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Ramirez, Julio C. "Vehicular CO2 Reduction in the United States." Digital Commons at Loyola Marymount University and Loyola Law School, 2014. https://digitalcommons.lmu.edu/etd/428.
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As a consequence of the Arab oil embargo in 1973, the United States enacted the first Corporate Average Fuel Consumption standards in 1975 through the Energy Policy Conservation Act enforced by the Environmental Protection Agency. These standards were to improve the fuel economy of passenger cars and light-trucks. Increasing the fuel efficiency of vehicles has not been the only goal of the Environmental Protection Agency. Along the way it has been responsible for many laws regulating the amount of harmful exhaust pipe emissions released into the environment from the combustion of petroleum fuels. This has been accomplished by (but not limited to) requiring catalytic converters on vehicle exhaust systems, the elimination of lead from gasoline, and putting limits on smog causing nitrous oxides (NOx), sulfur oxides (SOx) and tailpipe particulate matter. In the United States, it is estimated that as of 2011, when compared to the Commercial and Residential, Agricultural, Electricity, and other industries, the transportation sector accounts for 28% of GHG (primarily CO2) emissions. According to the National Oceanic Atmospheric Administration (NOAA), global CO2 concentrations in the environment have exceeded historic natural occurring levels. Since CO2 is a gas that naturally traps heat, it is believed to be the main cause of global warming. As a response to the threat of global warming, the United States once again has passed new CAFE standards for model year vehicles 2017 through 2025 to decrease the dependency on petroleum fuels and reducing CO2 in the environment. Enforced by the EPA and National Highway Transportation Safety Administration (NHTSA), the law aims to double the current combined fuel efficiency of passenger cars and light-trucks by 2025 to 54.5 miles per gallon while capping the limit of tailpipe CO2 emissions to 163 grams per mile.
As a responsible consumer, selecting a vehicle with high fuel efficiency and low CO2 emissions will play a key role in reduction of CO2 emissions in the automotive sector. The environment is something that the entire global population has in common, making us environmental stakeholders. As such, we must do our part to preserve the environment for future generations. (Picture on cover courtesy of www.car-emissions-explained.co.uk)
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Windle, Christopher D. "Photocatalytic CO2 reduction by porphyrin rhenium dyads." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4594/.
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The storage of solar energy in chemical fuel is currently under intense investigation, but many of the challenges associated with this goal remain un- surmounted. The investigation of supramolecular assemblies, in which one unit harvests visible light and transfers energy or electrons to another catalytic unit capable of energetically uphill chemical transformations, is of importance. This thesis describes the synthesis, electrochemistry, photochemistry and visible light CO2 photoreduction ability of several rhenium tricarbonyl appended zinc porphyrins. The basic structure comprises a zinc tetraphenyl porphyrin in which one phenyl possesses a NHCO group bound to bipyridine. The bipyridine is complexed to a Re(CO)3X unit. Introduction of a methoxybenzamide spacer produced [Dyad 2 Pic][OTf] and its bromide analogue. Synthetic methodology was developed for the introduction of a methylene spacer to produce [Dyad 3 Pic][OTf] and its bromide analogue. Further synthetic efforts produced routes to novel porphyrin and rhenium complexes possessing phosphonic acid groups for anchoring to metal oxide surfaces. In the ground states of the two dyads there is little interaction between the metalloporphyrin and rhenium units. However, emission quenching of the porphyrin by the rhenium was demonstrated. Remote site photosubstitution was observed in [Dyad 2 Pic][OTf]. Electrochemical and steady state emission studies indicate that electron transfer is energetically favourable in all systems except Dyad 3 Br. All the catalysts developed produced catalytic quantities of CO under visible light in CO2 saturated DMF/TEOA 5/1. Activity increases in the order Dyad 1 < Dyad 2 < particle system < two components < Dyad 3, reaching a turnover number of 360 for [Dyad 3 Pic][OTf]. TRIR experiments demonstrated that the lifetime of charge separation in the dyads increases in the order [Dyad 1 Pic][OTf] < [Dyad 2 Pic][OTf] < [Dyad 3 Pic][OTf] and is 335 ps for [Dyad 3 Pic][OTf], consistent with catalytic activity. Reaction mixture analysis by UV-Vis and NMR spectroscopy and ESI mass spectrometry indicated hydrogenation of the porphyrin, the product of which is also active for CO2 photoreduction. ESI-MS studies showed that substitution of the picoline ligand by TEOA and DMF occurred. The Re and porphyrin units were successfully immobilised on TiO2 nanoparticles. The Re catalyst anchored on TiO2 is active for CO2 photoreduction under visible light. Addition of the porphyrin, and its selective excitation, produced catalytic quantities of CO (TON = 32). This confirmed sensitisation of the Re complex around the TiO2 particle. Electrochemical and steady state emission studies indicate a porphyrin to TiO2 then TiO2 to Re electron transfer mechanism is favourable.
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Rong, Yu. "FCC regeneration process design for co2 emissions reduction." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505485.
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Parra, Puerto Andrés. "Towards Artificial Photosynthesis: Photoelectrochemical CO2 Reduction to Solar Fuels." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/347965.
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This thesis is devoted to prove the concept of the CO(2) reduction to CH(4) with a decreasing in the voltage requirements using a photocatalytic mechanism. Subsequently, part of the solar energy is transferred to the reaction, obtaining an improvement in the total energy balance. The work developed intends first, to take advantage of the know features of the photoactive nanostructured materials obtained by anodization and hydrothermal synthesis (allowing to obtain better surface areas and improving the photon collection, light photosynthetic reactions). Second investigate the copper and copper oxide cathodes for the CO(2) electroreduction activity to CH(4) (dark photosynthetic reactions) using a complete cell to understand the parameters involved in the process and the products selectivity for each cathodes. And third the implementation of the photoanode and cathode in a photoelectrochemical complete cell.
Respect the photoactive materials we are going to talk about TiO(2) based nanostructured materials for water splitting. The first TiO(2) nanostructuration under study are nanotubes obtained by anodization of a Titanium foil using organic electrolytes. The TiO(2) crystal phase obtained by this technique was anatase. The next step in this material was the surface modification to improve the efficiency. To obtain this improvement the anodization process was done using two electrolytes in different steps. As sequence a porous surface with an increment in the surface area was obtained. After, the photoelectrochemical measurements were done in 1 M of sodium hydroxide (NaOH) under AM 1.5G illumination source to observe the photoactivity of these samples.
The second nanostructured materials under study were TiO(2) nanorods obtained by hydrothermal synthesis over a conductive glass substrate, Fluorine Tin Oxide (FTO). The nanorods using this technique have rutile structure. An optimization of two parameters involved in the hydrothermal synthesis was studied: (1) initial titanium precursor concentration and (2) increasing the chlorine concentration to obtain larger and thinner rods. To enhance the photoactivity of TiO(2) we try to incorporate other materials inside the structure. The materials selected were: tin which improves the charge carriers, vanadium which allows the absorption in the visible range and nitrogen doping to enhance the efficiency in the photoactivity of the material.
Concerning to methane production study, a discussion about the electrochemical CO(2) reduction activity over a copper based electrode using a hydrogen carbonate as supporting electrolyte was done, where the positive ions used are sodium and potassium. The first electrode selected is a pristine copper due to the interest of the methane production. The samples were characterized by scanning electronic microscopy (SEM) and X-Ray diffraction (XRD) to visualize the surface morphology and the crystal structure of the electrode. Afterwards, the electrochemical process is studied to understand the activity of these electrodes. Chronopotentiostatic (CP) experiments were done at different current densities to observe the activity as a function of the reached potential.
The second electrode under study was a copper oxide cathode. In the electrochemical experiments an effect was studied related to the electrochemical reduction of the different copper oxide layers generated during the thermal synthesis, leading to a catalytically active copper that enables carbon dioxide reduction. With this type of electrodes a time- dependence test was done to carefully study these crystallographic changes. Finally, another important variable for CO(2) conversion was studied, the humidification of the CO(2) gas stream before the introduction in the electrochemical cell with the impact on the faradaic efficiency of the process.
In the implementation in the PEC cell an evaluation of the photoanode and cathode was done. In this evaluation, the external potential requirements were studied concerning about the energy consumption and the benefit from the photoactivated process.Esta tesis se ha desarrollado con el objetivo de probar el concepto de la reducción del dióxido de carbono a metano, mediante una reducción de los potenciales necesarios usando un mecanismo fotocatalítico. Parte de la energía solar es transferida a la reacción obteniendo una mejora en el balance energético total. El trabajo desarrollado se focaliza primero en el estudio de materiales nanoestructurados fotoactivos basados en dióxido de titanio obtenidos por anodización, generando nanotubos, y por síntesis hidrotermal obteniendo nanohilos sobre un sustrato conductor transparente, los cuales permiten obtener mayores superficies activas mejorando la colección de fotones, similar a las reacciones luminosas en la fotosíntesis. En segundo lugar, se ha estudiado la electroreducción del dióxido de carbono a metano usando cátodos de cobre y oxido de cobre (similar a las reacciones oscuras de la fotosíntesis). Usando el cobre como cátodo, se ha observado la obtención de metano a diferentes densidades de corriente aplicadas para poder observar la productividad respecto al potencial medido. Para el caso de los cátodos de óxido de cobre, no se ha encontrado producción de metano pero si de etileno. En estos cátodos se ha observado un efecto proveniente de la reducción de las capas de los diferentes óxidos de cobre, generados en la síntesis térmica, hacia un cobre catalíticamente activo para la reacción de reducción del dióxido de carbono. Este efecto se ha estudiado profundamente mediante un estudio de los cambios cristalográficos y superficiales a determinados tiempos. Finalmente, se ha estudiado el efecto de la humidificación del dióxido de carbono (gas) previa a la entrada a la celda electroquímica. Como parte final se ha realizado una evaluación energética de los fotoánodos generados por síntesis hidrotermal y de los cátodos basados en cobre estudiados, para poder implementar ambos en una celda fotoelectroquímica completa. En esta parte se ha estudiado los valores de los potenciales externos necesarios para que se pueda dar la reacción, asumiendo un 100% de eficiencia hacia la producción de metano para los cátodos de cobre y de etileno para los de óxido de cobre.
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Grönninger, Philipp [Verfasser], and Dirk [Gutachter] Guldi. "Photocatalytic Reduction of CO2 / Philipp Grönninger ; Gutachter: Dirk Guldi." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1130869482/34.
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Touhami, Dalila. "Pyridine assisted CO2 reduction to methanol at high pressure." Thesis, University of Hull, 2015. http://hydra.hull.ac.uk/resources/hull:16572.
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Significant research efforts have been directed towards exploring electrocatalysts for the selective reduction of CO2 to fuels such as methanol. Bocarsly et al (Princeton University) have recently reported the use of aromatic amines (e.g. pyridine (C5H5N)) as electrocatalysts in aqueous electrolytes for the reduction of CO2 at low overpotentials (50-150 mV). Importantly, the CO2-pyridine reduction process was claimed to selectively produce methanol with Faradaic efficiencies of ~100% on p-GaP electrode and 22-30% on Pt and Pd electrodes. Moreover, the initially proposed mechanism based on a radical intermediate interaction with CO2 as a key step toward the production of methanol was subsequently disproved. In this project, methanol formation by the CO2-pyridine (C5H5N) system was assessed by conducting electrolysis under various conditions at platinum electrodes. High pressure CO2 was used with the aim of increasing the methanol yield. In the course of the present study, the bulk electrolysis confirmed the methanol production at 1 bar and at 55bar of CO2 in the presence of pyridine. However, the methanol yield was found to be persistently limited to sub-ppm level (< 1ppm) under all conditions investigated. The observed methanol yield limitation could not be overcome by the electrode reactivation techniques used. Moreover, the methanol formation seemed unaffected by the current density or the biasing mode. This was an indication of the independence of methanol production from the charge transfer on the electrode. In agreement with these observations, analysis of the voltammetric data supported by simulation revealed that the CO2-pyridine reduction system is mainly pyridinium assisted molecular hydrogen production under all conditions investigated. In particular, protonated pyridine (C5H5N) ‘pyridinium’ was confirmed to behave as a weak acid on platinum. It was found that CO2 is merely a proton source of pyridine reprotonation via the hydration reaction followed by carbonic acid dissociation. The reprotonation reaction coupled to the electrode reaction ultimately leads to the dihydrogen production. No direct contribution of CO2 in the reduction process was observed. The production of methanol seems to occur chemically rather than directly driven by the charge transfer on the electrode. The role of pyridine (C5H5N) appears to be restricted to assisting in the generation of the hydrogen necessary for the alcohol production.
