1. Catalytic hydro(deoxy)genation of furfural and modelling of its reaction kinetics : dissertationRok Šivec, 2024, doktorska disertacija Opis: In recent decades, there has been a growing interest in producing biofuels and biochemicals from renewable sources. Furfural stands as one of the ligno(hemi)cellulosic biomass derived platform chemical, which can be transformed into numerous value-added products.
The goal of this PhD was to systematically study hydrotreatment reactions of furfural under varying operating conditions and to gain insights into the reaction mechanism and kinetics. An extensive experimental and computational study of hydrogenation, hydrodeoxygenation, oligomerisation and etherification of furfural in a three-phase batch reactor was performed. The goals were divided into three consecutive objectives.
In the first part, hydrotreatment of furfural over Pd/C catalyst under various reaction conditions, including the solvent selection (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed, was studied. A reaction pathway network and a micro-kinetic model were developed, incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption, and surface reactions. These phenomena and their contribution to the surface coverages, TOF’s and global reaction rates were studied. The hydrogen presence on the catalyst surface was found to influence the main reaction pathway, leading to ring, aldehyde group or full hydrogenation.
In the second part, various monometallic catalysts (Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C, Cu/C) were tested at 100 -200 °C with 60 bar of hydrogen and tetrahydrofuran as solvent. A generalized reaction pathway network was developed. H2 temperature-programmed reduction (H2-TPR) and CO temperature-programmed desorption (CO-TPD) were conducted, and a regression analysis of the results was subsequently performed by numerical modelling and optimisation. The obtained adsorption and desorption kinetic parameters for active metallic sites were further used in a generalized micro-kinetic model, applicable to all tested catalysts. Pd/C exhibited high activity and non-selective hydrogenation of furfural, while other catalysts showed selective aldehyde group hydrogenation followed by deoxygenation, consistent with density functional theory (DFT) calculations. Ru/C uniquely produced 2 methyltetrahydrofuran and ring-opening products at 200 °C. In silico optimization of reaction conditions for promising catalysts ((Pd/C, Pt/C, Re/C, Ni/C) aimed to maximize the yield of the target product.
In the third part, the influence of support on catalytic activity was studied. Hydrotreatment of furfural over Pd/Al2O3, Pd/SiO2, Ru/Al2O3, Ru/SiO2, Ni/Al2O3, and Ni/SiO2 was performed between 150 - 200 °C, using 60 bar of hydrogen and tetrahydrofuran as solvent. The strength and rate of adsorption and desorption to/from acidic, metallic and interface site structures were determined, using H2-TPR, CO-TPD and NH3-TPD and subsequent regression analysis of the results by numerical modelling and optimisation. The resulting parameters were sequentially used in the generalized micro-kinetic model to quantify the contribution of the active metal (Ni, Pd, or Ru), support (Al2O3 or SiO2), interphase sites and their relationship on catalyst activity and selectivity. Evaluation of morphological and structural characteristics, adsorption/desorption and intrinsic reaction kinetics has indicated that the coverage of acidic sites (on alumina or silica) facilitated yielding ring hydrogenation and inhibited deoxygenation, decarbonylation and cyclic compound opening. The rates for aromatics or aldehyde functional groups were, nonetheless, affected in a different order.
The used and developed methods and findings of this PhD offer useful guidelines for transforming furfural into high-value chemicals through catalytic hydrotreatment, with significant implications for future research and industrial applications.
Ključne besede: lignocellulosic biomass, furfural, catalytic hydrogenation, micro-kinetic mass transfer model, reaction kinetics, first-principle methods, furfuryl alcohol, tetrahydrofurfuryl alcoholv, dissertations
Objavljeno v RUNG: 08.11.2024; Ogledov: 265; Prenosov: 4
 Celotno besedilo (9,22 MB) |
2. Reaction mechanism and microkinetics of heterogeneously catalysed lignin depolymerisation and (de)functionalization : dissertationTina Ročnik, 2024, doktorska disertacija Opis: Lignin, a complex aromatic polymer derived from lignocellulosic biomass, is a renewable resource for the production of aromatic-like chemicals and materials. However, its complex nature, depolymerisation and valorisation remain a major challenge for the bio-based community within biorefinery concepts. For this reason, lignin model compounds have been used to understand and design lignin depolymerisation, but insufficient attention has been paid to linking knowledge between simpler systems and applying it to a more complex problem. The objectives of this thesis were formulated accordingly to address the aforementioned gap in the literature. The objectives included a systematic approach correlating studies of lignin model compounds with lignin. Hydrodeoxygenation, cleavage of the β-O-4 bond and depolymerisation were investigated to evaluate the process- and structure-dependent correlations, effects on product distribution and kinetic parameters.
