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| 2. |
- 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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| 3. |
- Sauer, Christopher, 1993
(författare)
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Green Aromatics: Catalytic Valorisation of bio-derived 2,5-dimethylfuran over Zeolites and Zeotypes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses the use of biomass as a potentially green feedstock for the chemical industry in the urgent shift away from fossil resources. I elaborate on reasons why we cannot afford to burn virgin biomass for energy production, among them a variety of ecosystem services that forests and other lands provide. In addition, the utilisation of biomass should be focused on products that sequester and lock away carbon for more extended periods, e.g. timber, materials and chemicals. In particular, biomass can be used as an alternative "carbon neutral" feedstock for the chemical industry, where we can preserve the already existing chemical complexity in the bio-based molecules. One example is the upgrading of furans to benzene, toluene and xylene (BTX) aromatics with the help of zeolite catalysis. These aromatics are important commodity chemicals, where the shift to a bio-based resource could make use of already existing knowledge, catalyst and production infrastructure. However, research is necessary to understand these new feedstock molecules and their interaction with the catalysts and to enable the design of applicable catalysts. In order to study the interaction of the furans, in particular 2,5-dimethylfuran (2,5-dmf), I describe and discuss the development of an analytical methodology that utilises infrared spectroscopy and mass spectrometry for the on-line identification and quantification of product molecules during catalytic reactions. This on-line analysis method is then applied to the catalytic conversion of 2,5-dmf to aromatics over a range of zeolite and zeotype catalysts. In-depth studies with ammonia as a probe molecule of the catalytic active acid sites, as well as temperature programmed experiments with ammonia and 2,5-dmf give insights into product distribution, selectivity changes and deactivation of the catalyst. For example, olefins and aromatics are initially preferred products, while with increasing time on stream, the isomerisation of 2,5-dmf becomes dominant. The incorporation of Ga into the zeotype framework, resulting in a Ga-Silicate, shows how targeted catalyst design can increase overall aromatics production. This catalyst is also suitable for selective isomerisation of 2,5-dmf to 2,4-dimethylfuran, which has a rare substitution pattern. Finally, itwas found that the most valuable of BTX, p -xylene, can be produced more selectively when 2,5-dmf is pre-adsorbed onto zeolite ZSM-5 and then released during a temperature programmed product desorption.
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| 5. |
- Barišić, Antun, et al.
(författare)
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Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
- 2021
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Ingår i: Colloids and interfaces. - : MDPI. - 2504-5377. ; 5:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.
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| 6. |
- Halldin Stenlid, Joakim, 1987-
(författare)
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Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemical bond – a corner stone in science and a prerequisite for life – is the focus of this thesis. Fundamental and applied aspects of chemical bonding are covered including the development of new computational methods for the characterization and rationalization of chemical interactions. The thesis also covers the study of corrosion of copper-based materials. The latter is motivated by the proposed use of copper as encapsulating material for spent nuclear fuel in Sweden.In close collaboration with experimental groups, state-of-the-art computational methods were employed for the study of chemistry at the atomic scale. First, oxidation of nanoparticulate copper was examined in anoxic aqueous media in order to better understand the copper-water thermodynamics in relation to the corrosion of copper material under oxygen free conditions. With a similar ambition, the water-cuprite interface was investigated with regards to its chemical composition and reactivity. This was compared to the behavior of methanol and hydrogen sulfide at the cuprite surface.An overall ambition during the development of computational methods for the analysis of chemical bonding was to bridge the gap between molecular and materials chemistry. Theory and results are thus presented and applied in both a molecular and a solid-state framework. A new property, the local electron attachment energy, for the characterization of a compound’s local electrophilicity was introduced. Together with the surface electrostatic potential, the new property predicts and rationalizes regioselectivity and trends of molecular reactions, and interactions on metal and oxide nanoparticles and extended surfaces.Detailed atomistic understanding of chemical processes is a prerequisite for the efficient development of chemistry. We therefore envisage that the results of this thesis will find widespread use in areas such as heterogeneous catalysis, drug discovery, and nanotechnology.
