| Light olefins(C2=-C4=)are important basic chemical raw materials.Linear α-olefin(LAOs),as important intermediates,are used in a large number of commercial products such as polymers,surfactants and additives.However,the production of C2=-C4= and LAOs depends on the traditional petrochemical production technology.With the rapid growth of national economy,the rapid consumption of petroleum resources and their non-renewable,the non-petroleum route chemical technology is imperative.Fischer-Tropsch Synthesis(FTS)is one of the research focuses in recent years.The non-petroleum route of direct production of high value-added basic chemicals such as C2=-C4= and LAOs can simplify the production process,and the raw materials are easy to obtain and have higher economy.The primary products of FTS reaction are mainly straight-chain alkanes and α-olefin.The selectivity of target products is restricted by the distribution of ASF products due to the secondary reaction initiated by the readsorption of primary products and the reaction mechanism of FTS,and the total olefin selectivity needs to be further improved.Therefore,it is of great significance to explore the main influencing factors affecting the selective secondary reaction of olefins.The modification of catalyst surface properties has an important effect on the secondary reaction of olefins.Fe-based catalysts have high activity and primary olefin selectivity in FT reaction.Based on this,Fe-based catalysts were modified from two aspects of support and active components,respectively,to explore the influence of surface hydrophilicity and additives modification on the catalytic performance of FTS.Combined with XRD,SEM,FT-IR,In situ DRIFT,TG-DSC,CO-TPD,H2-TPR,XPS and BET characterization methods,the effect of Fe/Si composite oxide on product distribution and the mechanism of action were deeply explored.The main research contents and results are as follows:(1)Based on the surface modification of SiO2 carrier,the hydrophilic groups on the surface of SiO2 carrier were modified under different calcination atmosphere and pretreatment solvent conditions respectively,and then Fe/modified SiO2 supported catalysts were prepared by impregnation method.FT-IR and In situ DRIFT showed that the hydroxyl group was decreased and the C-H bond was increased in N2 calcination atmosphere.The adsorption peak area of C-H bond increased firstly and then decreased with the increase of temperature in ethanol atmosphere.CA test showed that Fe2O3/SiO2-N2(Ethanol)catalyst was the most hydrophilic.The catalyst treated with ethanol is easier to reduce at 400℃-750℃ than the catalyst treated with water.The morphology of the catalyst is like a coral reef with porous structure,which is conducive to the uniform distribution of active components and promotes the reduction of Fe2O3.Compared with other catalysts,The CH4 selectivity of Fe2O3/SiO2-N2(Ethanol)catalyst was the lowest,and the LAOs selectivity and O/P value were both improved after the reaction.(2)Based on the preparation and modification of Mn-modified Fe3O4 composite MAG catalyst,Mn-modified Fe3O4 microspheres were synthesized by solvothermal method in one step,and then the modified Fe3O4 was dispersed by ethanol and compounded on MAG to prepare xMn-yFe3O4/MAG catalyst.The results show that the morphology of MAG is rose-shaped and has a unique layered structure.The results of CO-TPD and H2-TPD show that the 1Mn-5Fe3O4/MAG catalyst corresponds to the desorption peak of strong CO adsorption in the temperature range of 250℃-550℃,and the peak area is the largest.The addition of Mn promoter can improve the surface alkaline of the catalyst,enhance the adsorption of CO,and inhibit the adsorption of H2.Under 280℃ and 1.5 MPa,CO conversion rate of 1Mn-5Fe3O4/MAG is 78.53%,O/P value is 5.01,selectivity of LAOs is 60.43%.The CO conversion and O/P values of 1Mn-10Fe3O4/MAG is 91.3%,4.69 and 56.14%respectively.With the increase of Mn content,Fe-Mn interaction was enhanced and catalyst activity decreased. |
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