Design Of Novel Cobalt Catalysts Supported On Activated Aluminum Oxide And Study On Their Catalytic Performance In Fischer–Tropsch Synthesis

Fischer-Tropsch synthesis?FTS? is an important routetoconvert coal, natural gas and biomass into clean fuels and chemicals via syngas. Fe- and Co-supported catalysts are often used in the process. Co-supported catalysts have attractedgrowing interest owing to their unique properties, such as a satisfactory selectivity of long chain hydrocarbon and the stability towards thermal sintering. Moreover, the supports of Co-supported catalysts have great influences on the selectivity and activity.Alumina is the most popular industrial support using in many reaction processes. To improve the catalytic properties of catalysts, the crystalline structures, specific area, pore size, pore volume of alumina were investigated.The structure of the active phases and the interactions between the support and the metal of the Co-supported catalysts were not clear until now. With the development of material science, the F-T catalysts with clear structure of active phases could be designed using the well-defined metal and oxides nanocrystals.We have designed and synthesized Co/?-Al₂O₃ nanocomposites with the attachment of Co nanocrystals on the ?-Al₂O₃ nanocrystals. With the aid of many characterization techniques, we investigated the exposed crystal surface of ?-Al₂O₃ nanocrystals, the interactions beween the exposed crystalline structures of ?-Al₂O₃ nanocrystals and Conanocrystals, the catalytic performance of the FTS process and the structure-activity relationship of Co/?-Al₂O₃ nanocomposites catalysts.Moreover, metal organic framework materials are three-dimensional nano porous materialswhich have been widely investigated for the last ten years. MOFspossess high thermal stability, high specific area, high pore volume, uniform and adjustable pore size, and medium interaction between Al and Co.Therefore, MOFS may be an effective support in the Co-supported catalysts for the FTS process.In this thesis, Co/?-Al₂O₃ nanocomposites and Co/MIL-53?Al? catalysts were synthesized. These Co-supported catalysts were characterized by transmission electron microscopy?TEM?, X-ray diffraction?XRD?, temperature programmed reduction?TPR?, N2 adsorption-desorption, hydrogen chemisorption and oxygen titration technologies.The catalytic performance of the Co-supported catalysts for the FTS process was evaluated on a fixed bed reactor.The effects of the morphology of alumina nanocrystalssupports, the synthesis methods for Co-supported catalysts on and the structures of the active phases for catalytic performance of the FTS process have been investigated. The results are as follows.1. The alumina nanocrystals with different morphologies have been obtained using Al?NO3?3·9H₂O and aluminium isopropoxide as alumina precursors. The ?-Al₂O₃-NS nanocrystalswith regular shaped morphologies and narrow pore size distribution mostly exposed the?110? crystal facets of ?-Al₂O₃?account for 70% of the total exposed surface?.2. Co-supported catalysts have been synthesized by the incipient-wetness method and the chemicaldeposited method. With the incipient-wetness method, the Co/?-A₂O₃-NR-I catalystspossess the highest CO conversion?32.5%? and C5+ selectivity?76.3%? because of the more catalytic active sites.Besides, the Co/?-A₂O₃-NS-D catalysts obtained via the chemicaldeposited method shown the highest CO conversion?40.03%?, C5+ selectivity?73.58%? due to the unique structures of Co on the ?-Al₂O₃ nanocrystals.3. TheMIL-53?Al? supports have been prepared using Al?NO3?3·9H₂O and terephthalic acid. The MIL-53?Al? materials with three-dimensional porous structures, high thermal stability, high specific area, high pore volume, uniform and adjustable pore size were investigated. Then, Co/MIL-53?Al? catalysts with different Co content have been synthesizedvia theincipient-wetness method. Co/MIL-53?Al? catalysts shown good catalytic activity that higher than catalytic performance of commercial alumina supported cobaltdue to the unique structures of MIL-53?Al?.