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| 7. |
- Moth-Poulsen, Kasper, 1978
(författare)
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Molecular Systems for Solar Thermal Energy Storage and Conversion
- 2013
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Ingår i: Organic Synthesis and Molecular Engineering. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. ; , s. 179-196
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Using a synthetic approach to organic materials chemistry, this book sets forth tested and proven methods and practices that make it possible to engineer organic molecules offering special properties and functions. Throughout the book, plenty of real-world examples demonstrate the countless possibilities of creating one-of-a-kind molecules and supramolecular systems to support a broad range of applications. The book explores applications in both materials and bioorganic chemistry, including molecular electronics, energy storage, sensors, nanomedicine, and enzyme engineering.Organic Synthesis and Molecular Engineering consists of fourteen chapters, each one contributed by one or more leading international experts in the field. The contributions are based on a thorough review and analysis of the current literature as well as the authors' firsthand experience in the lab engineering new organic molecules. Designed as a practical lab reference, the book offers:Tested and proven synthetic approaches to organic materials chemistryMethods and practices to successfully engineer functionality into organic moleculesExplanations of the principles and concepts underlying self-assembly and supramolecular chemistryGuidance in selecting appropriate structural units used in the design and synthesis of functional molecules and materialsCoverage of the full range of applications in materials and bioorganic chemistryA full chapter on graphene, a new topic generating intense researchOrganic Synthesis and Molecular Engineering begins with core concepts, molecular building blocks, and synthetic tools. Next, it explores molecular electronics, supramolecular chemistry and self-assembly, graphene, and photoresponsive materials engineering. In short, it offers everything researchers need to fully grasp the underlying theory and then build new molecules and supramolecular systems.
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| 8. |
- Arvidsson, Adam, 1990
(författare)
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Partial methane oxidation from electronic structure calculations
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Investigating catalytic reactions with computational methods is a powerful approach to understand fundamental aspects of catalytic reactions and find ways to guide catalytic design. Partial methane oxidation is one example of a reaction with intriguing challenges, where a detailed atomistic approach may help to unravel the bottlenecks of this, as of yet, inefficient reaction. Although methane only needs one oxygen atom for conversion to methanol, the direct oxidation is difficult; it is in fact so difficult that at many oil extraction sites, the methane that inevitably accompanies the crude oil is flared into carbon dioxide and water as gas-phase methane is too inconvenient to store and transport.The main challenge with partial oxidation of methane is to selectively control the oxidation and steer it towards methanol and prevent over-oxidation to CO2. There exist natural enzymes that can partially oxidize methane to methanol at ambient pressure and temperature, although very slowly. One inorganic analogue to these naturally occurring enzymes are zeolites, a porous material that can readily be synthesized and that have been shown to convert methane to methanol at ambient conditions with a high selectivity (>90 %). This has been realized for zeolites ion-exchanged with different metals, such as iron, cobalt, nickel, and copper. Although there have been many attempts to determine the active site for the reaction, there is still no consensus. One candidate that has been put forth is a [Cu-O-Cu]2+ motif experimentally characterized in the ZSM-5 zeolite. In this thesis, partial oxidation of methane is investigated, focusing on this dimer motif. By combining density functional theory calculations with microkinetic modelling, the catalytic performance of the dimer motif is investigated with a simple reaction mechanism for copper, but also with the copper atoms exchanged with nickel, cobalt, iron, silver, or gold. From these results, it is clear that this particular dimer site is a relevant candidate only for copper, and can be excluded in the continued search for active sites in nickel, cobalt, and iron ion-exchanged ZSM-5.To further understand how methanol is formed and interacts with Cu-ZSM-5, experimental and calculated infrared frequencies are compared for methanol and other adsorbates. The partial oxidation of methane is also studied for other systems with oxidants other than oxygen. In particular, methane oxidation with H2S to CH3SH and H2 is explored on molybdenum sulfide clusters.
