| Light olefins are important basic organic chemical raw materials.Fischer Tropsch synthesis(FTS)with syngas as raw material can directly produce high value-added chemicals such as light olefins and oxygenates,which can effectively alleviate the dependence on petroleum resources.However,due to the influence of the Anderson-Schulz-Flory(ASF)distribution,the products of traditional FT reaction are widely distributed and the selectivity of designed products is low.Therefore,realizing the regulation of product distribution,inhibiting the secondary reaction of primary olefins and improving the selectivity of target products are the key problems that need to be solved urgently.To the end,hydrophilic hydroxyapatite(HAP)was used as the support of Fe-based catalyst,which was then modified by alkali metal promoters to improve the readsorption of primary olefins and the adsorption and diffusion behavior of H2O,to achieve the purpose of regulating product distribution.Combined with XRD,SEM,TEM,CA,TG-DSC,FT-IR,XPS,and UV-vis-DR characterization methods,the physicochemical properties of the catalyst before and after the reaction,and the effect of Fe/HAP catalyst on the product distribution in FTS were investigated.The main contents and results are as follows.(1)Fe/HAP catalysts were prepared by impregnation method using hydroxyapatite as support.The effects of HAP and SiO2 on the catalytic performance of Fe-based catalysts for FT synthesis were compared.The results of FT-IR showed that Fe/HAP catalysts were rich in hydroxyl groups.Hydrophilicity of the catalysts was proved by contact angle test and H2O-TPD.Compared with Fe/SiO2 catalyst,C2-C40 selectivity decreased to 17%,the selectivity of C5+ increased from 23.4%to 42.7%,and CO2 selectivity was less than 30%over Fe/HAP catalyst.The results showed that HAP had a good dispersion effect on the active components,and its surface hydrophilicity and alkalinity significantly inhibited the secondary hydrogenation reaction of primary olefins.Also,it was beneficial to the chain growth of the hydrocarbons.(2)Fe/HAP catalysts with 3%-10%iron contents were prepared by impregnation method,and the effects of iron loading and reduction temperature on catalytic performance were investigated.Fe/HAP catalyst showed the best catalytic performance at the loading and reduction temperature of 5%and 260℃,respectively.(3)With the addition of Na,K and Zn promoters,the modified Fe/HAP catalysts were used in the Fischer-Tropsch synthesis.Combined with the results of XPS and chemisorption,the electron transfer effect between promoters and Fe was favorable to the adsorption of CO and inhibited the hydrogenation of the catalysts.The C2-C4=selectivity for K modified catalyst was 34.2%.The C5+ selectivity of the Na modified catalyst was 42.7%,and the CH4 selectivity reduced to 17.4%. |
