| 1. |
- Maurina Morais, Eduardo, 1989
(författare)
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Synthesis of protic ionic liquids. Challenges and solutions for the synthesis of pure compounds.
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The urgent need to diversify our energy matrix is responsible for a renewed interest in fuel cell technology, which can use hydrogen gas, a renewable green fuel, as an energy source. This technology is currently a commercially available option, however, it still requires technological improvements before it can be widely used for different applications. One way this technology could potentially be improved is by increasing its temperature range of operation by developing new, anhydrous proton conducting materials. Protic ionic liquids, which are organic salts with low melting temperatures, are interesting candidates for this application, since they can conduct protons in the operational conditions of fuel cells and without the need of water. These compounds can be synthesized by a simple acid-base neutralization reaction, but certain considerations must be taken in order to obtain high quality (dry and pure) protic ionic liquids. In this thesis, a series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98-99% m/m) and dry (128-553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is consists of only glass and chemically resistant polymer(PTFE and PVDF) parts, which avoids other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). The resulting ionic liquids were carefully analyzed by spectroscopic and thermal analysis methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.
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| 2. |
- Singh, Shivangi, 1996
(författare)
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Investigating hydrothermal stability and influence of water on the activity of Cu-CHA catalysts for NH3-SCR
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Selective catalytic reduction of nitrogen oxides (NOx) with NH3 as a reducing agent (NH3- SCR) is a leading technology for diesel exhaust emission control. Cu-exchanged zeolites with the chabazite structure (Cu-CHA) have emerged as the preferred catalysts thanks to its high activity and hydrothermal stability. Hydrothermal stability is related to dealumination, i.e. removal of aluminum from the zeolite framework to form extraframework aluminum, at high temperatures in the presence of water vapor. Copperexchanged chabazite (Cu-CHA) zeolites have higher hydrothermal stability compared to H-chabazite (H-CHA). To understand the delayed dealumination of Cu-CHA catalysts, we have investigated the reaction paths for dealumination in H-CHA and Cu-CHA using density functional theory (DFT) calculations combined with microkinetic modeling. We find that Cu-CHA and H-CHA follow similar four-step hydrolysis processes, yet the dealumination of Cu-CHA has higher energy barriers, suggesting stabilization of the CHA structure by Cu ions. Furthermore, the preferred reaction product upon complete dealumination of Cu-CHA is a copper-aluminate like species bound to the zeolite framework. The microkinetic analysis quantifies the increased stability of Cu-CHA as compared to H-CHA. In addition to the high-temperature dealumination, we investigated the role of water on low-temperature SCR by experimentally measuring the activity and reaction order of water. The reaction order of water is found to be increasingly negative with increasing water pressure. DFT calculations reveal that water blocks the active Cu-sites and a DFT-based microkinetic model reproduces the measured change of reaction order with water pressure.
