No description available.

A catalytic route to hydrogen production via thermochemical water splitting is highly desirable because it directly converts thermal energy into stored chemical energy in the form of hydrogen and oxygen. Recently, the Davis group at Caltech reported an innovative low-temperature (max 850°C) catalytic cycle for thermochemical water splitting based on sodium and manganese oxides (Xu, Bhawe and Davis, PNAS, 2012). The key steps are thought to be hydrogen evolution from a Na₂CO₃/MnO mixture, and oxygen evolution by thermal reduction of solids formed by Na⁺ extraction from NaMnO₂. Our work is aimed at understanding the fundamental chemical processes involved in the catalytic cycle, especially the hydrogen evolution from water. In this project, efforts are made to understand the interactions between the key components (Na, O₂, CO₂, and water) in the hydrogen evolution steps on a well-defined MnO(100) single crystal surface, utilizing x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). While some of the behavior of the catalytic system is observed with the model system developed in this work, hydrogen is only produced from water in the presence of metallic sodium, in contrast to the proposal of Xu et al. that water splitting occurs from the reaction of water with a mixture of Na₂CO₃ and MnO. These differences are discussed in light of the different operating conditions for the catalytic system and the surface science model developed in this work. / Ph. D.

It was found that laser modified wood surfaces can be bonded together to create a wood composite without the need of any additive. This bonding method removes the need of applying adhesive, potentially lowers cost, and eliminates off gassing of petroleum resins, creating a wood product with many eco-friendly attributes. This body of work outlines a) initial chemical analysis of the laser modified surface b) its bond strength and c) the optimization of factors that control the strength of the bond. Surface chemical analysis on laser modified wood was conducted using photo acoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-Ray photoelectron spectroscopy (XPS). Light microscopy and scanning electron microscopy were utilized for surface topology analysis.Differential scanning calorimetry (DSC) quantified the thermal properties of the modified wood surface. Screening of multiple factors that would contribute to surface modification and adhesion was performed utilizing mechanical testing. Optimization of significant factors that affect bond strength was determined statistically utilizing a design of experiment approach. Chemical analysis of the laser modified surface revealed changes in the carbonyl and aromatic regions indicating modification of the hemicellulose and lignin components, intensifying with increasing laser modification.The C1/C2 ratios found via XPS revealed that one or more of the following is occurring: more extractives have moved to the surface, condensation reactions among lignin units, and the loss of methoxy and breakage of aryl ether linkages occurred.Microscopy images showed color changes to a darker caramel color with a smoothing of surface topology, suggesting the occurrence of the softening and/or melting of wood polymers. DSC verified chemical and/or physical changes in the wood with the modified material now having a glass transition temperature between 130-150°C.DOE found that laser parameters (power and focus) as well as hot press parameters (temperature and pressure) were significant in optimizing the bond. The impact of the study is the first documentation of the ability to laser modifies wood surfaces and subsequently bond them together. The ability of the wood polymers at the surface to undergo flow at elevated temperature is implicated in the adhesion mechanism of the laser modified wood. / Master of Science

