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Effects of Zn promoter on the structure and Fischer-Tropsch performance of iron catalyst

Keywords: F-T synthesis,Fe-Zn catalyst,Zn promoter

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The effects of Zn(100 gFe/x gZn,x=7~100) on the textural properties,reduction behavior and structural changes during reduction and reaction of the Fe-Zn catalysts were studied by using N2 physical adsorption,X-ray diffraction(XRD),Mssbauer spectroscopy(MES),H2 differential thermogravimetric analysis(H2-DTG) and CO temperature-programmed reduction(CO-TPR).The F-T performances of the catalysts were investigated in a fixed-bed reactor under the conditions of H2/CO = 2.0,260 ℃,1.5 MPa and 4 000 mL/(g·h).The results show that,with the increase of Zn content in catalysts,the phases of catalysts transform from α-Fe2O3 and ZnFe2O4 to ZnFe2O4 and ZnO,where ZnO appears just beyond the stoichiometry of Zn/Fe(1∶2).The presence of ZnFe2O4 plays an important role in catalysts.In the fresh catalysts,ZnFe2O4 can enhance the dispersion of Fe phase and thus enlarge the surface area.For the reduced and used catalysts,ZnFe2O4 not only inhibits the excessive reduction and carbonization,but also improves the stability of the iron carbide phase.F-T tests show that the fast deactivation was observed in the un-promoted catalyst,but the catalytic activity was stabilized by ZnFe2O4 in Zn-promoted catalysts.In addition,high olefin selectivity is observed in Fe-Zn catalysts which gradually decreases to same content as that of un-promoted catalyst probably due to the change of phases at the beginning of reaction.


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