The catalytic reactions were carried out in batch reactor and the conditions were applied and intensified according to the knowledge gained during the experimental work. The liquid samples for monomer yield evaluation were analysed by GC-MS, while the structural characteristics of lignin and oligomeric fragments, e.g. molecular weight, functionality/reactivity and structural features, were examined by SEC, quantitative 31P and 2D-HSQC NMR. Kinetic modelling was performed to determine the kinetic parameters (e.g. kinetic constants and activation energies) describing defunctionalisation, β-O-4 bond cleavage and depolymerisation.
The study with monomeric lignin compounds contributed to the understanding of the key parameters leading to condensation during hydrotreatment. The unsaturated alkyl side-chain of eugenol and the reactive hydroxyl groups bound irreversibly and formed the carbonaceous species, while 4-propylphenol and 4-propylguaiacol provided important insights into the contribution of steric hindrances to a favourable reaction mechanism. An initial assessment of β-O-4 cleavage was performed with β-O-4-model compound, 2-phenoxy-1-phenylethanol, and linked to the lignin macromolecule by process- and structure-dependent correlations. Although the lignin model compound lacks the structural complexity of lignin, important insights into possible reaction processes were gained and accurate kinetic parameters were determined. Furthermore, lignin isolated in 50 vol% EtOH/H2O solutions was depolymerised and the optimal
reaction conditions were defined at a temperature of 275 °C and a pressure of 1.5 MPa with regard to the product distribution and the changes in the structural characteristics of the corresponding oligomeric fragments. Depolymerisation of lignins isolated in different EtOH/H2O solutions showed the importance of the structural features, especially ethoxylation degree and the content of β-O-4 or α-ethoxylated β-O-4 bonds. A higher ethoxylation degree of lignin reduced its potential to depolymerise and achieve the theoretical monomer yield. Therefore, the structural characteristics of lignin play the main role in designing and prediction of lignin depolymerisation.
The thesis represents a systematic approach of increasing the complexity of structures exposed to hydrodeoxygenation and depolymerisation. The approach contributed to incorporating the knowledge gained from less complex model compounds to real lignin samples by tailoring and designing lignin depolymerisation to exploit the potential of lignin for biorefinery concepts.
Ključne besede: model compounds, hydrodeoxygenation, organosolv lignin, depolymerisation, structural characteristics, kinetic modelling, dissertations
Objavljeno v RUNG: 08.11.2024; Ogledov: 265; Prenosov: 3
Celotno besedilo (5,04 MB) |
3. Quantitative detection of Microcystis aeruginosa (cyanobacteria) in water using single domain antibodies (VHH) : dissertationGbenga Folorunsho Oginni, 2024, doktorska disertacija Opis: Microcystis aeruginosa accumulation in freshwater poses a significant threat to aquatic organisms and human health. The toxicity of Cyanobacteria metabolites urges for the development of methods for their rapid and efficient detection but what is still almost completely missing is the availability of reagents for the quantification of M. aeruginosa cells in water to monitor the fluctuations of its population. In this study, nanobodies against cell surface antigens of the toxic Cyanobacteria M. aeruginosa were recovered bywhole-cell panning of a naive phage display library. Six unique sequences were identified and three of them sub-cloned and purified as fusion immunoreagents together with either green fluorescent protein or Avi-Tag to be used for diagnostics. Theirspecificity and sensitivity were evaluated by immunofluorescence, by fluorescent and colorimetric cell ELISA and by thermal lens spectrometry (TLS). No cross-reactivity with unrelated microalgae was detected, and both ELISA and TLS methods provided a linear range of detection of several logs. The limit-of-detection of TLS was as low as 1 cell/ml.
