Chimie organométallique résonne avec catalyse homogène, et chimie des surfaces avec catalyse hétérogène. Mais la frontière établie entre ces deux domaines est en réalité très mince. Leur rapprochement aboutit dans les années 1990 au développement d’une nouvelle science : la chimie organométallique de surface, qui souligne leur complémentarité. L’objectif de cette science, dans laquelle s’inscrit ce travail de thèse, est de créer des catalyseurs hétérogènes à partir de composés organométalliques. Notre objectif est d’apporter une contribution à la compréhension de la formation de nanoparticules de platine - métal incontournable en catalyse hétérogène - sur des supports de silice amorphe, et ce grâce à la chimie organométallique. Au cours de ce travail, une palette de catalyseurs Pt/SiO2 a été préparée à partir de trois précurseurs de platine : le composé classique H2PtIVCl6.xH2O et deux composés organométalliques PtII(η 4-C8H12)Cl2 et Pt0(η 2-C7H10)3 , et de trois supports : une silice commerciale (Davison), une silice mésoporeuse SBA-15 synthétisée au laboratoire et unesilice naturelle, la diatomite. De plus, l’étude du catalyseur de référence au platine « EuroPt-1 » a permis de développer une méthodologie de suivi operando par Spectroscopie Infrarouge à Transformée de Fourier par Réflexion Diffuse (DRIFTS) de l’adsorption du monoxyde de carbone (CO) sur les différents sites d’une nanoparticule de platine. En conclusion, les catalyseurs préparés à partir de Pt0(η 2-C7H10)3 s’avèrent être plus actifs qu’EuroPt-1 pour la réaction d’oxydation du CO, ce qui démontre le potentiel d’utilisation des composés organométalliques dans le domaine de la catalyse hétérogène. / Organometallic chemistry resonates with homogeneous catalysis, and surface chemistry with heterogeneous catalysis. But the frontier between these two fields is very thin. In the 90’s, these fields approached each other and led to the development of a new science: organometallic surface chemistry, which underlines their complementarity. The goal of this science, with which this work is associated, is to create heterogeneous catalysts from organometallic compounds. Our goal is to contribute to the understanding of platinum nanoparticle formation - platinum being an important metal in heterogeneous catalysis - onto amorphous silica supports, thanks to organometallic chemistry. During this work, various Pt/SiO2 catalysts were prepared fromthree platinum precursors: the classical one, H2PtIVCl6.xH2O and two organometallic compounds PtII(η 4-C8H12)Cl2 et Pt0(η2-C7H10)3, and involved three supports: a commercial silica (Davison), a mesoporous silica SBA-15 synthesized in the laboratory, and a natural silica, the diatomite. Moreover, the study of the standard platinum reference catalyst “EuroPt-1” lead to the development of a methodology of operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) of carbon monoxide (CO) adsorption on the different sites of a platinum nanoparticle. Catalysts prepared from Pt0(η 2-C7H10)3 are more active than EuroPt-1 for the CO oxidation reaction, and this work shows the potential of organometallic precursors in the domain of heterogeneous catalysis.

In dieser Dissertation wird der Einfluss unterschiedlicher Sauerstoff-Koordinationsgeometrien um ein zentrales Kobaltatom evaluiert. Genauer werden Oxide, die tetraedrisch und oktaedrisch koordiniertes Kobalt enthalten, synthetisiert und charakterisiert. Zudem wird ihre Aktivität in Hinblick auf die Sauerstoffentwicklungsreaktion (OER) unter alkalischen Bedingungen untersucht. Die elektrochemischen Analysen zeigen dabei, dass Materialien, die Kobalt in tetraedrischer Sauerstoffkoordination enthalten, die besseren Katalysatorvorläufer für die OER sind. Weiterhin kann demonstriert werden, dass das Herauslösen von inaktiven Metallen aus einer Struktur die Aktivität erhöht. Darauf basierend wird das neue Material Zn0.35Co0.65O vorgeschlagen. Es kristallisiert in der Wurtzitstruktur und enthält nur tetraedrisch koordinierte Atome. In alkalischen Lösungen wandelt sich die Wurtzitstruktur über die Zwischenstufe Co(OH)2 zum gamma-Co(O)OH um, und nahezu alles Zink wird aus der Struktur herausgelöst. Dadurch wird ein Material mit einer großen elektrochemisch aktiven Oberfläche gewonnen, das unterkoordinierte CoO(6-x) Oktaeder als aktive Zentren für die OER enthält. Hierdurch wird eine herausragende katalytische Leistung erreicht. Um weitere Einblicke in die OER zu generieren, wird Diffuse Reflexions UV/Vis (DRUV) Spektroskopie verwendet. Es werden neuartige Durchflusszellendesigns vorgeschlagen, die es erlauben, DRUV Spektren während der Katalyse aufzunehmen, d.h. operando. Durch diesen spektroelektrochemischen Ansatz werden Veränderungen der Katalysatoren während der OER beobachtet. So kann die Phasenumwandlung von Zn0.35Co0.65O erfolgreich verfolgt werden. Ebenso kann gezeigt werden, dass CoAl2O4 und Co2SnO4 nur an ihrer Oberfläche katalytische Aktivität aufweisen. Durch den Vergleich mit ex situ Analysen werden eindeutige Struktur-Eigenschaftsbeziehungen vorgeschlagen und tiefere