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Woolerton, Thomas William. "Development of enzymatic H2 production and CO2 reduction systems." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:393741ac-94b1-4d56-b680-d9a434db77e2.
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One of today’s most pressing scientific challenges is the conception, development and deployment of renewable energy technologies that will meet the demands of a rapidly increasing population. The motivation is not only dwindling fossil fuel reserves, but also the necessary curtailment of emissions of the greenhouse gas carbon dioxide (a product of burning fossil fuels). The sun provides a vast amount of energy (120,000 TW globally), and one major challenge is the conversion of a fraction of this energy into chemical energy, thereby allowing it to be stored. Dihydrogen (H₂) that is produced from water is an attractive candidate to store solar energy (a ‘solar fuel’), as are high energy carbon-containing molecules (such as CO) that are formed directly from carbon dioxide. One key aspect is the development of catalysts that are able to offer high rates and efficiencies. In biology, some microbes acquire energy from the metabolism of H₂ and CO. The biological catalysts - enzymes - that are responsible are hydrogenases (for the oxidation of H₂ to protons); and carbon monoxide dehydrogenases (CODHs, for the oxidation of CO to CO₂). These redox enzymes, containing nickel and iron as the only metals, are extraordinary in terms of their catalytic characteristics: many are fully reversible catalysts and offer very high turnover frequencies (thousands per second are common), with only tiny energy input requirements. This Thesis uses a hydrogenase from the bacterium Escherichia coli, and two CODHs from the bacterium Carboxydothermus hydrogenoformans, as the catalysts in H2 production and CO₂ reduction systems. Chapter 3 describes the concept and development not of a solar fuel system, but of a device that catalyses the water-gas shift reaction (the reaction between CO and water to form H₂ and CO₂) - a process of major industrial importance for the production of high purity H₂. Chapters 4, 5 and 6 detail photochemical CO₂ reduction systems that are driven by visible light. These systems, operating under mild, aqueous conditions, involve CODHs attached either to TiO₂ nanoparticles that are sensitised to visible light by the co-attachment of a ruthenium-based dye complex, or to cadmium sulfide nanomaterials that, having a narrow band gap, are inherently photoexcitable by visible light. The motivation here is not the construction of technological devices; indeed, the enzymes that are used are fragile, highly sensitive to oxygen, and impossible to scale to industrial levels. Rather, the drivers are those of scientific curiosity (can the incorporation of these remarkable biological catalysts enable the creation of outstanding solar fuel devices?), and of producing systems that serve as benchmarks and inspiration for the development of fully synthetic systems that are robust and scalable.
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Wilson, Solita. "Activation and Reduction of Carbon Dioxide Using Bis-Mesityl Imidazole Ylidene." Youngstown State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1559308312820674.
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Ka, Seon Young. "Studies on the Reactivity of a Bis–Mesityl Imidazolyl Carbene Intermediate toward Carbon Dioxide and Stability of the Resulting Carboxylate." Youngstown State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1566315034568426.
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Jikai, Zhang. "CDM projects and China’s CO2 emission reduction in 2006-2020." Thesis, KTH, Industriell ekologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-58646.
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The Clean Development Mechanism under Kyoto Protocol created a new age for current global emission situation. China, who owns over one third of the whole CDM projects in the world, occupies the main part of CDM development. As one of the biggest and most active economy, China declared that they would reduce their carbon emission by 40%-45% per unit GDP in 2020 compared with the 2005 level, in which CDM has the chance to highlight its value. By the day 28 April 2010, there are 814 registered CDM projects distributed in different provinces in China mainland and this number is still increasing rapidly. Because of large number of CDM projects and the significantly distinct situations in different regions of China, the author chooses two provinces, Shandong and Shaanxi, in east and west of China respectively, as representative samples to do this study. This essay investigates the current situation of CDM projects in those two provinces, and studies the contribution of these projects to emission reduction of Shandong and Shaanxi provinces in last and the next several years. The result shows that CDM projects do contribute to future potential emission reduction but their contribution are limited in these two provinces.
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Pastor, Hernandez Ernest. "Transient spectroscopic studies of photocatalysts for CO2 and proton reduction." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/44182.
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In this thesis, optical and electrochemical techniques are used to study the factors controlling catalytic function in solar-to-fuel conversion systems. Chapter 3, the first results chapter, considers a system for CO2 reduction based on a Re photocatalyst anchored to TiO2. This chapter reports evidence that the immobilisation of the photocatalyst via covalent bonds improves the stability of one of the key reaction intermediates resulting in higher catalytic yields. This chapter also provides insight into the nature and timescale of the steps in the mechanism of CO2 reduction. Chapter 4 considers a proton reduction system based on a Ru absorber, a Ni electrocatalyst and a sacrificial electron donor. This chapter discusses the mechanism behind the strong pH dependence in this system. The results show that whereas the electron transfer between the dye anions and the electrocatalyst is pH independent, the generation of dye anions and the catalytic function of the electrocatalyts have opposite pH-dependencies. Chapter 5 considers a photocathode for proton reduction based on a Cu2O/Al:ZnO buried p-n junction with protection and catalyst layers. The results presented show that the buried junction controls charge separation and the photocurrent onset. Furthermore, the catalyst layer is found to slow down charge recombination and help achieve high reduction yields. This chapter also discuses the mechanism of proton reduction and how the nature of the rate-limiting step has an impact in the recombination kinetics. Chapter 6 discusses the use of transient absorption spectroscopy to study high refractive index materials with high quality interfaces. This chapter investigates light interference effects in TiO2, Cu2O and a CH3NH3PbI3 perovskite device. The results show that interference effects in these materials can dominate their transient spectra, hindering its interpretation. However, it is found that this spectroscopy can also be used to extract information about the changes of the refractive index.
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Xue, Congcong. "Electrocatalytic and Photocatalytic CO2 Reduction by Ru-Re Bimetallic Complexes." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462205030.
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Ngo, Thuhuong T. "Photocatalytic Reduction of CO2 with Tunable Bandgap and Bandedge Materials." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6551.
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Solar energy is a sustainable resource which has substantial potential to meet the increasing demand for renewable energy. Though there has been some success in harvesting solar energy for electricity production, converting solar energy to chemical energy as fuels is still a challenge due to low efficiency.
Since the discovery of TiO2 photocatalysts for splitting water (4) and reducing CO2 (5) to form useful chemical feedstock such as H2, CO and CH4, much research has been done to increase the efficiency of photocatalysts. However, the current conversion efficiency of photocatalysts remains low (~5%) (6, 7). Issues being addressed include the wide bandgap and mismatched band edge for reactions (thermodynamic energy for reaction), poor quantum efficiency of the photon collector systems, high recombination of e-/h+ pairs and limitation in the rate of charge transfer from photocatalyst to reactants.
This work focuses on improving efficiency of photocatalysts for fuel production through several approaches: (1) engineering a metal-organic-framework (MOF) to have proper band gaps and band edges for targeted reactions and for enhancing photoadsorption in the visible light range, (2) tuning an ABO3-type perovskite for desired bandgaps and thermodynamically favored bandedges for CO2 reduction with water in visible light range.
A porphyrin-based Ti-MOF is studied for CO2 photoreduction to gaseous chemical fuels such as CH4 and CO. The porphyrin linkers allow porphyrin-based MOF-525 to achieve narrow bandgap (Eg = ~1.7eV) to absorb visible light, indicating its ability to harvest more solar energy than conventional TiO2. Ti/Zr-MOF-525 also exhibited the appropriate energy level alignment for CO2 and H2O redox reaction for CO and CH4 production. Its CO2 photoreactivity under visible light was demonstrated in a photoreaction, illuminated by 150W Xenon solar simulator. Interestingly, Ti/Zr-MOF-525 demonstrates a selectivity toward CH4, a more valuable fuels than CO. The gas phase reaction condition is an advance over liquid photoreaction. The catalyst stability was also studied and presented. After 3 cycles of reactions, Ti/Zr-MOF-525 is relatively stable for CO2 photoreduction and able to maintain its photoreactivity at about 60-65% of fresh catalyst. The reduction of reactivity is due to a less stable fresh catalyst.
When investigating LaCr1-xFexO3 perovskite oxides for photocatalyst, it was found that when replacing Cr ions at the B sites of LaCrO3 by Fe ions, the bandgap does not follow a linear trend in regards to metal ratio composition but rather reflects the smaller bandgap of LaFeO3. Bandedges were successfully measured for the new synthesized materials. At x = 0.25, the conduction band potential remains similar with x = 0. However, at x = 0.75, the conduction band potential was more negative than either perovskites at x = 0 or x = 1. Future simulation of density of state could address this interesting observation. CO2 reduction relativities of each perovskites were predicted well by their measured bandgaps and bandedges. Among five studied perovskites, synthesized LaCr0.25Fe0.75O3 (x = 0.75) is the most active for CO2 photoreduction under visible illumination at room temperature thanks to its small bandgap (2.0 eV) and its suitable bandedges for CO2 photoreduction.
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Yu, Xiang. "Photocatalytic conversion of methane and reduction of CO2 with H2O." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R022/document.
