Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2023
Thesis Language: Turkish
Student: Gülce ÇAKMAN
Supervisor: Fatma Suna Balcı
Open Archive Collection: AVESIS Open Access Collection
Abstract:
One of the most effective approaches in controlling the emission of carbon dioxide (CO2), which has a significant share in greenhouse gas emissions, is conversion of CO2 into products with high-added value. Methanation and reverse water-gas shift (rWGS) reactions, which occur through CO2 hydrogenation, are an environmentally friendly approach both by providing energy generation and by waste disposal. The kinetic barrier, which is evident at low/medium temperatures, requires the use of catalysts in these reactions. The structure of support material is as important as the active metal for product selectivity while the active metal plays an important role in high conversion. Ordered mesoporous carbons (OMCs) are suitable catalyst support materials due to their high surface area, high thermal and mechanical stability. The targeted reactions are carried out only by kinetic control mechanism since the tunable ordered mesopore structure of these structures reduces mass transfer limitations. In this study, SBA-15 synthesis was carried out using different silica sources (TEOS and Na2SiO3) and synthesis parameters (silica amount, silica-micelle interaction time and template extraction method) in the selection of templates with suitable properties for the synthesis of CMK-3, which is one of the most important structures of OMC family. CMK-3 syntheses were carried out using furfuryl alcohol as carbon source with SBA-15 templates with high surface areas (>700 m2/g) and ordered hexagonal mesoporous ( 6 nm) structures. It was observed CMK-3 with better textural properties were synthesised by gradually increasing of polymerization temperature. Mono/bimetallic catalysts (Co-Ni/CMK-3) were synthesized using different catalyst synthesis methods (impregnation, one-pot and microwave). It was determined that catalysts having high surface areas (> 1000 m2/g) and mesopores ( 3 nm) were synthesized by N2 sorption analysis. The most successful active metal loading was obtained by microwave method without destroying the support structure. Successful loading of active components onto the support structure was determined by EDS, ICP and XPS analyses. The activities of catalysts with the targeted properties in CO2 hydrogenation reaction were tested in a differential reactor with feed molar ratio of 4:1 (H2:CO2), 1 atm and 250-550 oC. Reaching the highest conversion (70.8%) and CH4 selectivity (73.3%) values at 500 oC in the presence of non reduced bimetallic catalyst ((5Ni-5Co/CMK-3)MW) synthesized by using microwave, indicates that the catalyst is effective for methanation reaction. rWGS reaction was also found to be active at 400 oC with 51.9% CO2 conversion and 40.9% CO selectivity.
Key Words : Ordered mesoporous carbon, template structure, characterization, CO2 hydrogenation reaction, selectivity