Einsichten in die katalytisch aktiven Strukturmotive erhalten. / In this PhD thesis, the influence of different coordination geometries of oxygen atoms around a central cobalt atom is evaluated. Specifically, oxides containing tetrahedral and octahedral coordinated cobalt are synthesized, characterized and their activity towards the OER under alkaline conditions is evaluated. The electrochemical analyses reveal, that materials containing cobalt in tetrahedral oxygen coordination are better precatalysts for the OER. Furthermore, it is demonstrated that leaching of inactive metals from a structure increases the activity as well. Based on the previous mentioned, the new material Zn0.35Co0.65O is proposed. It crystallizes in the wurtzite structure and contains solely tetrahedrally coordinated atoms. In alkaline solutions, it transforms from wurtzite structure via a hydroxide to gamma-Co(O)OH, and nearly all Zn is leached from the structure. By this, a material with a large electrochemically active surface area is generated, that contains under-coordinated CoO(6-x) octahedra as active centers for the OER. Thus, outstanding catalytic performance is achieved. To generate further insights into the OER, diffuse reflectance ultraviolet visible (DRUV) spectroscopy is facilitated. Novel flow-cell designs are proposed, that allow to record DRUV spectra of catalysts under working conditions, i.e. operando. By this spectroelectrochemical approach, changes the catalysts undergo during the OER are observed. The phase transitions of Zn0.35Co0.65O are successfully followed, and it can be further shown, that CoAl2O4 and Co2SnO4 are only active at their surface. By comparison to ex situ analyses, clear structure-activity correlations are proposed, and deeper insights in the catalytically active structural motifs are obtained.

A globalização da economia e dos negócios consolida um novo contexto de competição acirrada, de mercados mutantes, onde não é mais possível auscultar o passado para orientar as decisões do agora e muito menos do futuro. Com isso surgem as crises, os concorrentes mudam rapidamente sua forma de competir, surgem novos conceitos que são aplicados na gestão e organização dos negócios, novas tecnologias aparecem com ciclos de vida cada vez mais curtos, tornando obsoletas as que estão em uso. Nos setores empresariais mais afetados pelo novo ambiente, onde o acirramento da competição está mais presente e visível, parece estar sendo cada vez mais difícil para uma empresa sozinha enfrentar a concorrência. Surgem, então, alguns indícios de que as empresas estão buscando outras formas de gestão e de atuação para competir, que incluem inclusive a competição conjunta. Ou seja, uma forma de competição diferente entre as empresas, nas quais algumas se unem a outras empresas para disputar o mercado com outros agrupamentos e ou aglomerados de empresas. Esta união já foi evidenciada através de diferentes formatos supra-empresas. Dentre esses formatos destacam-se os clusters de negócios e as redes de negócios, nos quais a governança transcende as fronteiras de uma empresa isolada, atingindo a todo o aglomerado. A preocupação da presente pesquisa foi verificar se, dentro de agrupamentos de empresas denominados pela literatura como clusters, existem ou não, dentre as empresas nele instaladas, algumas que, também, se orientam por estratégias supraempresas de redes de negócios, e não só por estratégias de clusters. Isso foi verificado pela pesquisa, que, em dois clusters de negócios importantes para seus países, o do vinho do Porto, no Vale do Douro, em Portugal, e o de vinhos de mesa do Vale dos Vinhedos, na Serra Gaúcha, no Brasil, encontrou empresas orientadas por uma estratégia dual, isto é, por estratégia de cluster e por estratégia de rede de negócios. E esse achado é novo na literatura de entidades supra-empresas, até porque essas próprias entidades só recentemente tornaram-se conhecidas e objetos raras pesquisas. Foi, também, preocupação da pesquisa que embasou esta tese, verificar se o fato constatado de existirem empresas orientadas por estratégia dual contribuía ou não para um aumento em suas respectivas capacidades de competição, o que, também, acabou sendo comprovado. / The globalization of the economy and business consolidates a new context of fierce competition, changing markets, where you can no longer hear the past to guide the decisions of the now much less of the future. With that come the crisis, the competitors rapidly change its manner to compete, new concepts are applied in management and business organization, new technologies appears with lifecycles each time shorter, making obsolete the ones in use. In the business sectors most affected by the new environment, where increased competition is more present and visible, seems to be increasingly difficult for one company alone to face the competition. Then we see some evidence that companies are seeking other forms of management and performance to compete, including even the competition in conjunct. In other words, a form of competition of companies in which they