In strongly correlated electron systems the intricate interplay between electronic correlation effects and the tendency to form bands leads to a wealth of fascinating physical phenomena. The theoretical description of such systems is extremely complex and cannot be tackled exactly, so that ingenious modelling based on approximations must be utilized. Experiments are of utmost importance in this regard, since they provide a way to test and verify models, or to help devise better ones. This Dissertation deals with strongly correlated uranium intermetallic systems. The interesting phases they can adopt include heavy fermion behaviour, unconventional superconductivity, hidden and multipolar order, and exotic induced magnetism. Here the hybridization between the 5f states and the conduction electrons drives the physics. The description of the 5f states is therefore of utmost importance. However, since there is no clear hierarchy of interactions like Coulomb repulsion, spin-orbit coupling, hopping and crystal-field, the modelling is difficult. This is in strong contrast to the more spatially localized 4f states of, e.g., cerium compounds. It is far from clear how to quantitatively describe the electronic structure of uranium intermetallics and whether, for example, an itinerant band approach or an impurity-type model, taking local degrees of freedom explicitly into account, would be a better starting point. In intermetallics, the situation is aggravated by the fact that the modelling lacks important pieces of information. This is not least due to the fact that understanding the formal valence, the filling of the 5f shell, and the relevant symmetries of the $5f$ electrons are experimentally demanding tasks. This Dissertation, therefore, aims at developing new methods and Ans\'atze in this direction. We use x-ray spectroscopy to investigate the electronic structure, and in particular element-specific Inelastic X-ray Scattering (IXS); resonant (RIXS) at the U M(5) edge and non-resonant (NIXS) at the U O(4,5) edge. Both methods are innovative. For the first time, valence band RIXS measurements with sufficient resolution (150 meV) can be carried out at the U M(5) edge to measure ff excitations in intermetallic uranium compounds. Their existence, if present, provides information about the formal valence or main atomic configuration that determines the symmetry. The orientation dependence of the mutipolar excitations in NIXS (with restrictions also in RIXS), in turn, provides information about the orbital occupation. Atomic full-multiplet calculations are indispensable here. In addition, photoelectron spectroscopy (PES) is applied, both in the soft as well as in the hard x-ray regime (HAXPES), to investigate the hybridization and localization of the 5f electrons. The energy dependence of the cross-sections allows to determine the orbital contributions in the valence band, so that parameters like, e.g., the double-counting correction for the LDA+DMFT calculations, performed by Prof. A. Hariki from the Osaka Metropolitan University, can be determined from tuning the calculations to the experimental data. This combination of PES and DFT+DMFT provides a reliable new quantitative insight into the number of electrons in the 5f shell and their degree of delocalization. We consider UGa(2) and UB(2), respectively, as benchmark localized and itinerant systems and investigate them with IXS and PES. UGa(2) is a high-moment ferromagnet, with U-U distances above the Hill limit, while UB(2) is paramagnetic and clearly below the Hill limit. We observe sharp multiplet excitations of the 5f2 configuration in the IXS spectra of UGa(2), but none in the spectra of UB(2). The comparison of the spectra with full-multiplet calculations shows that in UGa(2) the U 5f2 configuration dominates and, from the orientation dependence (RIXS and NIXS), the crystal-field ground state can be determined. We show that the magnetism of this compound is of the induced type. The cross-section based analysis of the valence band PES data with the LDA+DMFT approach shows that the filling of the 5f shell is similar in both compounds, but that the distribution among different configurations is considerably wider in UB(2). Also the time-dependent charge correlation functions of UGa(2) and UB(2) show a larger itinerancy in the latter compound. The peculiarity and novelty about this combined study is that a reliable quantitative description of the electronic structure is achieved. This allows, for the first time, an accurate estimation of the 5f occupation and a quantitative description of the U\ 4f core-level PES spectra. This study paves the way to a systematic classification of uranium intermetallics. We further investigate the substitution series URu(2-x)Fe(x)Si(2) with PES. The systematic study of isostructural and/or isoelectronic series of compounds is crucial in unveiling the origin of their physical properties. URu(2)Si(2) exhibits hidden-order as well as superconductivity, and becomes antiferromagnetic upon Fe doping. Fe substitution seemingly involves the application of chemical pressure to the system. We measure the U 4f PES core-level of the URu(2-x)Fe(x)Si(2) substitution series and observe a non-monotonic shift of spectral weight. We argue that, besides chemical pressure, the Fe density of states at the Fermi level also plays a central role and we propose and extended Doniach diagram where the two effects compete. We also measure NIXS, confirming that the ground state symmetry is a singlet or quasi-doublet of the 5f2 configuration. The magnetic properties must then be understood, as in UGa(2), in terms of induced magnetism. We extend our study of the UT(2)Si(2) compounds to the case where T = Os, Ir, Pt and Au, i.e. 5d transition metals. Although the T= 3d and 4d transition metal systems have been extensively investigated, the T = 5d compounds lack systematic studies. The comparison of the NIXS spectra with multiplet calculations shows that also here the 5f2 dominates, only for T= Au it is not so clear. The absence of a strong directional dependence impairs the identification of the ground state symmetry. Valence band hard x-ray PES allows to probe the transition metal 5d states directly. U 4f core-level hard x-ray PES gives a qualitative indication of the filling of the 5f shell across the series. We then focus on hexagonal UNi(2)Al(3) and apply NIXS. Like isoelectronic and isostructural UPd(2)Al(3), it is a prototypical U heavy-fermion compound, showing antiferromagnetic order and unconventional superconductivity. We observe a strong directional dependence of the NIXS spectra at low temperatures. The possible ground-state symmetries of the 5f2 configuration that fit the NIXS data are in contradiction to previous proposals from fits of the static magnetic susceptibility. We put forward a new crystal-field model that describes the high temperature magnetic susceptibility and the NIXS data at low temperatures, and that explains the magnetism.