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La photocatalyse est l'une des technologies clés pour les applications liées à l'énergie propre et à l'environnement. Le nombre d'applications basées sur la photocatalyse a considérablement augmenté au cours des deux dernières décennies.L'activation photocatalytique des liaisons C-H est un domaine émergent. Cependant, en raison de sa grande stabilité, une grande quantité d’énergie est habituellement consommée pour sa conversion, ce qui reste un problème à résoudre. La conversion du méthane et le mécanisme réactionnel qui se produisent sur les nanocomposites métal-hétéropolyacide-oxyde de titane ont été étudiés aux chapitres 3 et 4. L'oxydation du méthane est effectuée depuis plus d'un siècle. Étant donné que l'oxygène est une molécule très réactive, le méthane peut réagir très rapidement avec l'oxygène moléculaire en produisant le CO2. Par conséquent, il est difficile d'obtenir un produit souhaité avec un rendement élevé et une sélectivité importante. Nous avons observé l'oxydation photocatalytique directe et très sélective du méthane en monoxyde de carbone dans les conditions ambiantes. Les catalyseurs composites à base de zinc, d'acide tungstophosphorique et d'oxyde de titane présentent des performances exceptionnelles dans cette réaction, une sélectivité élevée en monoxyde de carbone et un rendement quantique de 7.1% à 362 nm. La réaction se réalise selon le mécanisme de type Mars-Van Krevelen et implique la formation de méthoxy-carbonates de surface en tant qu'intermédiaires et un cycle d'oxydation et de réduction du zinc. Au cours des dernières décennies, des recherches approfondies ont été dédiées à la conversion directe du méthane en alcools ou en hydrocarbures supérieurs. Bien que la conversion directe du méthane en produits à haute valeur ajoutée ait un potentiel environnemental et commercial important, il n’existe aucun procédé à l’échelle commerciale. Nous avons découvert une conversion photochimique directe quantitative hautement sélective (>90%) du méthane en éthane à température ambiante sur un nanocomposite argent-hétéropolyacide-oxyde de titane. Le rendement en éthane atteint 9% sur les matériaux optimisés. Une efficacité quantique élevée, une sélectivité élevée et un rendement significatif en éthane, associés à une excellente stabilité, sont les principaux avantages de la synthèse quantitative de méthane à partir de méthane en utilisant l'approche de boucle photochimique. L'augmentation du taux de dioxyde de carbone dans l’atmosphère et l'épuisement des réserves de combustibles fossiles ont suscité de vives inquiétudes quant à l'impact ultérieur sur le climat mondial et l'approvisionnement futur en énergie. Le chapitre 5 porte sur l’efficacité du nouveau catalyseur pour la conversion sélective de CO2 en CO. Les nanocomposites acide de phosphotungstique-oxyde de titane contenant du zinc ont présenté une activité exceptionnelle atteignant 50 µmol CO/g·h et une sélectivité (73%) dans la réduction photocatalytique du CO2 en CO en présence d'eau. Les expériences infrarouges in situ suggèrent que la réaction implique des bicarbonates de zinc contenant des groupes hydroxyle. La décomposition sous irradiation de ces espèces de bicarbonate de zinc conduit à la production sélective de monoxyde de carbone et d'oxygène. Lors des réactions photocatalytiques, la différence de morphologie du catalyseur a généralement un effet significatif sur les performances photocatalytiques. Le chapitre 6 a étudié l'effet des cristaux monocliniques de vanadate de bismuth (BiVO4) avec un rapport contrôlé de facettes {010} et {110} sur la réduction photocatalytique de CO2 par H2O. La réaction sous irradiation est considérablement améliorée par la photodéposition sélective de co-catalyseurs de Cu et Co sur différentes facettes, fournissant un flux de charge selon le Z-schémaPhotocatalysis is one of the key technologies for clean energy and environmental applications. The number of applications based on photocatalysis has increased dramatically for the past two decades. Photocatalytic activation of C-H bonds is an emerging field. Methane is a promising source of energy with a huge reserve and is considered to be one of the alternatives to non-renewable petroleum resources because it can be converted to valuable hydrocarbon feedstocks and hydrogen through appropriate reactions. However, due to its high stability, high energy is usually consumed for its conversion, which remains a problem to be solved. Methane conversion and reaction mechanism occurring on metal-heteropolyacid-titania nanocomposites were investigated in Chapters 3 and 4. Oxidation of methane has been carried out for more than a century. Since oxygen is a very reactive molecule, methane can react very rapidly with molecular oxygen and is prone to total oxidation till CO2. Therefore, it is difficult to obtain a desired product with high yield and high selectivity. We report here direct and selective photocatalytic highly-selective oxidation of methane to carbon monoxide under ambient conditions. The composite catalysts on the basis of zinc, tungstophosphoric acid and titania exhibit exceptional performance in this reaction, high carbon monoxide selectivity and quantum efficiency of 7.1% at 362 nm. The reaction is consistent with the Mars-Van Krevelen type sequence and involves formation of the surface methoxy-carbonates as intermediates and zinc oxidation-reduction cycling. In the past few decades, extensive research has focused on the direct conversion of methane to alcohols or higher hydrocarbons. The current processes of converting methane to alcohols or olefins are complex and expensive, because they require an intermediate step of reforming methane to syngas. Although the direct conversion of methane to more valuable products has significant environmental and potential commercial value, there is no commercial scale process available. We uncovered highly selective (>90%) quantitative photochemical direct conversion of methane to ethane at ambient temperature over silver-heteropolyacid-titania nanocomposites. The ethane yield from methane reaches 9 % on the optimized materials. High quantum efficiency, high selectivity and significant yield of ethane combined with excellent stability are major advantages of methane quantitative synthesis from methane using the photochemical looping approach. The rise in atmospheric carbon dioxide and the depletion of fossil fuel reserves have raised serious concerns about the subsequent impact of CO2 on the global climate and future energy supply. The use of abundant solar energy to convert carbon dioxide into fuel, such as carbon monoxide, methane or methanol, solves both problems simultaneously and provides a convenient method of energy storage. Chapter 5 addresses a new efficient catalyst for selective CO2 to CO conversion. The zinc containing phosphotungstic acid-titania nanocomposites exhibited exceptional high activity reaching 50 µmol CO/g·h and selectivity (73%) in the CO2 photocatalytic reduction to CO in the presence of water. The in-situ IR experiments suggest that reaction involves zinc bicarbonates containing hydroxyl groups. The decomposition of these zinc bicarbonate species under irradiation leads to the selective production of carbon monoxide and oxygen. In photocatalytic reactions, the difference in catalyst morphology usually has a significant effect on the photocatalytic performance. Chapter 6 studied the effect of monoclinic bismuth vanadate (BiVO4) crystals with controlled ratio of {010} and {110} facets for photocatalytic reduction of CO2 by H2O. The reaction under irradiation is significantly enhanced by selective photo-deposition of Cu and Co co-catalysts over different facets providing Z-scheme charge flow
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Dattila, Federico. "Modelling and mapping pathways of electrochemical CO2 reduction on modified catalytic surfaces." Doctoral thesis, Universitat Rovira i Virgili, 2020. http://hdl.handle.net/10803/670954.
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La reducció de CO2 és l'únic procés per generar combustibles verds amb un impacte negatiu net en les emissions de CO2. Per tant, el desenvolupament futur de la nostra societat necessita una aplicació industrial d'aquesta tecnologia per produir productes químics d'ús intensiu com l'etilè. El coure és un material únic per catalitzar aquests productes, però, avenços significatius en aquest procés requereixen una comprensió teòrica profunda de la seva complexitat.
En aquesta tesi em vaig proposar desenvolupar mètodes teòrics per abordar els principals factors involucrats en la reducció de CO2 amb coure: (i) reconstrucció superficial a causa de potencial negatiu; (ii) efectes químics sobre la selectivitat; i (iii) l'efecte de l'electròlit. Els capítols I i II es van dedicar a les motivacions i mètodes i el Capítol 3 a comprovar resultats experimentals ben establerts. En el capítol 4 vaig investigar la reconstrucció del coure policristal·lí a potencials negatius. Aquest procés està impulsat per la polarització de la superfície, que promou dominis (100) i defectes. Seguint les previsions teòriques, vaig sintetitzar un catalitzador a base de coure eficaç per produir etilè amb alt rendiment. En el capítol V, vaig estudiar l'òxid de coure per investigar l'estat d'oxidació del coure, la seva coordinació i els llocs superficials actius cap a la producció de químics C2+. Entre els resultats, vaig demostrar que la polarització impulsa la reducció de CO2, mentre un nou intermedi, el glioxilato desprotonado, millora la selectivitat fins als C2+. En el capítol VI em vaig dedicar a efectes químics que influencien la reactivitat el coure. Adatomos de sofre, que actuen com a centres d'ancoratge, permeten la generació de formiat. Finalment, a l'apèndix A vaig introduir l'efecte dels cations sobre la reducció de CO2, que encara no es comprèn completament, però té una clara rellevància en la distribució del producte.La reducción de CO2 es el único proceso para generar combustibles verdes con un impacto negativo neto en las emisiones de CO2. Por lo tanto, el desarrollo futuro de nuestra sociedad necesita una aplicación industrial de esta tecnología para producir productos químicos de uso intensivo como el etileno. El cobre es un material único para catalizar estos productos, sin embargo, avances significativos en este proceso requieren una comprensión teórica profunda de su complejidad. En esta tesis me propuse desarrollar métodos teóricos para abordar los principales factores involucrados en la reducción de CO2 con cobre: (i) reconstrucción superficial debido a potencial negativo; (ii) efectos químicos sobre la selectividad; y (iii) el efecto del electrolito. Los capítulos I y II se dedicaron a las motivaciones y métodos y el Capítulo 3 a comprobar resultados experimentales bien establecidos. En el capítulo 4 investigué la reconstrucción del cobre policristalino a potenciales negativos. Este proceso está impulsado por la polarización de la superficie, que promueve dominios (100) y defectos. Siguiendo las previsiones teóricas, sinteticé un catalizador a base de cobre eficaz para producir etileno con alto rendimiento. En el Capítulo V, estudié el óxido de cobre para investigar el estado de oxidación del cobre, su coordinación y los sitios superficiales activos hacia la producción de químicos C2+. Entre los resultados, demostré que la polarización impulsa la reducción de CO2, mientras un nuevo intermedio, el glioxilato desprotonado, mejora la selectividad hasta los C2+. En el capítulo VI me dediqué a efectos químicos que influencian la reactividad del cobre. Adatomos de azufre, que actúan como centros de anclaje, permiten la generación de formiato. Finalmente, en el Apéndice A introduje el efecto de los cationes sobre la reducción de CO2, que aún no se comprende completamente, pero tiene una clara relevancia en la distribución del producto.
CO2 reduction is the only process which can generate green fuels with a net negative impact in CO2 emissions. Therefore, the future development of our society needs an industrial scale up of this technology, involving the production of heavily used chemicals such as ethylene. Copper is a unique material for catalyzing these C2+ products, however significant advances need a deep theoretical understanding of the complexity of this material under CO2 reduction conditions. In this thesis I aimed at developing theoretical methods to address the main factors involved in this process: (i) surface reconstruction at negative potential; (ii) chemical effects on copper selectivity; and (iii) the effect of the electrolyte. Chapters I and II were dedicated to the motivations and methods. After having benchmarked in Chapter 3 well-established experimental results, such as the morphology dependence of CO2 product distribution on copper local morphology, I investigated the reconstruction of polycrystalline copper at negative potentials. This process is driven by local surface polarization, which destabilizes close-packed domains and promotes (100) facets and defects. Following theoretical guidelines, I synthesized an effective copper-based catalyst with produced ethylene at high yield and high current density. In Chapter V I studied a complex oxide-derived copper material to provide insights about copper oxidation state, its coordination and surface ensembles active toward C2+ chemicals. Among the outcomes, I demonstrated that polarization drives CO2 reduction activity, whilst a newly reported intermediate, a deprotonated glyoxylate, triggers C2+ selectivity. In chapter VI I dedicated to chemical effects on copper reactivity. Sulfur adatoms, acting as strong tethering centers enable the generation of formate, a chemical employed as preservative for animal food stock. Finally, in Appendix A I introduced cation effect on CO2 reduction, not yet fully understood but having a clear relevance on product distribution.
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Möllersten, Kenneth. "Opportunities for CO2 Reductions and CO2-Lean Energy Systems in Pulp and Paper Mills." Doctoral thesis, KTH, Chemical Engineering and Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3398.
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The risk for climate change is a growing concern for theglobal society. According to what is known as the Kyoto Protocol,developed countries have committed themselves to reduce theirgreenhouse gas (GHG) emissions. The purpose of this thesis hasbeen to analyse opportunities for CO2 reductions in Swedish pulpand paper mills. The pulp and paper industry accounts forsignificant shares of the Swedish utilisationof both electricityand, in particular, biomass fuels. In this thesis, it has been agoal to focus not only on the technical potential of alternativesfor CO2 reductions in the energy systems of pulp and paper mills,but also on analysing the costeffectiveness of the studiedmeasures. Moreover, the analysis has covered questions concerningthe capacity and willingness among the actors involved with thepulp and paper millsenergy systems to realise CO2reduction potentials.
A broad techno-economical evaluation of available technologiesfor increased power production as well as more efficient energyutilisation is carried out. Furthermore, a more indepth analysisof pulp mill-based biomass energy with CO2 removal and permanentsequestration (BECS) is presented. An evaluation is made of thepotential for pulp and paper production with a negative CO2balance through the implementation of BECS. In recent yearsoutside suppliers, mainly energy service companies (ESCOs), havebegun to operate energy facilities in some Swedish pulp and papermills. Based on interviews with managers from pulp and papercompanies and ESCOs, the main driving forces behind theincreasing co-operation as well as the opportunities and riskswith energy related co-operation are presented.
Furthermore, the technical possibility of carbon-negativitythrough the implementation of BECS is discussed in relation tocarbon management on both corporate and global levels. The extentto which CO2-reducing measures in pulp and paper mills arerealised will have an impact on Swedens capacity to reachCO2 reduction targets. Whether or not technologies for CO2capture and sequestration are developed and implemented inSwedish pulp mills has a very large impact on the size ofSwedens long-term CO2 reduction potential. Moreover, thedevelopment of business and competence focus in pulp and papercompanies and ESCOs suggests that cooperation will become ofincreasing importance for future sustainable industrial energymanagement.
Keywords:CO2 reduction, pulp and paper industry, energysystem, biomass, CO2 capture and sequestration, black liquor,gasification, power production, outsourcing, sustainable energymanagement
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Pršlja, Paulina. "Theoretical Studies of Single-Site Catalysts for Efficient Electrochemical CO2 Reduction." Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/671468.