join other companies to compete in the market with others agglomerates of companies. This union has been evidenced by different formats of supra-companies. Among these formats we can highlight the business clusters and business networks, in which governance transcends the boundaries of a single company, reaching the entire agglomerate. The concern of this study was to determine if, within groups of companies named in the literature as clusters, exist or not among the companies in it, some of them that are also guided by supra-companies strategies of networks business, not just by cluster strategies. This was verified by this research, two clusters of important business in their countries, the Port wine, in the Douro Valley, Portugal, and the wines of Vinhedos Valley, in Serra Gaúcha, Brazil, we found companies oriented with a dual strategy, in other words, by cluster strategy and business network strategy. And this discover is new in the literature of supra-companies entities, because those entities themselves are not of very recent scholarship. Another concern of this research was to verify if the fact of companies driven by a dual strategy had contributed to an increase in their competitiveness, what the study also confirmed

A globalização da economia e dos negócios consolida um novo contexto de competição acirrada, de mercados mutantes, onde não é mais possível auscultar o passado para orientar as decisões do agora e muito menos do futuro. Com isso surgem as crises, os concorrentes mudam rapidamente sua forma de competir, surgem novos conceitos que são aplicados na gestão e organização dos negócios, novas tecnologias aparecem com ciclos de vida cada vez mais curtos, tornando obsoletas as que estão em uso. Nos setores empresariais mais afetados pelo novo ambiente, onde o acirramento da competição está mais presente e visível, parece estar sendo cada vez mais difícil para uma empresa sozinha enfrentar a concorrência. Surgem, então, alguns indícios de que as empresas estão buscando outras formas de gestão e de atuação para competir, que incluem inclusive a competição conjunta. Ou seja, uma forma de competição diferente entre as empresas, nas quais algumas se unem a outras empresas para disputar o mercado com outros agrupamentos e ou aglomerados de empresas. Esta união já foi evidenciada através de diferentes formatos supra-empresas. Dentre esses formatos destacam-se os clusters de negócios e as redes de negócios, nos quais a governança transcende as fronteiras de uma empresa isolada, atingindo a todo o aglomerado. A preocupação da presente pesquisa foi verificar se, dentro de agrupamentos de empresas denominados pela literatura como clusters, existem ou não, dentre as empresas nele instaladas, algumas que, também, se orientam por estratégias supraempresas de redes de negócios, e não só por estratégias de clusters. Isso foi verificado pela pesquisa, que, em dois clusters de negócios importantes para seus países, o do vinho do Porto, no Vale do Douro, em Portugal, e o de vinhos de mesa do Vale dos Vinhedos, na Serra Gaúcha, no Brasil, encontrou empresas orientadas por uma estratégia dual, isto é, por estratégia de cluster e por estratégia de rede de negócios. E esse achado é novo na literatura de entidades supra-empresas, até porque essas próprias entidades só recentemente tornaram-se conhecidas e objetos raras pesquisas. Foi, também, preocupação da pesquisa que embasou esta tese, verificar se o fato constatado de existirem empresas orientadas por estratégia dual contribuía ou não para um aumento em suas respectivas capacidades de competição, o que, também, acabou sendo comprovado. / The globalization of the economy and business consolidates a new context of fierce competition, changing markets, where you can no longer hear the past to guide the decisions of the now much less of the future. With that come the crisis, the competitors rapidly change its manner to compete, new concepts are applied in management and business organization, new technologies appears with lifecycles each time shorter, making obsolete the ones in use. In the business sectors most affected by the new environment, where increased competition is more present and visible, seems to be increasingly difficult for one company alone to face the competition. Then we see some evidence that companies are seeking other forms of management and performance to compete, including even the competition in conjunct. In other words, a form of competition of companies in which they join other companies to compete in the market with others agglomerates of companies. This union has been evidenced by different formats of supra-companies. Among these formats we can highlight the business clusters and business networks, in which governance transcends the boundaries of a single company, reaching the entire agglomerate. The concern of this study was to determine if, within groups of companies named in the literature as clusters, exist or not among the companies in it, some of them that are also guided by supra-companies strategies of networks business, not just by cluster strategies. This was verified by this research, two clusters of important business in their countries, the Port wine, in the Douro Valley, Portugal, and the wines of Vinhedos Valley, in Serra Gaúcha, Brazil, we found companies oriented with a dual strategy, in other words, by cluster strategy and business network strategy. And this discover is new in the literature of supra-companies entities, because those entities themselves are not of very recent scholarship. Another concern of this research was to verify if the fact of companies driven by a dual strategy had contributed to an increase in their competitiveness, what the study also confirmed

