Effect Of Surface Hydrophilic And Hydrophobic Modification Of Fe-based Catalyst On The Product Distribution In CO Hydrogenation

Fischer-Tropsch synthesis(FTS)process for producing high value-added chemicals through non petroleum routes has important practical significance for the rational utilization of energy resources and ensuring energy strategic security in China.In FTS,Fe-based catalysts exhibit excellent activity and primary olefin selectivity.However,producing olefins with high selectivity is technically challenging.The preparation of novel catalysts is essential for further controlling the product distribution of Fe-based catalysts in CO hydrogenation and enhancing olefin selectivity.Focusing on the surface modification of Fe-based catalysts,this paper aims to improve olefin selectivity and reduce CO2 selectivity by reducing the occurrence of secondary reaction of primary olefins and inhibiting the activity of water-gas shift reaction.Surface hydrophobic and hydrophilic modified Fe based catalysts with good dispersion were prepared using silanization reaction and alcohol solvent impregnation method.Combined with a series of characterization methods and CO hydrogenation performance tests,the influence of surface hydrophilic modification of Fe-based catalysts on the product distribution of CO hydrogenation and the related mechanism were explored.The main research content and results were as follows:(1)Fe/SiO2-PFTS catalysts with different Fe contents and surface hydrophobicity were obtained by Stober method,silanization reaction,and impregnation method.The effect of surface hydrophobicity modification on the product distribution of CO hydrogenation was studied.The results showed that the series Fe/SiO2-PFTS with different Fe loadings exhibited strong hydrophobicity,and the samples still exhibited hydrophobicity after reaction;As the Fe loading increased,the adsorption of CO on the catalyst increased.In CO hydrogenation,compared with pure Fe2O3,the CO2 selectivity on catalyst 5Fe/SiO2-PFTS decreased from 36.17%to 14.59%,and the selectivity for light olefins increased from 17.15%to 29.41%.Compared with traditional coating methods,the loading of Fe active components on the hydrophobic surface effectively reduced the steric hindrance effect,enabling the desorption of primary olefins during reaction,reducing the extent of secondary reactions,and significantly reducing the WGS reaction activity.(2)Fe/SiO2-HEC catalysts with different Fe contents and hydroxyethyl cellulose(HEC)content was prepared using the Stober method and step-by-step impregnation method.The effect of surface hydrophilicity modification on product distribution in CO hydrogenation was studied.The results showed that when the HEC loading amount was constant,poor Fe dispersion was found with the increase of Fe content.When the Fe loading amount was constant,the hydrophilicity of the catalyst increased significantly with the increase of HEC content.In CO hydrogenation,compared with Fe2O3,the CO2 selectivity on catalyst 20Fe/SiO2-HEC(2:1)decreased from 37.14%to 22.96%,the selectivity for light olefins increased from 17.15%to 28.54%,and the O/P ratio(C2=-C4=/C20-C40)increased from 0.63 to 2.93.Compared with direct hydrophilic modification catalysts,Fe/SiO2-HEC maintains higher selectivity for light olefins and inhibits WGS activity.