Ključne besede: cyanobacteria, nanobodies, phage display, thermal lens spectrometry, dissertations
Objavljeno v RUNG: 10.09.2024; Ogledov: 564; Prenosov: 11
Celotno besedilo (3,80 MB) |
4. Green synthesis of Zeolitic Imidazolate Frameworks and their evaluation for ▫$CO_2$▫ capture in humid conditions : dissertationAljaž Škrjanc, 2024, doktorska disertacija Opis: Emissions of green-house gasses have been in the forefront of scientific research in recent decades. One of the approaches towards reducing the amount of green gas CO2 in the atmosphere is its capture and storage with subsequent conversion where pure enough CO2 can be regenerated. While CO2 capture widely utilizes two mature technologies, amine absorption and cryogenic distillation, they both have significant downsides, in either cost or potential new danger to the environment. To that end an adsorption-based CO2 capture has seen quite a lot of interest in recently. Nanoporous materials have been extensively studied for this application, starting with zeolites, followed by aluminophosphates and also the new members of the porous materials group, the so called reticular porous materials. Metal-Organic Frameworks (MOFs), the first discovered reticular porous materials have shown very promising results for post combustion CO2 capture and recently also for in-door and direct air capture. MOFs are in general enough thermally stable for CO2 capture, their main weakness for wide applicability is sometimes lower selectivity for CO2 in real gas mixtures and lower stability in humid conditions.
Zeolitic imidazolate frameworks (ZIFs), a subgroup of MOFs, have in recent years been extensively studied for sorption applications, also CO2, due to their superior stability and kinetics for vapour/gas adsorption if compared to carboxylate-based MOFs. While extensively studied, an overview of articles shows that most research is limited to a limited set group of frameworks, with ZIF-8 being used in more than half of ZIF papers. While ZIF-8 has successfully been prepared in water and even in solvent-free conditions, the rest of the ZIFs synthesis still heavily rely on solvothermal synthesis with formamide based solvent systems and synthesis times upwards of 5 days. Even in the case of ZIF-8, while greener synthesis approaches are available, dimethylformamide (DMF) synthesis still prevails in the cases tested for CO2 capture, mainly due to the increased CO2 uptake resulting from the synergistic contribution of the remaining DMF solvent in the pores.
The goal of this thesis was to develop green synthesis approaches, both solvothermal and mechanochemical, for known ZIFs and then to extend the scope towards preparation of new ZIF materials. The goal for latter was to experimentally determine the optimal topology and functionality of ZIFs for CO2 adsorption in humid conditions. Model humid gas isotherms were developed and measured for a series of ZIFs with mostly SOD (sodalite) and RHO framework topologies and Zn and Ni as metal nodes. Finally, some novel bio-based binder materials were tested for the use with ZIFs.
The sorption tests revealed than the SOD topology ZIFs have high potential for CO2 sorption applications, as the adsorption is rapid and further combination of terminally functionalised imidazoles in those frameworks drastically increases the frameworks affinity for CO2 at lower pressures. With most common 4,5- functionalised imidazole having hydrophilic functional groups, the challenge of competitive water sorption still remains. On the other hand some hydrophobic 4,5-substituted sodalite ZIFs, both with 4,5-dichloroimidazole, show excellent CO2 sorption and even complete hydrophobicity. The results led us to hypothesize that further research on ZIFs- for CO2 capture has to shift form 2 substituted sodalite frameworks to 4,5 substituted frameworks with strongly dipolar hydrophobic groups. The hydrophilic polar groups currently in use lead to issues with competitive water adsorption, due to their potential to form hydrogen bonds with water. Furthermore, some new agar and alginate based shaping methods were tested, as both potential binders are not environmentally toxic and are already used on the industrial scale world-wide for other applications.
