary to adapt chemical reactions to ecologic constraints. Oxidation reactions are useful transformations. Nevertheless, reaction conditions used are frequently harsh, with oxidants used in stoichiometric amount (often harmful or toxic), and lead to products formation with low selectivity. Biological systems such as metalloenzymes, are able to perform small organic molecule oxidation following O₂ activation. These reactions are achieved in physiological conditions, and with a high selectivity. Deciphering the reaction mechanism of these biological catalysts has stimulated the development of synthetic analogues such as non heme iron(II) complexes bearing amine/pyridine ligands. Reaction of these Fe(II) precursors with H₂O₂ or a single oxygen atom leads to formation of Fe(III)-OOH, Fe(III)-(O₂) and Fe(IV)=O, identified as potent oxidizing species in biological systems such as cytochromes P450. In this work, ligands were functionalized to graft iron(II) complexes on gold surface or in the β-lactoglobuline protein in order to use O₂ as oxidant or to improve yields and selectivity, respectively. Complexes grafted on gold surface were characterized by cyclic voltammetry, AFM and XPS. It has been demonstrated that it is possible to exchange exogenous ligands of the iron complex grafted on gold electrode. Preliminar reactivity tests using this grafted complex and O₂ were performed. A new artificial metalloenzyme was synthesized by covalent grafting of a functionalized iron(II) complex on β-lactoglobuline. The system was characterized, and a new method of iron(II) titration in the protein was devised. Using hydrogen peroxide, an Fe(III)-(η²-O₂) intermediate was generated and indentified in the biohybrid system, and catalytic thioanisole oxidation was observed. Interestingly, the sulfoxide product formation was shown to be enantioselective under these conditions.

<p dir="ltr">Metal speciation and structure can be influenced by the deposition method used during synthesis, interactions with the support, and by post-deposition treatments and reaction conditions experienced during its lifetime of carrying out a catalytic reaction. Supported metal particles of different size contain different surface structures and coordination environments, which may not only influence reaction rates but also the interconversion between agglomerated metallic domains and dispersed metal atom or ion sites. Here, we address the influence of post-deposition treatments and support properties on the structural interconversion of Pd and Cu on aluminosilicate chabazite (CHA) zeolites, Pt on gamma-alumina (γ-Al2O3), and Pd on amorphous oxides (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3). The fundamental insights from these studies can be used to design catalysts used widely in automotive exhaust aftertreatment systems, including Pd-exchanged zeolites for passive NOx (x = 1,2) adsorbers (PNA), Cu-exchanged zeolites for NOx (x = 1,2) selective catalytic reduction (SCR), Pt/Al2O3 for NH3 oxidation, and Pd/oxides for three-way catalysts (TWC). Incipient wetness impregnation (IWI) and colloidal methods were used to prepare Pd nanoparticles deposited on CHA zeolites with distinct Pd nanoparticle sizes and distributions. These Pd-CHA samples were used to investigate the effects of Pd particle size distribution on structural interconversion between ion-exchanged Pd and agglomerated Pd domains under realistic operating conditions. Smaller Pd nanoparticles had larger fractions of agglomerated Pd that converted to ion-exchanged Pd2+ sites at fixed air treatment temperatures (598–973 K) and H2O pressures (2–6 kPa H2O), consistent with thermodynamic predictions from DFT calculations. Furthermore, the addition of H2O during air treatment of different Pd nanoparticles (2–14 nm) inhibited the formation of ion-exchanged Pd2+ (thermodynamics), but not the rate of redispersion (kinetics). This demonstrates that, regardless of Pd nanoparticle size, water vapor in automotive exhaust streams facilitate metal sintering in PNA applications. Aqueous-phase exchange of Cu on CHA zeolites with varying support properties (i.e., number of paired Al sites in the 6 membered ring) were used to prepare materials with distinct types and numbers of extraframework Cu species (Cu2+, CuOH+). These Cu-CHA materials were used to analyze Cu structural changes before and after exposure to hydrothermal aging conditions. In the absence of H2O, some Cu2+ sites condense to form binuclear Ox-bridged Cu species that can be reduced with H2 to form Cu-hydride sites and reject H2O, leading to a sub-stoichiometric H2 consumption (H2/Cu < 0.5). In the presence of H2O, all nominally isolated Cu2+ species convert to [CuOH]+ structures, which can subsequently be reduced by H2 to form a Cu-hydride and reject H2O, leading to stoichiometric H2 consumption (H2/Cu ~ 0.5). Furthermore, the presence of H2O led to reduction features in H2 temperature programmed reduction (TPR) profiles that were similar among Cu-CHA materials, regardless of the initial Cu2+ speciation, further supporting the proposal that all nominally isolated Cu2+ sites convert to a similar [CuOH]+ motif. This demonstrates how water influences Cu speciation on CHA materials of varying origin or treatment history, aiding in quantifying SCR-active isolated Cu ions and SCR-inactive Cu species (e.g., CuO, CuAl2O4). Pt supported on γ-Al2O3 were prepared with different average Pt particle sizes (2–13 nm) by increasing the temperature of post-deposition air treatment (523–873 K). This suite of materials was interrogated