Formic acid (FA) has been considered as one of the most promising materials for hydrogen storage today. The catalytic decarboxylation of formic acid ideally leads to the formation of CO2 and H2, and such CO2/H2 mixtures can be successfully applied in fuel cells. A large number of transition-metal based homogeneous catalysts with high activity and selectivity have been reported for the formic acid decarboxylation. In this presentation, we report ruthenium and rhodium complexes containing an N, N′-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. Among them, the Ru complex could provide a TOF (turnover frequency) of 12 000 h–1 and a TON (turnover number) of 350 000 at 90 °C in the HCOOH/HCOONa aqueous solution. In addition to that, efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO by this Ru complex. Moreover, well-defined ruthenium (II) PN3P pincer complexes were also developed for the reversible reaction-hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF and TON up to 13,000 h-1 and 33,000, respectively, in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from the air into formate was conducted in the presence of an amine, allowing easy product separation and catalyst recycling.

Perovskite-type oxides show irrefutable potential for feasible thermochemical solar-driven CO2 conversion. These materials exhibit the exact characteristics required by the low temperature reverse water-gas shift chemical looping process. These properties include structural endurance and high oxygen redox capacity, which results in the formation of numerous oxygen vacancies, or active sites for CO2 conversion. A major drawback is the decrease in oxygen self-diffusion with increasing perovskite particle size. In this study, the La0.75Sr0.25FeO3 (LSF) perovskite oxide was combined with various supports including popular redox materials CeO2 and ZrO2 along with more abundant alternatives such as Al2O3, SiO2, and TiO2, in view of its potential application at industrial scale. Supporting LSF on SiO2 by 25% mass resulted in the largest increase of 150% in CO yields after reduction at 600 °C. This result was a repercussion of significantly reduced perovskite particle size confirmed by SEM/TEM imaging and Scherrer analyses of XRD patterns. Minor secondary phases were observed during the solid-state reactions at the interface of SiO2 and TiO2. Density functional theory-based calculations, coupled with experiments, revealed oxygen vacancy formation only on the perovskite phase at these low temperatures of 600 °C. The role of each metal oxide support towards suppressing or enhancing the CO2 conversion has been elucidated. Through utilization of SiO2, the reverse water-gas shift chemical looping process using perovskite-based composites was significantly improved.

The anthropogenic carbon dioxide (CO2) emission into the atmosphere, mainly through the combustion of fossil fuels, has resulted in a balance disturbance of the carbon cycle. Overwhelming scientific evidence proves that the escalating level of atmospheric CO2 is deemed as the main culprit for global warming and climate change. It is thus imperative to develop viable CO2 capture and sequestration (CCS) technologies to reduce CO2 emissions, which is also essential to avoid the potential devastating effects in future. The drawbacks of energy-cost, corrosion and inefficiency for amine-based wet-scrubbing systems which are currently used in industry, have prompted the exploration of alternative approaches for CCS. Extensive efforts have been dedicated to the development of functional porous materials, such as activated carbons, zeolites, porous organic polymers, and metal-organic frameworks (MOFs) to capture CO2. However, these adsorbents are limited by either poor selectivity for CO2 separation from gas mixtures or low CO2 adsorption capacity. Therefore, it is still highly demanding to design next-generation adsorbent materials fulfilling the requirements of high CO2 selectivity and enough CO2 capacity, as well as high water/moisture stability under practical conditions. Metal-organic frameworks (MOFs) have been positioned at the forefront of this area as a promising type of candidate amongst various porous materials. This is triggered by the modularity and functionality of pore size, pore walls and inner surface of MOFs by use of crystal engineering approaches. In this work, several effective strategies, such as incorporating 1,2,3-triazole groups as moderate Lewis base centers into MOFs and employing flexible azamacrocycle-based ligands to build MOFs, demonstrate to be promising ways to enhance CO2 uptake capacity and CO2 separation ability of porous MOFs. It is revealed through in-depth studies on counter-intuitive experimental observations that the local electric field favours more than the richness of exposed nitrogen atoms for the interactions between MOFs and CO2 molecules, which provides a new perspective for future design of new MOFs and other types of porous materials for CO2 capture. Meanwhile, to address the water/moisture stability issue of MOFs, remote stabilization of copper paddlewheel clusters is achieved by strengthening the bonding between organic ligands and triangular inorganic copper trimers, which in turn enhances the stability of the whole MOF network and provides a better understanding of the mechanism promoting prospective suitable MOFs with enhanced water stability. In contrast with CO2 capture by sorbent materials, the chemical transformation of the captured CO2 into value-added products represents an alternative which is attractive and sustainable, and has been of escalating interest. The nanospace within MOFs not only provides the inner porosity for CO2 capture, but also engenders accessible room for substrate molecules for catalytic purpose. It is demonstrated that high catalytic efficiency for chemical fixation of CO2 into cyclic carbonates under ambient conditions is achieved on MOF-based nanoreactors featuring a high-density of well-oriented Lewis active sites. Furthermore, described for the first time is that CO2 can be successfully inserted into aryl C-H bonds of a MOF to generate carboxylate groups. This proof-of-concept study contributes a different perspective to the current landscape of CO2 capture and transformation. In closing, the overarching goal of this work is not only to seek efficient MOF adsorbents for CO2 capture, but also to present a new yet attractive scenario of CO2 utilization on MOF platforms.

