[ES] La presente tesis doctoral se sitúa en el marco de la actual transición energética, que plantea la sustitución progresiva de materias primas de origen fósil por fuentes renovables, tanto para la obtención de productos químicos como para la producción de combustibles. En este contexto de transición paulatina a las renovables, y teniendo en cuenta los últimos pronósticos, las fuentes fósiles (fundamentalmente gas natural) y derivados de la biomasa, jugarán un papel fundamental durante el cambio. Se ha llevado a cabo un estudio sobre el empleo de óxidos metálicos (basados en bronces de wolframio o en óxido de níquel), como catalizadores para: i) la transformación de derivados de biomasa: de glicerol a acroleína/ácido acrílico; y de compuestos oxigenados de cadena corta presentes en efluentes acuosos (procedentes de tratamientos de extracción de bio-aceites de pirolisis) a combustibles; y ii) la transformación de componentes del gas natural, concretamente la obtención de etileno a partir de etano, mediante deshidrogenación oxidativa (ODH). El trabajo se presenta desde una perspectiva de la química de materiales, haciendo hincapié en las propiedades fisicoquímicas de los distintos sistemas catalíticos, empleando técnicas de caracterización convencionales e in situ, además de reacciones modelo (transformación de metanol y etanol), con el objetivo de entender las funciones catalíticas presentes en cada caso. Tanto para la transformación de glicerol en fase gas, como para la valorización de mezclas acuosas de compuestos oxigenados de cadena corta, se han utilizado catalizadores basados en bronces de wolframio. Se ha tratado de poner de manifiesto la gran versatilidad composicional y estructural (con el consiguiente control de las propiedades funcionales), que presentan este tipo de materiales. En este sentido, las propiedades ácidas y redox de catalizadores W-V-O pueden ser moduladas, para una misma concentración de vanadio, mediante el control de la relación de fases cristalinas (hexagonal y monoclínica) del óxido de wolframio. Este efecto se ha estudiado empleando la transformación aeróbica de metanol como reacción "test", y tiene una gran influencia en la deshidratación oxidativa de glicerol a ácido acrílico. A su vez, mediante la sustitución isomórfica de wolframio por niobio (en el sistema WO3-Nb2O5) es posible controlar la relación de centros ácidos de tipo Brönsted y Lewis en la superficie de los materiales. Por un lado, los catalizadores con una alta relación Brönsted/Lewis se han mostrado más efectivos en la deshidratación de glicerol a acroleína, mientras que los catalizadores con altas concentraciones de centros de tipo Lewis presentan altos rendimientos a productos de condensación de compuestos oxigenados de cadena corta. Adicionalmente se han estudiado las diferencias entre catalizadores (bien óxidos mixtos W-V-O o W-Nb-O) preparados mediante un método hidrotermal o mediante reflujo, así como el efecto de la utilización de un soporte mesoporoso (KIT-6), sobre sus propiedades catalíticas en la transformación aeróbica en fase gaseosa de etanol y glicerol. Finalmente, en lo que concierne a la transformación de componentes del gas natural, se han empleado materiales basados en óxido de níquel (soportado sobre distintos óxidos y/o promovido con distintos metales) como catalizadores para la ODH de etano. En este caso el estudio se ha centrado fundamentalmente en dilucidar los efectos de promotores y soportes en la naturaleza y propiedades fisicoquímicas del óxido de níquel, los cuales dan lugar a un cambio drástico en sus propiedades catalíticas. Así, se ha observado que modificando la reducibilidad y las características superficiales del óxido de níquel es posible transformar un catalizador muy poco selectivo en la ODH de etano (como es el NiO, con una selectividad a etileno del 30 %) en uno de los catalizadores más selectivos para llevar a cab / [CA] Aquesta tesi doctoral es situa dins del marc de l'actual transició energètica, la qual planteja la substitució progressiva de les primeres matèries d'origen fòssil per fonts renovables, tant per a l'obtenció de productes químics com per a la producció de combustibles. En aquest context de transició gradual a les renovables, i tenint en compte els últims