The Research On Preparation And Characterization Of Ordered Mesoporous Alumina Supported Cobalt Catalysts And Its Performance On Fischer-tropsch Synthesis

Fischer-Tropsch synthesis(FTS)convers syngas(CO+H2)into clean hydrocarbon fuels or chemicals,which is of great significance and value to solve the current environment and energy problems.In this work,Order mesoporous alumina(OMA)with large surface area and high thermal stability was synthesized via ethanol evaporation induced self-assembly by using P123 as structure directing agent.The effects of preparation method and rare earth metals promoter on the structure of Co/OMA catalysts and their FTS catalytic performance were systematically studied.Cobalt based catalysts were prepared by incipient wetness impregnation the OMA.In order to reveal the relationship between structure and catalytic performance,the characteristic of the catalysts were identified by XRD?H2-TPR?BET?TEM techniques etc.I Study on the Co/OMA catalysts(1)?Co/OMA catalysts were prepared by incipient-wetness impregnation with cobalt nitrate dissolved in water or anhydrous solvents(ethanol,methanol,n-butanol).The effects of impregnation solution on the structure of Co/OMA catalysts and their FTS catalytic performance were systematically studied.The results indicate that catalysts impregnated with anhydrous solutions showed higher F-T reaction activity and C5+ selectivity than Co/OMA prepared using water solution.Characterization results indicate that Co/OMA catalysts prepared with water solutions destroyed the original structure of OMA,while catalysts anhydrous solutions have large surface areas?regular pore structure and higher metal dispersion degree,which may be the important reason for the difference of FTS performance between the two types of catalysts.(2)Influence of support calcination temperature on the structure and catalytic performance of Co/OMA catalysts for FTS was studied.The results show that the CO conversion and C5+ selectivity increased with the increase of calcination temperature.When the calcination temperature increased to 700 ?,Co/OMA show the best F-T performance.The characterization results show that the catalysts maintain the order mesoporous structure in the scope of 400-800 ?.In addition,the acid sites on the catalysts surface decrease with the increase of support calcination temperature,leading to the decrease of the interaction between cobalt oxygen species and carrier,and thus improved the reducibility of Co/OMA.Furthermore,low acidity can prevent the reaction of hydrogenolysis and isomerization,which appeared to be responsible for high C5+ hydrocarbon selectivity.The improvement of the reducibility of catalyst is the major reason for the improvement of catalytic activity(3)Influence of Co loadings on the catalytic performance of Co/OMA catalysts for FTS was also studied.The results show that when the loading amounts of cobalt increases from 10 wt%to 20 wt%,the conversion rate of CO gradually increased to the maximum value.The conversion rate of CO changed little when Co loadings continue to increase.The loadings of Co has little impact on C5+ selectivity in the investigation scale.II The study of cobalt catalysts supported on rare earth modified OMA(1)?Rare earth metal modified OMA was in-situ synthesized through a sol-gel route and then as support for the preparation of Co/R-OMA catalysts.The results show that Ce was favorable for CO conversion and La can improve C5+ selectivity significantly,while Y?Nd?Eu?and Ga have negative effect on the FTS performance of Co/OMA catalyst.The dispersion degree of cobalt species can be enhanced with the adding of Ce,and the reducibility of catalyst was also improved,which is helpful to the increase of FTS activity.While La has little effect on the reducibility of the catalyst.Perhaps the synergistic effect between La and cobalt is helpful to improve the selectivity of C5+.(2)Ce-doped OMA was synthesized in a sol-gel system and then as support for the preparation of Co/La/Ce-OMA catalysts,La promoter was introduced by incipient wetness impregnation method with ethanol solution of lanthanum nitrate.The results show that introduction of La further decreased the strong interaction between the carrier and the cobalt species and reduced the amount of CoAl2O4,thus improved the reducibility of catalysts.What's more,the introduction of La further improved the dispersion of cobalt species.These may be responsible for the improvement of the FTS catalytic performance of Co/OMA catalyst...