This research aims to provide a full view of knowledge in charcoal production for fossil coal replacement. Charcoal from biomass is a promising material to replace fossil coal, which is using as heating source or reactant in the industrial sector. Nowadays, charcoal with quality comparable to fossil coal is produced by high-temperature pyrolysis, but efficiency of the production is relatively low due to the trade-off between charcoal property and yield by pyrolysis temperature. Increasing charcoal yield by means of secondary char formation in pyrolysis of large wood particles is the primary method considering in this work. This research has explored increasing efficiency of charcoal production by bio-oil recycling and CO2 purging. These proposed techniques significantly increase concentration and extend residence time of volatiles inside particle of woodchip resulting extra charcoal. Characterization of charcoals implies negligible effect of these methods on charcoal properties such as elemental composition, heating value, morphological structure, and chemical structure. Besides, reactivity of charcoal slightly increased when these methods were applied. A numerical model of pyrolysis in a rotary kiln reactor has been developed to study the effect of design parameters and conditions in reactor scale. The simulation results showed fair prediction of temperature profiles and products distribution along the reactor length. Nonetheless, to deliver full knowledge in charcoal production, further works are planned to be done at the end of this doctoral research.

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Today’s society strives to eliminate the carbon dioxide (CO2) emissions, which is the main greenhouse gas emitted through anthropogenic activities and contributes to climate change. In this project utilization of CO2 emissions from waste to energy plants to carbohydrates via photocatalytic reduction with water and further carbon coupling reactions is investigated. Two routes for the synthesis of carbohydrates have been investigated. Both methods use photocatalytic reduction of carbon dioxide to methanol and then proceed via different steps to produce carbohydrates or their precursors. The first route uses aldol condensation as the main method for the formation of carbon-carbon bonds and the second route is based on the formose reaction that uses formaldehyde as a reactant. The waste incineration plant selected for this study was the one located in Kil, Sweden. This plant processes 15590 tons of waste per year and emits 16366.5 tons of carbon dioxide per year. In order to separate carbon dioxide from the flue gas stream, MEA absorption was chosen as the best option due to its high efficiency. The presented processes have negative carbon dioxide emissions due to the fact that they convert of 16.4% of the waste incineration CO2 emissions into useful products and do not generate any emissions of their own. The aldol condensation pathway exhibits an efficiency of 1.3% when considering only food industry products and 2.5% when including other products that are useful to manufacture solvents, lubricants, or pharmaceuticals. The total amount of food industry products obtained is 3.9 kg/h with the energy requirements being was 159550 kJ/kgproduct. The formose reaction route yields 15.4 kg/h of only food industry products, mainly glucose, and exhibits an efficiency of 5%. The power requirements equal to 90099 kJ/kgproduct. The formose route was found to have higher yield and efficiency, and to be more energy consuming but also more energy efficient. Economic data was difficult to find due to the fact that photocatalytic processes are not commercial yet. / Dagens samhälle strävar efter att eliminera koldioxidutsläppen (CO2), som är den viktigaste växthusgasen som släpps ut genom antropogena aktiviteter och påverkar klimat. Den här projekten undersöker användning av koldioxidutsläpp från avfall till energianläggningar till produktion av kolhydrater via fotokatalytisk reduktion med vatten och ytterligare kolkopplingsreaktioner. Projekten utforskar två vägar för syntes av kolhydrater. Båda metoderna använda fotokatalytisk reduktion av koldioxid till metanol. Kolhydrater eller deras ursprungsmaterial syntetiseras via olika steg nedströms den fotokatalitiska processen. Den första vägen använder aldolkondensation som huvudmetod av kol-kolbindningar och den andra vägen baseras på formosreaktionen som använder formaldehyd som reaktant. Den avfallsförbränningsanläggning