Recent advances in nanoscience and technology have provided the scientific community with new exciting opportunities to rationally design and fabricate materials at the nanometer scale with drastically different properties as compared to their bulk counterparts. A variety of challenges related to nanoparticle (NP) synthesis and materials characterization have been tackled , allowing us to make more homogenous, well defined, size- and shape-selected NPs, and to probe deeper and more comprehensively into their distinct properties. In this dissertation, a variety of phenomena relevant to nanosized materials are investigated, including the thermal stability of NPs and coarsening phenomena in different environments, the experimental determination of NP shapes, gaining insight into NP-support interactions, epitaxial relationships, and unusual thermodynamic and electronic properties of NPs, including the effect of adsorbates on the electron density of states of small clusters, and the chemical, and structural evolution of NPs under reaction conditions. In chapter 2, a general description of different characterization tools that are used in this dissertation is provided. In chapter 3, the details of two different methods used for NP synthesis, namely inverse micelle encapsulation and physical vapor deposition (PVD) are described. Chapter 4 describes the thermal stability and coarsening behavior of Pt NPs supported on TiO2(110) and γ-Al2O3 as a function of the synthesis method, support pretreatment, and annealing environment. For the Pt/TiO2(110) system, micellesynthesized NPs showed remarkable stability against coarsening for annealing temperatures up to 1060°C in vacuum, in contrast to PVD-grown NPs. When comparing v different annealing environments (H2, O2, H2O), Pt NPs on γ-Al2O3 annealed in O2 were found to be the least affected by coarsening, followed by those heated in H2O vapor. The largest NP growth was observed for the sample annealed in H2. The role of the PtOx species formed under oxidizing conditions will be discussed. In chapter 5, the shape of Pt and Au NPs and their epitaxial relationship with the TiO2(110) support was extracted from scanning tunneling microscopy (STM) measurements. Three main categories of NP shapes were identified, and through shape modeling, the contribution of facets with different orientations was obtained as a function of the number of atoms in each NP. It was also shown that the micellesynthesized Pt and Au NPs have an epitaxial relationship with the support, which is evident from the fact that they always have one symmetry axis parallel to TiO2(110) atomic rows in [001] directions. Chapter 6 describes how the presence of NPs on TiO2(110) surface affects its reconstruction upon high temperature annealing in vacuum. In contrast to NP-free TiO2(110) substrates, long and narrow TiO2 stripes are observed for Pt NP-decorated surfaces. This phenomenon is explained based on the stabilization of TiO2, induced by Pt NPs, which hinders the desorption of oxygen atoms in TiO2 to vacuum. In chapter 7, a systematic investigation of the thermodynamic properties of γ- Al2O3-supported Pt NPs and their evolution with decreasing NP size is presented. A combination of in situ extended x-ray absorption fine structure spectroscopy (EXAFS), ex situ transmission electron microscopy (TEM) measurements, and NP shape modeling is used to obtain the NPs shape, thermal expansion coefficient, and Debye vi temperature. The unusual thermodynamic behavior of these NPs such as their negative thermal expansion and enhanced Debye temperature are discussed in detail. Chapter 8 presents an investigation of the electronic properties of size-controlled γ-Al2O3-supported Pt NPs and their evolution with decreasing NP size and adsorbate (H2) coverage. The hydrogen coverage of Pt NPs at different temperatures was estimated based on XANES data and was found to be influenced by the NP size, and shape. In addition, correlations between the shift in the center of the unoccupied d-band density of states (theory) and energy shifts of the XANES spectra (experiment) upon hydrogen chemisorption as well as upon modification of the NP structure were established. Chapter 9 is dedicated to an operando study, describing the evolution of the structure and oxidation state of ZrO2-supported Pd nanocatalysts during the in-situ selective reduction of NO in H2 via EXAFS and XANES measurements.

