Master Degree / Yüksek Lisans Tezleri

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Author: search.filters.author.Kızılkaya, Ali CanSubject: search.filters.subject.Polymerization

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  • Master Thesis
    Molecular Modelling of the Effect of Alkali Promoters on Co Adsorption and Dissociation on the Co(111) Surface
    (2023) Kızılkaya, Ali Can; Kızılkaya, Ali Can; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Fischer-Tropsch Synthesis (FTS) is a surface polymerization process that has been industrially used to convert non-petroleum feedstocks to synthetic transportation fuels. Modification with an alkali promoter of the Co-based catalysts provided promising results to obtain hydrocarbons with enhanced olefin content in FTS. Activation of CO is the key factor to achieve desired end products in FTS, yet the mechanism related to the CO dissociation behavior on alkali promoted cobalt surfaces remains unknown. This study aims to examine the impact of alkali promoters (Li, Na, K) on the adsorption and dissociation characteristics of CO on the Co(111) surface using Density Functional Theory (DFT). Our results revealed that CO adsorption energy increased by 32-37% with alkali addition, yet H adsorption energy remained relatively unchanged. The effect of alkali addition on CO dissociation routes were also examined. The high activation barrier (>200 kJ/mol) makes it improbable for direct CO dissociation to occur on alkali promoted Co(111) surfaces under FTS conditions. For H-assisted pathways, alkali addition increased the activation barrier for HCO and H2CO dissociation, overall reducing the H-assisted CO dissociation rate. It was found that alkali addition makes the surface more carbophilic since the C adsorption energy increased by 7-11% upon alkali addition. Also, with increasing C concentration on the Co(111) surface, subsurface carbon geometries became more stable. Ultimately, it is concluded that alkali promoters of Li, Na and K have similar effects on CO adsorption and dissociation on the Co(111) surface.