som valts ut för denna studie var den i Kil, Värmland, Sverige. Denna anläggning behandlar 15590 ton avfall per år och släpper ut 16366,5 ton koldioxid per år. För att separera koldioxid från rökgasströmmen valdes MEA-absorption som det bästa alternativet på grund av dess höga effektivitet. De presenterade processerna har negativa koldioxidutsläpp på grund av att de omvandlar 16,4% av koldioxid från avfallsförbränning till användbara produkter och inte genererar  egna utsläpp. Aldolkondensationsvägen uppvisar en effektivitet på 1,3% om man endast beaktar livsmedelsindustrins produkter och 2,5% om man gör andra produkter som är användbara för att tillverka lösningsmedel, smörjmedel eller läkemedel. Den totala mängden av livsmedelsprodukter är 3,9 kg / h och energibehovet är lika med 159550 kJ / kg produkt. Formosreaktionsvägen ger 15,4 kg / h av livsmedelsindustrin produkt, huvudsakligen glukos, och uppvisar en effektivitet på 5%. Effektkraven är lika med 90099 kJ / kg produkt. Formosvägen visade sig ha högre utbyte och effektivitet och vara mer energikrävande men också mer energieffektiv. Ekonomiska data var svåra att hitta på grund av att fotokatalytiska processorn ännu inte är kommersiell.

Reverse Water Gas Shift Reaction (RWGS) är en attraktiv lösning för CO2-använding och minskning av utsläppen i atmosfären. Denna reaktion begränsas av termodynamiken och det finns problem med storskalig tillämpning. För att förbättra genomförandet av processen krävs utveckling av en effektiv katalysator. I mosats till typiska undersökningar som använder katalytiska metaller på en inert bärare, i denna undersökning användas en bimetallisk katalysator på en aktiv bärare.  RWGS-reaktionen studerades genom att använda Cu-Fe/CeO2-katalysator den K-promoterade motsvarigheten i olika mängder. Katalysatorerna testades i en fastbäddsreaktor. Katalysatorerna syntetiserades genom hydrotermisk metod och successiv impregnering av aktiva metaller. De framställda katalysatorerna analyserades med hjälp av BET-analys, H2-temperaturprogrammerad reduktion och röntgendiffraktion (XRD). Temperatur och H2/CO2 effekterna bedömdes. Experimentella resultat visade att Cu-Fe/CeO2 uppvisar avsevärd katalytisk aktivitet vid temperaturer högre än 500°C. Den CO2 omvandling med bimetalliska katalysatorn varierade mellan 24 % och 100 % avjämviktsvärdet med GHSV 360 000 h-1. Dessutom varierade CO selektivitet i intervallet mellan 70% och 95%. K-promoterad katalysator uppvisade lägre aktivitet antagligen på grund av partiell täckning av metalliska aktiva ytan, vilket resulterade i lägre omvandling (10%-~50% av jämviktsvärdet). Längre experiment (69-100 timmar) för de icke-promotoriserade katalysatorerna uppvisade inga avaktivering eller aktivitet/selektivitetsförlust i motsats till den K-promoterade katalysatorn som uppvisade en långsam aktivitetsavklingning troligen på grund av sintring. / Reverse Water Gas Shift Reaction (RWGS)is an attractive solution for CO2 utilizationand consecutive reduction of emissions in the atmosphere. This reaction is limited by thermodynamics while there are problems with its implementation at large scale. To improve the process implementation, development of an efficient and effective catalyst is required. Contrary to typical studies where catalytically active metals are deposited on inert supports, in this study the investigation of a bimetallic (Fe-Cu) catalyst on an active support was carried out. In particular, the RWGS reaction was studied over Cu − Fe/CeO2 catalyst with and without potassium promotion by means of catalytic activity tests in a fixed bed reactor. The catalysts were synthesized by hydrothermal method and successive impregnation of active metals. All the materials were characterized by means of BET analysis, H2 temperature programmed reduction and x-ray diffraction. The effects of temperature and H2/CO2 molar ratio were assessed. Experimental results showed that Cu −Fe and exhibit considerable catalytic activity at temperatures greater than 500°C. CO2 conversions of 24% to 100% of the equilibrium conversion were achieved at gas hourly space velocities of 360 000 h−1. Selectivity for CO varied between 70-95% Potassium promotion plausibly results to a partial coverage of active sites, and thus leading to lower conversion (10%-~50% of the equilibrium value). Longer runs (69-100h) showed no signs of deactivation and activity/selectivity loss for the unpromoted catalysts, while the K-promoted catalyst exhibited a slow activity decay probably due to sintering.

