| 1. |
- Sauer, Christopher, 1993
(författare)
-
Green Aromatics: Catalytic Valorisation of bio-derived 2,5-dimethylfuran over Zeolites and Zeotypes
- 2022
-
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.
|
|
| 2. |
- Shwan, Soran, 1984
(författare)
-
Metal-exchanged zeolites for NH3-SCR applications - Activity and Deactivation studies
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emissions of nitrogen oxides (NOX) formed during the burning process in internal combustion engines is a major contributor to global air pollutions. One effective way to reduce NOX in lean environments, i.e. oxygen excess is selective catalytic reduction with ammonia (NH3-SCR). Metal-exchanged zeolites have proven to be active as SCR catalysts, where copper and iron are the most common metals. When using metal-exchanged zeolites in exhaust aftertreatment systems, several challenges arise. Resistance towards hydrothermal deactivation and chemisorption of impurities on the active sites of the catalyst are two of the more important challenges. Temperatures between 600-700oC can be seen during regeneration of the particulate filter, which usually is placed upstream close to the SCR catalyst in the exhaust aftertreatment system, and therefore hydrothermal stability of the metal-exchanged zeolite is crucial. Furthermore, high tolerance against catalyst poisons which originate from (bio-) fuels and lubricating oils is desired, where phosphorous and potassium are among the more important poisons. In this thesis thermal and chemical deactivation of iron-exchanged zeolite BEA as SCR catalyst is experimentally studied with special focus paid on the active iron species. Based on the experimental results a kinetic model is developed to predict the decreased activity of the catalyst after deactivation. Several characterization techniques are used to evaluate and correlate structural changes in the catalyst with the decreased activity. Catalysts are prepared and characterized using BET, XPS, XRD, TPD, in-situ FTIR and UV-Vis. The catalytic performance of the samples is measured using a flow-reactor system.It is concluded that the hydrothermal deactivation of Fe-BEA is a result of migration of isolated iron species forming iron cluster inside the zeolite pores and iron particles located on the external surface of the zeolite crystals. Further, it is shown that the growth of iron clusters and particles can be partially reversed by high temperature hydrogen treatment. The chemical deactivation due to phosphorous exposure is the result of formation of metaphosphates replacing hydroxyl groups on the active isolated iron species. Furthermore, the chemical deactivation of Fe-BEA by potassium is concluded to be due to exchange and loss of active isolated iron species in the zeolite forming smaller iron clusters inside the zeolite pores.A kinetic model where different iron species are included was developed based on the hydrothermal deactivation experiments and validated using phosphorous and potassium exposed samples. By fitting and fix the kinetic parameters towards a fresh sample, the decreased SCR activity can be predicted by just decreasing the number of active iron sites, representing loss of active iron species due to hydrothermal treatment and poisoning.The effect of gas atmosphere during solid-state ion-exchange of copper-zeolites was studied as well. It is concluded that copper becomes highly mobile due to formation of copper-ammine complexes in presence of NH3 after reduction of CuII to CuI by adding NO in the exposing gas during the solid-state ion-exchange. Copper-exchanged zeolites could be prepared by exposing physical mixtures of copper-oxides with zeolites to NO and NH3 at as low temperature as 250oC.Finally, the ammonia formation during the rich period of NOX storage and reduction (NSR) cycles was studied using kinetic modeling for the possibility of combining NSR and SCR catalysts in the exhaust aftertreatment system. It is concluded that the formation of ammonia is due to stored NOX and hydrogen from the gas in the first half of the catalyst. However, it was further concluded that the formation of ammonia is delayed due to formation of N2O from stored NOX and formed NH3.
|
|
| 3. |
- Halldin Stenlid, Joakim, 1987-
(författare)
-
Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
- 2017
-
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.