<p>Although Cu-SSZ-13 zeolites are used commercially in diesel engine exhaust after-treatment for abatement of toxic NO_x pollutants via selective catalytic reduction (SCR) with NH₃, molecular details of its active centers and mechanistic details of the redox reactions they catalyze, specifically of the Cu(I) to Cu(II) oxidation half-reaction, are not well understood. A detailed understanding of the SCR reaction mechanism and nature of the Cu active site would provide insight into their catalytic performance and guidance on synthesizing materials with improved low temperature (< 473 K) reactivity and stability against deactivation (e.g. hydrothermal, sulfur oxides). We use computational, titration, spectroscopic, and kinetic techniques to elucidate (1) the presence of two types of Cu²⁺ ions in Cu-SSZ-13 materials, (2) molecular details on how these Cu cations, facilitated by NH₃ solvation, undergo a reduction-oxidation catalytic cycle, and (3) that sulfur oxides poison the two different types of Cu²⁺ ions to different extents at via different mechanisms. </p><p><br></p> <p> </p> <p>Copper was exchanged onto H-SSZ-13 samples with different Si:Al ratios (4.5, 15, and 25) via liquid-phase ion exchange using Cu(NO₃)₂ as the precursor. The speciation of copper started from the most stable Cu²⁺ coordinated to two anionic sites on the zeolite framework to [CuOH]⁺ coordinated to only one anionic site on the zeolite framework with increasing Cu:Al ratios. The number of Cu²⁺ and [CuOH]⁺ sites was quantified by selective NH₃ titration of the number of residual Brønsted acid sites after Cu exchange, and by quantification of Brønsted acidic Si(OH)Al and CuOH stretching vibrations from IR spectra. Cu-SSZ-13 with similar Cu densities and anionic framework site densities exhibit similar standard SCR rates, apparent activation energies, and orders regardless of the fraction of Z₂Cu and ZCuOH sites, indicating that both sites are equally active within measurable error for SCR. </p><p><br></p> <p> </p> <p>The standard SCR reaction uses O₂ as the oxidant (4NH₃ + 4NO + O₂ -> 6H₂O + 4N₂) and involves a Cu(I)/Cu(II) redox cycle, with Cu(II) reduction mediated by NO and NH₃, and Cu(I) oxidation mediated by NO and O₂. In contrast, the fast SCR reaction (4NH₃ + 2NO + 2NO₂ -> 6H₂O + 4N₂) uses NO₂ as the oxidant. Low temperature (437 K) standard SCR reaction kinetics over Cu-SSZ-13 zeolites depend on the spatial density and distribution of Cu ions, varied by changing the Cu:Al and Si:Al ratio. Facilitated by NH₃ solvation, mobile Cu(I) complexes can dimerize with other Cu(I) complexes within diffusion distances to activate O₂, as demonstrated through X-ray absorption spectroscopy and density functional theory calculations. Monte Carlo simulations are used to define average Cu-Cu distances. In contrast with O₂-assisted oxidation reactions, NO₂ oxidizes single Cu(I) complexes with similar kinetics among samples of varying Cu spatial density. These findings demonstrate that low temperature standard SCR is dependent on Cu spatial density and requires NH₃ solvation to mobilize Cu(I) sites to activate O₂, while in contrast fast SCR uses NO₂ to oxidize single Cu(I) sites. </p><p><br></p> <p> </p> <p>We also studied the effect of sulfur oxides, a common poison in diesel exhaust, on Cu-SSZ-13 zeolites. Model Cu-SSZ-13 samples exposed to dry SO₂ and O₂ streams at 473 and 673 K. These Cu-SSZ-13 zeolites were synthesized and characterized to contain distinct Cu active site types, predominantly either divalent Cu²⁺ ions exchanged at proximal framework Al sites (Z₂Cu), or monovalent CuOH+ complexes exchanged at isolated framework Al sites (ZCuOH). On the model Z₂Cu sample, SCR turnover rates (473 K, per Cu) catalyst decreased linearly with increasing S content to undetectable values at equimolar S:Cu molar ratios, while apparent activation energies remained constant at ~65 kJ mol^-1, consistent with poisoning of each Z₂Cu site with one SO₂-derived intermediate. On the model ZCuOH sample, SCR turnover rates also decreased linearly with increasing S content, yet apparent activation energies decreased monotonically from ~50 to ~10 kJ mol^-1, suggesting that multiple phenomena are responsible for the observed