Master Degree / Yüksek Lisans Tezleri

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Access Right: Open AccessSubject: search.filters.subject.Manganese

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  • Master Thesis
    Effects of Oxygenation in Stratified Reservoirs on Concetrations of Manganese and Iron in Bottom Sediments
    (Izmir Institute of Technology, 2019) Vural Aydın, Buse; Elçi, Şebnem; Ökten, Hatice Eser
    Iron and manganese accumulation in drinking water reservoirs is a challenging issue and should be controlled in order to prevent their adverse effects on human health. Accumulation of these elements not only clogs pipeline systems but also causes stains on fixtures and laundry. In addition, high concentrations of iron and manganese may lead to various health problems when ingested. This study focuses on the release mechanism of iron and manganese from sediments to water column and investigates methods to prevent this release. Effects of lack of hypolimnetic aeration, acid-base condition and thermal stratification on iron and manganese concentrations at water column were investigated through laboratory experiments. Experiments showed that total iron (Fe) and ferrous iron (Fe2+) concentrations in the water column decreased gradually following aeration in hypoxia conditions. A similar behavior was also observed for manganese concentrations. However, the concentration of dissolved manganese (Mn) in alkaline water condition is observed to be less than the aerated water case. This is an indication that iron and manganese react differently under different acidity of water in consideration.
  • Master Thesis
    Effects of Manganese Promotion on Reactants and Intermediates of Fischer Tropsch Synthesis on a Model Cobalt Surface-A Density Functional Theory Investigation
    (Izmir Institute of Technology, 2019) Gençoğlu, Merve; Kızılkaya, Ali Can; Sevinçli, Haldun
    The effects of manganese promotion on the adsorbates and specific elementary reactions of Fischer-Tropsch Synthesis (FTS) was investigated using periodic Density-Functional Theory (DFT) calculations on a close packed cobalt surface, Co(111). In particular the effects of MnO promotion on the adsorbates of CO, HCO, CH, CH2, C2H2, OH, H2O, C, O and on the reactions of direct CO dissociation, H-assisted CO dissociation and carbon hydrogenation were studied for MnO coverages of 0.25 ML and 0.11 ML. Mn was modeled in the chemical form of MnO. MnO was modeled as a singular monomer on the Co(111) surface, based on the findings from experimental studies. The results indicate that MnO promotion increases the adsorption energies of all adsorbates, except H and C2H2. In particular, CO and H2O adsorption energies increase significantly, which indicate that the selectivity increases to long chain hydrocarbons is mainly due to an increased surface coverage of CO with respect to H. The results also indicate that the relative effect of MnO on adsorption energies are strongly dependent on MnO coverage. MnO promotion is found to decrease the activation barriers for HCO and CH formation, while increasing the activation barriers for direct CO dissociation and HCO dissociation. The results point out that MnO does not promote the direct dissociation of CO and the activity increase due to Mn promotion is most probably due to a H or OH assisted CO dissociation pathway or another rate limiting step.