Accelerated carbonation is a new CO2 storage method under development as a solution for climate change caused by anthropogenic activities. In accelerated carbonation an alkaline source such as minerals or industrial residues react with carbon dioxide in a presence of slightly acidic solution to produce stable solid carbonates. There are varieties of accelerated carbonation routes which differ in process condition.</p><p>The aim of this study was to evaluate and compare the potential of a slurry route process and a wet route process for the carbonation of basic oxygen furnace (BOF) slag using the CO2 emitted by a conventional natural gas power plant.</p><p>For this purpose a life cycle assessment (LCA) study was performed based on principles and guidelines provided by ISO 14040:2006 and routines and data provided by the SimaPro v8 software package. The material and energy requirements for each of the steps involved in the carbonation process, i.e. pre-treatment of raw material, CO2 compression, transportation, carbonation step, after-treatment and landfill, were calculated and included in the LCA study.</p><p>The slurry and wet route resulted in net CO2 reduction of 87.4% and 72.3% respectively.  However, a positive contribution to other environmental issues was observed with the wet route leading to higher impact mainly due to high heating requirement. An exception was contribution of slurry route to abiotic resource depletion, which was higher for the slurry route due to high water requirement. A general conclusion was that the electricity consumption is the main cause of environmental issues. Sensitivity analyses showed that the environmental impacts are dependent on the transportation distance and electricity source, while no dependence was observed with respect to construction of the carbonation plant.

Tesis por compendio / [ES] El consumo actual de combustibles fósiles supone la emisión de millones de megatones de CO2 cada año, lo que ha tenido consecuencias potencialmente catastróficas como el efecto invernadero, la acidificación de los océanos y la eutrofización de las aguas, entre otras. Por lo tanto, la utilización de CO2 para la producción de combustibles y productos químicos de valor ha atraído mucho interés a lo largo de los años, especialmente empleando luz solar. A lo largo de los años, se han probado una gran variedad de materiales para tecnologías fotocatalíticas, principalmente TiO2, CdS, LDH, MOF y nitruros de carbono, entre otros. A pesar de esto, todos estos materiales adolecen de importantes inconvenientes, como una insuficiente captación de luz, estabilidad o baja producción. Y, por lo tanto, su aplicación en posibles tecnologías industriales fotocatalíticas es muy limitada a nivel industrial. Además de los procesos fotocatalíticos, que se componen principalmente de portadores de carga fotogenerados que facilitan las reacciones redox, los procesos fototérmicos representan una alternativa atractiva para las futuras tecnologías solares. La amplia utilización del espectro solar, el rápido calentamiento por irradiación de luz a través de "nanocalentadores" y "electrones calientes" que interactúan con sustratos son algunas de las características que conducen a los altos rendimientos catalíticos que generalmente se observan en las reacciones fototérmicas. En la presente tesis doctoral, se han empleado diferentes materiales, como clústeres de Fe incrustados en grafeno dopado con nitrógeno, hidroxiapatita dopada con Co y nanopartículas de Ru soportadas sobre titanato de estroncio, como catalizadores fototérmicos para la hidrogenación selectiva de CO2 a CO o metano, tanto en flujo discontinuo como continuo. Admás, se han investigado muchos factores que influyen en esta reacción, como la naturaleza de los grupos/nanopartículas metálicas incrustadas, las cantidades de dopantes y la influencia de la irradiación incidente, entre otros. Además de la catálisis fototérmica, la actual tesis doctoral también aborda procesos fotocatalíticos como la ruptura del agua o la reducción del O2 a H2O2, empleando nuevos compuestos de nitruro de carbono. Ya sea sensibilizando el fotocatalizador para la absorción de luz visible o mejorando las propiedades electrónicas mediante la formación de heterouniones, se lograron resultados fotocatalíticos notables. / [CA] El consum actual de combustibles fòssils suposa l'emissió de milions de megatons de CO2 cada any, cosa que ha tingut conseqüències potencialment catastròfiques com l'efecte hivernacle, l'acidificació dels oceans i l'eutrofització de les aigües, entre