Ključne besede: carbon capture, synthesis, metal-organic frameworks, zeolitic imidazolate frameworks, nanoporous materials, dissertations
Objavljeno v RUNG: 10.09.2024; Ogledov: 686; Prenosov: 21
Celotno besedilo (15,56 MB) |
5. Detection of gamma-ray sources and search for dark matter signals with Cherenkov Telescope Array surveys : dissertationVeronika Vodeb, 2024, doktorska disertacija Opis: Gamma rays serve as important messengers in modern astrophysics, offering insights into the most energetic processes in the cosmos. Advancements in gamma-ray astronomy, facilitated by international scientific collaboration, have expanded its reach and capabilities. The Fermi-Large Area Telescope (Fermi-LAT) has so far contributed immensely to our understanding of the gamma-ray sky at GeV energies, surveying numerous source classes. At the same time, ground-based observatories like H.E.S.S., MAGIC, VERITAS, HAWC, and LHASSO, enable the exploration of high-energy (HE) phenomena across various energy scales, reaching the PeV range. The collective data from Fermi-LAT and ground-based instruments provide a comprehensive picture of cosmic phenomena across diverse energy regimes. Efforts to catalog HE gamma-ray sources have resulted in the detection of several thousand sources at GeV, including Pulsar Wind Nebulae (PWNe), Supernova Remnants (SNRs), pulsars, blazars, and Gamma-Ray Bursts (GRBs), with the observational capability to study their spectral and spatial morphology enhancing our understanding of their origin and evolution.
Looking ahead, the Cherenkov Telescope Array (CTA) represents the next frontier in ground-based gamma-ray astronomy. Operating at very high energies (VHE) between 20 GeV and 300 TeV, CTA's improved sensitivity, angular resolution, and expanded field of view (FoV) promise enhanced imaging of extended sources and performance of large-scale surveys. CTA's Key Science Projects (KSPs) include the Extragalactic (EGAL) survey, a survey of a quarter of the extragalactic sky, and the Galactic Plane Survey (GPS), a survey of the entire Galactic Plane (GP). The KSPs will receive dedicated observation time and careful planning to ensure the optimization of their scientific output. As CTA is currently entering the construction phase, simulations are being extensively employed to predict its response to various signals, playing a vital role in comprehending CTA's response and sensitivity to different signals. The derived predictions are paving the way for estimating the CTA's scientific output, informing the observational strategy, and ensuring its success in maximizing the contribution to HE gamma-ray astronomy.
In this thesis, I contribute to assessing the sensitivity of the CTA surveys, particularly the GPS and the EGAL survey, to diverse astrophysical sources and signals. Focusing on the GPS, I delve into understanding the detectability of pulsar halos, which emit multi-TeV gamma rays, the detection of which was recently reported by the HAWC Observatory. The study involves a spatial-spectral likelihood analysis, evaluating sensitivity to simple Gaussian extended sources and physically modeled sources. Employing a template-fitting approach, I analyze CTA's GPS sensitivity to extended sources and explore the prospects for pulsar halo detection and characterization. A preliminary population study addresses the visibility of pulsar halos to CTA's GPS and explores the angular sensitivity to extended sources. The thesis sets the detectability prospects of pulsar halos with CTA and investigates what fraction of the preliminary pulsar halo population CTA will be able to probe.
The thesis extends its exploration into the persistent mystery of dark matter (DM), a fundamental puzzle in cosmology. The search for DM signals remains a vigorous pursuit in the physics community, utilizing various astrophysical messengers resulting from DM particle annihilation or decay. I investigate the potential of CTA's GPS to detect dark sub-halos within our galaxy, utilizing a similar approach as in the sensitivity assessment to pulsar halos, applied to recent sub-halo population simulations. Furthermore, the thesis addresses the intricate task of disentangling DM components from astrophysical contributions in the observed gamma-ray sky. In terms of the EGAL survey, employing advanced statistical methods such as the cross-correlation technique, I explore the prospects of using CTA's EGAL survey to correlate the Extragalactic Gamma-ray Background (EGRB) with galaxy catalogs, providing insights into DM properties.
While traditional methods rely on likelihood analysis with background subtraction or template fitting, the emergence of supervised machine learning (ML) offers a novel, potentially more effective approach for cataloging the sky. The thesis touches upon the usability of ML in the high and VHE gamma-ray sky. My study focuses on CTA's GPS and utilizes deep-learning-based algorithms in a detection pipeline for the automatic classification of extended sources from gamma-ray data.
As CTA stands at the forefront of gamma-ray astronomy as the next-generation observatory, the research presented in this thesis contributes a small step towards answering the open questions about pulsar halos and DM, showcasing the potential breakthroughs that may emerge from CTA's observations. The detailed likelihood analysis performed aims to advance our understanding of these enigmas, from the physical intricacies of pulsar halos to the elusive nature of DM, driven by curiosity about the continuous exploration of the Universe's mysteries.