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| 3. |
- Boge, Lukas, 1987
(författare)
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Lipid-based liquid crystals as drug delivery vehicles for antimicrobial peptides
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of antimicrobial resistance is a great challenge within the health sector around the world. The demand for new efficient treatments is alarming in order to treat various bacterial infections in the near future. Antimicrobial peptides (AMPs) are a group of novel antibiotics that have gain more and more attraction the past decade. However, AMPs suffers from relatively low stability due to proteolytic and chemical degradation. As a consequence, carrier systems protecting the AMPs are highly needed for achieving efficient treatments. In this thesis, lyotropic liquid crystalline (LC) structures consisting of cubic glycerol monooleate/water and hexagonal glycerol monooleate/oleic acid/water have been examined as carriers for three AMPs (AP114, DPK-060 and LL-37). Both bulk gels and discrete dispersed structures, i.e. cubosomes and hexosomes have been studied. Moreover, two different peptide loading approaches for the cubosomes were tested and compared; pre- and post-loading. Characterization of the LC structures was performed using small-angle x-ray scattering (SAXS), dynamic light scattering, ζ-potential, and cryogenic transmission electron microscopy (Cryo-TEM) and peptide loading efficacy by liquid chromatography. The antimicrobial effect of the AMP loaded LC nanoparticles (LCNPs) was studied in vitro using minimum inhibitory concentration (MIC) and time-kill assays. Proteolytic protection was investigated by incubating the formulations with two elastases and the antimicrobial effect after proteolysis was studied using radial diffusion assay (RDA). Results showed that the most hydrophobic peptide (AP114) was prone to induce an increase in negative curvature of the bulk cubic LC gel, hence pushing the system towards a hexagonal structure. The most polar peptide (DPK-060) induced a decrease in negative curvature while LL-37 did not change the LC phase at all. The hexagonal LC phase was not affected by any of the AMPs. The cubic pre- and post-loaded LCNPs displayed promising antimicrobial activity, and sometimes could a synergetic effect be observed, resulting in a slightly better activity than the unformulated AMP. The hexagonal LCNPs were found to be very efficient in encapsulating the AMPs, but did not display any antimicrobial effect, indicating insufficient delivery of peptide to the bacteria. Moreover, cubosomes post-loaded with LL-37 was found to protect the peptide from proteolytic degradation, resulting in a significant better bactericidal effect after proteolysis.
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| 4. |
- Sauer, Christopher, 1993
(författare)
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Green aromatics for a bio-based economy - Valorization of biomass derived model compounds over zeolites studied by online analysis
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the strive towards sustainable chemical production, its carbon-based products can no longer be produced from fossil resources but need to be manufactured from a renewable feedstock. Simple aromatic building blocks like benzene, toluene and xylenes (BTX) can be obtained by catalytic valorization of biomass derived platform molecules such as furans provided efficient catalysts can be formulated. To evaluate catalysts for the conversion of furans to BTX and study the involved catalytic reactions, advanced analytical methods are needed. The observation of dynamic responses in catalytic activity and selectivity necessitates time-resolved analysis of rather complex hydrocarbon (HC) streams. In this work, an online analysis method combining Fourier transform infrared spectroscopy and ion molecule reaction mass spectrometry has been developed for the direct monitoring of the effluent stream during conversion of furans over zeolite catalysts. The sampling frequency is shown to be at least 4 per minute, which is considerably higher compared to that of separation-based methods operating on time scales of several minutes. A wide range of HCs and other smaller molecules is identified and individual species quantified simultaneously. The carbon balance of around 90% shows that the vast majority of the complex HC stream is indeed analysed. The developed online analysis has been applied to catalytic step-response experiments, where different zeolites were exposed to concentration steps of 2,5-dimethylfuran at steady temperatures. It is found that the HC stream consists of a range of olefins and aromatics, including BTX. Most interestingly, 2,5-dimethylfuran is isomerized to 2,4-dimethylfuran as well as 2- and 3-methyl-2-cyclopenten-1-one. The formation of BTX is linked to the availability of olefins, which is supported by temperature programmed desorption experiments. Furthermore, to build understanding of the catalytic mechanisms, surface species were characterised in situ by use of diffuse reflectance infrared Fourier transform spectroscopy. It is clear that upon adsorption, 2,5-dimethylfuran interacts with the zeolite structure and undergoes transforming reactions to olefins and aromatics upon temperature increase, but further studies are necessary to comprehend how the rather low selectivity towards BTX can be increased by catalyst design.