poisoning behavior and consistent with findings that SO₂ exposure led to additional storage of SO₂-derived intermediates on non-Cu surface sites. Changes to Cu²⁺ charge transfer features in UV-Visible spectra were more pronounced for SO₂-poisoned ZCuOH than Z₂Cu sites, while X-ray diffraction and micropore volume measurements show evidence of partial occlusion of microporous voids by SO₂-derived deposits, suggesting that deactivation may not only reflect Cu site poisoning. Density functional theory calculations are used to identify the structures and binding energies of different SO₂-derived intermediates at Z₂Cu and ZCuOH sites. It is found that bisulfates are particularly low in energy, and residual Brønsted protons are liberated as these bisulfates are formed. These findings indicate that Z₂Cu sites are more resistant to SO₂ poisoning than ZCuOH sites, and are easier to regenerate once poisoned. </p>

Tesis por compendio / [ES] El cambio climático es una de las amenazas de nuestro tiempo. Los gases de efecto invernadero, como el CO2, son los principales causantes de este fenómeno, siendo necesario disminuir urgentemente sus emisiones. En 2019, la Comisión Europa presentó el "Pacto Verde Europeo", que será clave para alcanzar un objetivo tremendamente ambicioso para nuestra región: la neutralidad climática de aquí a 2050. Las estrategias de descarbonización incluidas en su hoja de ruta van a implicar necesariamente la transición energética de los combustibles fósiles a las energías renovables, reduciendo de forma masiva la liberación de CO2. En este sentido, el desarrollo de tecnologías efectivas de Captura, Almacenamiento y Uso del Carbono (CAUC) permitirá la valorización del CO2, evolucionando hacia una economía de carbono circular. La presente Tesis Doctoral se enmarca en el diseño, síntesis y caracterización de sistemas catalíticos heterogéneos innovadores basados en metales capaces de transformar el CO2 en otros productos de valor añadido. Entre un amplio catálogo de reacciones que "conectan" el CO2 con diversos compuestos basados en carbono, esta Tesis se centrará principalmente en la síntesis de dos moléculas C1 plataforma de interés industrial: el metanol y el metano. Los Capítulos 3 y 4 están dedicados a la síntesis de metanol, un proceso exotérmico limitado termodinámicamente debido a la estabilidad inherente de la molécula de CO2, así como a la presencia de la reacción competitiva RWGS. Por un lado, el Capítulo 3 se centra en el efecto promotor del galio sobre las propiedades estructurales, electrónicas y catalíticas de materiales basados en Cu/ZnO (sistemas CZG). Mediante un enfoque espectroscópico-catalítico multidisciplinar se ha comparado el efecto promotor del Ga3+ dopado en la red de un ZnO tipo wurtzita presente en un catalizador Cu/ZnO/Ga2O3 con el de una fase de galato de zinc (ZnGa2O4). Por otro lado, en el Capítulo 4 se muestra un catalizador bifuncional que contiene nanopartículas de Cu de 2 nm y especies Cu+, con el objetivo de enfrentarse a la inherente baja actividad de estas pequeñas partículas, hecho que impide mejorar la eficiencia atómica de los catalizadores, dificultando así la obtención de resultados catalíticos competitivos en la hidrogenación de CO2. La realización de un estudio espectroscópico detallado (combinado con cálculo teórico y ensayos catalíticos) sobre un catalizador óxido mixto de Cu-Mg-Al derivado de un precursor de hidrotalcita tras calcinación y posterior reducción (CuHT-230) pone de manifiesto el papel clave de los iones Cu+ dopados en estructura en la producción de metanol. El éxito de las tecnologías CAUC a medio-largo plazo dependerá no solo del desarrollo de catalizadores competitivos, sino también de su capacidad para operar en condiciones de reacción más suaves, permitiendo que estos procesos sean viables económicamente. Por ello, el concepto de eficiencia energética se abordará en el Capítulo 5, a través de un innovador diseño de catalizador tipo "shell/core" formado por un núcleo de rutenio metálico y una envoltura de carburo de rutenio, sintetizado via hidrotermal. Este sistema (Ru@EDTA-20) exhibe una actividad excepcionalmente alta para la hidrogenación de CO2 a metano a bajas temperaturas (160-200 °C) con