Ključne besede: high-energy gamma-ray astronomy, astroparticle physics, Cherenkov Telescope Array, pulsar halos, dark matter, dissertations
Objavljeno v RUNG: 06.06.2024; Ogledov: 975; Prenosov: 11
Celotno besedilo (36,25 MB) |
6. Degradation of microplastics in the environment : dissertationVaibhav Budhiraja, 2024, doktorska disertacija Opis: Plastics are based on organic polymers that are sensitive to the environment in which they find themselves and will gradually decay through a variety of chemical reactions. This process is of great importance for the transformation and persistence of microplastics (MPs) that pollute the environment. The rate of degradation depends on two major factors: Firstly, the intrinsic properties of the polymers, such as chemical structure, molecular weight, crystallinity and the presence of additives, fillers or reinforcement and secondly, the environment to which they are exposed. The degradation rate of plastic will vary in different environmental matrices like soil, freshwater, seawater, wastewater, land etc., as well as in diverse environmental conditions like UV radiation, temperature, humidity, the effect of pollutants etc. Plastic mainly undergoes two fundamental reactions: oxidation and hydrolysis and the chemical structure of the polymer and its additives plays a key role in the degradation mechanism of plastic. Polyolefins having a carbon-only main chain are resistant to hydrolysis but susceptible to oxidation, whereas polyesters and polyamides containing heteroatoms are sensitive to hydrolysis and much more resistant to oxidation.
In the context of the present work, five different studies were done involving both naturally degraded plastic and accelerated weathering of plastics in the form of small particles, MPs. In the first study, natural degraded polyethylene (PE) and polypropylene (PP) samples with a life span of more than forty years were collected from the environment and their physiochemical properties were analysed. The results show that red coloured PE samples were more degraded as compared to blue coloured samples, indicating that pigment plays a key role in the degradation. The PP sample shows extreme surface degradation, leading to fragmentation and the generation of MPs. In the second study, the effect of hydrodynamic cavitation on MPs in waste water treatment plant sludge was evaluated. PE, PP, polyethylene terephthalate and polyamide were extracted from the sludge. It was found that hydrodynamic cavitation does not disintegrate the MPs, although it removes some toxic metals and shows cell disruption mechanisms.
Other studies were done with accelerated weathered MPs, which include PE, PP and tire wear particles (TWP), that were treated in accordance with an ISO 4892 standard weathering procedure that mimics natural weathered conditions. In the third study, we used weathered PE films to evaluate the synergistic adsorption behaviour of two pollutants, namely triclosan (TCS) and methylparaben (MeP). It was found that weathered MPs adsorb more pollutants and the adsorption behaviour of TCS is enhanced in the presence of MeP. In the fourth study, the magnetic extraction of pristine and weathered PE and TWP particles was performed. The results confirmed that the magnetic
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extraction of weathered MPs is difficult as compared to pristine MPs as their surface becomes more hydrophilic with weathering. In the fifth study, the effect of weathering on the density of PE and PP was evaluated. We found that weathering enhances the density of polyolefins, which is one of the main reasons for the observed sinking of polyolefin MPs in water.
Ključne besede: accelerated weathering, aging, density, magnetic separation, pigment, plastic degradation, pollutants, polyethylene, polyolefin, polypropylene, sinking, tire wear particles, dissertations
Objavljeno v RUNG: 04.06.2024; Ogledov: 1264; Prenosov: 0
Celotno besedilo (7,35 MB) |
7. Strategy for rural heritage regeneration in China : integrating community and government in governance: a case study of traditional villages in Luoning county :Wendi Wang, 2024, doktorska disertacija Opis: The Chinese countryside has long been associated with cultural continuity, albeit in contradictory ways. It has been marginalized for several decades, while all development efforts have focused on urbanization. However, as the tensions and paradoxes of modern urban life become increasingly obvious, the countryside is once again recognized as an enduring symbol of authentic national values. Chinese traditional cultural heritage is rooted in Chinese traditional villages. In fact, being built before the coming of the Republic of China, those villages nowadays still possess a great deal of very important material and immaterial forms of cultural heritage, as a historical record of the Chinese nation development.
