The objective of this thesis is to investigate the photocatalytic activity in nanosized TiO2 structures. Two different structures were used for two different reaction systems. In the first part of the study, TiO2 coated on glass beads by a sol-gel procedure were used to test the photocatalytic CO2 reduction reaction with H2O and H2 in the gas phase. The results of photocatalytic CO2 reduction reaction revealed that CO2 reduction step of the overall reaction proceeds in dark / while illumination is required for water splitting reaction. In the second part of the study, Photocatalytic oxidation activity of the commercial TiO2 powders mixed with grout and plaster were studied for a potential commercial self cleaning material. A method based on gas phase benzene oxidation was developed for testing TiO2 added cement based self cleaning surfaces. This method was used to screen 15 commercial TiO2 samples with and without cement. Based on this method a commercial TiO2 sample (S9) was selected for further use. Surface of 15 commercial TiO2 samples were characterized by using NO and CO2 as probe molecules. Photocatalytic benzene oxidation experiments showed that using TiO2 on the surface lead to more effective surfaces in terms of photocatalytic activity. TiO2 was bound to surface by inorganic materials without much activity loss. This kind of amount optimization is of commercial importance.

<p>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 mills’energy systems to realise CO2reduction potentials.</p><p>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.</p><p>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 Sweden’s 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 ofSweden’s 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.</p><p><b>Keywords:</b>CO2 reduction, pulp and paper industry, energysystem, biomass, CO2 capture and sequestration, black liquor,gasification, power production, outsourcing, sustainable energymanagement</p>

<p>The increased concentration of greenhouse gases in theatmosphere, in particular CO₂, is changing the Earth’s climate. Accordingto the Kyoto protocol, where the international community agreedon binding emission targets, developed countries are committedto reduce their greenhouse gas emissions. The increased use ofbiomass in energy systems is an important strategy to reduce CO₂emissions. The purpose of this thesis has been toanalyse the opportunities for Sweden to further reduce CO₂emissions in the energy system, by rationallyutilising woody biomass energy. The characteristics of currentcommercially operating biofuel-based CHP plants in Sweden aresurveyed and systematically presented. A consistent andtransparent comprehensive reference base for system comparisonsis given. Furthermore, the fuel effectiveness and contributionto CO₂reduction is calculated. The governmentalsubsidies of the CHP plants’investment, expressed as costof specific CO₂reduction, appears to be low.</p><p>The competitiveness of biomass-fuelled energy production inrelation to fossil-based production with carbon capture isanalysed, showing that the biomass-fuelled systems provide acompetitive option, in terms of cost of electricity andefficiencies. The remaining Swedish woody biofuel potential ofat least 100 PJ/yr is principally available in regions with abiomass surplus. Transportation is therefore required to enableits utilisation in a further national and international market.Refining the biofuel feedstock to pellets, or even furtherrefining to motor fuels (DME, methanol or ethanol) or power,could facilitate this transport. Different options for fuelrefining are studied and compared. The entire fuel chain, fromfuel feedstock to end users, is considered and CO₂emissions are quantified. Substituting fuelpellets for coal appears to be the most costeffectivealternative and shows the largest CO₂reduction per energy unit biofuel. Motor fuelsappear more costly and give about half the CO₂reduction. Transportation of the upgraded biofuelpellets is highly feasible from CO₂emissions point of view and does not constitute ahindrance for further utilisation, i.e. the pellets can betransported over long distances efficiently with only limitedemissions of CO₂.</p><p>Bioenergy utilisation has additional features forenvironmental improvement, apart from the CO₂aspect. Waste heat from biofuel-based CHP can becost-effectively used in conjunction with sewage treatment. Theincoming sewage water to the nitrification process can bepreheated with the waste heat, and thereby substantiallyenhance the nitrification and the reduction of ammoniumnitrogen during the winter season.</p><p><b>Keywords:</b>CO₂reduction, energy system, biofuel, CHP, refining,fuel pellets, ethanol, methanol, DME, fuel substitution, sewagewater, nitrification.</p>

