Study On The Catalytic Performance Control Of Cobalt-based Catalysts For Fischer-tropsch Synthesis

Inner Mongolia Autonomous Region is rich in coal resources,and the development of clean and efficient coal technology is crucial for the optimal use of energy.The Fischer-Tropsch synthesis reaction is a reaction that converts CO and H₂into long chain hydrocarbons.Among the reported catalysts,cobalt-based catalysts have higher activity and chain growth ability.In this thesis,starting with the structure and composition of the catalyst,we first design the Al₂O₃support with different morphology and study its influence on the structure and performance of Cobalt-based catalysts and cobalt-ruthenium cocatalysts.Secondly,the effects of Zr O₂promoters on the structure and performance of the co-based catalysts with different morphologies were explored.Finally,the effect of the crystal structure evolution of the metallic cobalt during the Fischer-Tropsch reaction on the performance of the catalyst was investigated.The main results are summarized as follows:(1)The Al₂O₃ carriers with different morphologies were prepared and their surface properties were studied.F-Al₂O₃,the flower-like support formed by the self-assembly of uniform vertical strips,have the most acidic sites on the surface,which will promote the adsorption of the reaction molecules.The rough surface of the nanorod-shaped support R-Al₂O₃ has the largest specific surface.The surface-cracked diamond-shaped support Sh-Al₂O₃ has the most stable surface hydroxyl groups.(2)The influence of the support morphology on the structure and performance of the catalyst was studied.The Al₂O₃ support effect can regulate the oxygen vacancies(V_o)on the surface of fresh catalysts.The fresh 20%Co/F-Al₂O₃ catalyst with highest surface oxygen vacancies shows only Co-hcp(hexagonal close-packed)elemental cobalt after H₂ pretreatment.The catalyst of this structure has the best Fischer-Tropsch activity.(3)The effect of co-catalytic active component Ru⁰ on the structure and performance of 20%Co/?-Al₂O₃ catalyst with different morphologies was studied.The addition of Ru could increase the reduction ability of cobalt catalyst,the number of active cobalt particles and the dispersion of cobalt particles as well as the catalytic activity,but did not affect the crystal structure of the active component Co⁰ and the order of oxygen vacancies on the surface of the catalyst.Therefore,the order of activity of the three catalysts is the same as that before the addition of Ru.(4)The effect of Zr O₂ promoter on the structure and performance of 20%Co/?-Al₂O₃ catalyst with different morphologies was studied.It was found that Zr O₂enhances the hydrogenation ability of the catalyst and is beneficial to the formation of short-chain hydrocarbons.Zr O₂ has an effect on the formation of surface oxygen vacancies.And it was still the F-Al₂O₃ supported catalyst to expose only the co-hcp crystal form and its overall activity was the best.(5)Two kinds of carbon-supported cobalt-based catalyst were prepared by pyrolysis and carbonization with Co-MOF and Co-ZIF as precursor.The crystal transformation of the active component Co in the catalyst and its effect on the activity of Fischer-Tropsch reaction were investigated.It was found that the reason for the C₅₊selectivity jump of Co@C-MOF catalyst was that the intermediate of Co₂C on the surface of the catalyst changed into a phase of active Co-hcp for Fischer-Tropsch reaction.