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| 5. |
- Carlsson, Andreas
(författare)
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Synthesis and spectroscopic characterization of emerging synthetic cannabinoids and cathinones
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The application of different analytical techniques is fundamental in forensic drug analysis. In the wake of the occurrence of large numbers of new psychoactive substances possessing similar chemical structures as already known ones, focus has been placed on applied criteria for their univocal identification. These criteria vary, obviously, depending on the applied technique and analytical approach. However, when two or more substances are proven to have similar analytical properties, these criteria no longer apply, which imply that complementary techniques have to be used in their differentiation.This work describes the synthesis of some structural analogues to synthetic cannabinoids and cathinones based on the evolving patterns in the illicit drug market. Six synthetic cannabinoids and six synthetic cathinones were synthesized, that, at the time for this study, were not as yet found in drug seizures. Further, a selection of their spectroscopic data is compared to those of already existing analogues; mainly isomers and homologues. The applied techniques were mass spectrometry (MS), Fourier transformed infrared (FTIR, gas phase) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. In total, 59 different compounds were analyzed with the selected techniques.The results from comparison of spectroscopic data showed that isomeric substances may in some cases be difficult to unambiguously identify based only on their GC-MS EI spectra. On the other hand, GC-FTIR demonstrated more distinguishable spectra. The spectra for the homologous compounds showed however, that the GC-FTIR technique was less successful compared to GC-MS. Also a pronounced fragmentation pattern for some of the cathinones was found.In conclusion, this thesis highlights the importance of using complementary techniques for the univocal identification of synthetic cannabinoids and cathinones. By increasing the number of analogues investigated, the more may be learnt about the capabilities of different techniques for structural differentiations, and thereby providing important identification criteria leading to trustworthy forensic evidence.
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| 6. |
- de Reijer, Guido J.L. 1997
(författare)
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Catalyst Design for the Valorisation of Biomass-derived Furans into Aromatics
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Anno 2023, mankind must strive towards a more sustainable chemical industry; one that does not solely rely on fossil fuels but also utilises renewable feedstocks such as biomass. Biomass can be catalytically converted into commodity chemicals such as aromatics, through intermediates like furans. Aromatics serve as building blocks for everyday materials. In this work, the conversion of one type of furans, 2,5-dimethylfuran, was studied at elevated temperatures in a flow reactor by using a selection of microporous, acidic catalysts. The effluent gas stream was analysed with Fourier-transform infrared spectroscopy and mass spectrometry. Zeolitic catalysts with the MFI-framework were synthesised bottom-up through hydrothermal synthesis, with aluminium or gallium substituted in their framework. Structural analysis was performed comprising X-ray fluorescence, X-ray diffraction, physisorption, thermogravimetric analysis, scanning electron microscopy, and acidity analysis by NH3-TPD. Both aluminium and gallium-substituted zeolites were active for converting 2,5-dimethylfuran into aromatics, of which Ga-MFI displayed superior benzene production and catalyst lifetime. Catalyst deactivation was caused by the loss of strong and extra-framework acid sites due to the coking. After deactivation towards aromatics, the intermediate products formed on weak acid sites such as 2,4-dimethylfuran, were detected as the main products. It was found that an increase in gallium content increases catalytic activity until a limit of Si/Ga=13 was reached, at which the synthesis of the catalyst also yielded an inactive, amorphous phase. Increasing the crystallisation duration enabled approaching this limit and forming phase-pure MFI zeolite with a Si/Ga ratio of Si/Ga=17. Mesopores were introduced to the catalyst to improve the mass transfer of reactants and products. Even though the total production of aromatics and the catalyst lifetime remained unchanged, its number of acid sites was halved implying that each acid site was able to produce twice as many aromatics.