d'altres. Per tant, la utilització de CO2 per a la producció de combustibles i productes químics de valor ha atret molt interès al llarg dels anys, especialment emprant llum solar. Al llarg dels anys, s'han provat una gran varietat de materials per a tecnologies fotocatalítiques, principalment TiO2, CdS, LDH, MOF i nitrurs de carboni, entre d'altres. Tot i això, tots aquests materials pateixen importants inconvenients, com una insuficient captació de llum, estabilitat o baixa producció. I, per tant, la seva aplicació a possibles tecnologies industrials fotocatalítiques és molt limitada a nivell industrial. A més dels processos fotocatalítics, que es componen principalment de portadors de càrrega fotogenerats que faciliten les reaccions redox, els processos fototèrmics representen una alternativa atractiva per a les futures tecnologies solars. L'àmplia utilització de l'espectre solar, l'escalfament ràpid per irradiació de llum a través de "nanoescalfadors" i "electrons calents" que interactuen amb substrats són algunes de les característiques que condueixen als alts rendiments catalítics que generalment s'observen en les reaccions fototèrmiques. En aquesta tesi doctoral, s'han emprat diferents materials, com clústers de Fe incrustats en grafè dopat amb nitrogen, hidroxiapatita dopada amb Co i nanopartícules de Ru suportades sobre titanat d'estronci, com a catalitzadors fototèrmics per a la hidrogenació selectiva de CO2 a CO o metà, tant en flux discontinu com continu. A més, s'han investigat molts factors que influeixen en aquesta reacció, com ara la naturalesa dels grups/nanopartícules metàl·liques incrustades, les quantitats de dopants i la influència de la irradiació incident, entre d'altres. A més de la catàlisi fototèrmica, l'actual tesi doctoral també aborda processos fotocatalítics com ara la ruptura de l'aigua o la reducció de l'O2 a H2O2, emprant nous compostos de nitrur de carboni. Ja sigui sensibilitzant el fotocatalitzador per a l'absorció de llum visible o millorant les propietats electròniques mitjançant la formació d'heterounions, es van assolir resultats fotocatalítics notables. / [EN] Fossil fuel consumption accounts for millions of megatons of CO2 emitted every year, which has led to potentially catastrophic consequences such as the greenhouse effect, ocean acidification and water eutrophication, besides others. Thus, the utilization of CO2 for fuels and value chemicals has attracted much interest over the years, especially employing solar light. Over the years, a variety of promising materials have undergone trial for potential photocatalytic technologies, mainly TiO2, CdS, LDHs, MOFs and carbon nitrides among others, yet all these materials suffer from important drawbacks such as insufficient light harvesting, stability, or low production outputs, hence limiting their application in potential photocatalytic industrial technologies. Besides photocatalytic processes, mainly comprising of photogenerated charge carriers that facilitate redox reactions, photothermal processes represent an attractive alternative for future solar technologies. Broad utilization of the solar spectrum, strong heating upon light irradiation through "nano-heaters" and possibly "hot electrons" interacting with either semiconductors or substrate molecules are some characteristics that lead to the high catalytic outputs generally observed in photothermal reactions. In the current doctoral thesis, different materials such as Fe clusters imbedded on nitrogen doped graphene, Co doped hydroxyapatite and Ru nanoparticles supported on strontium titanate have been employed as photothermal catalysts for the photothermal hydrogenation of CO2 to either CO or methane, under both batch and flow conditions. Thus, many factors influencing this reaction have been investigated, such as the nature of embedded metallic clusters/nanoparticles, dopant amounts and the power of incident irradiation among others. Besides photothermal catalysis, the current doctoral thesis also addresses photocatalytic processes such as water splitting or O2 reduction to H2O2, employing novel carbon nitride composites. By either sensitizing the photocatalyst for visible light absorption or enhancing the electronic properties through heterojunction formation, remarkable photocatalytic outputs were achieved. / Szalad, H. (2024). Production of Solar Fuels Employing Different Materials Via Photocatalytic or Photothermal Pathways [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/206848 / Compendio

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