APRÈN. Portal de la producció docent del professorat de la UPC

The present degree thesis consists on the effect of metallic glasses (MGs) addition onto titanium dioxide for hydrogen production via photocatalysis, whereas the MGs are intended to work as co-catalysts, lowering activation energy and efficiently separating photogenerated charges. Metallic glasses have an amorphous structure which provides them a high amount of active sites, although it might come at the expense of a decreased conductivity. Pd77Si16.5Cu6.5 (MG1) and Cu47Zr47Al6 (MG2) have been our choices as cocatalysts. Catalysts samples will be obtained via ball milling and sol-gel. An increase on hydrogen production from raw titania was found upon using 2% addition of MG1 milled during 45m at 50Hz, confirming it can effectively work as a cocatalyst. Surface Plasmon Resonance, known to enhance charge separation and solar light absorption, was noticed on the sample milled at 30Hz, albeit its hydrogen production was still unimpressive. Finally, non-calclined lyogels showed an oustanding hydrogen production rate and a twofold increase was found on the sol-gel samples that were not calcined compared to the calcined ones.

This study focuses on Dry Reforming of Methane (DRM) to convert greenhouse gases, CO₂ and CH₄, into valuable syngas. Six Ni-based catalysts supported on CeO₂ were evaluated, with particular attention to the effects of Fe addition and synthesis methods. The bimetallic catalyst with 8 wt% Ni and 2 wt% Fe showed the best activity, especially those prepared by ball milling (BM) compared to incipient wetness impregnation (IWI). Stability tests revealed that BM catalysts had higher resistance to deactivation. Characterization studies (XPS, SEM, Raman) confirmed superior metal-support interactions, smaller particles, and less sintering in BM catalysts, highlighting the method's effectiveness.

The uncontrolled and increasing greenhouse gas emissions to the atmosphere, and the continuous alerts from the scientific community about the potential unprecedented and utterly negative impacts global warming could lead humanity towards, has increased the preocupation of regional, local, national and international governments to tackle a proper, efficient and sustainable energy transition in a rapid manner. It is predicted that in less than a hundred years, global temperatures of the earth could have risen between 0.3 and 1.7 ºC, the lattter being fatal in terms of ice melting in the poles, sea level increase, large migration scenarios due to infertile land and dried lands, and mass extinction of many species altering the global ecosystem. [1] The designed and desired energy transition will inevitably face many difficulties and governments are starting to work on the pathways towards a clean and sustainable energy system of the future based mainly on renewable energy sources. A grid based mainly on renewable intermittent and unpredictable sources will undoubtedly change how energy systems are perceived. Concepts like the baseline generation will radically change, while concepts like grid flexibility and stability, and security of supply, ought to be reconsidered in order to efficiently adapt to the new reality. In this new reality, energy storage shall play an unprecedented and fundamental role in order to provide the renewable energy mix with enough security of supply and grid flexibility. From the sustainable point of view, and especially the efficient and reasonable management of resources like lithium or cobalt, required for the most common electric battery systems, lithium-ion batteries, diversification of energy storage solutions is necessary to ensure an equal and distributed resource availability and accessibility. Depending on the purpose and objective of each energy storage system, there are many different solutions to be considered, like compressed air systems, pumped hydropower storage, or flywheels among many others. Green hydrogen, produced with clean energy sources, and conceived as an energy vector as it takes energy to generate which is liberated when combusted, will inevitably play a key role in the future energy system, as another form of energy storage solution. One of the main areas in which hydrogen is called to be part of the solution is mobility. Fuel powered private and public transport vehicles (cars,buses, planes or ships), are one of the most polluting systems in Europe. Substitution of mobility solutions to clean electric options is therefore key, and one of the primary objectives of international institutions. Hydrogen fuel cell electric vehicles are conceived as one of the alternative solutions to the most conventional battery electric vehicles, especially in large vehicles like buses, trucks, ships or even planes. Large scale hydrogen production has traditionally been achieved through the use of natural gas in a process that emits greenhouse gases, so it cannot be conceived as green. However, electrolysis of water through the use of alkaline electrolysers mainly, has more recently emerged as a clean, renewable technique to generate what is known as green hydrogen. Even though alkaline electrolysis is a mature, large-scale technique, other technologies are being considered, still in the R&D process, to constitute the future green hydrogen mix, along with electrolysis. One of the most renown and investigated technology is photocatalysis. Photocatalysis is a process that uses photogenerated electron- hole pairs in an illuminated semiconductor, directly to activate the redox reaction of, for instance, water splitting, generating hydrogen and oxygen. Properly understanding the physical properties and behaviours of electrons in the semiconductor, and applying solid-state physics, semiconductor, and photovoltaic principles in photocatalytic cells is the main objective of this project, especially dealing with the use of carrier-selective contacts, and more specifically on the use of transition metal oxides as hole transport layers for anatase titania/gold based photocatalytic cells. In the experimental part of this project, then, combinations with other materials conceived as carrier-selective contacts as magnesium and titanium carbonate (MXene) are also combined with the transition metal oxides in order to try and enhance hydrogen production

