The Fabrication,Characterization Of Metal-oxide Nanocomposite Catalyst And Their Application In Fischer-tropsch Synthesis

Fischer-Tropsch synthesis is a very important heterogeneous catalytic reaction.Especially today with the coming of post-oil era,and new alternative energy technology is not mature.Fischer-Tropschsynthesis is also a reaction with complex reaction network.The product ranges from not only olefin and alkanes,but also alcohol,ketone,aldehyde,carboxylic acid et al.oxygenated organic compounds,to CO₂,H₂O et al.inorganic compounds.However,the reaction mechanism is still unclear up to now.For years,researchers have tried to obtain one catalyst with both high activity and high target product selectivity.The main methods used includingadding some basic promoters to change the electric property of the catalysts,and adding some inert promoters to change the structure of the catalysts and so on.Even though there is much progress,the ideal controllable product distribution is still not achieved.In this thesis,we adopted a unique catalyst fabrication method.The small structural unit of the catalyst was first synthesized,assembled to be nano-complex structural catalyst.The main work in this thesis is as follows:1.Iron based catalyst is a commonly used Fischer-Tropsch catalyst.Because of its low price,high WGS?water gas shift?activity,it can be applied in low H₂/CO ratio syngas reaction condition.In this thesis,we used pyrolysis method to prepare iron oxide and Mn/Fe nanocomposite nanoparticles,which were then assembled with alumina gel to nanocomposite catalyst.The result showed that compared with traditional iron-based alumina Fischer-Tropsch catalyst,our iron oxide-alumina nanocomposite catalyst has higher low olefin selectivity and higher reaction activity under similar situation.This is closely related with itsunique nanocompositestructure.Iron oxide nanoparticle is covered by the alumina nanoparticle,which stops its growing up in the reaction and keeps its morphology.This unique structure provides more activity site,improves the reactivity.At the same time,compared with traditional catalyst,the weak metal-support interaction is also an important reason for the better reactivity.2.The CeO₂ nanoparticles fabricated by hydrothermal method have small size and narrow size distribution,which can be modified by oleic acid,changing from water-soluble to oil-soluble.After assembling with Mn/Fe nanocomposite catalyst in weak polarity solvent,its Fischer-Tropsch reaction property was tested.The characterization result showed that:this Mn/Fe/Cenanocomposite catalyst had higher surface area and the addition of Mn improved the selectivity to C_2-4 olefin.Mn/Fe/Cenanocatalyst with high Mn/Fe ratio can improve the catalyst's thermal stability,reduce the decreasing ratio of C_2-4 olefin/C_2-4 alkane caused by high temperature,and improve low carbon olefin selectivity.3.Ru nanoparticles were prepared by polyol reduction method and modified by different kinds of protectors.Then they were assembled with alumina sol to be nanocomposite catalyst.The characterization result showed that the surface organic compounds of Ru nanoparticles modified by 1-16 Mercaptan compared with Ru nanoparticles modified by oil amine was more difficult to remove,which obviously affected the Fischer-Tropsch synthesis activity.In addition,catalyst modified by 1-16 Mercaptanshowed no catalytic activity,however,catalyst modified by oil amine showed high catalytic activity.Simultaneously,the selectivity of Fischer-Tropsch synthesis product was also affected by surface modification.Compared with the catalysts without surface modification,Ru-alumina catalyst modified by oil amine has higher CH₄ selectivity.At 603K,the selectivity to CH₄ is more than 90%.