In den letzten Jahrzehnten haben Tischlaserquellen eine bemerkenswerte Entwicklung durchlaufen. Sie sind nun in der Lage, maßgeschneiderte ultrakurze Mehrfarben-Laserpulse zu erzeugen, die es ermöglichen, die elektronische Dynamik in Materialien auf ihrer natürlichen Zeitskala von Attosekunden zu untersuchen. In dieser Arbeit werden verschiedene Kombinationen von elektrischen Feldern genutzt, von extrem-ultravioletten (XUV) bis nahinfraroten Wellenlängen, um komplexe Elektronendynamiken in Atomen und chiralen Medien zu erforschen, zu rekonstruieren und zu kontrollieren. Dabei werden grundlegende Konzepte der Licht-Materie-Wechselwirkung eingeführt, einschließlich starker Feldprozesse, die im Kern der Attosekundenspektroskopie liegen. Ein Schwerpunkt liegt auf der Nutzung eines XUV-Pulses in Kombination mit einem nahinfraroten Puls, um den Bevölkerungstransfer zu hohen Drehimpulszuständen in Heliumatomen zu untersuchen. Durch Manipulation der Laserparameter wird die Rolle des AC Stark-Effekts von gebundenen Zuständen in der beobachteten Dynamik identifiziert. Weitere Untersuchungen umfassen die Verwendung eines bicirculären elektrischen Feldes zur Induktion von HHG in Argon, wobei Anzeichen einer starken Feldfangung von Elektronen in angeregten Zuständen im HHG-Spektrum entdeckt werden. Die Arbeit zeigt die entscheidende Rolle angeregter Zustände in der HHG auf. Zusätzlich wird die Anwendung synthetischer chiraler Felder erforscht, um Chiralität auf achirale Objekte wie Atome zu übertragen, und es wird eine Verbindung zwischen synthetischen chiralen Feldern und strukturiertem Licht hergestellt. / In recent decades table-top laser sources have undergone remarkable development and are now capable of generating tailored ultrashort multicolor laser pulses, enabling the study of electronic dynamics in materials on their natural timescale of the attoseconds. In this thesis work various combinations of electric fields spanning from extreme-ultraviolet (XUV) to near-infrared wavelengths are used to investigate, reconstruct and control complex electron dynamics in atoms and chiral media. The initial chapter of this thesis introduces the fundamental concepts underlying light-matter interaction, including strong field processes which lie at the core of attosecond spectroscopy. The second chapter focuses on the utilization of an XUV pulse combined with a near-infrared pulse to study population transfer to high angular momentum states in helium atoms. By manipulating laser parameters, the study identifies the significant role played by the AC Stark shift of bound states in the observed dynamics. In the third chapter a bicircular electric field is employed to induce HHG in argon. Changing the timedelay between the two frequencies, indications of strong field trapping of electrons in excited states are uncovered within the HHG spectrum, confirming the existence of long-lived trajectories lasting multiple optical cycles. The study conclusively demonstrates the crucial role of excited states in HHG. The fourth chapter explores the application of synthetic chiral fields—whose polarization traces a chiral curve over the optical cycle—to imprint chirality on achiral objects such as atoms, both in the low- and strong-field regime. Moreover, the thesis establishes a connection between synthetic chiral fields and structured light, introducing chiral vortex beams with azimuthally varying handedness.

<p>Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects.</p><p>In this thesis, some atomic, molecular and cluster systems (clusters of O₂, CH₃Br, Ar/O₂, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using <i>ab initio</i> methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of <i>ab initio</i> and molecular dynamics (MD) methods.</p><p>Results on the dissociation behavior of CH₃Br and O₂ molecules in clusters are presented. The dissociation of the Na₂ molecule has been characterized and the molecular field splitting of the Na 2<i>p</i> level in the dimer has been measured. The molecular field splitting of the CH₃Br 3<i>d</i> level has been measured and the structure of CH₃Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O₂, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.</p>

Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects. In this thesis, some atomic, molecular and cluster systems (clusters of O2, CH3Br, Ar/O2, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using ab initio methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of ab initio and molecular dynamics (MD) methods. Results on the dissociation behavior of CH3Br and O2 molecules in clusters are presented. The dissociation of the Na2 molecule has been characterized and the molecular field splitting of the Na 2p level in the dimer has been measured. The molecular field splitting of the CH3Br 3d level has been measured and the structure of CH3Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O2, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.