pronòstics, les fonts fòssils (principalment el gas natural) i els derivats de la biomassa, exerciran un paper fonamental durant aquest canvi. S'ha dut a terme un estudi sobre la utilització d'òxids metàl·lics (basats en bronzes de wolframi o en òxid de níquel), com a catalitzadors per a: i) la transformació de derivats de la biomassa: de glicerol a acroleïna/àcid acrílic; i de compostos oxigenats de cadena curta presents en efluents aquosos (procedents de tractaments d'extracció de bio-olis de la piròlisi) a combustibles; i ii) la transformació de components del gas natural, concretament l'obtenció d'etilè a partir d'età, mitjançant la deshidrogenació oxidativa. El treball es presenta des del punt de vista de la química de materials, posant l'accent en les propietats fisicoquímiques dels diferents sistemes catalítics, utilitzant tècniques de caracterització convencionals i in situ, a més de reaccions model, amb l'objectiu d'entendre les funcions catalítiques presents en cadascun dels casos. Tant per a la transformació del glicerol en fase gasosa com per a la valorització de les mescles aquoses de compostos oxigenats de cadena curta, s'han utilitzat catalitzadors basats en bronze de wolframi. S'ha intentat posar de manifest la gran versatilitat de composicions i estructures (amb el conseqüent control de les propietats funcionals) que presenten aquest tipus de materials. En aquest sentit, les propietats àcides i redox dels catalitzadors de W - V - O poden ser modulades, per a una mateixa concentració de vanadi, mitjançant el control de la relació de fases cristal·lines (hexagonal i monoclínica) de l'òxid de wolframi. Aquest efecte s'ha estudiat utilitzant la transformació aeròbica de metanol com a reacció "test", i presenta una gran influència en la deshidratació oxidativa de glicerol a àcid acrílic. Al mateix temps, mitjançant la substitució isomòrfica de wolframi per niobi (en el sistema WO3 - Nb2O5), és possible controlar la relació de centres àcids de tipus Brönsted i Lewis en la superfície dels materials. Per una part, els catalitzadors que presenten una relació Brönsted / Lewis alta s'han mostrat més efectius en la deshidratació de glicerol a acroleïna, mentre que els catalitzadors amb unes altes concentracions de tipus Lewis presenten alts rendiments a productes de condensació de compostos oxigenats de cadena curta. Addicionalment, s'han estudiat les diferències entre catalitzadors (ja siguin òxids mixtos W-V-O o W-Nb-O) preparats mitjançant un mètode hidrotermal o mitjançant un mètode de reflux, així com l'efecte que presenta la utilització d'un suport mesoporós (KIT-6), sobre les seves propietats catalítiques en la reacció de transformació aeròbica en fase gasosa d'etanol i glicerol. Finalment, pel que fa referència a la transformació de components del gas natural, s'han utilitzat materials basats en òxid de níquel (suportat sobre diferents òxids i/o promoguts amb diferents metalls) i catalitzadors per a la deshidrogenació oxidativa d'età. En aquest cas, l'estudi s'ha focalitzat principalment en dilucidar els efectes de promotors i suports en la naturalesa i propietats fisicoquímiques de l'òxid de níquel, els quals impliquen un canvi dràstic en les seves propietats catalítiques. Així doncs, s'ha observat que modificant la reductibilitat i les característiques superficials de l'òxid de níquel és possible transformar un catalitzador molt poc selectiu en la deshidrogenació oxidativa de l'età (com és el cas del NiO, amb una selectivitat a l'etilè del 30%) en un dels cata / [EN] The present doctoral thesis is set within the scope of the current energy transition, which considers the progressive substitution of non-renewable fossil sources by renewable feedstocks for the production of chemicals and fuels. In this context of gradual transition, and according to recent energy outlooks, fossil sources (especially natural gas) and biomass feedstocks will play a key role during the shift. A study on the use of metal oxides (based on tungsten bronzes or nickel oxides) as catalysts for different reactions has been conducted. Particularly, they have been studied as catalytic materials for: i) the transformation of biomass-derived feedstocks: glycerol transformation into acrolein/acrylic acid, and the transformation