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El desenvolupament de l’electroquímica té el potenciar d’utilizar el CO2 com a matèria primera per a la producció sostenible de compostos i materials i té un gran impacte en la indústria química. El catalitzador “de lloc únic” (single site catalyst) és un material prometedor per aconseguir elevades activitats y selectivitats cap a la formació de CO i hidrocarburs C1. L’estructura única d’aquest catalitzador derivat de carboni redueix la competència d’aquests processos amb d’altres processos catalítics com la hydrogen evolution reaction (HER) perquè el single site catalyst requereix la unió de l’hidrogen a la part superior. En aquesta tesi s’han aplicat mètodes DFT i conceptes electroquímics per tal d’entendre els processos de reducció de CO2. Al tercer capítol es descriu la importància de les característiques estructurals del single site catalyst, juntament amb els conceptes relacionats amb la química de coordinació necessaris per a entendre l’activitat del catalitzador en la reacció electroquímica de reducció del CO2 (eCO2RR). L’objectiu del capítol 4 és establir correlacions experimentals i teòriques entre les propietats fisicoquímiques i catalítiques de la eCO2RR que dona com a producte CO per al catalitzador del MNC. El procés de reconstrucció de les nanopartícules de Ni mitjançant la desintegració de Ni(CO)2 en materials de carboni dopats amb N es descriu al capítol 5. Per últim, en el capítol 6 es descriu la selectivitat dels productes de reducció de CO2 tenint en compte com afecta el potencial i la temperatura sobre el catalitzador modelat de CoTPP/MWCNT.El desarrollo de la electroquímica tiene el potencial de utilizar el CO2 como materia prima para la producción sostenible de compuestos y materiales y tiene un gran impacto en la industria química. El catalizador “de sitio único” (single site catalyst) es un material prometedor para lograr una elevada actividad y selectividad hacia CO e hidrocarburos C1. La estructura única de este catalizador derivado de carbono reduce la competencia de estos procesos con otros procesos catalíticos como la reacción hydrogen evolution reaction (HER) porque el single site catalyst requiere la unión de hidrógeno en la parte superior. En esta tesis, métodos DFT y conceptos electroquímicos computacionales han sido aplicados para entender los procesos de reducción de CO2. En el capítulo 3 se describe la importancia de las características estructurales del single site catalyst, además de los conceptos relacionados con la química de coordinación que se aplican para comprender la actividad del catalizador en la reacción electroquímica de reducción de CO2 (eCO2RR). El objetivo del capítulo 4 es establecer correlaciones experimentales y teóricas entre las propiedades fisicoquímicas y catalíticas para la eCO2RR hacia CO para el catalizador del MNC. El proceso de reconstrucción de las nanopartículas de Ni mediante la desintegración de Ni(CO)2 en materiales de carbono dopados con N se describe en el capítulo 5. Por último, en el capítulo 6 se describe la selectividad de los productos de reducción de CO2 teniendo en cuenta cómo afecta el potencial y la temperatura sobre el catalizador modelado de CoTPP/MWCNT.
The development of electrochemistry has the potential to use CO2 as a feedstock for the sustainable production of chemicals and materials and it has an important impact on the chemical industry. Single site catalyst is a promising new material for achieving high activity and selectivity towards CO and C1 hydrocarbons. The unique structure of carbon-based catalyst makes it a good compressor of competing Hydrogen evolution reaction (HER) because the single site requires an ontop binding of hydrogen. In this thesis, I applied DFT methods and computational electrochemical concepts for understanding the processes of CO2 reduction (eCO2RR). In chapter 3 I described the importance of single-site structural features catalyst, besides the basic concept of the coordination chemistry that is applied to understand eCO2RR activity of the catalyst. The aim of chapter 4 was to establish experimental and theoretical correlations between physicochemical and catalytic properties for the eCO2RR towards CO for MNC catalyst. The process of reconstruction of Ni nanoparticles by the disintegration of Ni(CO)2 on N-doped carbon materials is described in chapter 5. Finally, in chapter 6 I unraveled the selectivity of CO2 reduction products that were influenced by potential and the temperature over modeled CoTPP/MWCNT catalyst.
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Neri, G. "The electro- and photochemical reduction of CO2 mediated by molecular catalysts." Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3007220/.
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In this work, molecular complexes of transition metals have been synthesised and studied for their CO2 reduction ability, either in an electrochemical or photochemical system, with a focus on complexes of nickel with derivatives of the macrocycle cyclam (cyc, cyc = 1,4,8,11-tetraazacyclotetradecane) which are well-known for being extremely active CO2 reduction electrocatalysts in water. The cyc framework has been modified with functional groups suitable for binding to semiconductor oxides to obtain the new complexes Ni(cycC) and Ni(cycP) (cycC = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid, cycP = {[(1,4,8,11-tetraazacyclotetradecan-1-yl)methyl]phosphonic acid}), and their electrochemical activity towards CO2 reduction in water has been evaluated. Modification of the ligand framework in the 6 position with a carboxylic acid does not change the CO2 reduction activity of the complex Ni(cycC) at pH 5, through the use of electrochemical and spectroscopic techniques it was found that there is a large increase in the CO2 reduction activity at pH 2, proposed to be due to the protonated carboxylic acid acting as an internal proton source. When Ni(cycC) was immobilised on TiO2 electrodes it was possible to measure the rate of photoinduced electron transfer by using μs-s transient absorption spectroscopy (TAS) under argon in the presence of a hole scavenger, however the carboxylic acid proved unstable under CO2. Ni(cycP) was synthesised to provide a stronger binding group to the surface. It was found that functionalisation on the 1 position affected the CO2 reduction activity in a negative way, however the complex was able to bind strongly to both TiO2 and ZrO2. ZrO2 nanoparticles modified with Ni(cycP) and a ruthenium dye were able to reduce CO2 to CO in water at pH = 4, with higher rates and turnover numbers compared to the components in solution, when illuminated with visible light. The improvement in activity for the heterogeneous photocatalyst was attributed to a faster electron transfer from the immobilised dye to the immobilised catalyst, calculated through detailed steady-state and transient spectroscopies, which prevented charge recombination. In collaboration with the University of Cambridge, Ni(cycP) has been immobilised on ZnSe quantum dots (QDs) and it has been proven to be an effective photocatalyst for CO2 reduction to CO in water. We have carried out a detailed ultrafast TAS study on suspensions of the modified QDs, and it has been found that in the presence of a hole scavenger, upon illumination the electrons are excited from the VB to the conduction band (CB), however they rapidly decay to trap states close to the CB to generate a long lived signal. When Ni(cycP) is present, faster decay of the trapped electron signal is observed, which is assigned to fast electronic transfer from the QDs to Ni(cycP). The knowledge of the mechanisms for CO2 reduction will allow rational design of better catalysts for CO2 reduction. In collaboration with the Rutherford Appleton Laboratories, we have designed an in situ spectroelectrochemical Sum Frequency Generation (SEC-SFG) technique using the ULTRA laser at the Central Laser facility. We have demonstrated the technique by analysing the redox behaviour of a well-known CO2 reduction catalyst, [Mn(bpy)(CO)3Br]. We were able to observe the redox species at the electrode surface as a Cyclic Voltammogram was carried out, and to propose the orientation of the species at the surface. Furthermore, the same technique has been applied to the study of the absorption mechanism of Ni(cycC) on the mercury surface, the first step in the catalytic cycle.
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Meredith, Sylvia. "Synthesis of a Zinc Dipyrrin Complex for Photocatalytic Reduction of CO2." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/honors/645.
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Zinc dipyrrin complexes have the potential to act as cheap, effective photosensitizers. Synthesizing and studying different types could lead to more efficient solar energy harvesting processes, especially the production of solar fuel. Here, two attempts to synthesize 1,3,7,9-tetraphenyl-5-mesityldipyrromethene are reported and discussed. According to 1H NMR, the first synthesis attempt was not successful. The second synthesis attempt was not purified effectively, so 1H NMR produced inconclusive results. Further purification strategies or alternate synthesis methods are required.
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Ruiz, Valencia Azariel. "A new microbiological way for CO2 reduction : from discovery to development." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2019. http://www.theses.fr/2019ENCM0002.
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A l'Institut Européen des Membranes, un nouveau procédé microbiologique de réduction du CO2 en formiate a été découvert. Le premier objectif de ces travaux de thèse était de reproduire les essais de réduction du CO2 dans des conditions de référence, avec une nouvelle ampoule de biocatalyseur commandée chez le même fournisseur de souches que pour les essais préliminaires conduits au Laboratoire. Mais, ces tests n'ont pas permis de réitérer les résultats obtenus, c'est-à-dire la production de formiate. Une mutation de la souche a été suspectée et la souche qui avait été conservée lors des tests préliminaires a donc été mise en œuvre. Néanmoins, de nouveaux soucis de reproductibilité ont été mis en évidence. Une analyse biochimique a finalement révélé que la souche supposée être le catalyseur de la réduction du CO2 était en fait en consortium avec d’autres bactéries. En parallèle, une méthode fiable basée sur le marquage au 13C du CO2 et son suivi par RMN a été développée au Laboratoire pour suivre l'assimilation du 13CO2. Les différentes souches ont été isolées et testées séparément pour la réduction du CO2. L'analyse RMN a démontré que la contamination majoritaire, dont la présence était inattendue, est le vrai catalyseur de la réduction du 13CO2 en 13C-formiate.Le 13C-formiate a été ensuite quantifié par une méthode GC-MS mise au point au Laboratoire. Les effets de différents paramètres de réaction sur les performances de réaction ont alors été investigués. Ces essais ont permis notamment de mettre en évidence un système enzymatique intracellulaire qui pourrait catalyser la réduction du CO2 et d'identifier un possible donneur d'électrons. En effet, l'addition de Poly-3-HydroxyButyrate (PHB) dans la suspension bactérienne a permis d'améliorer significativement la productivité en formiate, ce qui laisse supposer que ce polymère de stockage de l'énergie pourrait être la source d’électrons utilisée pour la réduction du CO2.Néanmoins, ce stock intracellulaire de PHB, formé pendant l'étape de pré-culture, est fini et peut s'épuiser pendant la réaction. Ceci explique pourquoi la capacité du biocatalyseur à utiliser les électrons d’une cathode polarisée a été évaluée pour la réduction du CO2. Des essais préliminaires ont démontré la faisabilité de ce dispositif par l'établissement d'un courant CO2-dépendant dans un bio-électrolyseur. Des densités de courant entre 1.2 to 3.2 A·m-2 ont été obtenues, ce qui correspond à des flux volumétriques de CO2 réduit entre 12 to 30 mL CO2·(g cellule sèche)-1.j-1. Jusqu'à présent, ce nouveau bioprocédé a été opéré sur 25 jours. Par comparaison à la littérature, ce bioprocédé est particulièrement intéressant car (i) le flux de CO2 réduit est significatif et que (ii) aucun ajout de cofacteur, molécule organique, H2 ou photons au milieu de réaction n'est nécessaireAt the European Institute of Membranes, a new microbiological process for CO2 reduction into formate was discovered. The first objective of this PhD work was to reproduce the CO2 reduction tests in reference conditions, with a new biocatalyst vial ordered to the same strain provider as for the prior trials at the Lab. However, these tests did not allow to reiterate the results obtained previously, i.e. formate production. A strain mutation was suspected and the strain that was stored during the preliminary tests was thus implemented. Nevertheless, new reproducibility problems were encountered. A biochemical analysis revealed finally that the strain assumed to catalyze the CO2 reduction was in consortium with other bacteria. In parallel, a reliable methodology based on CO2 labelling by 13C and NMR monitoring was developed at the Lab to follow 13CO2 assimilation. The different strains were isolated and tested separately regarding CO2 reduction. The NMR analysis demonstrated that the principal contamination, whose presence was unexpected, was the true biocatalyst of the 13CO2 reduction into 13C-formate.The 13C-formate was then quantified by a GC-MS method that was developed at the Lab. The effects of different reaction parameters on the reaction performances were thereafter investigated. These tests allowed notably to evidence an intracellular enzymatic system that could catalyze the CO2 reduction and to identify the possible electron donor. Indeed, addition of Poly-3-HydroxyButyrate (PHB) in the bacterial suspension enhanced significantly the formate production, suggesting that this energy storage polymer could be the electron source required for the CO2 reduction.Nevertheless, this intracellular PHB stock, formed during the bacteria culture step, is finite and can be exhausted during the reaction. This explains why the ability of the biocatalyst to recover electrons from a polarized cathode for CO2 reduction was assessed. Preliminary tests demonstrated the feasibility of this bio-electrochemical approach by the establishment of a CO2-dependant reduction current in a bio-electrolyzer. Current densities from 1.2 to 3.2 A·m-2 were obtained, which corresponds to volumetric flows of reduced CO2 ranging from 12 to 30 mL CO2·(g dry-cell)-1·d-1. Up to now, this new bioprocess was operated over 25 day. Regarding literature, this bioprocess is particularly interesting because (i) the volumetric flow of reduced CO2 is significant and (ii) no adding of cofactor, organic molecules, H2 or photons to the reaction medium is required
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Arar, Joseph I. "A model to evaluate CO2 emission reduction strategies in the US." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1186020342.