In this work, experimental and theoretical approaches are applied to the study of chemical reaction dynamics. In Chapter 2, two applications of transition state theory are presented: (1) Application of microcanonical transition state theory to determine the rate constant of dissociation of C2F3I after π∗ ← π excitation. It was found that this reaction has a very fast rate constant and thus is a promising system for testing the statistical assumption of molecular reaction dynamics. (2) A general rate constant expression for the reaction of atoms and molecules at surfaces was derived within the statistical framework of flexible transition state theory. In Chapter 4, a computationally efficient TDDFT approach was found to produce useful potential energy surface landscapes for application to non-adiabatic predissociative dynamics of the molecule CS2 after excitation from the ground state to the singlet C-state. In Chapter 5, ultrafast experimental results of excitation of CS2 to the predissociative neutral singlet C-state is presented. The bandwidth of the excitation laser was carefully tuned to span a two-component scattering resonance with each component differently evolving electronically with respect to excited state character during the quasi-bound oscillation. Scalar time-resolved photoelectron spectra (TRPES) and vector time-resolved photoelectron angular distribution (TRPAD) observables were recorded during the predissociation. The TRPES yield of photoelectrons was found to oscillate with a quantum beat pattern for the photoelectrons corresponding to ionization to the vibrationless cation ground state; this beat pattern was obscured for photoelectron energies corresponding to ionization from the vibrationally excited CS2 cation. The TRPAD data was recorded for two general molecular ensemble cases: with and without a pre-excitation alignment laser pulse. It was found that in the case of ensemble alignment (Chapter 6), the “molecular frame” TRPAD (i.e. TRMFPAD) was able to image the purely valence electronic dynamics of the evolving CS2 C-state. The unaligned ensemble TRPAD observable suffers from excessive orientational averaging and was unable to observe the quantum beat. Engineering efforts were also undertaken to eliminate scattered light background signal (Chapter 7, Appendix A) and improve laser stability as a function of ambient pressure (Appendix B) for TRMFPAD experiments. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-09-11 22:18:20.89

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

Heutzutage wächst die Nachfrage nach neuartigen Geräten, die teilweise (hybrid) oder völlig aus organischen halbleitenden Materialien hergestellt sind. Der Grund dafür sind die geringen Herstellungskosten sowie die hohe Flexibilität im Moleküldesign und damit einstellbare optische, elektronische und Spintronik-Eigenschaften. Bisher sind mit großem Erfolg organische Leuchtdioden (OLED), organische Solarzellen und gedruckte organische Elektronik-Bauelemente hergestellt worden. Auf Grund ihrer langen Spin-Lebensdauer sind Moleküle auch für Spintronik-Anwendungen sehr geeignet. In dieser Arbeit wurden die elektronischen und optischen Eigenschaften von vier ausgewählten Molekülen analysiert. Davon wurden Kupfer- und Mangan-Phthalocyanin (CuPc und MnPc) für die Untersuchung der Anordnung des Energieniveaus an der Metall-Organischen Halbleitern (M-O) Grenzfläche verwendet. Außerdem werden die andere zwei Moleküle tris(8-hydroxy-quinolinato) Aluminium(III) (Alq3) und N,N’-diphenyl-N,N’-bis(1-naphthyl)-1,1’-biphenyl-4,4’-diamine (α-NPD) häufig in OLED-Strukturen als Elektron- beziehungsweise Loch-Leiter verwendet. Die Proben sind mittels organischer Molekularstrahl-Abscheidung (OMBD) auf Co (oder Au) Folien beziehungsweise auf einseitig poliertem Si(111) Einkristall hergestellt worden. Im ersten Teil der Arbeit wurde die Entwicklung der Grenzfläche zwischen CuPc und Co (oder Au) Substrat mittels Valenzband- und Inverser Photoelektronen-spektroskopie (VB-PES und IPES) analysiert und herausgefunden, dass ein „Öffnung“ der Bandlücke mit dem Wachstum der Molekularschicht erfolgt. Ähnliches findet bei die MnPc/Co-Grenzfläche statt. Diese Erkenntnisse sind sehr wichtig für die Entwicklung von zukünftigen leistungsfähigen Spintronik Geräten. Der zweite Teil fokussiert auf die Änderungen der elektronischen Eigenschaften von MnPc und Alq3 während der Oxidation (O2-Aussetzung) beziehungsweise Reduktion (Kalium-Abscheidung). Abgesehen von den VB-PES und IPES Messungen, bieten die Röntgenphotoelektronenspektroskopie (XPS) und die Röntgen-Nahkante- Absorptions-Spektroskopie (NEXAFS) wichtige Informationen w. z. B. die Menge von K in der Molekülschicht und den Spin-Zustand im undotierten und im dotierten MnPc. Der dritte Teil beschäftigt sich mit den optischen Eigenschaften von MnPc, Alq3 und α-NPD als Reinmaterialien sowie mit K-dotierten Molekülen, in situ verfolgt mittels spektroskopischer Ellipsometrie (SE). Vom SE-Spektrum wurde der Imaginärteil der dielektrischen Funktion abgeleitet. Während α-NPD fast keine Änderung im Absorptionsspektrum nach der Dotierung zeigt, zeigt Alq3 dagegen ein Wandel zu einer dotierten Phase mit kleine Änderungen im Spektrum. Dabei hat MnPc drei stabile dotierte Phasen mit großen spektralen Änderungen. Außerdem zeigt die Oxidation von MnPc umgekehrt Eigenschaften zur dotierten Phase. Alle diese Messungen sind einzigartig und sehr wichtig für die Entwicklung von OLED und Spintronik Geräten.