of short-chain oxygenates present in aqueous effluents (derived from extraction processes of pyrolysis bio-oils) into fuels; and ii) the valorization of natural gas components, i.e. the transformation of ethane into ethylene by oxidative dehydrogenation. The work is presented from a materials chemistry perspective, emphasizing the physicochemical characteristics of the different catalytic systems by using conventional and in situ characterization techniques and model reactions (gas phase methanol and ethanol transformation); with the aim of understanding the specific catalytic functionalities present in each case. For both gas phase glycerol transformation and the valorization of short-chain oxygenates aqueous mixtures, catalyst based on tungsten oxide bronzes have been used. The compositional and structural versatility of this structural types (with the subsequent control of their functional properties) will be highlighted. In this sense, the acid-redox properties of W-V-O catalysts can be modulated by controlling the crystalline phase composition in the materials (i.e. hexagonal and monoclinic polymorphs of tungsten oxide) at a fixed V concentration. This effect has been studied by using the gas-phase aerobic transformation of methanol as a surface test reaction. The concentration of the hexagonal and monoclinic polymorphs in the catalysts has also an important influence in the gas-phase transformation of glycerol into acrylic acid. Also, it is possible to control the Brönsted/Lewis acid nature of the surface by the isomorphic substitution of Nb for W in WO3-Nb2O5 system. On the one hand, catalysts showing a higher proportion of Brönsted acid sites are more effective in the glycerol dehydration to acrolein. On the other hand, materials with a higher concentration of Lewis acid sites display high yields to condensation products in the aqueous phase valorization of short chain oxygenates. Additionally, the differences between W-V-O and W-Nb-O catalysts prepared by both reflux and hydrothermal methods have been studied. Also the effect of adding a mesoporous KIT-6 silica as support on the catalytic performance in the gas phase transformation of ethanol and glycerol will be underlined. Considering the transformation of natural gas components, nickel oxide-based materials were chosen (either supported on different oxides and/or promoted with different metals) to perform the oxidative dehydrogenation (ODH) of ethane. In this case the study has been focused on elucidating the effects of both promoters and supports on the nature and physicochemical features of nickel oxide, which lead to a drastic change in the catalytic behavior of these materials. This way, it has been observed that by the modification of the reducibility and the chemical nature of nickel oxide, it is possible to transform an apparently non-selective catalyst in the ODH of ethane (like NiO, showing a selectivity to ethylene of ca. 30 %) into one of the most selective catalysts reported in the literature (presenting a selectivity to ethylene of ca. 90 %). / También me gustaría agradecerle al Prof. Avelino Corma, investigador principal del proyecto SEV-2012-0267, a través del cual he podido realizar mi tesis doctoral enel Instituto de Tecnología Química (SVP-2014-068669). / Delgado Muñoz, D. (2019). Catalytic valorization of natural gas and biomass-derived feedstocks by metal oxides [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/122298 / TESIS

This work deals with the optimization of the preparation process of WO3 photoanodes nad their characterization. For compositions were prepared, which were applied to a substrate via spin-coating process and subsequently annealed at 450 °C. The length of milling of precursor particles contained in the coating formulations determined properties of deposited layers. were examined for. The additivity of the individual compositions was also observed. The structure of the layers was observed by optical microscopy and scanning electron microscopy (SEM), their composition by the X-ray diffraction (XRD) and their thickness and surface roughness was defined by contact profilometry. Photoelectrochemical properties of the prepared layers were also investigated by linear voltametry and chronoamperometry.