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Ezeh, Collins Izuchukwu. "Novel materials for CO2 adsorption and reduction to methanol via hydrogenation." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/48570/.
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Sorption-enhanced catalysts are highly favored to improve the synthesis of methanol by hydrogenation process. This requires the development of selective catalysts and CO2 adsorbents that are sufficiently stable to tolerate cyclic regeneration during operation. The present work focuses on the assessment of the adsorption performance of novel layered double hydroxides acting as supports for copper based catalysts in the reduction of CO2 to methanol. Emphasis is placed on the stability and capacity of hybrids prepared using various preparation routes in order to optimize the CO2 uptake and conversion to methanol per mass of the catalyst. This parameter is crucial in the industrial implementation of the technology as it dictates the size of the adsorption units and reactors required. The co-precipitation of Cu2+, Zn2+ and Zr4+ species onto well-dispersed layered double hydroxides is shown to be an effective preparation method that ensures adequate interaction between the catalysts and the support. Prior to the synthesis of the material, individual enhancement of the catalyst and the LDH template were carried out respectively. The catalysts were prepared via various facile methods. Calcination of the catalysts facilitated the mixture of the Cu catalyst with the respective support bolstering the formation of intermolecular oxo-bridges which resulted to the thermal stability of the catalysts. The thermal performance of the catalysts was directly related to the increase in calcination temperature. However, this temperature was capped at 673K beyond which denaturing of the catalyst occurs. For all given preparation method, comparing the different catalysts based on the Cu-loading, the performance trend is as follows: CP > DP > IM. Other factors experimented to affect the thermal properties of the catalysts include the Cu-loading and heating rate. To improve CO2 adsorption, amine modified Layered double hydroxide (LDHs) were prepared via the conventional, ultrasonic and hydrothermal routes, followed by MEA extraction. A comparative study was conducted with consideration of the effect of functionalization route on the adsorption capacity, regeneration and lifetime of the adsorbent. It is revealed that increase in amount of SDS has an adverse effect on the CO2 adsorption performance by protonating considerable amount of active amino groups. This performance trend was observed across all experimented temperature with the CO2 adsorption capacity decreasing with increase in temperature. After amine modification, adsorption capacity increased by ca. 75-90% and ca.10-30% at 55 oC and 80 oC, respectively. However, by sonochemical modification, the adsorption capacity showed an increase from 12-108% depending on sonic intensity. This is attributed to the enhanced deprotonation of activated amino functional groups via the sonochemical process. Subsequently, this improved the effective amine efficiency by 60% of the conventional. In addition, the sonochemical process improved the thermal stability of the adsorbent as well as reducing the irreversible CO2 uptake, CUirrev, from 0.18 mmol/g to 0.03 mmol/g; hence improving the lifetime and ease of regenerating the adsorbent. This is presented by subjecting the prepared adsorbents to series of thermal swing adsorption (TSA) cycles until its adsorption capacity goes below 60% of the original CO2 uptake. While the conventional adsorbent underwent a 10 TSA cycles before breaking down, the sonochemically functionalized LDH went further than 30 TSA cycles. However, adsorbents prepared via hydrothermal route showed a better CO2 uptake capacity than sonochemical and conventional adsorbents. This is attributed to the decrease in weak basic sites (OH- groups) and moderate basic sites (M-O) and subsequent increase in number of strong basic sites (O2-). Therefore, the sonochemical-assisted hydrothermal treatment promoted the adsorption capacity of the adsorbent. However, the cyclic adsorption efficiency of the hydrothermally prepared sample was lowest ca. 53% compared to 76% and 60% for the sonochemical and conventional process respectively. Adopting the obtained factors for optimum synthesis and operation of both CuO/ZnO/ZrO2 catalyst and Mg-Al LDH adsorbent, a composite catalyst consisting of CuO/ZnO/ZrO2 catalyst on LDH template was synthesised and analysed for CO2 uptake capacity and catalytic activity with variation in Al3+ and Zr4+ compositions. The deposition of the catalyst on the LDH support was found not to alter significantly the CO2 uptake of the hydrotalcites but helps to maintain the surface heterogeneity. Characterization tests shows an improvement in structural modification. However, this is subject to the proportion of the considered varied metals. In addition, despite the high thermal stability of Zr4+, the composite material was observed to weaken in stability with increase in Zr4+ content. Nonetheless, the CO2 uptake capacity was observed to increase. A thorough kinetic analysis demonstrates that the adsorption mechanism is attributed to the chemical nature of the metals which promoted chemisorption as the dominating adsorption mechanism with little contribution from physisorption. CO2 conversion and methanol yield were also dependent on the nature and composition of the cations as well as the operating temperature. Al3+:(Al3++Zr4+) ratio of 0.4 was obtained as the best cation mix to attain maximum methanol yield. A preliminary catalyst screening shows that Cu/ZnO/ZrO2/Mg-Al LDH is a promising candidate to catalyze simultaneous adsorption and reduction of CO2 for methanol synthesis.
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Day, Alex. "Gas Chromatography Analysis of CO2 Reduction Photocatalysis with Zinc Dipyrrin Complexes." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/honors/498.
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Bis(1,3,7,9-tetramethyl-5-mesityldipyrrinato)zinc(II) (ZnDPY) was synthesized in the lab by the McCusker group and a procedure was created to analyze its ability as a photosensitizer, a molecule that provides the energy for the reaction to occur by capturing light energy and turning it into a form that can be used by the photocatalyst. While more work is needed, preliminary steps have been made to create a process that can analyze the amount of carbon monoxide produced by a photocatalytic CO2 reduction reaction with ZnDPY as the photosensitizer. Progress has been made via the setup of a reaction apparatus, targeted gas chromatography (GC) peak separation, and GC calibration. More work will need to be done in order to determine the optimal reaction mix to showcase the sensitizer’s potential.
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Zhang, Xizi. "Understanding Electrochemical CO2 Reduction using Polycrystalline Au Electrode in WiS Electrolyte." Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:107947.
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Thesis advisor: Dunwei WangElectrochemical CO2 reduction reaction (CRR) provides a solution to both the increasing global demand of energy by forming valuable chemical products for fuel production, and global warming by reducing the amount of CO2 in the environment. To efficiently reduce CO2, we sought to understand the reaction mechanism using a polycrystalline Au electrode and the super concentrated LiTFSI solution (WiS) as the electrolyte. By varying both the electrolytic potential and the concentration of WiS, we investigated the factors determining product selectivity and found that reaction kinetics and mass transport together direct the selectivity towards CO. We probed the rate limiting step (RLS) of CO2 reduction by observing the variation of product distribution with water availability in solution, and discovered that the RLS was likely to involve only a single electron transfer to form COO*–. Lastly, we proposed that in WiS, H2O were the dominant proton sources for both CO2 reduction and H2 evolution reactions. In 21m WiS, the competing hydrogen evolution reaction was kinetically inhibited, so CO production was favored with a selectivity of 90% at a potential as early as -0.4V vs RHE. This study demonstrated the great potential of WiS as a platform for studying multi-proton, multi-electron transfer reactions
Thesis (BS) — Boston College, 2018
Submitted to: Boston College. College of Arts and Sciences
Discipline: Scholar of the College
Discipline: Chemistry
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Alghamdi, Ahlam. "Exploring New Applications of Group 7 Complexes for Catalytic and CO2 Reduction Using Photons or Electrochemistry." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35234.
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This thesis focuses on the synthesis, characterization and reactivity of group VII transition metal complexes. It begins with exploring a new pincer geometry of Re(I) compounds and then examining both Re(I) and Mn(I) compound as homogenous catalysts for photocatalytic and electrocatalytic reduction of CO2. In the first chapter, I focus on some recently reported approaches to photocatalytic and electrocatalytic reduction of CO2 using homogenous catalysts of transition metal.
The second chapter presents efforts to capture Re(I) in a neutral N,N,N pincer scaffold and the resulting enhanced absorption of visible light. Most of these results have appeared in a publication. In this thesis, I only present my work on rhenium compounds that are supported by the bis(imino)pyridine ligand and an examination of the differences in properties between the bidentate and tridentate ligand geometries. Later I examine both tridentate and bidentate complexes for the photocatalytic and electrocatalytic reduction of CO2 to CO.
The failure of tridentate Re1 bis(imino)pyridine compounds to reduce CO2 to CO prompted a change in direction to rhenium compounds that are supported with diimine ligands. Thus, I choose 4,5-diazafluoren-9-one as supporting ligand for rhenium and manganese. This chapter explained the reasons behind choosing these particular ligand and metal combinations. ReI and Mn1 compounds of 4,5-diazafluoren-9-one have shown activity for the photocatalytic and electrocatalytic reduction of CO2 to CO.
In the fourth chapter, as rhenium and manganese compounds of 4,5-diazafluoren-9-one have shown the great ability of CO2 reduction to CO, the focus here was to modify the ligand by attaching a photosensitizer to the ligand in order to prepare supramolecular complexes that may increase the efficiency and yield of reduction products. In this chapter, I examined two types of the photosensitizer; tris(bipyridine)ruthenium(II)chloride and osmium dichloro bis(4,4'-dimethyl-2,2'-bipyridine).
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Huang, Shiow-Jing. "Study of copper underpotential deposition on Au and Pt disk electrode and electrocatalyst." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1323447585.
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Lou, Yaoyin. "Electrochemical processes as a pre-treatment step before biological treatment : Application to the removal of organo-halogenated compounds." Thesis, Rennes, Ecole nationale supérieure de chimie, 2019. http://www.theses.fr/2019ENCR0057.
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Le couplage d’un traitement électrochimique avec un procédé biologique est une alternative prometteuse pour la dégradation de composés organo-halogénés biorécalcitrants dans l’environnement. Les procédés d’électroréduction, connus pour couper sélectivement la liaison carbone-halogène, ont été mis en oeuvre afin de réduire la toxicité des molécules cibles et augmenter leur biodégradabilité avant une minéralisation totale des polluants par un traitement biologique. Pour améliorer le rendement de déchloration, la cathode préalablement nickelée a été modifiée par des nanoparticules d’argent car l’argent est considéré comme l’un des meilleurs catalyseurs pour couper sélectivement la liaison carbonehalogène. Le feutre de graphite a été choisi comme support d’électrode pour sa grande surface spécifique. Le principal produit de déchloration de l’alachlor s’est révélé être biorécalcitrant. Pour surmonter ce problème, un traitement par procédé électro-Fenton a été mis en oeuvre pour dégrader les polluants cibles. Une amélioration significative de la biodégradabilité de la solution d’alachlor a pu être observée après le traitement électro- Fenton, et qui est renforcée quand l’atome de chlore a été préalablement éliminé de la structure de l’alachlor par électroréduction. Le bismuth a été également utilisé comme support d’électrode du fait de sa grande surtension visà- vis de la réduction de l’eau. Une grande sélectivité a pu être obtenue sur cathode de bismuth lors de la réduction d’herbicides du type chloracétamide. La réduction électrochimique du dioxyde de carbone a également été réalisée sur électrode de bismuth modifiée par des nanoparticules d’argent comme autre application de cette nouvelle électrodeElectrochemical process coupling with a biological treatment is a promising alternative for the degradation of biorecalcitrant organo-halogenated compounds in the environment. The electroreduction treatment, known to cut selectively carbon-halogen bonds, was first implemented to decrease the toxicity of the target molecules and increase their biodegradability before a complete mineralization of the pollutants by a biological treatment. To improve the dechlorination efficiency, the cathode was modified by silver nanoparticles after a previous nickelisation, since silver is considered as one of the best electrocatalysts to selectively cleave the carbonhalogen bond. The graphite felt was chosen as the electrode support due to its high specific surface area. For alachlor herbicide, deschloroalachlor, the main by-product after dechlorination, was still biorecalcitrant. To overcome this issue, electro-Fenton treatment, in which hydroxyl radicals were generated to degrade the target pollutants, was implemented. Significant improvement of biodegradability of the alachlor solution was observed after electro-Fenton treatment, which was further improved when the chlorine atom was beforehand removed from the alachlor structure by the electroreduction process. Bismuth was also used as electrode support due to its high overpotential for hydrogen evolution. A high selectivity of chloroacetamide herbicides reduction was observed on the bismuth based cathode. As an extended application of the bismuth based cathode, the electrochemical reduction of carbon dioxide was performed on Bi electrode modified by silver nanoparticles
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Goodman, Joseph. "Economic and technical study of carbon dioxide reduction technologies." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-10182006-153257/.