una selectividad a CH4 del 100%, superando a catalizadores de bibliografía que normalmente operan a mayores temperaturas (400-500 °C). Por último, en el Capítulo 6 se estudia un catalizador modelo compuesto por un alumino-silicato bidimensional sintetizado sobre una superficie de Ru(0001), investigación realizada durante mi estancia internacional en el Laboratorio Nacional de Brookhaven (Nueva York, EE.UU.). La combinación de estos materiales en el mismo composite permite la creación de un nanoespacio confinado que puede emplearse como nanorreactor. En este proyecto, se seleccionó la reacción de formación de agua como modelo, que se exploró a nivel fundamental en el sincrotrón NSLS-II. / [CA] El canvi climàtic és una de les amenaces del nostre temps. Els gasos d'efecte d'hivernacle, com el diòxid de carboni, són els principals causants d'aquest fenomen, sent necessari reduir urgentment les seues emissions. En 2019, la Comissió Europea va presentar el "Pacte Verd Europeu", que serà clau per a aconseguir un objectiu tremendament ambiciós per a la nostra regió: la neutralitat climàtica d'ací a 2050. Les estratègies de descarbonització incloses en el seu full de ruta implicaran necessàriament la transició energètica dels combustibles fòssils a les energies renovables, reduint de manera massiva l'alliberament de CO2. En aquest sentit, el desenvolupament de tecnologies efectives de Captura, Emmagatzematge i Ús del Carboni (CEUC) permetrà la valorització del CO2, evolucionant cap a una economia de carboni circular. La present Tesi Doctoral s'emmarca en el disseny, síntesi i caracterització de sistemes catalítics heterogenis innovadors basats en metalls capaços de transformar el CO2 en altres productes de valor afegit. Entre un ampli catàleg de reaccions que "connecten" el CO2 amb diversos compostos basats en carboni, aquesta Tesi se centrarà principalment en la síntesi de dues molècules C1 plataforma d'interés industrial: el metanol i el metà. Els Capítols 3 i 4 estan dedicats a la síntesi de metanol, un procés exotèrmic limitat degut tant a l'estabilitat inherent de la molècula de CO2 com a la presència de la reacció competitiva RWGS. D'una banda, el Capítol 3 se centra en l'efecte promotor del gal·li sobre les propietats estructurals, electròniques i catalítiques de materials basats en Cu/ZnO (sistemes CZG). Mitjançant un enfocament espectroscòpic-catalític multidisciplinari s'ha comparat l'efecte promotor del Ga3+ dopat en la xarxa d'un ZnO (wurtzita) present en un catalitzador Cu/ZnO/Ga2O3 amb el d'una fase de ZnGa2O4. D'altra banda, en el Capítol 4 es mostra un catalitzador bifuncional que conté nanopartícules de Cu de 2 nm i espècies Cu+, amb l'objectiu d'enfrontar-se a la inherent baixa activitat d'aquestes petites partícules, fet que impedeix millorar l'eficiència atòmica dels catalitzadors, dificultant així l'obtenció de resultats catalítics competitius en la hidrogenació de CO2. La realització d'un estudi espectroscòpic detallat (combinat amb càlcul teòric i assajos catalítics) sobre un catalitzador òxid mixt de Cu-Mg-Al derivat d'un precursor de hidrotalcita després de calcinació i posterior reducció (CuHT-230) posa de manifest el paper clau dels ions Cu+ dopats en estructura en la producció de metanol. L'èxit de les tecnologies CEUC a mig-llarg termini dependrà no solament del desenvolupament de catalitzadors competitius, sinó també de la seua capacitat per a operar en condicions de reacció més suaus, permetent que aquests processos siguen viables econòmicament. Per això, el concepte d'eficiència energètica s'abordarà en el Capítol 5, a través un innovador disseny de catalitzador tipus "shell/core" format per un nucli de ruteni metàl·lic i un embolcall de carbur de ruteni, sintetitzat mitjançant tractament hidrotermal. Aquest sistema (Ru@EDTA-20) exhibeix una activitat excepcionalment alta per a la hidrogenació de CO2 a metà a baixes temperatures (160-200 °C) amb una selectivitat a CH4 del 100%, superant a catalitzadors de bibliografia que normalment operen a majors temperatures (400-500 °C). Finalment, en el Capítol 6 s'estudia un catalitzador model compost per un alumino-silicat bidimensional sintetitzat sobre una superfície de Ru(0001), investigació