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| 7. |
- Espegren, Fredrik, 1989
(författare)
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Tellurium interaction with surfaces in the containment and sea-salt residue
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the event of a nuclear accident, the release of radionuclides is always a concern. The extent of such releases is affected by several factors, for example type of atmosphere, temperature, and what structural materials are present during the accident. The release of tellurium is especially worrying due its volatility, reactivity, and decay product of iodine. Moreover, the radiological and chemical toxicity of tellurium will during an accident be considerably problematic, to the public and nature. This work is divided into two experimental parts in order to determine: (1) the interaction between tellurium and metallic structural material found in the containment and (2) investigate the potential effect when using seawater as a coolant focusing on sea-salt residue. All experiments were performed at the relevant temperature (depending on the which part) under oxidizing and inert conditions and for the containment experiments humidity was also investigated. The structural material investigated were the metal surfaces aluminum, zinc, and copper with the aim of determining morphology, chemical speciation and if a reaction occurred between the metal surface and tellurium. For the investigation of seawater, determining if a chemical reaction(s) between tellurium and sodium chloride occurs and at what temperature. Results from the containment experiments using a furnace showed signs of possible reaction between tellurium and the copper surface under inert humid conditions close to room temperature. Otherwise, tellurium deposition occurred on the metal surfaces with no observable chemical reaction and no strong attachment to the surface. The deposit formed on the surfaces and the observed chemical species under the different conditions, determined using different spectroscopy methods, were as follows: TeO2 under oxidizing with (crystal structure paratellurite) and without humidity (crystal structures: paratellurite and orthorhombic), Te-metallic under inert conditions both with and without humidity, and finally Cu7Te4 was seen in the deposits on the copper surface under humid inert conditions. For the seawater investigation, two methods where used thermogravimetric analysis and furnace experiments. The results from these methods showed that under inert conditions, no indication of interaction was seen. However, for oxidizing conditions an interaction for all samples was observed that prevented an otherwise seen mass increase of the tellurium reference. Through the furnace experiments, the appearance of the samples at increasing temperatures were studied and used to support the thermogravimetric analysis.
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| 8. |
- Han, Joonsoo, 1990
(författare)
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NH3-SCR chemistry for NOx abatement: Influence of zeolite support on N2O formation & phosphorus species addition.
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different lattice arrangements of Si, Al, and O atoms result in a variety of pore dimensions and zeolite channel network systems, giving rise to different physicochemical environments inside the catalyst cage. The objective of the thesis work was to understand the influence of zeolite topology on NH3-assisted SCR chemistry over CHA, MFI, and BEA frameworks, on the formation of N2O and the addition of phosphorus species to attain fundamental insight into NOx emission control. A variety of characterization techniques and mechanistic experimental protocols were used to examine Cu2+ ions coordinated with 1Al and 2Al in frameworks, denoted as Z2Cu and ZCuOH, respectively. Catalytic activity tests were performed to investigate the influence of ammonium nitrate (AN)-forming N2O and phosphorus species on DeNOx performance over the Cu-impregnated CHA, MFI, and BEA. In Paper I, ammonium nitrate (AN) formation and decomposition were thoroughly investigated to see the effect of zeolite topology, copper species, and water vapor on the N2O formation in NH3 SCR of NOx at low temperatures. Three different Cu/zeolites (CHA, MFI, and BEA) were used, and these were compared with H/zeolites as the reference. H2 temperature programmed reduction and in-situ IR spectroscopy suggest that the CHA framework structure is more favorable than MFI and BEA to form AN inside the catalyst cage. AN formation was enhanced in the presence of Cu ions over the Cu/zeolites. Catalyst activity tests demonstrated that Cu/CHA has a potential for uncontrolled N2O emission in transient conditions despite it shows lower N2O formation over standard and fast SCR reaction due to a highly stabilized AN inside the catalyst cage at low temperatures. This indicates pros and cons of AN stability over CHA in NH3-SCR systems. The critical effect of water vapor on AN formation and decomposition was found. The water vapor causes the cleavage of Cu dimers into Cu2+-OH groups, which are responsible for NO oxidation forming NO+ and surface nitrates. Thus, it results in the formation of fewer surface nitrates, leading to less AN and less N2O formation in wet conditions. In Paper II, phosphorus poisoning of different zeolite topologies was investigated. Fresh Cu/zeolites (CHA, MFI, and BEA) were used as the reference, and these were compared with P-poisoned Cu/zeolites. X-ray powder diffraction (XRD) revealed that the MFI framework was vulnerable to phosphorus species attack, resulting in the deformation of the framework structure. A variety of phosphorus species, such as PO-3, PO3- 4, and P2O5 populations, were observed over Cu/zeolites with Xray photoelectron spectroscopy. Transient response methodologies suggest that ZCuOH sites were significantly poisoned by PO-3 and PO3- 4 over Cu/CHA. Accordingly, a promoted or deteriorated redox feature of Cu ions (i.e., Z2Cu and ZCuOH) was suggested. A significant drop in catalytic activity was demonstrated over Cu/MFI in catalytic activity tests. It is suggested that MFI framework deformation, such as pore-blockage, local expansion, and cracking, impedes the mobility of Cu+(NH3)2 complexes at low temperatures under standard SCR conditions. Consequently, we hypothesize that MFI framework degradation hinders the formation of NH3-solvated Cu dimer complexes, which are responsible for O2 activation.