The objective of this final master's project was to study the adverse impacts of thermo-mechanochemistry applied in the preparation of heterogeneous catalysts for CO oxidation and COPrOx reactions. The process was carried out in the gas phase using a tubular reactor, where the conversion and selectivity curves of both reactions were analyzed. Gas emissions from the reactor were monitored using gas chromatography analysis with argon as an inert carrier gas. Different mechanochemical catalyst synthesis processes were performed, varying the temperature and duration of the Au/CeO_2 catalyst synthesis process. These temperature changes were achieved by adding external energy in the form of heat. In the laboratory, the experimental reaction system was designed and implemented, the Au/CeO_2 catalyst was prepared using the mechanochemical technique with a ball mill, experiments were conducted, and the samples were characterized. Additionally, an economic study and a brief assessment of the environmental impact were carried out. The efficiency of the samples was compared based on two main parameters: the temperature and duration of the Au/CeO_2 mechanochemical synthesis. The best results were obtained in the CO oxidation with catalyst synthesis at room temperature, while in COPrOx, optimal results were achieved using samples heated to 50ºC and subsequently cooled. These findings highlight the importance of carefully controlling the synthesis parameters to maximize the efficiency of heterogeneous catalysts in both reactions.

La fotocatàlisi per a la producció d'hidrogen consisteix a afavorir la reacció de la descomposició de l'aigua o la deshidrogenació d'un bioalcohol mitjançant l'ús de la llum solar i la presència d'un fotocatalizador, és a dir, l'absorbidor de llum, per a produir H2. En aquests últims anys de creixent interès i inversió en energies renovables, la fotocatàlisi per a la producció d'hidrogen s'ha convertit en una de les branques més prometedores i en auge del sector, ja que és una tècnica neta i té una elevada relació energia/massa d'H2, solucionant així el problema de l'emmagatzematge energètic. Tradicionalment, els sistemes fotocatalítics consisteixen en un Z-scheme (només un contacte selectiu), mentre que les cèl·lules solars necessiten un absorbidor i dos contactes selectius. Aquesta tesi busca implementar la metodologia fotovoltaica en sistemes fotocatalítics, estudiant diversos contactes selectius i l'efecte de dipols i la passivació. L'objectiu és trobar un substitut de la predilecció actual pels metalls nobles (Au, Pt i Pd) com a contactes selectius dipositats en un absorbidor de TiO2. Per a ser adequat per a aplicacions a gran escala, ha de ser eficient, estable i assequible, tres conceptes que s'han tingut en compte al llarg del projecte. L'augment de la producció d'hidrogen a partir de la deshidrogenació fotocatalítica d'alcohol mitjançant contactes selectius s'ha verificat amb l'estudi de Mg, WOx, V2Ox i MXenes (Ti3C2Ox). Un estudi en profunditat dels diferents mètodes de fabricació ha permès optimitzar la deposició de MXenes aconseguint, quan es combina amb nanopartícules d'or fotodepositades, una millora del 225% en comparació amb la referència amb només nanopartícules d'or. A més, hem pogut justificar, amb una R2 d'un 95,8%, la producció d'hidrogen introduint una nova figura de mèrit: ?m, que es relaciona amb la transmitància i la conductivitat de les mostres. La passivació, tant l'etching d'àcid fluorhídric com les capes de passivació, han demostrat ser clau per a desfer-se dels dangling bonds i evitar així la recombinació. Un estudi d'optimització del gruix de ZnO i Al2O3 com a capes de passivació ha permès un augment del 113% en la producció total en comparació amb la mostra de referència de sol TiO2. D'altra banda, l'ús de la molècula orgànica dipolar PAMAM ha incrementat la producció total en un 13,8% en el cas de nanopartícules d'or drop cast. Això és el resultat de la característica estabilitzadora que el PAMAM proporciona a les nanopartícules d'or que d'una altra manera s'aglomeren, aconseguint així un menor ritme de degradació.