Through the examination and study of traditional villages in Luoning, and the perspective of theories of architectural conservation theory, community co-construction, and private-public partnership, the dissertation proposes a hybrid county governance model to maximize the stakeholder's functions roles, and operational procedures in the preservation and development of the traditional villages. Thus, through the integration of three stability perspectives—cultural, economic, and social —the dissertation provides the government's optimization strategy for heritage preservation.
In the first case study, the governance of Zhangzhuang's traditional village is examined. The village's residents share responsibility for one another and are frequently connected by strong family ties and regular community organization in decision-making. Unfortunately, this thriving community-led government is insufficiently prepared to deal with the expanding tourism industry, it fails when it comes to overarching development objectives, and it lacks substantial experience in the preservation of historic structures.
The Second case study investigates the government-led traditional types of villages. These are characterized by low public and community participation, and underdeveloped commodity economies, but being usually of outstanding importance, they result rich in traditional material and intangible cultural resources and have great potential for developing a tourism sector. Government-led efforts to reactivate the development of these villages have the advantages of credibility and authority, preferential policy formulation, and government short-term funding. However, these villages face severe problems in terms of community involvement, complementary market economies, and insufficient long-term government funding. This condition is investigated in the second case of the government's conception and promotion of the "Hou Shangzhuang Village Traditional Village Restoration" project. Despite some initial success, the project came to a standstill due to the competing interests of businesses, the government, and the community.
The third case study looks into traditional villages where the primary development component is driven by businesses, creating conditions for the growth of a market economy. The analysis demonstrates that enterprise investments benefit from complementary capital input, resource integration, and effective management. However, the issue of uneven income and benefit distribution, as well as excessive consumption of public resources, pose a serious threat to both: the authenticity and integrity of cultural heritage, as well as the fair and sustainable development of local communities. This situation is examined in the case study of Qianhe Village, where the tourism industry has grown through multiple investment operations by private enterprises.
The dissertation examines diverse hybrid governance models for each of these three different cultural, social, and economic heritage contexts. In specific it points to the role of government to efficiently design, validate, and promote responsive solutions for the resilience of cultural heritage of traditional villages in China.
Ključne besede: Heritage, Traditional Chinese village preservation, planning and management, Government, Governance, Participation, Community Co-construction
Objavljeno v RUNG: 11.03.2024; Ogledov: 1547; Prenosov: 27
Celotno besedilo (9,17 MB) |
8. Morphological dependencies : a dissertationGuy Tabachnick, 2023, doktorska disertacija Opis: This dissertation investigates morphological dependencies: correlations between two lexically specific patterns, such as selection of inflectional affixes. Previous work has established that such correlations exist in the lexicon of morphologically rich languages (Ackerman et al., 2009; Wurzel, 1989), but has not systematically tested whether speakers productively extend these patterns to novel words. I present a series of corpus and nonce word studies—in Hungarian, Czech, and Russian—testing whether speakers vary their selection of suffixed forms of novel words based on the forms of that word that are presented to them. In all three cases, speakers vary their responses in accordance with the provided stimuli, demonstrating that they have learned and productively apply morphological dependencies from the lexicon.
I present a theoretical account of morphological dependencies that can account for my experimental results, based on the sublexicon model of phonological learning (Allen & Becker, 2015; Becker & Gouskova, 2016; Gouskova et al., 2015). In this model, speakers index lexically specific behavior with diacritic features attached to underlying forms in lexical entries, and learn generalizations over sublexicons defined as words that share a feature. These generalizations are stored as constraints in phonotactic grammars for each sublexicon, enabling speakers to learn phonological and morphological dependencies predicting words that pattern together. This model provides a unified treatment of morphological dependencies and generalizations that are phonological in nature. My studies show a wide range of learned effects, not limited to those that follow an organizational principle like paradigm uniformity. The sublexicon model assumes that speakers can learn arbitrary generalizations without restrictions, giving it needed flexibility over more restrictive models which rely on notions of morphophonological naturalness.
Ključne besede: inflectional affixes, nonce word study, lexical productivity, morphological dependencies, diacritic features, dissertations
Objavljeno v RUNG: 04.03.2024; Ogledov: 1352; Prenosov: 10
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