| Fischer-Tropsch synthesis(FTS)is an important way to achieve the clean utilization of coal.In recent years,preparation of target products(olefins,a-olefins,gasoline,and diesel oil,etc.)through FTS has become a research hotspot in the field of C1 chemistry.It is an important research topic to develop novel catalysts with controlled product selectivity by adjusting the factors that affect the product distribution.The distribution of FTS products is affected by reactions such as primary reaction,olefin secondary reaction and water gas shift reaction(WGS).The product distribution shows low selectivity of olefins and high by-production of CO2.However,the secondary reaction of olefins and WGS reaction are closely related to the adsorption and desorption behaviors of olefins and H20.Therefore,through the control of the hydrophilic and hydrophobic modification of the catalyst,the adsorption and desorption behavior of olefins and H2O can be effectively modified to affect the secondary reaction and WGS reaction,so that the target product can be effectively controlled.In this paper,the effect of adsorption and desorption behaviors of olefins and H20 on the distribution of products was studied.A hydrophilic/hydrophobic modified iron-based catalyst was designed and prepared to explore the effect of the hydrophilic/hydrophobic modification on the catalytic performance.Combined with XRD,FT-IR,TEM,TG,H2-TPR and other characterizations,the effect of hydrophilic/hydrophobic modification on the adsorption and desorption behavior of olefins and H2O on the distribution of FTS reaction products was thoroughly investigated.The specific research includes the following aspects:1.Hydrothermal method,Stbber method and silanization were used to prepare core-shell iron-based catalysts modified by different hydrophobic groups(-CH3,-(CH3)2,-(CH3)3).The surface of Fe2O3 core is uniformly coated with SiO2 shell.The hydroxyl groups on the surface of SiO2 shell react with the silylation reagent to achieve the hydrophobic modification of the catalyst surface with-CH3,-(CH3)2,-(CH3)3 groups.The Si02 shell can be viewed as a vital bridge and ties linking Fe and methyl groups.Compared to unmodified core-shell catalysts,the catalytic performance of Fe@Si-(CH3)3 was most clearly changed:C2 = Z C4= selectivity was 30.12%,CO2 selectivity was 19.38%.It indicates that the hydrophobic modification by trimethylation contributes to the reduction of CO2 selectivity.The above-prepared catalysts modified by different hydrophobic groups were modified by K,and the olefin selectivity was significantly improved.The K modified trimethyl hydrophobic catalyst was prepared by in-situ modification,mechanical mixing and incipient wetness impregnation.The method of impregnation was more appropriate.The selectivity of CO2 was significantly reduced and the olefin selectivity was significantly improved.2.To further explore the effect of trimethylation on the distribution of FTS products,the trimethyl modified sample prepared above was subjected to multiple high-temperature calcinations to remove a variety of impurities from the sample,and-(CH3)3 modified catalyst was prepared.The strongly hydrophobic catalyst(Fe2O3@SiO2-(CH3)3)showed high activity and stability for CO hydrogenation with very low CO2 selectivity(less than 5%)and higher C2= ＝ C4= selectivity.Combined with the corresponding characterization analysis,it was found that the trimethyl-modified hydrophobic surface can inhibit the re-adsorption of water,significantly inhibited WGS activity and thus inhibited the production of CO2-3.Chitosan-supported iron-based caftalysts with polar groups such as hydroxyl and amino groups on the surface were prepared.The polar group significantly inhibits the re-adsorption of olefins and reduces the ability of secondary hydrogenation of olefins,so the olefin selectivity is significantly increased.K-Fe/CTS has better Fischer-Tropsch synthesis performance:CO conversion is 68%,2=-C4= selectivity is 51.95%. |
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