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Kour, Gurpreet. "First principles investigations on transition metal based electrocatalysts for efficient clean energy conversion." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232798/1/Gurpreet_Kour_Thesis.pdf.
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This dissertation relates to the application of density functional theory to the design of novel nanoelectrocatalysts for various electrochemical reduction reactions such as carbon dioxide reduction reactions, carbon monoxide reduction reactions and nitrogen reduction reactions. Many electrocatalysts with high activity, excellent selectivity and stability were designed and engineered using first principle calculations. These findings could potentially guide the experimentalists for creating clean and sustainable energy resources.
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Kriescher, Stefanie M. A. Verfasser], Matthias [Akademischer Betreuer] [Wessling, and Rüdiger-Albert [Akademischer Betreuer] Eichel. "Electrochemical CO2 reduction / Stefanie M. A. Kriescher ; Matthias Wessling, Rüdiger-Albert Eichel." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1125973048/34.
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Wang, L. "Electrochemical and spectroscopic studies of copper oxide modified electrodes for CO2 reduction." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1532101/.
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The global carbon balance has changed substantially with major increases in atmospheric CO2 levels by anthropogenic emission, causing growing concerns about global warming and extreme climate issues. This is one of the crucial global challenges in the 21st century. Electrochemical reduction of CO2 is a promising technology to convert CO2 to chemicals and fuels. There are various candidate materials for CO2 reduction, but only copper and copper oxide catalysts are effective for the reduction of CO2 to hydrocarbons and organic substances. This research aims to explore CuO nanoparticle materials for CO2 reduction by electrochemical and spectroscopic studies. Different techniques are used in this research. The electrochemical behaviour of CuO was monitored by cyclic voltammetry. The oxidation states and proportion of different components of copper were investigated by ex situ XPS and Raman spectroscopy. A novel in situ spectroelectrochemical experiment was designed using electrocatalysis and FTIR technique to study adsorption of solution species onto the CuO surface. Two types of buffer solutions with five pH values, from pH 4 to pH 11, were introduced to investigate the appropriate pH conditions for the CO2 reduction processes. Based on the present experimental data and further analysis, it reveals the electrochemical behaviour of CuO catalyst, including the reduction reaction equations, proportion of different oxidation states and adsorption species at different applied potentials. The pH 4 solutions shows the most suppression of current magnitude in cyclic voltammograms in CO2 saturated conditions. CuO was reduced to Cu2O and Cu at cathodic potential, then oxidised to CuO in pH 4 and 7 solutions, while oxidised to Cu(OH)2 in higher pH solutions after application of one cyclic potential. The lower pH conditions show better stability of CuO catalyst after multi-cyclic sweeps. Therefore, the pH 7, 8 and 9 solutions are shown to be suitable pH conditions for CO2 reduction on CuO catalyst. The major liquid phase product of CO2 electrochemical reduction obtained in our study was formic acid. Combining our research results, a reaction pathway is proposed. Adsorbed CO2- is the first reduction step and carboxyl is an important intermediate to form formic acid. Finally, several future areas of research are proposed to improve the understanding of the CO2 reduction processes on CuO catalyst. Copper oxide materials of different oxidation states and mixed phases can be used to clarify the active sites. Gas phase products and quantitative liquid phase products can be measured to study the reduction rate and efficiency.
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Parker, Simon. "Anchored photo-electro-catalysts for CO2 reduction based on transition metal complexes." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/13396/.
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Ono, Takashi. "Second-Row Transition-Metal Complexes Relevant to CO2." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/276964.
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dinucleares de rutenio que contienen ligandospolypyridyl. Estos complejos se han aplicado para las reacciones catalíticas, tales como la reducción de CO2 y la oxidación del agua y sustrato orgánico. En la primera, las actividades catalíticas hacia la reducción de CO2 se han investigado desde el punto de vista de las propiedades electrónicas y estéricas de los catalizadores, así como su nuclearidad. En el segundo, la aplicación de mono-y dinucleares complejos de Ru-aqua que contienen ligando tridentadoaniónico hacia reacción de oxidación se ha estudiado. Además, una reactividad potencial de dianión molibdato, que puede ser considerado como modelo homogéneo de catalizadores de óxido de metal heterogéneos para la transformación de CO2 se ha estudiado.This thesis has been focused on the synthesis and characterization of a series of new mono- and dinuclear ruthenium complexes containing polypyridyl ligands. These complexes have been applied for the catalytic reactions, such as CO2 reduction and oxidation of water and organic substrate. In the first, the catalytic activities toward CO2 reduction have been investigated from the viewpoint of electronic and steric properties of the catalysts as well as their nuclearity. In the second, the application of mono- and dinuclear Ru-aqua complexes containing anionic tridentate ligand toward oxidation reaction has been studied. Additionally, a potential reactivity of molybdate dianion, which can be considered as homogeneous model of heterogeneous metal oxide catalysts for CO2 transformation has been studied.
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Rasheed, Senan. "Photocatalytic Carbon Dioxide Reduction with Zinc(II) Dipyrrin Photosensitizers and Iron Catalyst." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/etd/3730.
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Much of the energy used in the United States and around the globe is obtained from petroleum, natural gas, and coal. Photocatalytic CO2 reduction can be used to transform CO2 to useful fuels and making fossil fuels more renewable. Input of energy is required, and the sun can provide the required energy for this transformation. Photosensitizer, catalyst, and electron donor are required for photocatalytic CO2 reduction.
Due to lack of earth-abundant sensitizers, zinc dipyrrin complexes were synthesized by previous group members and have been used as photosensitizers in this research. The ground and excited state electrochemical properties of two zinc dipyrrin complexes were determined in polar and nonpolar solvents and the measured potentials were used to match the zinc sensitizers with an energetically appropriate iron porphyrin catalyst and a benzylthiol sacrificial electron donor. Lastly, pure CO2 gas was used as the source of carbon for the reduction of CO2 by photocatalysis with the zinc photosensitizers, iron catalyst and sacrificial electron donor. The products formed in headspace were analyzed by GC
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Wolff, Niklas von. "Reaction mechanisms of CO₂ activation and catalytic reduction." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS580.
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L’utilisation du dioxyde de carbone (CO₂) comme source de composés C1 pour la chimie fine est intéressante d’un point de vue économique et pour des raisons écologiques. Issu de l’oxydation de la matière carbonée, le CO₂ est un gaz non-toxique, abondant et peu coûteux. Sa transformation en produits chimiques présentant de hautes valeurs ajoutées est actuellement entravée par sa stabilité thermodynamique. Afin de développer de nouveaux processus et catalyseurs pour la réduction catalytique du CO₂, une compréhension détaillée des mécanismes réactionnels de l’activation et de la réduction de ce gaz est nécessaire. En utilisant comme catalyseurs des paires de Lewis frustrée (FLPs) contenant une base azotée liée à un ion silicénium, les influences respectives de l’adduit CO₂-FLP et du réducteur ont été déterminées expérimentalement et par calcul DFT dans le cadre de l’hydroboration du CO₂ en équivalent de méthanol. Une nouvelle réaction visant à la création de liaisons carbone–carbone par le transfert du fragment pyridyle de molécules de pyridylsilanes (C₅H₄N–SiMe₃) sur le CO₂ était également étudiée. Le mécanisme réactionnel de cette transformation a été établi sur la base de calculs théoriques. Nous avons montré le double rôle du CO₂ qui est à la fois un réactif et un catalyseur de la réaction de transfert du groupe pyridyle. La compréhension fine de cette réaction nous a permis de l’étendre à la formation de sulfones et sulfonamides qui sont des groupements chimiques essentiels dans le domaine pharmaceutique. En utilisant le SO₂ à la fois comme catalyseur et réactif, des silanes aromatiques et hétéro-aromatiques ont été transformés en sulfones correspondants en une seule étape. Finalement, nous avons trouvé un couplage croisé original, de type Hiyama, entre espèces aromatiques électrophiles et des espèces C(sp2)–Si nucléophiles en présence de SO₂The use of CO₂ as a C1 chemical feedstock for the fine chemical industry is interesting both economically and ecologically, as CO₂ is non-toxic, abundant and cheap. Nevertheless, transformations of CO₂ into value-added products is hampered by its high thermodynamic stability and its inertness toward reduction. In order to design new catalysts able to overcome this kinetic challenge, a profound understanding of the reaction mechanisms at play in CO₂ reduction is needed. Using novel N/Si+ frustrated Lewis pairs (FLPs), the influence of CO₂ adducts and different hydroborane reducing agents on the reaction mechanism in the catalytic hydroboration of CO₂ were investigated, both by DFT calculations and experiments. In a second step, the reaction mechanism of a novel reaction for the creation of C–C bonds from CO₂ and pyridylsilanes (C₅H₄N–SiMe₃) was analyzed by DFT calculations. It was shown that CO₂ plays a double role in this transformation, acting both as a catalyst and a C1-building block. The fine understanding of this transformation then led to the development of a novel approach for the synthesis of sulfones and sulfonamides. Starting from SO₂ and aromatic silanes/amine silanes, these products were obtained in a single step under metal-free conditions. Noteworthy, sulfones and sulfonamides are common motifs in organic chemistry and found in a variety of highly important drugs. Finally, this concept was extended to aromatic halides as coupling partners, and it was thus shown for the first time that a sulfonylative Hiyama reaction is a possible approach to the synthesis of sulfones
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Migliaccio, Luca. "Bimetallic catalysts for CO2 electroreduction." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14470/.
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Over the last decades, many steps have been taken in the search for an effective method to reduce carbon dioxide to small organic molecules that can be used as fuel or building blocks for the chemical industry. The object of this work is to prepare two bimetallic electrocatalysts utilizing Cu combined with Au or In for the efficient and selective reduction of CO2 to CO, HCOOH and small fuels molecules. The copper-gold electrode is prepared through the electrodeposition of Cu on the surface of Au, using the underpotential deposition (UPD) technique to obtain a copper monolayer. The prepared electrode shows a high current density compared to Au electrode. Bimetallic metal oxides of CuInO2 is used as the precursor to prepare Cu-In alloys electrodes for electrochemical reduction of CO2. The electrocatalyst preparation is carried out using a thermal reducing treatment able to form different catalytic surfaces with different Cu-In alloys or single-phase metals. The best sample shows a high faradaic efficiency toward CO (71%) at the low overpotential of −0.8 V vs RHE. This study shows two examples of scalable and inexpensive preparation methods of bimetallic surfaces, which may use as selective electrocatalysts for the aqueous reduction of CO2.
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Dilla, Martin [Verfasser], and Robert [Akademischer Betreuer] Schlögl. "Fundamental studies of photocatalytic CO2 reduction on TiO2 / Martin Dilla ; Betreuer: Robert Schlögl." Duisburg, 2019. http://d-nb.info/1191691284/34.
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Bumroongsakulsawat, Palang. "Kinetics and scale-up of electrochemical reduction of aqueous CO2 at Sn Cathodes." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/23834.