The climate change is a global problem that is affecting the environment of our planet and whose main cause is the use of energy sources with associated emissions of pollutants. In this work a proposal of two models (M1 and M2) of an integrated system that includes a nuclear reactor with a gas turbine to produce electricity and thermal energy in a clean way is presented. The reactor considered in the proposal is a high temperature helium cooled nuclear reactor similar to the GTHTR300. The useful thermal energy of cogeneration is used to produce hydrogen by methanol steam reforming (MSR) in a catalytic reactor. The main data have been extracted from reports of the pilot plant of the Laboratory of Catalysis of the INTE, Technical University of Catalonia situated in the EEBE campus. As one of the results it has been obtained the quantity of hydrogen produced per unit of thermal energy produced by the nuclear reactor. According to the proposal, the hydrogen will be stored and subsequently consumed in a fuel cell of the PEMFC (Proton Exchange Membrane Fuel Cell) type. As an example, supply of electric energy to off-grid homes in Spain is considered. In addition, an indicator called coefficient of performance (COP), has been introduced that allows to characterize the efficiency of the two proposed models.

Hydrogen stands as a good energy vector to replace fossil fuels due to its high energy density and green production. Moreover, hydrogen can be used to complement other green energy sources. One of the most craved methods to harvest H2 is photocatalysis: semiconductor catalysts when irradiated by the solar light produces charge carriers that can intervene and enhance the rate of REDOX reactions. The parallelism with photovoltaics is obvious, we need energetically and spatially separated charge carriers such that recombination is avoided and they can intervene in the desired processes. Therefore this work aims to use one of the most recent change of paradigm in photovoltaic cells to enhance efficiency: Selective contacts. With this approach cells are understood as an absorber and two filters that let one charge carrier out and blocks the other. Consequently, we will consider photocatalyst as such. To do so, P90 T iO2 based catalysts where used to optimize the experimental set-up while the P90 T iO2/Au production was increased by 15% with a simple heat treatment. Bismuth vanadate absorbers have been used to verify the filtering behavior of several metal co-catalyst, even thought the overall production was low. Hence, a quick Z-scheme structure was synthesised to combine bismuth vanadate with titanium dioxide leading to poor results but opening the door for another interesting research path. In addition, silicon supported titania sol-gel thin films where used to selectively deposited new selective charge carrier filters resembling the patterned contacts of Interdigitated Back-Contacted photovoltaic cells. Amorphous silicon and magnesium electron transport layers were paired with gold nanoparticles as hole transport layer. From that, a highly interdigitated magnesium pattern was able to double the production of the sol-gel titania and gold nanoparticles reference sample. Furthermore, the increase in efficiency due to pattern optimisation and selective contact use, accurately fitted the Langmuir–Hinshelwood Kinetic Model for heterogeneous catalysis.