|
|
| 4. |
- Karlsson, Rasmus, 1987-
(författare)
-
Theoretical and Experimental Studies of Electrode and Electrolyte Processes in Industrial Electrosynthesis
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heterogeneous electrocatalysis is the usage of solid materials to decrease the amount of energy needed to produce chemicals using electricity. It is of core importance for modern life, as it enables production of chemicals, such as chlorine gas and sodium chlorate, needed for e.g. materials and pharmaceuticals production. Furthermore, as the need to make a transition to usage of renewable energy sources is growing, the importance for electrocatalysis used for electrolytic production of clean fuels, such as hydrogen, is rising. In this thesis, work aimed at understanding and improving electrocatalysts used for these purposes is presented.A main part of the work has been focused on the selectivity between chlorine gas, or sodium chlorate formation, and parasitic oxygen evolution. An activation of anode surface Ti cations by nearby Ru cations is suggested as a reason for the high chlorine selectivity of the “dimensionally stable anode” (DSA), the standard anode used in industrial chlorine and sodium chlorate production. Furthermore, theoretical methods have been used to screen for dopants that can be used to improve the activity and selectivity of DSA, and several promising candidates have been found. Moreover, the connection between the rate of chlorate formation and the rate of parasitic oxygen evolution, as well as the possible catalytic effects of electrolyte contaminants on parasitic oxygen evolution in the chlorate process, have been studied experimentally.Additionally, the properties of a Co-doped DSA have been studied, and it is found that the doping makes the electrode more active for hydrogen evolution. Finally, the hydrogen evolution reaction on both RuO2 and the noble-metal-free electrocatalyst material MoS2 has been studied using a combination of experimental and theoretically calculated X-ray photoelectron chemical shifts. In this way, insight into structural changes accompanying hydrogen evolution on these materials is obtained.
|
|
| 5. |
- van den Bossche, Maxime, 1989
(författare)
-
Methane oxidation over palladium oxide. From electronic structure to catalytic conversion
- 2017
-
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.
|
|
| 6. |
- Wojas, Natalia
(författare)
-
The dynamic surface nature of calcite and its role in determining the adsorptive stability toward hydrophobizing carboxylic fatty acids
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calcium carbonate has attracted a lot of interest over the centuries. Nowadays, mainly as mineral pigment and filler, it has a wide use in technological applications ranging from paper, construction, polymers, and environmental solutions to consumer goods. Amongst these uses, the filler pigment is required to display either hydrophilicity (for applications in aqueous colloidal systems, including, for example, in paper and emulsion paints), or, in contrast, oleophilicity (for applications in contact with oil-based systems, such as plastics and volatile solvent-containing sealants). To achieve oleophilicity, and resulting hydrophobicity, the filler is surface treated, typically using carboxylic fatty acids. In this thesis, effects of humidity and fatty carboxylic acids vapor on CaCO3 surface wettability and nanomechanical properties were studied, with the aim to gain knowledge on layer packing density and order, as well as resistance to water exposure and mechanical wear. A better understanding of the dynamic nature of the calcite surface presented in this work allows the industry to increase sustainable control over materials production and storage. First, a setup combining an atomic force microscope (AFM) with a humidifier was used to map nanomechanical properties of growing surface domains (hydrated form of CaCO3) formed by ion dissolution, diffusion, and redeposition, a process that is not reversible upon drying. Secondly, AFM and contact angle goniometer measurements showed that the stability of the calcite surface improves with increasing carboxylic acid chain length (C2 to C18). Meanwhile, X-ray photoelectron spectroscopy and vibrational sum frequency spectroscopy techniques demonstrated that a coherent layer with maximum packing density of carboxylate and carboxylic acid species was achieved with the use of stearic acid (C18) with high enough vapor pressure and exposure time. The AFM images successfully visualized that a complete C18 monolayer is capable of countering nano-wear of the calcite surface despite the humidity (under the range of loads investigated in this work) and the layer has self-healing properties, while calcite displayed high abrasive wear. Further, when calcite coated by a highly packed monolayer of C18 was covered with a water droplet, a large contact angle hysteresis resulted in a coffee ring effect (CRE). That is leading to formation of hillocks at the contact line consisting of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules transported from the bare calcite region that also is created next to the droplet edge. Interestingly, C18 coated calcite remained considerably more stable in the case where a water droplet saturated with octanoic acid was used instead of water; thus, it was concluded that the CRE can be contained via reduction of the liquid surface tension and contact angle hysteresis.