Dans ce travail, nous développons deux grands axes de recherche liés aux carbonates fondus. Le premier est l'optimisation des piles à combustible à base de carbonates fondus, avec deux approches : (i) l'amélioration de la durée de vie de la cathode grâce à des couches ultra-minces d'oxydes métalliques élaborés par la technique de dépôt de couches atomiques; (ii) la modification des électrolytes Li-K et Li-Na par addition de Cs ou de Rb. Le second est consacré à la valorisation du CO2 par sa réduction électrochimique dans les électrolytes à carbonates fondus, où nous analysons la réduction du CO2 par chronopotentiométrie et chronoamperométrie. Finalement, afin de tester les modifications subies par certains des composants analysés dans les deux premières parties, nous avons installé et adapté une configuration de cellule complète couplée à la chromatographie en phase gazeuse. Nous avons obtenu quelques résultats significatifs dans l’ensemble des approches abordées ; en ce qui concerne le point (i), nous avons constaté que TiO2 et CeO2 sont appropriés pour protéger la cathode contre la corrosion sans affecter ses propriétés électrochimiques en réduisant presque de moitié la dissolution du Ni. Les résultats obtenus pour le point (ii) sont également fructueux, car nous avons établi une méthode pour comparer deux électrolytes différents en déterminant les coefficients de diffusion des ions superoxyde et du dioxyde de carbone. Nous avons également comparé les performances de la cathode de NiO dans les électrolytes modifiés avec Cs et Rb. De ces études, nous avons constaté que l'addition de Cs améliore significativement le coefficient de diffusion de CO2 en réduisant la résistance de transfert de charge et la résistance totale à l'électrode, étant l'additif le plus prometteur testé ici. En ce qui concerne la réduction du CO2, nous avons constaté que la réaction implique des espèces adsorbées et instables et se produit en deux étapes à un électron ou une étape à deux électrons ; ainsi, il s’agit très probablement d’un mécanisme de réduction simultanée d’espèces adsorbées et dissoutes. Finalement, nous avons effectué les premiers tests sur cellule complète MCFC dans notre laboratoire, obtenant une performance et une puissance acceptables. Cependant, de petites améliorations sont encore nécessaires pour pouvoir tester les composants modifiés de cellule MCFC. / In this work, we develop two major research routes related to molten carbonates. The first one is the molten carbonate fuel cell optimization, with two approaches: (i) cathode lifetime improvement through ultra-thin layers of metal oxides deposited by atomic layer deposition; (ii) Li-K and Li-Na electrolyte modification by Cs or Rb additions. The second one is dedicated to CO2 valorization through its electrochemical reduction in molten carbonate electrolytes, where we analyze CO2 reduction by means of chronopotentiometry and chronoamperometry. Finally, in order to test some of the component modifications described in the two first parts, we installed and adapted a single-cell setup coupled to gas chromatography. We obtained some significant results in all the approaches; concerning point (i), we found that TiO2 and CeO2 are suitable for cathode corrosion protection without affecting the electrochemical properties of the electrode and reducing almost by half the dissolution of Ni. The results obtained from point (ii) are also fruitful, since we established a method for comparing two different electrolytes and obtained the diffusion coefficients of the superoxides and carbon dioxide. We also compared the performance of the state-of-the-art NiO cathode in Cs and Rb modified electrolytes. From these studies, we found that Cs addition improves significantly the CO2 diffusion coefficient and reduces the charge transfer and total resistance at the electrode, being a promising additive. Regarding CO2 reduction, after all the tests performed, we found that the reaction involves adsorbed and instable species and occurs in two one-electron steps or in two-electron unique step; thus, it follows most probably a mechanism of simultaneous reduction of the adsorbed and dissolved species. Finally, we performed the first MCFC single-cell tests in our laboratory obtaining an acceptable cell performance and output power. However, small improvements are still necessary to be able to test MCFC modified components.