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| 9. |
- Liu, Yuan
(författare)
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Theoretical Studies of Natural Gas Hydrates and H-bonded Clusters and Crystals
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis H-bonded systems (natural gas hydrates, water clusters, and crystal ice) are studied by density functional theory (DFT) computations.Natural gas hydrates (NGHs) play an important role in energy and environmental fields: NGHs are considered as a promising backup energy resource in the near-future due to their tremendous carbon content; improper exploration of NGHs could induce geological disasters and aggravate the greenhouse effect. In addition, many technologies based on gas hydrates are being applied and developed. The thermodynamic stabilities of various water cavities in different clathrate crystalline phases occupied by hydrocarbon gas molecules are studied by dispersion-corrected hybrid functionals. The Raman spectra of C-C and C-H stretching vibrations of hydrocarbon molecules in various water cavities in the solid state are derived. The trends of C-H stretching vibrational frequencies are found to follow the prediction by the “loose cage ─| tight cage” model. In addition, the trends and origins of 13C NMR chemical shifts of hydrocarbon molecules in various NGHs are presented. These theoretical results will enlarge the database of C-C and C-H stretching vibrational frequencies and 13C NMR parameters of hydrocarbon molecules in NGHs, and provide valuable information to help identify the types of clathrate phases and varieties of guest molecules included in NGHs samples taken from natural sites.The behavior of water clusters may help to understand the properties of its liquid and solid states. The thermodynamic stabilities and IR spectra of a small-, medium-, and large-sized water cluster are studied in this work. After full optimization of (H2O)20,54,100 using the hybrid functional B3LYP, the electronic energies, zero-point energies, internal energies, enthalpies, entropies, and Gibbs free energies of the water clusters are computed. The OH stretching vibrational IR spectra of (H2O)20,54,100 are also presented and split into sub-spectra for different H-bond types based on the specific contributions from each group. It is found that the OH stretching vibrational frequencies of water are sensitive to the conformations of the H-bonds and the vibrations of the H-bonds belonging to different types are located in separated regions in the IR spectra. Thus, the spectroscopic fingerprints will reflect the H-bond topology of the water molecules in a water cluster.Ice XI has been suggested to be involved in the process of planetary formation as a considerable electric field might be formed from the ferroelectric ice XI in space. IR and Raman spectroscopic technology can be directly used to identify the occurrence of ferroelectric ice XI in laboratory or extraterrestrial settings. Due to the difficulty for DFT to describe non-covalent systems, the performance of 16 different DFT methods applied on the ice Ih, VIII, IX, and XI crystal phases are assessed. Based on the computational accuracy and cost, the IR and Raman spectra of ice Ih and XI are derived and compared. The librational vibrations are found to be the identifier which can be used to distinguish ice Ih and ice XI in the universe. In addition, the existence only one kind of H-bond in ice Ih is demonstrated from the overlapping sub-spectra for different types of H-bonded pair configurations in 16 isomers of ice Ih.The region of water under negative pressure is an exotic land in lack of exploitation. Guest free clathrate hydrate (clathrate ice) of sII type has been recently confirmed experimentally at negative pressure. Does any other clathrate ice phase exist at negative pressure region? Since clathrate hydrate are isostructural with silica clathrate minerals and semiconductor clathrates, and crystal structure prediction by analogy with known structures and first-principles computations is an effective way to find new crystalline phases of solid materials, we are motived to look for new clathrate ice phases from silica or semiconductor clathrate materials based on first-principles computations. Borrowing the idea new clathrate frameworks of ZnO and SiC can be constructed by connecting their bubble clusters in different ways, new clathrate ice phases (sL, sL_I, sL_II, and sL_III) are generated by connecting the water bubble clusters according to different rules. Using the non-local dispersion-corrected vdW-DF2 functional, clathrate ice sL with ultralow density (0.6 g/cm3) is predicted by first-principles phase diagram computations to be stable under larger negative pressures than the sII phase. The phase diagram of water is thus extended into the lower negative pressure region.
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| 10. |
- van den Bossche, Maxime, 1989
(författare)
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Methane oxidation over palladium oxide. From electronic structure to catalytic conversion
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding how catalysts work down to the atomic level can provide ways to improve chemical processes on which our contemporary economy is heavily reliant. The oxidation of methane is one such example, which is important from an environmental point of view. Methane is a potent greenhouse gas and natural and biogas vehicles need efficient catalysts to prevent slip of uncombusted fuel into the exhaust. Commercial catalysts for methane oxidation are often based on palladium or platinum. Metallic palladium, however, is easily converted to palladium oxide when the engine is operated at oxygen rich conditions. In this thesis, various aspects of complete methane oxidation over PdO(101) are investigated with computational methods based on density functional theory (DFT). PdO(101) is the active surface for methane oxidation, and firstly, the reaction intermediates CO and H are studied in detail. Possible pathways for H2 adsorption, dissociation and eventual water formation are investigated, in connection to core-level spectroscopy experiments. Similarly, the adsorption configurations for carbon monoxide on clean and oxidized palladium are examined with a combination of DFT calculations, core-level and infrared spectroscopy. Secondly, a detailed kinetic model is constructed that describes the catalytic conversion of CH4 to CO2 and H2O over PdO(101). This is done in a first-principles microkinetics framework, where the kinetic parameters are obtained by applying density functional and transition state theory. The kinetic model provides a fundamental understanding of findings from reactor experiments, such as the rate limiting steps and poisoning behaviour, and shows qualitatively different behaviour of adsorbates on oxide as compared to metal surfaces. Lastly, limitations of the commonly used class of generalized gradient functionals are illustrated in the computation of several properties of adsorbates on metal oxide surfaces. These include core-level shifts and thermodynamic and reactive properties of adsorbates on the PdO(101) surface. Similarly, the description of several molecular and cooperative adsorption processes are also found to be sensitive to the applied exchange-correlation functional on the BaO(100), TiO2(110) and CeO2(111) surfaces.
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