realitzada durant la meua estada internacional en el Laboratori Nacional de Brookhaven (Nova York, els Estats Units). La combinació d'aquests dos materials en el mateix "composite" permet la creació d'un nano-espai confinat que pot emprar-se com nano-reactor. En aquest projecte, es va seleccionar la reacció de formació d'aigua com a model, que es va explorar a nivell fonamental en el sincrotró NSLS-II. / [EN] Climate change is one of the existential threats of our times. Greenhouse gases (GHG), such as carbon dioxide, are primary drivers of this phenomenon, and their emissions need to be urgently reduced. In 2019, the European Commission presented the European Green Deal, which will help the EU to attain an ambitious goal for our region: to become carbon-neutral by 2050. The decarbonization strategies included in the roadmap towards net-zero emissions will imply the energy transition from fossil fuels to renewable energies, with a massive reduction of CO2 deliverance. In this sense, the development of effective Carbon Capture and Storage (CCS) and Carbon Capture and Utilization (CCU) technologies will allow the valorization of CO2, evolving into a circular carbon economy. The present Doctoral Thesis focuses on the design, synthesis and characterization of innovative heterogeneous metal-based systems, which are able to transform CO2 into value-added products. Among a wide catalogue of reactions that "connects" CO2 with various carbon-based compounds, this thesis will be devoted to the synthesis of two C1 platform chemicals of industrial interest: methanol and methane. Chapters 3 and 4 are dedicated to methanol synthesis, a highly hampered exothermic process due to the inherent stability of the CO2 molecule and the presence of the competitive reverse water-gas shift reaction (RWSG). On the one hand, Chapter 3 is focused on the promoting effect of gallium on the structural, electronic, and catalytic properties of Cu/ZnO based materials (CZG systems). In particular, the promoting effect of Ga3+-doped in the wurtzite ZnO lattice of a Cu/ZnO/Ga2O3 catalyst is compared to that of a zinc gallate (ZnGa2O4) phase following a multimodal spectroscopic-catalytic approach. In Chapter 4, a bifunctional catalyst containing 2 nm Cu nanoparticles and Cu+ species is presented, to overcome the "assumed" low activity of small copper particles that prevents obtaining high atom efficiency and competitive catalytic results in the CO2 hydrogenation to methanol. A detailed spectroscopic study (combined with theoretical calculations and catalytic tests) performed on a Cu-Mg-Al mixed oxide catalyst derived from a hydrotalcite precursor by calcination and further reduction (CuHT-230) highlights the key role of doped Cu+ ions in methanol production. The success of CCU technologies in the medium-long term will depend not only on the development of competitive catalysts but also on their ability to operate under milder reaction conditions, which will make these processes economically viable. Consequently, the energy efficiency issue will be addressed in Chapter 5 with the innovative design of a core-shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide, synthesized via hydrothermal treatment. This catalyst (Ru@EDTA-20) exhibits exceptional high activity for CO2 hydrogenation to methane (Sabatier reaction) at low temperatures (160-200 °C) with 100% selectivity to CH4, outperforming the state of the art catalysts operating at 400-500 °C. Finally, Chapter 6 covers the investigation carried out on a model ruthenium-based catalyst composed of a 2D-bilayered aluminosilicate grown over a Ru(0001) surface during my international short-term stay at Brookhaven National Laboratory (New York, USA). The combination of these materials in a composite allows the creation of a confined nano-space that can be exploited as a nano-reactor. In this project, water formation reaction (WFR) was selected as model reaction, which was fundamentally explored at NSLS-II synchrotron. / Cored Bandrés, J. (2022). Innovative Design of Heterogeneous Catalysts with Improved CO2 Hydrogenation Performance [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/182403 / Compendio

Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.