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| 9. |
- Hansson, Niklas, 1992
(författare)
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The Influence of Hydrogen on the Radiolytic Oxidation of UO2
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spent nuclear fuel from the nuclear fuel cycle contains radiotoxic nuclides which must be safely stored for over 100 000 years. The Swedish final repository concept, KBS-3, is based on engineered and geological barriers that prevent the nuclear fuel from coming in contact with groundwater, which is the most credible vector to transport the radionuclides into the biosphere. In the safety assessment of a repository, the water intrusion scenario must therefore be investigated. The UO2 matrix contains the majority of the long-lived radiotoxic elements. As the U(IV) form is highly insoluble, the release of the radiotoxic nuclides is largely governed by oxidation of the UO2 matrix into the much more soluble U(VI) form. Oxidation can occur due to the formation of radiolytic oxidants through the ionization or excitation of water molecules in contact with fuel. Oxidation of UO2 pellets using external Am-241 sources was studied under conditions where the UO2 surface and the source were separated by 30 µm water. H2 was shown to suppress the surface oxidation as well as dissolution. This was shown by direct measurement of the surface oxidation state using XPS, as well as through concentration measurements in solution using mass spectrometry (ICP-MS). Oxidative dissolution of 10 and 24 wt% Pu-doped MOX pellets was also studied under Ar and D2 atmospheres. The D2 atmosphere suppressed the uranium dissolution. However, corrosion of the stainless-steel materials present in the autoclave system was also observed. A calculation model was also developed for calculating dose-rates from α-doped UO2 based material.
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| 10. |
- Landälv, Ludvig, 1982-
(författare)
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Thin Film and Plasma Characterization of PVD Oxides
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite(WC-Co) coated with different combinations of carbide, nitride and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings are especially desired because of their possible high hot hardness, chemical inertness with respect to the workpiece, and their low friction.This thesis deals with process and coating characterization of new oxide coatings deposited by physical vapor deposition (PVD) techniques, focusing on the Cr-Zr-O and Al-Cr-Si-O systems.The thermal stability of α-Cr0.28Zr0.10O0.61 deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was investigated after annealing up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudo-binary oxide system also opens up design routes for pseudo-binary oxides with tunable microstructural and mechanical properties.The inherent difficulties of depositing insulating oxide films with PVD, demanding a closed circuit, makes the investigation of process stability an important part of this research. In this context, we investigated the influence of adding small amount of Si in Al-Cr cathode on plasma characteristics ,process parameters, and coating properties. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating.This work shows small improvements in cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at % Si in the Al70Cr30-cathode. This also led to fewer droplets at low cathode current and intermediate O2 flow. A larger positive effect on cathode erosion was observed with respect to cleaning the cathode from oxide contamination by increasing cathode current with 50%. However, higher cathode current also resulted in increased amount of droplets in the coating which is undesirable. Through plasma analysis the presence of volatile SiO species could be confirmed but the loss of Si through volatile SiO species was negligible, since the coating composition matched the cathode composition. The positive effect of added Si on the process stability at the cathode surface should be weighed against Si incorporation in the coating. This incorporation may or may not be beneficial for the final application since literature states that Si promotes the metastable γ-phase over the thermodynamically stable α-phase of pure Al2O3, contrary to the effect of Cr, which stabilizes the α-phase.
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