The aim of this master's final thesis is the production of hydrogen (H2) from a mixture containing water (H2O) and ethanol (EtOH) by means of a photocatalytic process using TiO2 loaded with three different metals acting as co-catalysts. This reaction was carried out in gas phase and continuous mode inside a tubular glass photoreactor containing the photocatalyst impregnated in a filter paper sheet and a light source acting as a solar simulator. H2 generation was monitored by gas chromatography analysis with argon (Ar) acting as inert gas carrier. Several experiments were carried out, comparing different metals at different concentrations in order to study synergies between them, and also switching between UV and visible light to and assess the occurrence of the Localized Surface Plasmon Resonance (LSPR). The work developed at the laboratory includes the design and implementation of the experimental set-up, the preparation of the TiO2-based photocatalytic powder by ball milling technique, and the impregnation of the powder into the filter paper, as well as the performance of photocatalytic experiments and the characterization of the samples. The performance of the samples was compared depending on parameters such as the chosen combination of metals, total metal load, metal proportions, change in the synthesis parameters, etc. Finally, the best results in terms of H2 production were obtained with a sample of TiO2 containing 1 wt.% of PdPtAg metals in a 35:35:30 proportion. With a gas flow rate of 20 mL/min, having H2O and EtOH in a 9:1 proportion, and irradiating at 85 mW/cm2 (measured at 365 nm) of UV and visible light, a maximum production of 4.73 μmol H2/min and Apparent Quantum Yield of 4.8%, were obtained.

The motivation of this thesis is to solve the two main problems of space exploration: the lack of fuel to perform space exploration beyond the Moon or Mars, and the limitations generated by the launching of large amounts of fuel from Earth to perform long distance missions. In this thesis we study the possibility of using lunar resources to produce fuel from them and not needing the raw material from Earth, the location of these resources on the Moon and the different methods to extract them. In order to favor a reliable study, a propulsive characterization test is carried out with a fuel composed only of resources available on the Moon: aluminum and oxygen. For this test, a hybrid rocket will be designed and manufactured to test the fuel. The results of this test will be used to study the effectiveness of this combination of lunar materials as a propellant. Obtaining feasible results in the test would be a milestone in space research, since it is estimated that the use of lunar resources for fuel production would drastically reduce the cost of space missions, thus allowing the possibility of solar system exploration and a future space economy. The fact of being able to obtain fuel from the Moon would expand our frontiers since it opens the door to the idea of being able to obtain it also from different bodies of the solar system. Thus, this thesis is a good starting point for future research on obtaining rocket fuel from the raw materials of other planets or asteroids, and consequently, to the long-term goal of establishing a sustainable presence on the Moon

The aim of this master's project is the production of hydrogen (H2) from mixtures containing water and ethanol (molar relation H2O:C2H5OH=9:1) using a photocatalytic process with metal/TiO2 nanoparticles. The solid-liquid-gas heterogeneous reaction was carried out in a stainless-steel falling film microreactor working in continuous mode, using two catalytic plates, one of them containing 16 microchannels and the other containing 32 microchannels, and also a LED source of 365 nm. In the development of the project different experiments were carried out. First of all, it realized the solid-gas interaction using a bubbler which contained water and ethanol, with a gas flow of 20 ml/min. After this, it realized the experiment in solid-liquid-gas phase, where the liquid (water and ethanol) was fed through the top slit and introduced into the microchannels by gravity and capillary forces. In this experiment the gas was applied in counter-current and I used different flow rates of gas and liquid to observe the trend of hydrogen production. Moreover, after these experiments were carried out at room temperature, further tests were performed at different temperatures (50ºC and 75ºC). The work developed in the laboratory includes the experimental set-up, the preparation of the method to immobilized the catalyst in the microchannels, the preparation to add the metal nanoparticles in the reaction plate and the performance of photocatalytic experiments. Finally, the best results were obtained in solid-liquid-gas interaction using the catalytic plate containing 16 microchannels. It used a liquid flow rate of 0,58 ml/min, a gas flow rate of 20 ml/min and the microreactor was heated at 75ºC. In this case the maximum hydrogen production was 157,7 µmol/(min•gcat).

El hidrógeno es un vector energético que puede ayudar a gestionar mejor la energía en el futuro de manera limpia. Para su aplicación energética resulta imprescindible producirlo a partir de substratos renovables, como agua y moléculas orgánicas. En este trabajo se van a desarrollar fotocatalizadores de TiO2 decorados con nanopartículas de Au con distintas propiedades geométricas y electrónicas y se va a estudiar su comportamiento en la generación fotocatalítica de hidrógeno en el laboratorio.