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Electrochemical reduction of CO2 in aqueous buffer solutions of different pHs at tin electrodes was studied. The partial current densities exhibited the expected two Tafel regions; with increasingly negative electrode potential, the first to be encountered depended on pH strongly, while the second showed only weak dependence. Formate and CO were observed as the main products. In the range of potentials studied, the highest charge yield of 0.67 was achieved at -1.55 V (AgCl|Ag) in 0.5 M NaOH saturated with 1 atm CO2 with a total current density of 36.2 A m-2. pH was also found to affect the formation ratios of CO to formate, the value of which ranged from 1 to 0.15 as pH was increased from 2.9 to 7.8. However, pH was not an ideal variable to adjust the product distributions because lower pH led to a lower charge yield of CO2 reduction due to increasingly competing hydrogen evolution. Two mathematical kinetic models based on slightly different concepts were developed to quantify the dependence of the formation ratios on pH and to predict partial current densities of CO2 reduction at different pHs and electrode potentials. The first model assumed that there could be multiple reactions having different stoichiometric coefficients of proton consumption occurring simultaneously; the greater the coefficient, the stronger was the preference for CO production from the reaction. The other concept was that there were multiple protonation states of the intermediate in CO2 reduction; the higher the protonation state, the higher was the tendency to form CO from the intermediate. Both concepts allowed variations of the product ratios as a function of pH, but the latter model was preferred because more accurate predictions of the partial current densities were achieved and a generalised reaction mechanism could be derived. Electrochemical reduction of CO2 in 0.5 M NaOH saturated with 1 atm CO2 at tin-coated graphite felt electrodes was also studied. Tin was deposited on graphite felt from aqueous solutions of 0.3 M K2[Sn(OH)6], 0.4 M KOH and 0.5 M K3PO4. The effects of electrode potential and electrolyte flow rates on the performances of CO2 reduction at 3D electrodes were explored. The best performance was achieved at -1.62 V (AgCl|Ag) and 99 ml min-1 electrolyte flow rate; the total current density and the charge yield of formate were 971 A m-2 and 0.58, respectively. Accumulation of gas bubbles composed of H2 and CO was found to have detrimental effects on superficial electrolyte conductivities and mass transport of CO2, but can be partially alleviated by increasing the electrolyte flow rate. Two mathematical models were developed to include the effect of flow rates into account in predicting total current densities and formate charge yields from 3D electrodes. The first model assumed that the gas bubbles inside porous electrodes travelled at the same velocities as the electrolyte solutions; this led to highly under-predicted potential drops across the electrode thickness and over-predicted total current densities. On the other hand, the second model allowed slip between bubble flows and electrolyte flows, resulting in more accurate predictions. Bubbles were found to travel 0.0016 times slower than electrolyte flow velocities.
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Xu, Chaochen. "Transition Metal-Based Electrocatalysts for Highly Selective C02 Reduction." Thesis, 2020. http://hdl.handle.net/2440/129118.
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The electrochemical CO2 reduction reaction (CRR) can combine carbon cycling with renewable energy to convert CO2 into high-value carbonaceous feedstocks. However, this process su ers from kinetically sluggish because of the complicated electron transfer and high energy barriers involved. Well-designed transition metal materials as promising electrocatalysts show remarkable catalytic activities for the CRR. Therefore, this Thesis is to study the catalytic activity and selectivity on these transition metal catalysts, and a fundamental understanding of the catalytic mechanism is given through a series of experimental and computational results using advanced synthesis methods, electrochemical measurements, material characterization including microscopy and spectroscopy, synchrotron-based X- ray spectroscopy, in situ spectroscopy, and density functional theory (DFT) calculations. The scope of this Thesis is narrowed to nanoscale and sub-nanoscale engineered 3d-block transition metal (mainly, Fe, Co, Ni, Cu) catalysts for the CRR process. In this Thesis, the rst section introduces research progress including catalytic performance and mechanisms on sub-nanoscale 3d-block transition metal catalysts for the CRR. The second section consists of published and submitted works: (1) The rst project starts with the investigation of the CRR on Ni catalysts. We engineered and alloyed Ni with Cu to obtain ultrasmall graphene-encapsulated Ni-Cu bimetallic catalysts. The Cu-lean catalyst exhibited signi cant activity and selectivity, and the highest Faradaic e ciency (FE) toward CO was 90% at -1.0 V vs. RHE. By coupling synchrotron-based X-ray absorption and in situ Raman spectroscopy studies, we found that there is a negative correlation with the Cu content in Ni-Cu catalyst and CO selectivity due to redistribution of the 3d electrons from Ni and Cu. (2) Because of the high catalytic activity was received on ultrasmall Ni-Cu particles, the second project aims to fabricate sub-nanoscale transition metal catalysts for the CRR. We synthesized atomically dispersed Fe immobilized within N-doped carbon nanosheets. The optimal Fe catalyst achieved FE of 90% toward CO at -0.58 V vs. RHE. A series of controlled tests revealed that there is a synergistic e ect between the Fe sites and the pyrrolic-N-framework which promotes the catalytic activity of CO evolution. (3) The third work is based on the previous Fe catalyst and investigates the unique single-atom Cu catalyst (Cu-N4-NG). The chemical structure and coordination environment of Cu-N4-NG were identi ed using synchrotron-based characterization. Compared to a traditional bulk Cu catalyst, Cu-N4-NG performed a FE of 80.6% towards CO at -1.0 V vs. RHE. The experimental results revealed that the presence of Cu-N4 moieties largely promotes CO2 activation and water dissociation, showing CO2 reduction is kinetically preferred on Cu-N4-NG. Also, the computational investigation suggested a thermodynamic explanation that CO2 reduction is less hindered on Cu-N4-NG compared to hydrogen evolution. (4) Although high FEs were obtained on single-atom transition metal catalyst shown in the previous two works, the two catalysts were not strictly single-atom catalysts with a uniform structure of M-N4, some coordination defects existed. Thus, graphene- supported metal phthalocyanine catalysts with M-N4 structure were reported in the fourth work, which achieved almost 100% CO2 conversion to CO on graphene- supported cobalt phthalocyanine. Further experimental studies showed that the phthalocyanines with graphene were signi cantly activated than the pure ones. A series of control tests uncovered that the graphene substrate facilitates electron transfer between the catalyst and CO2 molecules, which increased CO selectivity.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering and Advanced Materials, 2020
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Cheng, Yi-Hsin, and 鄭怡馨. "Cu2-xS Decorated on SnS2 Nanocomposite: Boosting up Photocatalytic CO2 Reduction by Surfactant Modification." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2mqsnf.
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碩士國立臺灣科技大學
化學工程系
107
This study uses an artificial photosynthesis system to reduce carbon dioxide to hydrocarbons as an alternative energy source with an aim to improve the environmental and energy issues. In this study, the solvothermal method using Sn, Cu, S with different mixed surfactants was used to synthesize tin disulfide and copper sulfide. The energy band gap and position of the two materials are suitable for carbon dioxide reduction reaction, and the two semiconductor materials can be mixed as hetero-junctions. It can effectively separate electrons and holes after excitation, reduce the phenomenon of electron-hole radiation recombination, and make more excitons drift to the surface of the material for carbon dioxide reduction reaction. We use the surfactant and prove that it can increase the dispersibility of particles, enhance crystallinity, and improve the quantum efficiency of carbon dioxide reduction reaction. In this study, first we analyze the characteristics of crystal structure, composition, and optical properties, and then perform gas chromatography studio. We found that the hetero-structure of tin disulfide and copper sulfide can produce acetaldehyde and small amounts of ethanol and methanol. With the photochemical quantum conversion efficiency up to about 0.061%. The reaction quantum efficiency was optimized by controlling the mixing ratio of tin disulfide, copper disulfide and changing the surfactant. By mixing the surfactant with its hetero-structure, a higher yield of acetaldehyde product can be obtained effectively. Compared with different ratios, photochemical quantum conversion efficiency can be increased to 0.313% with tin sulfide and copper sulfide mixed in a ratio of 1:1:2 with the cationic surfactant CTAB. From this study, it is proved that p-n hetero-junction structure with surfactant can increase the uniformity and dispersion of tin disulfide and copper sulfide, enhance crystallinity, and improve the photocatalyst carbon dioxide reduction reaction effectively.
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"CO2 Photocatalytic Reduction to Fuels." Master's thesis, 2014. http://hdl.handle.net/2286/R.I.25145.
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abstract: A new photocatalytic material was synthesized to investigate its performance for the photoreduction of carbon dioxide (CO2) in the presence of water vapor (H2O) to valuable products such as carbon monoxide (CO) and methane (CH4). The performance was studied using a gas chromatograph (GC) with a flame ionization detector (FID) and a thermal conductivity detector (TCD). The new photocatalytic material was an ionic liquid functionalized reduced graphite oxide (IL-RGO (high conductive surface))-TiO2 (photocatalyst) nanocomposite. Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV-vis absorption spectroscopy techniques were employed to characterize the new catalyst. In the series of experiments performed, the nanocomposite material was confined in a UV-quartz batch reactor, exposed to CO2 and H2O and illuminated by UV light. The primary product formed was CO with a maximum production ranging from 0.18-1.02 µmol(gcatalyst-hour)-1 for TiO2 and 0.41-1.41 µmol(gcatalyst-hour)-1 for IL-RGO-TiO2. A trace amount of CH4 was also formed with its maximum ranging from 0.009-0.01 µmol(gcatalyst-hour)-1 for TiO2 and 0.01-0.04 µmol(gcatalyst-hour)-1 for IL-RGO-TiO2. A series of background experiments were conducted and results showed that; (a) the use of a ionic liquid functionalized reduced graphite oxide -TiO2 produced more products as compared to commercial TiO2, (b) the addition of methanol as a hole scavenger boosted the production of CO but not CH4, (c) a higher and lower reduction time of IL-RGO as compared to the usual 24 hours of reduction presented basically the same production of CO and CH4, (d) the positive effect of having an ionic liquid was demonstrated by the double production of CO obtained for IL-RGO-TiO2 as compared to RGO-TiO2 and (e) a change in the amount of IL-RGO in the IL-RGO-TiO2 represented a small difference in the CO production but not in the CH4 production. This work ultimately demonstrated the huge potential of the utility of a UV-responsive ionic liquid functionalized reduced graphite oxide-TiO2 nano-composite for the reduction of CO2 in the presence of H2O for the production of fuels.Dissertation/Thesis
M.S. Chemical Engineering 2014
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Gante, Caruso Hernane. "Reduction of CO2 Emissions from Cement Plants." Thesis, 2007. http://hdl.handle.net/10012/3005.
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Reduction of CO2 Emissions from Cement Plants
Governments around the world have been pressured by society to discuss environmental issues, and global warming is one of the most controversial debates. The Kyoto Protocol is an agreement made under the United Nations Framework Convention on Climate Change (UNFCCC). Under Kyoto protocol some countries committed to reduce their Greenhouse Gas (GHG) emissions. The Intergovernmental Panel on Climate Change (IPCC) has predicted global rise in temperature and carbon dioxide is a major greenhouse gas responsible for global warming. The cement industry contributes approximately five per cent of the total CO2 emitted worldwide.
Currently Canada sustains a very aggressive objective to reduce GHG emissions to support the Kyoto Protocol. It is clear that international affairs and global polices will affect different sectors and even though cement production and distribution is constrained by location and natural resource availability, the major cement producers around the globe will be required to meet more stringent environmental regulations.
Kyoto presents a ‘cap and trade’ mechanism that requires countries to reduce, on average, 5.2 per cent below their 1990 baseline. This reduction must take place between 2008 and 2012. Although these caps are country specific, most countries are requiring industries to have particular objectives for reduction. This can be seen especially in European countries.
The credit trade opportunity increases the possibility for an economical justification of new and environmentally friendly solution for GHG emissions abatement.
St Marys Plant, located in St Marys, Ontario, was used as a case study to evaluate the results of various modifications on cement plants operation that can impact on the plant CO2 emissions. An economic model which objective is to highlight the best selection strategy to reduce CO2 emissions with the least cost was developed using St Marys Plant data as part of this thesis.