<p>To achieving successfully commercial nuclear fusion energy, fully understanding of the interaction between plasma particles and plasma facing components is one of the essential issues. Tungsten, due to good thermal and mechanical properties such as high thermal conductivity and melting temperature, is one of the most promising candidates. However, the plasma facing components interacting with the extreme environmental conditions such as high temperature and radiation may lead to nanostructure formation, sputtering and erosion that will lead to material degradation. And these deformations may influence not only properties of plasma facing components but also might affect the plasma itself. For example, the contamination of plasma with a few amounts of tungsten, a high Z element, as a result of erosion or sputtering may cause core plasma cooling that results in loss of plasma confinement. Additionally, the retention of hydrogen isotopes, especially tritium, in tungsten is essential issue because of its radioactivity and market value.</p> In this study, deuterium trapping in tungsten is analyzed by molecular dynamics method and the effect of pre-irradiation on trapping is studied. Non-cumulative studies show that the increase in the energy of hydrogen isotopes rises the absorption rate, the initial implantation depth, and the average resting time for initial implantation. Additionally, the effect of implanted deuterium due to pre-irradiation on the hydrogen isotopes trapping is analyzed by combining both cumulative and non-cumulative simulations, and results indicate that while the increase in the pre-irradiation time raises the absorption rate of deuterium with higher energy than 80 eV, it causes a decrease the initial implantation depth and the average resting time for initial implantation because of deuterium-deuterium interactions. Additionally, the deuterium-deuterium interactions may transfer enough energy to implanted deuterium to start a motion which may lead to deeper implantation or escaping from the surface of tungsten. The escaping from surface as a result of deuterium-deuterium interaction could explain the decrease in accumulation rate of deuterium while absorption rate rises.

Title: Automation of dust charging experiment Author: Radim Pechal Department: Department of Surface and Plasma Science Supervisor: RNDr. Jiří Pavlů, PhD. Supervisor's e-mail address: Jiri.Pavlu@mff.cuni.cz Abstract: Since the dust grains are expected to cause problems during operation of tokamaks, there is a developing research of these devices which raises interest in dust grain charging processes research as well. Clarification of the dust grain charging processes may help with their solutions. This thesis deals with an issue of designing a part of a new experimental setup for dust grain research built at the Department of Surface and Plasma Science, Charles University in Prague. The base of this experimental setup is original linear quadrupole trap enabling dust grain trapping and its charging by electron, ion, and UV beams. In the thesis, a method of stabilization of one part of grain oscillation frequency detection is described. The thesis is focused on a development of a control unit and high voltage power supply for an image intensifier. To measure charging processes tungsten dust grains were used. This material will be probably used in construction of ITER tomakak. Electron equilibrium characteristics and other parameters were measured. Two samples of tungsten dust grains were used for...

A cross-time study has been made on the erosion behaviour of Gas-Tungsten Arc Welding (GTAW) for pure tungsten electrode. Its behaviour during arcing was analyzed and compared from the points of view of metallurgical changes in electrode due to long-term operation. Metallographic studies of the electrodes indicate that the crack formation and grain growth during periodic temperature variations. These observations are discussed theoretically based on the experimental results and the thermal expansion parameters of Tungsten.