Thesis advisor: Matthias Waegele / Heterogeneous electrocatalytic reduction is an environmentally friendly method for the conversion of abundant feedstock molecules into valuable products. Examples include the reduction of carbon dioxide to hydrocarbons and the reduction of nitrate to ammonia. Heterogeneous electrocatalysis occurs at the interface between an electrode and an electrolyte. Interfacial properties, such as surface morphology, interfacial electric field, interfacial water structure, and local pH, can substantially influence the activity and selectivity of electrocatalytic reduction processes. However, a comprehensive, molecular-level understanding of how these interfacial properties control electrocatalysis is still largely lacking to date. To develop such an understanding, it is essential to probe the properties of the electrocatalytic interface under operating conditions. This great experimental challenge is further compounded by the fact that the interface often undergoes dynamic changes during catalysis. In this thesis, we took a multimodal approach to characterize the aqueous electrolyte/copper interface during CO2/CO reduction and hydrogen evolution. Copper is the only pure metal that promotes the reduction of CO2/CO to hydrocarbons at significant reaction rates. The hydrogen evolution reaction is the main competing reaction in aqueous electrolytes. It is therefore essential to understand how these reactions are controlled by the properties of the interface. In the first part of this thesis, we employed in-situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and surface-enhanced Raman spectroscopy (SERS) to investigate dynamic changes of the copper electrode surface. We found that the polycrystalline copper electrode surface undergoes a reconstruction process upon adsorption of CO. The formation of nanoscale metal clusters on the electrode manifests itself by the appearance of a new CO stretch band, which arises from a CO sub-population bound to undercoordinated copper atoms. The formation of these clusters is reversible, that is, they disappear upon desorption of CO. This work demonstratesthat a reaction intermediate such as CO can induce dynamic and reversible changes in the surface morphology of a heterogeneous catalyst. Because the changes are reversible, they would escape ex situ measurements. Our findings highlight the need for probing catalytic surfaces under operating conditions. In the second part of this thesis, we focused on how the electrolyte influences electrocatalysis at the aqueous electrolyte/copper electrode interface. Specifically, we explored the mechanisms by which cations of the supporting electrolyte affect the reduction of CO and the hydrogen evolution reaction on copper. With differential electrochemical mass spectrometry (DEMS), we determined to what extent the reduction of CO to ethylene is affected by the identity of the cations of the supporting electrolyte. Ethylene is produced in the presence of methyl4N+ and ethyl4N+ cations, whereas this product is not synthesized in propyl4N+- and butyl4N+-containing electrolytes. With SEIRAS, we found that an intermolecular interaction between surface-adsorbed CO and interfacial water is disrupted in the presence of the two larger cations. This observation suggests that this interaction promotes the hydrogenation of surface-bound CO to ethylene. This work illustrates that weak intermolecular interactions can substantially influence electrocatalytic processes. In a related study, we examined the effect of alkali metal cations of the supporting electrolyte on the hydrogen evolution reaction. We found that, in alkaline conditions, changing the cation from Na+ to Cs+ has no measurable effect on the HER. Because it is well-established that Cs+ promotes the reduction of CO2/CO to hydrocarbons, the results illustrate the changing the alkali cation enables the selective promotion of this pathway under alkaline conditions. Further, we found that in 0.1 M solutions of NaOH and CsOH of the highest commercially available purity grades, trace impurities of iron deposit on the copper electrode during the hydrogen evolution reaction. Because iron is a better catalyst for the hyrogen evolution reaction than copper, the rate of the hydrogen evolution reaction is enhanced by up to a factor of 5. These findings demonstrate that trace impurities of this ubiquitous metal pose a great challenge for the development of selective catalytic processes for CO2/CO reduction. This thesis provides a critical study of how the interfacial properties change under the electrocatalytic reduction of CO2/CO and hydrogen evolution conditions. The properties of both Cu electrode and the electrolyte contribute to the control of the selectivity of these complex electrocatalytic processes. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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Piston rings cause significant friction losses within internal combustion engines. Especially the first compression ring, which is pressed onto the liner by high cylinder pressure, contributes significantly to the total friction loss of the piston assembly. The tribological behavior of the oil scraper ring is mainly related to the pretensioning force and can lead to high losses even at low and idle speed. Due to this, there is always a markable risk of wear for the contact surfaces of the piston rings and the cylinder. “Diamond-like carbon” coatings on the surface of the piston rings can prevent wear and are able to reduce friction in the ring-liner-contact. The purpose of this work was to investigate the tribological benefit of this coating-system on the compression and oil scraper ring. Experimental studies were carried out on a fired single-cylinder engine using the Indicated Instantaneous Mean Effective Pressure-method (IIMEP) for the crank angle-resolved detection of the piston assembly’s friction force. To be able to determine the component-related fractions of the friction loss and to quantify the hydrodynamic and asperity related parts locally and time dependent, an EHD/MBS model of the engine was created in AVL EXCITE and a simulative investigation was performed. This simulation was validated by the experimental work and provided detailed information about the individual contact conditions and gap height of each tribological contact of the piston group. The combined approach of measurement and simulation enabled the prediction of tribological aspects and performance in parameter studies on a virtual engine test bed.