St Marys Plant achieved a significant result of 23.6 per cent reduction in CO2 emissions per tonne of cement produced. The results were achieved mainly by applying a progressive approach prioritising project implementation effort and feasibility.
St Marys main steps were 1) implementation of a more robust maintenance system, 2) plant optimization and Kiln expert system; 3) alternative fuels and 4) major equipment modifications.
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Tai, Chin-Chih, and 戴清智. "Photocatalytic Reduction of CO2 and H2O." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/41572345033592386664.
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碩士國立成功大學
環境工程學系
88
From the viewpoint of environmental problems, photocatalytic reduction of CO2 to valuable compounds has been a subject of extensive investigation. However, reduction of CO2 often requires severe operation conditions, e.g, high pressures and/or high temperatures [32]. Alternatively, photocatalytic reduction of carbon dioxide with hydrogen may also be accomplished by photoirradiation. Hydrogen is an important molecule not only as a clean-energy source but also a chemical reagent. Therefore, technique development for H2 production with less energy consumption is a crucial and important subject for creating a future energy-utilization system. Photoactive elements such as Zr, Ti, Cu and Zn were incorporated into MCM-41, ZSM-5 and ZSM-48 via the MW-accelerated synthesis process. These photocatalysts were also synthesized hydrothermally. By XRD, FT-IR, and UV-VIS spectroscopies and N2 physisorption studies, it is clear that the photoactive element was incorporated into MCM-41, ZSM-5 and ZSM-48. However, incorporation of photoactive element in ZSM-5 or ZSM-48 by the MW-accelerated synthesis processes was not effective. Experimentally, in a total reflection photoreactor, the photocatalytic reduction of CO2 with H2O on Zr-MCM-41 catalyst was highly enhanced. Photocatalytic decomposition of CO2 with H2O on Zr-MCM-41 yielded 68 μmol CO hr-1(g ZrO2)-1 and 108 μmol H2 hr-1(g ZrO2)-1, respectively. The photocatalytic reduction of CO2 with H2O on the Ti-MCM-41 catalyst was not as effective as that on Zr-MCM-41. Fine structures of the copper oxide clusters in MCM-41 and ZSM-48 in catalytic reduction of NO with benzene were studied by in-situ X-ray absorption spectroscopy. The EXAFS spectra of the copper oxides in MCM-41 indicated that about 3.037 nearest oxygen atoms bonded to the center copper atoms with a Cu-O bond distance of 1.89 A. Reduction of the catalyst in hydrogen at 573 K led to the formation of copper species with a Cu-Cu bond distance of 2.55 A. The coordination number (CN) of the reduced copper species in MCM-41 was 7.67 approximately. In the NO reduction process, Cu3O2 clusters were formed in the channels of MCM-41 via incorporation of oxygen into the metallic copper and cause the matrix disrupted. The Cu3O2 may be oxidized to Cu3O3 by NO with yield of N2 molecules.
44
Barradas, Sean. "CO2 activation and functionalization." Thesis, 2012. http://hdl.handle.net/10210/5754.
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M.Sc.An Acinetobacter sp. strain RFB1 isolated in our laboratory has been shown to have the ability to metabolise inorganic cyanide salts, CO 2, and bicarbonate. The enzyme aggregate responsible for the conversion of these substrates, is located extra-cellularly. Resolution of the extra-cellular complex, a crude enzyme filtrate, was attempted in order to characterise the protein responsible for the reduction of CO 2. The crude enzyme filtrate was separated by means of molecular exclusion chromatography and afforded three fractions with molecular masses ranging from 76 000 to 191 000. Analysis by SDS-electrophoresis, showed that the first protein fraction contained more than ten proteins. Certain of these proteins were identified in the second fraction and other proteins in the third protein fraction. This implies that some denaturation already occurred during molecular exclusion separation. The functionali7ation of CO 2 by protein fractions 1 and 3 supports this argument, and, in addition , cyanide ions were only reduced by fractions 1 and 2. Fatty acids, ranging with chainlengths between C5 and C25, were shown to be present and certain fatty acids were unequivocally identified by GC-mass spectroscopy as the products resulting from CO2 functionali7ation and carbon-carbon bond formation. Ferrous ions, in an optimal concentration of 250 gg cm', were necessary and served as an essential ingredient of the reaction mixture. A rather unusual result was, however, that apart from an initial, relatively small uptake of Fe(II), significant amounts of Fe(III) were not formed and the Fe(II) concentration remained approximately constant during the reaction. This implies that the formed Fe(M) is rapidly reduced to Fe(II) again. Spectroscopic measurements, furthermore, strongly suggested the involvement of an iron-sulphur cluster in a cyclic redox process wherein both Fe(II) and Fe(III) are involved. Carefully conducted experiments pointed to light as the outside source of energy. Qualitative similarities with an artificial photosynthetic process, formulated earlier by J-M. Lehlliii, can be drawn and used partly to explain the experimental results.
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Hsu, Hsin-Cheng, and 許新城. "Graphene Oxide Based Photocatalyst for CO2 Reduction." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/79201113028210992482.
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博士國立臺灣科技大學
材料科學與工程系
102
Artificial photosynthesis is one of the solutions to solve global warming and mitigate the rising demands of energy consumption. Photocatalytic conversion of carbon dioxide (CO2) to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO2 reduction, resulting in solution for both the energy demands and environmental problems. This work describes a promising photocatalyst based on improved graphene oxides (iGOs), which have high photocatalytic conversion efficiency of CO2 to hydrocarbon fuels. Improved Hummer’s method has been applied to synthesize the GO based photocatalyst for the enhanced catalytic activity. The photocatalytic CO2 to methanol conversion rate on the pristine improved graphene oxide is 0.172 μmole g-1-cat. h-1 under visible light, which is four-fold higher than the pure TiO2 (P25). On the other hand, we have also synthesized a composite catalyst based on molybdenum disulfide-iGO system.The MoS2 nanosheet decorated improved graphene oxide (iGO) hybrid nanostructures are fabricated by a facial one-step hydrazine-assisted hydrothermal method. The photophysical properties of the synthesized photocatalysts have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV-Vis spectrometer, Ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and X-ray photoelectron spectroscopy (XPS). Enhanced visible light-driven activity for the CO2 photoreduction to solar fuel has been achieved. The average apparent CO2 reduction to solar fuel formation rate of MoS2 nanosheet decorated iGO composite is more than 10 times higher than the pristine iGO; or 40 times that of TiO2 (P25). The MoS2 nanosheet decorated iGO composite nanostructures makes an outstanding contribution to the excellent photocatalytic CO2 reduction.
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Baptista, Rita Helena Duarte. "Electrocatalysis of Formate Dehydrogenase Towards CO2 Reduction." Master's thesis, 2021. http://hdl.handle.net/10362/110680.
Full textAbstract:
The continuous strong growth of CO2 emissions and the intensification of environmental impacts caused by this gas have aroused an increasing interest in the development of strategies to transform CO2.
Formate dehydrogenases (FDH) are enzymes that perform the reversible interconversion of formate to CO2, hence these biocatalysts can transform CO2 into a compound that can be used either as a biofuel or as chemical precursor for sustainable chemical synthesis.
Reports on direct electrochemical approaches, avoiding kinetic limitations of the mediating molecules and additional steps of cofactors regeneration, have been scarce until recently. In this Thesis, the electrochemical characterisation of the molybdenum-containing FDH from Desulfovibrio desulfuricans (DdFDH) was accomplished through non-mediated methods, in the absence of added substrates (non-turnover conditions), for the enzyme physically adsorbed onto a pyrolytic graphite electrode, at pH 6.5. A redox process with formal potential of -124 ± 11 mV vs NHE was assigned to the redox pair Mo (VI/IV) of the active centre. The heterogeneous electron transfer rate constant increased with the scan rate, which is indicative of a good communication between the enzyme and the electrode.
The DdFDH catalytic response towards CO2 reduction was attained without mediators as well, upon the addition of saturated CO2 solution and sodium carbonate solution for the DdFDH adsorbed onto a stationary pyrolytic graphite electrode. The electrocatalysis towards CO2 reduction was also attained for DdFDH physically adsorbed on glassy carbon and graphite, under the hydrodynamic regime, and for the DdFDH encapsulated on felt carbon, a gas diffusion electrode.
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Bento, Marcos António Martins. "CO2 Reduction with Formate Dehydrogenase mimetic compounds." Master's thesis, 2020. http://hdl.handle.net/10362/115206.
Full textAbstract:
The atmospheric carbon dioxide (CO2) concentration has greatly increased in the last decades, mainly due to the excessive use of fossil fuels. The rising levels of this greenhouse effect gas are changing the climate, which will have irreversible and dramatic effects on our planet. Efficient and innovative solutions to tackle this problem are urgently needed. Several researchers around the world are developing new approaches to capture and convert CO2 into novel fuels and other chemicals with economical value. For that, different electro- and photochemical methodologies have been explored, using a variety of metal complexes as catalysts. In this work, we took inspiration from the active site of molybdenum-containing formate dehydrogenase enzymes to develop new inorganic molybdenum-based catalysts that convert CO2 into formate or other interesting added-value compounds. Our two main goals were to (i) synthesise ten molybdenum complexes and (ii) study their ability to catalyse the reduction of CO2 electrochemically. The complex ligands chosen were inspired in the dithiolene moiety of the cofactor that coordinates the molybdenum ion within the enzymes (dithiolene and derivative compounds) and also in different compounds previously described in literature (pincer-type and salen-type units). All complexes synthesised were characterised by elemental analysis and spectroscopic methodologies (NMR, FTIR and UV-vis), as well as, electrochemically (cyclic voltammetry). Controlled potential electrolysis experiments showed that four of the new compounds synthesised are selective for the CO2 reduction to formate. These promising CO2 reduction catalysts will be further studied and improved in the near future.
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Silva, João Ricardo Gomes Vaz da. "Photocatalytic reduction of CO2 into renewable fuels." Master's thesis, 2015. https://repositorio-aberto.up.pt/handle/10216/89711.
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Wei, Hsieh-Yu, and 魏謝宇. "Graphene oxide as photoctalyst for CO2 reduction." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/66434866988277256907.
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碩士國立臺灣科技大學
材料科學與工程系
100
In this study, we investigate different oxidation processes of graphene oxide. The original process follows the modified Hummer’s method for the synthesis of graphene oxide (H GO). We also used another process that replaces NaNO3 during oxidation reaction with H3PO4 and called it improved graphene oxide (I GO). We studied the relation between the operating parameters in the oxidation process and methanol yield from the photocatalytic reduction of CO2. In our experiment, CO2 and water vapor continuously flow into the stainless steel reactor. Then, a 300 W ELH lamp was used to irradiate the photocatalyst. The product was then analyzed using GC-FID. The main product of the experiment was found to be methanol. In the synthesis of the photocatalyst, we tried to tune the parameters of H GO by changing the amount of KMnO4 during oxidation process. While the amount of KMnO4 increases, the band gap and oxidation level of the GO increases. However, the methanol yield decreases during the photocatalytic reduction reaction. We also tried to tune the parameters of I GO by changing the amount of H3PO4 during oxidation process. Similarly, the amount of H3PO4 increases, the band gap and oxidation level also increases. Importantly, the methanol yield would increase during the photocatalytic reduction reaction. However, excessive H3PO4 passivates the oxidation reaction thus decreasing methanol yield during photocatalytic reduction reaction. We believe that in the I GO oxidation process, adding H3PO4 could avoid the formation of C=O defects on graphene oxide basal plane. Therefore, I GO process contains less defect formation on graphene oxide basal plane than H GO process. For the optimized conditions, triple H3PO4 treatment (I-3P GO) achieved larger oxidation level and less defect formation. It did not only enhance hydrophilic properties of the catalyst but also promote photocatalytic reduction reaction. In the photocatalytic reduction reaction, we determined that the methanol yield can achieve up to 0.124 μmol g-1 hr-1 using triple H3PO4 treatment (I-3P GO) catalyst. The methanol yield is three times that of TiO2, which is the conventional catalyst in CO2 photoreduction.
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Silva, João Ricardo Gomes Vaz da. "Photocatalytic reduction of CO2 into renewable fuels." Dissertação, 2015. https://repositorio-aberto.up.pt/handle/10216/89711.
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