Study On The Preparation And Catalytic Performance Of Fe-Mo Carbide Catalysts For The Direct Synthesis Of Light Olefins From CO Hydrogenation

Light olefins are important basic feedstocks in chemical industries.Direct synthesis of light olefins from syngas via Fischer-Tropsch Synthesis(FTS)is one of the potential nonpetroleum routes and has received considerable attention.However,the yield of light olefins influenced by Anderson-Schulz-Flory(A-S-F)rules,the kinetics and thermodynamics,as well as the poor stability and reproducibility of the catalysts,severe secondary hydrogenation and other factors have limited FTS route as a commercial operation.Therefore,production of light olefins via FTS route calls for the development of effective catalysts to achieve high CO conversion,desired hydrocarbon distribution,favorable olefin selectivity and good stability.Molybdenum carbide catalyst has shown great prospects in the production of light olefins,which exhibits high CO conversion with high sulfur resistance.In our previous work,iron carbide catalyst has been particularly investigated,which exhibited high activity and strong chain propagation ability with high heavy hydrocarbon production in CO hydrogenation.In this study,multifunctional Fe-Mo carbide catalysts with high activity and light olefin selectivity and low C5+ selectivity in CO hydrogenation were prepared by carburization of Fe-Mo mixed oxides or the mixture of iron carbides and Molybdenum carbides following K modification by impregnation,based on the advantages of molybdenum carbide and iron carbide catalyst in CO hydrogenation.The optimum preparation conditions of P-M02C were investigated and then tested in CO hydrogenation.The textural properties,bulk structures,surface composition,adsorption and reduction behaviors of the catalysts were characterized by XRD,XPS,SEM,CO-TPD,TG,SEM,TEM,N2 adsorption-desorption methods,respectively.In addition,the catalytic performance of scaled-up catalyst was also investigated.Studies have shown that the optimum carburization conditions for the preparation of P-M02C were at 700 ? for 4 h at N2 atmosphere.The specific surface area of the catalyst decreased and the surface carbon depositions was increased with increase in carbonization temperature and duration time.It was found that the content of C5+ hydrocarbons decreased and the O/P was increased with prolonging the carbonization time at 700 ?,while the content of ?-Mo2C increased.The iron phase in the K/Mo-Fe catalysts is mainly a-Fe.The selectivity of light olefins changed little with different Fe/Mo molar ratio.The internal oxidation of iron carbide was suppressed in CO hydrogenation,with the incorporation of ?-Mo2C into the Fe-Mo-K catalyst prepared by mechanical mixing.At set reaction conditions of H2/CO of 2,GHSV of 1000 h-1,320 0C,and 1.5 MPa,the A-Fe-Mo-2-1-K catalyst showed the best performance the selectivity of light olefins in overall hydrocarbons and the C5+ selectivity reached 40%and 20%,respectively.High specific surface area molybdenum carbide catalyst was obtained by heating Mo-SiO2 at 700 ? in Ar gas via solid-solid carbonthermal reaction taking methyl as carbon source.The hybrid methyl Mo/SiO2 was achieved via a reaction between hydroxyl PMHS catalyzed by en and AHM/ethanol suspension,following with assembly of molybdenum species in hybrid methyl SiO2 sol.A-Fe-Mo-2-1-K catalyst prepared by mechanical mixing was used for amplification evaluation test In CO hydrogenation reaction,the pressure drop of the catalyst bed was increased due to the catalyst crushing of the catalysts and the oxidization of iron carbide to Fe3O4,resulting in the decrease in stability of the catalyst.