Photokatalytische Systeme sind in der Lage, lichtinduziert kleine Moleküle zu aktivieren. Für diesen komplexen Katalysevorgang ist ein Zusammenspiel mehrerer Komponenten wichtig, wie dem Photosensibilisator (PS) und dem Katalysator. Im Rahmen der vorliegenden Dissertation wurde auf verschiedenen Wegen versucht, photokatalytische Systeme auf Basis von Rhenium und 3d-Metallen zu optimieren. So konnten neue Komplexe auf Rheniumbasis synthetisiert und charakterisiert werden, welche zugleich als Photosensibilisator sowie Katalysator fungieren. Die Komplexe zeigen dabei nicht nur eine höhere Absorption, sondern auch eine höhere katalytische Produktivität, als deren mononuklearer Verwandte. Mittels DFT-Rechnungen und spektroskopischen Untersuchungen konnte gezeigt werden, dass ein kooperativer Vorgang stattfindet, bei dem eine Rheniumeinheit als PS, und eine als Katalysator agiert. Durch Zugabe eines externen PS konnte die katalytische Produktivität nochmals deutlich erhöht werden. Durch den zusätzlichen PS wird intermediär eine Rhenium-Rhenium-Spezies ausgebildet, welche CO2 kooperativ über beide Rheniumeinheiten aktivieren kann. Neben literaturbekannten PS auf Iridiumbasis wurden zudem neuartige Kupferphotosensibilisatoren genutzt. Verschiedene Derivate des Kupferphotosensibilisators wurden in der CO2-Reduktion und H2-Produktion getestet. Es zeigte sich, dass verschiedene elektronische Eigenschaften der PS Auswirkungen auf die Katalyseproduktivität haben. Zusätzlich wurden Katalysatoren auf Basis von 3d-Metallen konzipiert, welche abhängig von einem zusätzlichen PS sind. Bestrahlungsexperimente mit Iridium- und Kupfer-PS wurden durchgeführt und somit die Produktivität der einzelnen Katalysatoren bestimmt. Es konnte gezeigt werden, dass sowohl die Wahl des Liganden, als auch des Katalysatormetalls Einfluss auf Menge und Selektivität der Produkte hat. / Photocatalytic systems are capable of light-induced activation of small molecules. Among other things, this allows CO2 to be reduced to higher-energetic molecules. The interaction of several components, such as the photosensitizer (PS) and the catalyst, is important for this complex catalysis process. In this dissertation, attempts were made to optimize systems based on rhenium and 3d metals in various ways. One approach was to synthesize and characterize new rhenium-based complexes, which can act as PSs and catalysts at the same time. The complexes showed not only higher absorption but also higher catalytic activity than their mononuclear relative. Using DFT calculations and spectroscopic investigations, it was shown that a cooperative process takes place, in which one rhenium unit acts as a PS and one as a catalyst. By adding an external PS, the activity was significantly increased again. This forms a rhenium-rhenium species which is able to activate CO2 cooperatively via both rhenium units. In addition to iridium-based PS known from the literature, novel copper photosensitizers were also used for this purpose. In order to get a better understanding of the interaction of both components, different derivatives of the copper photosensitizer were tested in the activity towards CO2 reduction and H2 evolution reaction. The electronic influence of the PS on the catalytic activity could be elucidated by means of Stern-Vollmer quenching studies and DFT calculations. In addition, catalysts based on 3d metals were designed. Iron, cobalt and nickel were used as the central atom together with two different macrocyclic ligands. These monomolecular compounds are dependent on a PS. Furthermore, irradiation experiments with iridium and copper PS were carried out and the activity of the individual catalysts was thereby determined. It was shown that the choice of the ligand as well as the catalyst has an influence on the quantity and selectivity of the resulting products.

No description available.

No description available.