| Recently,the synthesis of high-quality liquid fuel from syngas derived from coal,natural gas,biomass,etc.,via Fischer-Tropsch(FT)synthesis has received more attention due to the complex situation of the worldwide petroleum market and the increasingly growing global environmental problem.However,the FT products,which are controlled by the Anderson-Schulz-Flory(ASF)polymerization kinetics,show the characteristics of broad product distribution and poor target selectivity.Therefore,How to solve problems above and reduce the by-products is important in both theoretical studies and practical applications,and it is still a challenging work in the domain of FT synthesis.In this thesis,based on the results of our previous studies and the published literature,the structure of HZSM-5 zsolite with different types and different Si/Al ratios was systematically analysed.Moreover,the FT reaction was studied over the HZSM-5 supported with Ru.These samples,including three new types of HZSM-5(small grain HZSM-5(KD-HZSM-5),hollow HZSM-5(KK-HZSM-5)and SAPO-34)and commercially available HZSM-5(SS-HZSM-5)as well as Q15,were characterized by XRD,TEM,SEM,physical and chemical adsorptions.And the structural,acidic and reductive properties of those samples were obtained.Besides,the mechanism of the the Ru/HZSM-5 and FT results was revealed.Meanwhile,the FT reaction of different Si/Al ratios supported Ru catalysts was also investigated.The main conclusions are summarized as follows.(1)The effects of different catalysts on the F-T reaction were studied.By using KD-HZSM-5,KK-HZSM-5 and SS-HZSM-5,which the molar ratio of Si/Al was kept at 60,as supports,respectively,3 wt.%Ru/HZSM-5 was prepared with the excessive impregnation method.The Ru/SAPO-34 and Ru/Q15 were also prepared using the same method.Then the FT reaction was performed in a fixed bed reactor under the condition of P=1.0 MPa,T=235 ?,H2/CO=2 and W/F=10.0 g h-mol-1.The results showed that the specific surface feature and unique channel structure of Ru/KK-HZSM-5 could affect the dispersion and reducibility of Ru species.Compared with other types of catalysts,Ru/KK-HZSM-5 showed the highest FT performance.Importantly,the modest acidic sites promote the long chain hydrocarbons of FT synthesis product occurred cracking and isomerization reaction.As a result,the selectivity of C5-C12 was improved significantly compared to traditional FT synthesis catalysts.(2)The stability and the products distribution of FT reaction over Ru/KK-HZSM-5 were investigated.The results showed the product of C2?C12 at TOS=50 h was higher than that at 10 h,and it gives priority to olefins.Moreover,with the TOS increasing from 10 h to 50 h,the CO conversion was slightly decreased from 39.90%to 31.56%,indicating that Ru/KK-HZSM-5 showed stability in FT synthesis.(3)The effect of the molar ratio of Si/Al on the FT reaction was comparably revealed.Using different Si/Al ratios of ZSM-5 as supports,namely SS-HZSM-5(Si/Al ratio=27,36,60,80 and 120)and KK-HZSM-5(Si/Al ratio=60,80 and 120),respectively,3 wt.%Ru/ZSM-5 was prepared by the excessive impregnation method.The structural,acidic and reductive properties of Ru/HZSM-5 were characterized by XRD,TEM,SEM,physical and chemical adsorptions.Then the FT reaction over the Ru/HZSM-5 was performed under the conditions of P=1.0 MPa,T=235 ?,H2/CO=2,W/F=10.0 g h-mol-1.The results suggest that wth the increase of Si/Al ratio,the FT activity is increased,while the CH4 selectivity is decreased.This is due to the fact that compared to the same series of other Si/Al ratios catalysts,Ru/KK-HZSM-5-120 or Ru/KK-HZSM-5-120 had larger specific surface area and moderate amount of acid.In particular,the special hollow structure of Ru/KK-HZSM-5 series catalysts showed higher reductivity to make it better than commercial series catalysts in catalytic activity.Besides,the selectivities of the gasoline and diesel are high. |
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