Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Effect of Sulfur on the Elementary Reactions of Fischer-Tropsch Synthesis on Cobalt Surfaces(Izmir Institute of Technology, 2020) Dağa, Yağmur; Kızılkaya, Ali CanIndustrial observations indicate that sulfur acts a poison for Fischer-Tropsch Synthesis (FTS) and surface science studies show that sulfur blocks the adsorption sites for reactants on cobalt surfaces. However, various experimental studies have indicated conflicting results about the effect of sulfur on cobalt FTS catalyst activity and selectivity. This study aims to clarify the effect of sulfur on cobalt FTS catalysts by molecular modelling of the elementary reactions of FTS on surfaces that are present on sulfur covered cobalt surfaces that are present in fcc-Co nanoparticles, using Density Functional Theory (DFT). For 0.25 ML sulfur coverage, it is found that on bare, C and O covered surfaces, S is the main dissociation product, while HS can be present on low coverages. Atomic sulfur decreases the adsorption energies of all species investigated, while the decrease is more pronounced for CO compared to H2. The effect of S on the elementary FTS reactions direct and H-assisted CO dissociation, carbon hydrogenation, carbon coupling and oxygen removal are also investigated. The results indicate that S inhibits mainly the oxygen removal reaction, in terms of both H2O and CO2. CO dissociation is not inhibited but rather slowed down, due to increasing activation barriers. It is also found that carbon hydrogenation barriers are significantly decreased, while carbon coupling barriers are unaffected. These results indicate that the intrinsic effect of sulfur poisoning would be to increase methane selectivity, while decreasing the selectivity to long chain hydrocarbons.Master Thesis Palladium Catalyzed Cross Coupling Reactions of Alkenyl Epoxides and Organoboronic Acid Esters(Izmir Institute of Technology, 2018) Eren, Ahmet; Artok, LeventIn organic chemistry, it is a useful method to form a new allylic compounds as a result of 1-3 substitution reactions of allylic compounds which have a good leaving group. These reactions usually require a metal catalyst but one of the most challenging aspects of these applications is the process regio and stereo selectivity for a wide variety of substrate types. Other compounds such as alkenyl epoxides are also useful for 1-3 substitution reactions. An advantage of using alkenyl oxirane compounds is that the oxirane ring is opened in the substitution step to form a hydroxyl group and resulted in the formation of allylic alcohols which are important intermediate product. Metal catalysed and regioselective reactions of terminal alkenyl epoxides with organoborons have been reported in the literature. However, there is no successful method for internal alkenyl oxiranes. Thus, in this study, 1-3 substitution reactions of alkenyl oxiranes were successfully applied, which yielded allylic alcohols with high regio- and stereoselectivity.