|
|
| 7. |
- Andersson, John, 1993
(författare)
-
Functional polymer brush coatings for nanoscale devices
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanobiotechnology is an interdisciplinary field that has garnered considerable attention for offering exciting new opportunities of studying and manipulating biomolecules at the nanoscale. This prospect bears large potential benefits in the field of medicine and the whole life science sector in general. Fabrication of different nanostructure devices that can handle liquids at the scale of biomolecules, such as nanochannels or nanopores, provide a good basis within nanobiotechnology. However, the materials of nanostructures tend to not interact with complex biomolecules in ways that are sufficiently specific or controlled. This issue can be avoided by functionalising the surface of nanostructures with different organic coatings, and polymer brushes have shown a diverse range of functionality in this regard. This thesis summarises efforts towards designing functional polymer brush coatings for nanoscale devices. Surface sensitive techniques are used to characterise the grafting of dense poly(ethylene glycol) brushes to various noble metals and silicon dioxide. The new functionalisation protocol for polymer brushes on silicon dioxide provides excellent biofunctionality and is demonstrated to be compatible with two different nanostructures. The specific hydrogen-bond mediated interaction between a poly(ethylene glycol) brush and poly(methacrylic acid) in solution at low pH is shown to make the polymer brush reversibly stimuli-responsive. Preliminary results further demonstrate how this interaction can be controlled electrochemically and indicates its suitability as a macromolecular gating mechanism for nanosized openings. Finally, characterisation and fabrication of plasmonic nanopore arrays with separately functionalisable compartments using electron beam lithography techniques is presented.
|
|
| 8. |
- White, Jai, 1991-
(författare)
-
From Facets to Flow: The Electrooxidation of Glycerol on Pd-based catalysts
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glycerol, a by-product of biodiesel refineries, has uses in industries such as cosmetics, food, and pharmaceuticals. However, its usage is small compared to the amount of glycerol produced from biodiesel production. Therefore, there is an opportunity to use glycerol, an important platform chemical, as a cheap feedstock for the synthesis of valuable chemicals. These chemicals can be formed in aqueous media through the glycerol electrooxidation reaction (GEOR) on the anode with hydrogen gas concurrently generated on the cathode. This thesis focuses on the GEOR in alkaline media on Pd and PdNi catalysts. The works compiled here evaluate the GEOR using electrochemical methods such as cyclic voltammetry, galvanostatic polarisation curves, chronoamperometry and chronopotentiometry. Pd and PdNi catalysts were fabricated through chemical synthesis, and electrodeposition onto Ni substrates. Singularly oriented Pd crystal facets were studied, showing those approximating Pd (111) as the most active. Similarly faceted bimetallic PdNi nanoparticles proved significantly more active than pure Pd. Effects of mass transport, studied for Pd/NiRDE and PdNi/NiRDE, indicated performance effects linked to diffusion and underutilisation of thicker catalyst layers. In aerated solutions, industrially relevant current densities were achieved on PdNi/Nifoam in concentrated electrolytes at elevated temperatures for extended periods. The analysis of glycerol oxidation products, formed during steady state measurements, was done using high performance liquid chromatography. The two major products were consistently shown to be glycerate and lactate. This work, covering many aspects of the GEOR, shows that Pd-based catalysts have potential for future industrial application.