Die Anzahl neurodegenerativer Erkrankungen nimmt in unserer Gesellschaft stetig zu. Obwohl inzwischen eine Reihe genetischer Ursachen identifiziert worden sind, wird auch der Einfluss von Umweltfaktoren bei der Pathogenese dieser Erkrankungen zunehmend in Betracht gezogen. Der Beitrag von ultrafeinen Partikeln aus Industrie und Umwelt auf neurodegenerative Erkrankungen steht daher zunehmend im Fokus der Forschung. Die Translokation von ultrafeinen Partikeln bzw. Nanopartikeln ins Gehirn ist bekannt. Die Charakterisierung neuro- und gliotoxischer Wirkungen von Nanopartikeln in einem in vitro System war deshalb Ziel dieser Arbeit. Untersucht wurden Wolframcarbid-Partikel mit und ohne Cobalt, die im Herstellungsprozess von Hartmetallen von Bedeutung sind. Die meisten toxikologischen Daten wurden bisher mit mikrokristallinen WC-Pulvern an Lungenzellen bzw. -gewebe erhoben. Da aber die Verarbeitung von nanoskaligen Partikeln bessere Eigenschaften der Hartmetalle bewirkt, nimmt das Interesse an toxikologischen Studien mit WC-Nanopartikeln zu. Da die Gefahr der Translokation und Akkumulation im Gehirn beim Einatmen von Stäuben am Arbeitsplatz besteht, wurde erstmalig die Toxizität von WC-NP mit und ohne Cobalt auf Zellen des Gehirns untersucht. Für die Durchführung wurden primäre Neuronen, Astrozyten und Mikroglia sowie die Oligodendrozyten-vorläuferzelllinie OLN-93 der Ratte eingesetzt. Alle untersuchten Partikel konnten mittels Elektronenmikroskopie, ICP-Massenspektrometrie und Durchflusszytometrie in den verschiedenen Zelltypen nachgewiesen werden. Untersuchungen mit Cytochalasin D (Inhibitor der Aktinpolymerisation) deuteten auf zell- und partikelspezifische Aufnahmemechanismen hin. Experimente mit Cobaltchlorid und Natriumwolframat konnten beweisen, dass nicht die gelösten Ionen für die Toxizität von WC-Co ursächlich waren, sondern die Partikelform von entscheidender Bedeutung ist. Es zeigte sich jedoch, dass einige der WC-Co verursachten Effekte vermutlich auf dem Cobaltanteil beruhen. Offensichtlich dienen WC-Co-NP als Vehikel, um Cobalt in die Zellen einzuschleusen. Zur toxischen Wirkung trägt auch das Reaktionsvermögen von WC und Cobalt an der beiderseitigen Grenzfläche bei, denn dadurch können in der Zelle vermehrt reaktive Sauerstoffspezies gebildet werden. Im Rahmen der Untersuchungen wurden die zeit- und konzentrationsabhängigen Effekte der Nanopartikelexposition auf die Vitalität, die Proliferation, das Adhäsionsverhalten, das mitochondriale Membranpotential und die Induktion apoptotischer und nekrotischer Zelluntergänge untersucht. Dabei wurden verschiedene Vitalitäts- und Proliferationstests angewendet, um die häufig beobachteten Wechselwirkungen zwischen Reagenzien und Nanopartikeln auszuschließen. Nicht alle untersuchten Nanopartikel erwiesen sich in den durchgeführten Experimenten als akut toxisch. Nur eine Exposition mit WC-Co-NP führte nach 72 h zu einer deutlich verringerten Vitalität und Proliferation bei Astrozyten und OLN-93 Zellen. Eine Exposition mit WC-Co-NP zeigte des Weiteren eine geringe Induktion von Apoptose und Nekrose bei Astrozyten, nicht aber bei OLN-93 Zellen. Neurone wiesen nach einer Exposition mit NP eine wenig verringerte Vitalität auf. Es wurde festgestellt, dass erst die primäre Schädigung von Astrozyten zu einer sekundären Neuronenschädigung führt. Bei der Bewertung der NP-Toxizität müssen daher unbedingt die Wechselwirkungen der Zellen bedacht werden. Die Exposition mit WC- und WC-Co-NP beeinflusste das mitochondriale Membranpotential und das Adhäsionsverhalten der untersuchten Zellen. Neuronen und OLN-93 Zellen zeigten nach NP-Exposition eine verminderte Adhäsion. Auch physiologische Kalziummessungen lieferten einen Hinweis für die veränderte Funktionalität glialer Zellen nach einer NP-Exposition. Des Weiteren wurde die Expression einiger Gene, bedeutend für Adhäsion und extrazelluläre Matrix, mit realtime RT-PCR bei OLN-93-Zellen und Astrozyten überprüft. Es konnte eine Regulation von Mmp9, Timp1, Lama3, Tgfbi, Col8a1 und Hmox1 gezeigt werden. Zusammenfassend lässt sich feststellen, dass die ausgewählten Nanopartikel nicht per se neuro- und gliotoxisch wirkten. Die Partikel können anhand abnehmender Toxizität wie folgt geordnet werden: WC-Co > WC 100na > WC 10n. Auch die Reaktionen der Zellen fielen unterschiedlich aus: die Astrozyten erwiesen sich als die sensitivsten Zellen. Eine Exposition des Gehirns mit WC-Co-NP in hohen Konzentrationen oder über einen längeren Zeitraum könnte also weit reichende Folgen haben, angefangen bei einer gestörten Signalweiterleitung über eine erhöhte Permeabilität der Blut-Hirn-Schranke bis hin zu neurodegenerativen Veränderungen. Diese und weitere Untersuchungen könnten bei der Erstellung von Arbeitsrichtlinien im Umgang mit Hartmetallen, deren Ausgangsmaterial nanoskalige Pulver sind, hilfreich sein und damit einen Beitrag zum Schutz der Arbeiter liefern.