to isolate the effects of Pt particle size on NH3 oxidation rates and selectivities during conditions relevant to NH3 slip applications in diesel exhaust aftertreatment. For all Pt particle sizes, NH3 oxidation rates displayed a hysteresis with temperature, with high rates measured during temperature decreases than during temperature increases. Smaller Pt particles (2 nm) had lower rates (per surface Pt, quantified by CO chemisorption) than larger Pt particles (13 nm), signifying that NH3 oxidation is a structure-sensitive reaction. Furthermore, surfaces of Pt particles restructure under NH3 oxidation reaction conditions, influencing effective Pt oxidation states, surface structures (numbers and types of exposed Pt sites), and surface coverages of intermediates leading to the observed hysteresis in rate. These findings demonstrate that Pt particles undergo dynamic structural changes during reaction, influencing their ability to convert NH3 to environmentally benign products in NH3 slip applications. The influence of treatment conditions, support properties, and initial Pd particle size and distribution on the kinetics of nanoparticle sintering were investigated to identify which material properties allow maintaining high dispersion to maximize metal utilization for three way catalysts (TWC) during the conversion of regulated pollutants (CO, hydrocarbons, NOx). Pd was deposited by IWI methods to generate polydiserse particle size distributions, and using colloidal Pd nanoparticle solutions to generate monodisperse size distributions, onto various supports (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3) and subjected to aging under oxidative and reductive conditions relevant for TWC operation. The average Pd particle size for all materials increased with treatment time under both reductive and oxidative environments. For samples prepared with IWI (i.e., log normal distribution of Pd particle sizes), reductive aging treatments led to higher sintering rates than oxidative treatments. In contrast, for samples prepared using colloidal Pd solutions (i.e., normal distribution of Pd particle sizes), oxidative aging treatments led to higher sintering rates than reduction treatments. Furthermore, after the same treatment condition and time, samples prepared with IWI resulted in higher average Pd particle sizes. These results indicate that more monodisperse initial Pd particle size distributions lead to lower sintering rates, providing guidance to design of supported metal TWCs with improved metal utilization during their lifetimes. Here, the combination of synthesis approaches to prepare a suite of model (e.g., powder) supported metal catalysts of varying structure and composition, interrogated using site and structural characterizations and steady-state and transient kinetic measurements, along with predictions from theoretical calculations, enabled unraveling the influence of material properties and gas environments that affect metal speciation, structure, and oxidation state in real-world aftertreatment systems that use more complex catalytic architectures (e.g., layered washcoats) and reactor designs (e.g., monoliths). This approach provides insights into the fundamental thermodynamic and kinetic factors influencing metal restructuring and interconversion under realistic conditions encountered in automotive exhaust aftertreatment applications, and the kinetic and mechanistic factors that underlie complex phenomena (e.g., reaction rate hysteresis) from data measured in the absence of hydrodynamic artifacts. The overall approach used in this work enabled development of synthesis-structure-function relationships on various metal supported catalysts for automotive exhaust aftertreatment applications, which can provide guidance for material design and treatment strategies to form and retain desired metal structures throughout the material lifetime, including synthesis, reaction, and regeneration treatments.</p>

Commercial fuels are mixtures with large numbers of components. Continuous thermodynamics is a technique for modelling fuel mixtures using a probability density function rather than dealing with each discreet component. The mean and standard deviation of the distribution are then used to model the chemical reactions of the mixture. This thesis develops the necessary theory to apply the technique of continuous thermodynamics to the oxidation reactions of hydrocarbon fuels. The theory is applied to three simplified models of hydrocarbon oxidation: a global one-step reaction, a two-step reaction with CO as the intermediate product, and the four-step reaction of Müller et al. (1992), which contains a high- and a low-temperature branch. These are all greatly simplified models of the complex reaction kinetics of hydrocarbons, and in this thesis they are applied specifically to n-paraffin hydrocarbons in the range from n-heptane to n-hexadecane. The model is tested numerically using a simple constant pressure homogeneous ignition problem using Cantera and compared to simplified and detailed mechanisms for n-heptane. The continuous thermodynamics models are able not only to predict ignition delay times and the development of temperature and species concentrations with time, but also changes in the mixture composition as reaction proceeds as represented by the mean and standard deviation of the distribution function. Continuous thermodynamics is therefore shown to be a useful tool for reactions of multicomponent mixtures, and an alternative to the "surrogate fuel" approach often used at present.