Browsing by Subject "catalysis"
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(2021)Plasmonic catalysis utilises light energy to drive chemical reactions. Compared to conventional catalytic processes, which are run by high temperatures and pressures, light-driven processes can lower energy consumption and increase selectivity. Conventional plasmonic nanoparticles (Ag, Au) are relatively scarce and expensive, and therefore the use of materials with earth-abundant elements in plasmonic catalysis is widely pursued. Despite their good optical properties, plasmonic nanoparticles are often unsuitable catalysts. Hybrid catalysts, structures consisting of a light-harvesting plasmonic part and a catalytical centre of different material, have emerged as an opportunity to address these challenges and obtain desired properties. This thesis consists of two parts: In the first part, properties of plasmonic materials are described, and previous studies of hybrid catalysts with earth-abundant plasmonic materials are reviewed. Experimental work on plasmonic-catalytic nanohybrids, with TiN as the plasmonic part and Pd as the catalytic entity, is described in the second part. In this context, a Pd/TiN (Pd nanoparticles supported into TiN) catalyst was synthesised, characterised and applied to test catalytical reactions. Contrary to the hypothesis, light-induced rate enhancement was not observed in our current catalytical studies. These results call for further optimisation of synthesis and reaction conditions to prepare an earth-abundant, light-active catalyst.
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(2024)The development of active, stable, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is paramount for the large-scale deployment of hydrogen based clean energy technologies. Despite its apparent simplicity, the HER serves as a bridge between fundamental electrocatalysis research and practical catalyst design. Water splitting, a highly efficient and environmentally friendly method for hydrogen production, necessitates a stable, active, and abundant catalysts. While platinum (Pt)-based materials reign supreme in acidic electrolytes for their exceptional HER efficiency and durability, their scarcity and high-cost limit their widespread application. This study introduces a strategy to decrease the Pt loading in the catalyst by developing nanoparticles containing an ultralow Pt loading supported on tungsten oxide (W18O49). Remarkably, the activity of this developed system approaches that of commercially available 20% (wt.) Pt/C catalysts, even with a noble metal content of less than 2 wt.%. Notably, the optimal sample, Pt1.6/W18O49 (containing 1.6 wt.% Pt), demonstrates a superior Tafel slope and requires a mere 46 mV overpotential to achieve a current density of 10 mA cm-2. This work suggests that catalyst design and controlled synthesis can promote the HER and facilitate faster electron transfer even at low Pt loadings. This system exhibits exceptional stability, maintaining its performance for over 24 hours without significant degradation. This synergistic approach, employing minimal Pt supported on a W18O49 matrix, paves the way for addressing real-world challenges in hydrogen production.
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(2022)The opening segments give a summary of the history of catalysis in general and of frustrated Lewis pairs in particular, where both intra- and intermolecular types are discussed. In addition, the essences of the mechanisms of action of frustrated Lewis pairs are discussed, covering electric field, electron transfer and radical-type mechanisms. There is also a discussion on the activity of frustrated Lewis pairs towards dehydrogenation reactions, in which lies the main scope of this thesis. The background and intended parameters of the experimental aspects of this work are initially defined in the thesis scope, along with the practical considerations concerning the reagents, equipment, and special conditions for synthetic procedures also detailed here. The intention was to attempt to elucidate the extent of the impact of different factors, in this case solvent, Lewis acidity, Lewis basicity, and irradiation by blue LED, on dehydrogenation of various N-substituted pyrrolidine substrates. The subsequent section describes the synthetic procedures used for attempted syntheses of the amino-borane ligands. Not all syntheses of the desired ligands were successful, but there was enough success and enough pre-generated material to proceed to the next stage. Due to use of blue LED causing various potential radical side reactions, it was thought appropriate to describe the behaviour of both the sample and substrate blanks under irradiation, as well as the intended reactions during the screening process. Screening provided preliminary data on reaction determining factors, such as solvent, Lewis acidity of the catalyst, and substrate structure. Despite the relative difficulty and time-consuming nature of the catalyst syntheses, some interesting new modes of reactivity appear to be accessible, which may be worth investigating more in the future.
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(2023)Catechol is widely produced platform chemical, and many fine chemicals, including pharmaceuticals and pesticides, contain catechol moieties. Catechols are nucleophilic, but their polarity can be reversed by oxidizing them into electrophilic o-benzoquinones (OBQs). OBQs are highly reactive and react readily with nucleophiles but also with dienes, dienophiles and ylides. However, OBQs have many reactive sites, which often leads to lack of selectivity in reactions. In the literature review of this thesis, the methods to control selectivity in nucleophilic additions, cycloadditions and Wittig reactions of OBQs are reviewed. Selectivity is often increased by blocking undesired reactive sites by substituents. If substituents can’t be altered, it is possible to control selectivity by choice of catalysts and substrates as well as stoichiometric ratios of substrates. In addition, the literature review will also focus on how the use of o-benzoquinones have been utilized in organic synthesis. In the experimental part, nucleophilic additions of amino acids and silyl enol ethers to o-benzoquinones are studied in practice. Reactions of amino acids with OBQs resulted only in polymerization despite the efforts to control the selectivity. However, ZnCl2 catalysed addition of silyl enol ethers into OBQs yielded only 1,4-addition products. The method was then optimized with two model reactions after which 30 different 1,4-addition products were successfully synthesized. For most of these products this method is the only proven synthesis route.
Now showing items 1-4 of 4