No description available.

This study produced and analyzed shaped tungsten wire tips formed through electrochemical etching. Specifically, the cone length and the radius of curvature of the tip were analyzed. Having the tips move dynamically through an electrolytic solution, such as potassium hydroxide, and tuning the initial starting depth of the tungsten wire along with the dynamic speed of the tungsten wire as it passed throughout the solution allowed various types of tip profiles to be produced. The tip's radius of curvature was able to be reproduced with an accuracy between 88 - 92 %. The method provided would be applicable for the production of various styles of liquid-metal ion source (LMIS) probes and scanning probe microscope (SPM) tips.

The general objective of this thesis is the analysis of selective reactions for group VI grafted metal complexes via methods and principles of SOMC. For this objective, three approaches have been chosen. The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing heterogeneous catalysis and more specifically the different approaches to support catalysts on surfaces. The concept of catalysis by design is introduced as a new way to use the surface as a ligand. Chapter 2 presents the results of a library of well-defined catalysts of group VI with identical catalytic functionality, but different ligand environment. The results reveal, that metal-carbynes are able to switch their catalytic reactivity based on the substrate that they are contacted with. The difference in reaction mechanisms and the differing reactivities towards the substrates are presented. It can be concluded that the classical ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas cyclic alkanes yield exclusively higher and lower homologues of the substrate without polymeric products. Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products is analyzed. It is presented, that the ligand environment of the catalysts is showing an influence in the selectivity. Rates of cis/trans isomerization of the products are high and are approaching thermodynamic equilibrium at high conversion. Product isomerization, thermodynamic equilibrium and reactivity differences between liquid phase and gas phase products are analyzed. Chapter 4 presents the full characterization of tungsten-hydrides by selective transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show, that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes. Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the generated tungsten-hydroxides of chapter 4.

Catalysis, which is primarily a molecular phenomenon, is an important field of chemistry because it requires the chemical conversion of molecules into other molecules. It also has an effect on many fields, including, but not limited to, industry, environment and life Science[1]. Surface Organometallic Chemistry is an effective methodology for Catalysis as it imports the concept and mechanism of organometallic chemistry, to surface science and heterogeneous catalysis. So, it bridges the gap between homogenous and heterogeneous catalysis[1]. The aim of the present research work is to study the effect of Nitrogen surface ligands on the activity of Alkane, Propane in particular, metathesis. Our approach is based on the preparation of selectively well-defined group (VI) transition metal complexes supported onto mesoporous materials, SBA15 and bearing amido and/or imido ligands. We choose nitrogen ligands because, according to the literature, they showed in some cases better catalytic properties in homogenous catalysis in comparison with their oxygen counterparts[2]. The first section covers the modification of a highly dehydroxylated SBA15 surface using a controlled ammonia treatment. These will result in the preparation of two kind of Nitrogen surface ligands: - One with vicinal silylamine/silanol, (≡SiNH2)(≡SiOH), noted [N,O]SBA15 and, - Another one with vicinal bis-silylamine moieties (≡SiNH2)2, noted [N,N]SBA15[3]. The second section covers the reaction of Schrock type Tungsten Carbyne [W(≡C- tBu)(CH2-tBu)3] with those N-surface ligands and their characterizations by FT-IR, multiple quantum solid state NMR (1H, 13C), elemental analysis and gas phase analysis. The third section covers the generation of the active site, tungsten hydride species. Their performance toward propane metathesis reaction using the dynamic reactor technique PID compared toward previous well-known catalysts supported on silica oxide or mesoporous materials[4]. A fairly good turn over number (TON = 43) has been obtained following hydrogen treatment of tungsten alkylidyne supported on [N,O] SBA151100, in comparison with TON of zero in the obtained with [N,N] SBA15 and classical SiO2 silica support. Therefore, the cooperation between silylamine and silanol in close vicinity are required to improve the efficiency of the catalyst in the metathesis of propane.