|
|
| 9. |
- Chen, Si, 1985
(författare)
-
Miniaturized localized surface plasmon resonance biosensors
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abstract Reliable and sensitive biosensors are required for fast and accurate diagnostics. Localized surface plasmon resonances (LSPRs) in noble-metal nanoparticles possess very high refractive index sensitivity close to the metal surface and therefore constitute an attractive biosensing platform. In this thesis, label-free biosensing with LSPR was investigated and demonstrated. The spatial sensing ranges of the particles were determined by thin layer deposition of dielectric materials. A comparison between the classical SPR and LSPR was performed using the same experimental setup. No obvious performance difference between the two sensing techniques was found. The versatility of the LSPR sensing technique was demonstrated by miniaturization of the sensor area, which could be reduced down to ~250 nanoparticles without compromising the short-term noise level. To further miniaturize the LSPR sensor, multiple single nanoparticles were measured using hyperspectral imaging. It was shown that by combining LSPR refractive index sensing and an enzyme linked immunoassay (ELISA), i.e. a horseradish peroxidase catalyzed precipitation, an extremely low surface coverage of enzyme molecules could be detected on single isolated nanoparticles. In a follow up investigation, electron beam lithography (EBL) and hyperspectral imaging were combined to enable simultaneous measurements of up to 700 individual particles. This made it possible to study statistical variations between the sensor particles. The observed variations in the responses from individual particles were interpreted as a result of large variations in sensitivity over the particle surface combined with the size distribution of the precipitate. In a separate study, a photo functionalization strategy compatible with LSPR biosensors was investigated. A biotin moiety was successfully functionalized with UV light on a self-assembled monolayer of photoactive nitroindoline on gold surfaces. Adsorption of streptavidin and streptavidin conjugated HRP to the surface-bound biotin could be monitored by the LSPR sensor. This strategy might be utilized for spatially localized surface functionalization for multiplexed miniaturized LSPR sensors. In summary, despite many experimental problems, the results discussed in this thesis point towards a number of important biosensing applications of plasmonic nanoparticles.
|
|
| 10. |
- Asfaw, Habtom Desta
(författare)
-
Multifunctional Carbon Foams by Emulsion Templating : Synthesis, Microstructure, and 3D Li-ion Microbatteries
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon foams are among the existing electrode designs proposed for use in 3D Li-ion microbatteries. For such electrodes to find applications in practical microbatteries, however, their void sizes, specific surface areas and pore volumes need be optimized. This thesis concerns the synthesis of highly porous carbon foams and their multifunctional applications in 3D microbatteries. The carbon foams are derived from polymers that are obtained by polymerizing high internal phase water-in-oil emulsions (HIPEs).In general, the carbonization of the sulfonated polymers yielded hierarchically porous structures with void sizes ranging from 2 to 35 µm and a BET specific surface area as high as 630 m2 g-1. Thermogravimetric and spectroscopic evidence indicated that the sulfonic acid groups, introduced during sulfonation, transformed above 250 oC to thioether (-C-S-) crosslinks which were responsible for the thermal stability and charring tendency of the polymer precursors. Depending on the preparation of the HIPEs, the specific surface areas and void-size distributions were observed to vary considerably. In addition, the pyrolysis temperature could also affect the microstructures, the degree of graphitization, and the surface chemistry of the carbon foams.Various potential applications were explored for the bespoke carbon foams. First, their use as freestanding active materials in 3D microbatteries was studied. The carbon foams obtained at 700 to 1500 oC suffered from significant irreversible capacity loss during the initial discharge. In an effort to alleviate this drawback, the pyrolysis temperature was raised to 2200 oC. The resulting carbon foams were observed to deliver high, stable areal capacities over several cycles. Secondly, the possibility of using these structures as 3D current collectors for various active materials was investigated in-depth. As a proof-of-concept demonstration, positive active materials like polyaniline and LiFePO4 were deposited on the 3D architectures by means of electrodeposition and sol-gel approach, respectively. In both cases, the composite electrodes exhibited reasonably high cyclability and rate performance at different current densities. The syntheses of niobium and molybdenum oxides and their potential application as electrodes in microbatteries were also studied. In such applications, the carbon foams served dual purposes as 3D scaffolds and as reducing reactants in the carbothermal reduction process. Finally, a facile method of coating carbon substrates with oxide nanosheets was developed. The approach involved the exfoliation of crystalline VO2 to prepare dispersions of hydrated V2O5, which were subsequently cast onto CNT paper to form oxide films of different thicknesses.
|
|
