Research On The Interaction Between Iron Oxide And SiO₂ Aerogel And Pretreatment

Iron-based catalysts have become one of the most industrially valuable catalysts of Fischer-Tropsch synthesis?FTS?.Research and development of iron-based catalyst is the key link in Fischer-Tropsch synthesis technology.Fresh iron-based catalysts usually need to be activated to improve the FTS performances.Complex phase transformation would take place during the activation and reaction process.The FTS performances will change with the phases and content of iron oxide and iron carbide which form during the activation process.These phase transformation are affected by the physical chemistry properties of the catalyst,activation conditions and reaction conditions etc.Therefore,under the same reaction conditions and activation conditions,it is significant to effectively regulate the physical chemistry properties of catalyst and then optimize the FTS activity and stability.In this work,the model catalyst with SiO₂aerogel supported Fe-based was prepared by hydrothermal method.The different pretreatment conditions before activation and the different contents of SiO₂aerogel were investigated to modulate the physical chemistry properties of the catalyst,and then regulate the phase transformation and the FTS performance.?1?75Fe/100SiO₂catalyst was pretreated in oxygen atmosphere and argon atmosphere.The physical chemistry properties of the catalysts were characterized by N₂physical adsorption,XRD,XPS,TPR,TPH,LRS and HRTEM.Compared to the fresh catalyst,most of the carbon generated from raw material was removed in the O₂-pretreated catalyst and the initial phase was transformed from Fe₃O₄phase to?-Fe₂O₃phase.The activated catalyst has a high degree of reducion and carburization which increased the amount of iron carbide.At the same time,the amount of carbon deposition decreased.The Ar-pretreated catalyst was still covered with a lot of graphite carbon.The interaction between Fe and SiO₂was strengthened which made it more difficult for catalyst to reduce and carburize.The amount of iron carbides decreased after activation.Meanwhile,the amount of carbon deposition increased.Results of fixed-bed microreactor performance are as follows:compared to the fresh catalyst,the FTS activity and WGS?Water-Gas Shift?activity of the O₂-pretreated catalyst increased.The FTS activity of the Ar-pretreated catalyst decreased.?2?The catalysts of 100Fe,75Fe/100SiO₂and 20Fe/100SiO₂pretreated by O₂are used as model catalysts.The physical chemistry properties of the catalysts were characterized by N₂physical adsorption,XRD,XPS,TPR,TPH and LRS.In terms of chemical effects,the interaction between Fe and SiO₂resulted in the transfer of electrons from Fe species to Si species in the catalyst,which enhanced the Fe-O bond and inhibited the reduction and carbonization of the catalyst.The iron carbide phase was stabilized and the formation of carbon deposition was inhibited.In terms of structural effects,SiO₂aerogel improved the dispersion of catalyst,decreased the crystallite size and increased the specific surface area of the catalyst.Results of fixed-bed microreactor performance are as follows:The 75Fe/100SiO₂catalyst had the best reactivity and stability,followed by 100Fe and 20Fe/100SiO₂.