Research Of Preparation And Characterization Of Cobalt-Iron Based Catalysts For F-T Synthesis And The Reaction Performance

Fischer-Tropsch (F-T) synthesis is one of the key processes converting coal derived syngas( H₂+CO) into hydrocarbons and other chemicals. And the catalyst development is the key technology of F-T synthesis,Co and Fe are the two important catalysts of F-T synthesis generally used. Comparing with the cobalt-based catalysts, the content of the product olefin using iron-based catalyst for F-T synthesis is higher, the methane selectivity is lower, and it requests high temperature and pressure; the cobalt-based catalyst for F-T synthesis is different, the content of heavy product is higher, the methane selectivity is higher, but it requests lower temperature and pressure. When iron and cobalt are used as the active component of a catalyst at the same time, the catalyst performance is not the simple sum of iron and cobalt catalyst as a single active component. The main purpose of this paper was to preliminarily explore the preparation and catalytic properties of cobalt-iron-based bimetallic catalyst.A series of cobalt-iron-based catalysts were prepared by wet impregnation, they were evaluated in a slurry phase reactor with a volume of one liter. The properties of the catalysts were characterized by BET, SEM, XRD, TPR, TEM, and so on.This work was main composed of the following aspect:(a) The influence of different iron contents on the structure and reaction performance of the catalysts. The results showed that the addition of iron can improve the pore structure of the catalysts and increase the dispersion of the active component, but the more iron content, not the better properties of the catalysts. The test results of F-T synthesis showed that the addition of a small amount of iron can increase the conversion rate of CO and the selectivity of the C₅⁺ product.(b) Catalysts were respectively prepared using activated alumina andγ-alumina as carriers, to investigate the difference of the properties of the catalysts prepared by different carriers. The results indicated that the surface area and average pore size of the catalyst prepared byγ-Al₂O₃ were relatively large, active species were dispersed better, the restored temperature was lower. Also the CO conversion activity of catalyst prepared byγ-Al₂O₃ was much higher than the catalyst prepared by activated Al₂O₃.(c) Adding Mn promoter to the 3%Fe-15%Co/γ-Al₂O₃ catalyst was to investigate the influence of Mn promoter on the structure and reaction performance of the catalysts. The results showed that suitable amount of Mn can improve the structure of the catalyst, its surface area and average pore size slightly increased. Analysis by XRD showed that Mn was beneficial to the dispersion of the activated phase; H₂-TPD showed that the addition of Mn can increase the number of absorpted active hydrogen site and promote the formation of multi-center active adsorption site. In the 3%Fe-15%Co/γ-Al₂O₃ catalyst, added Mn can increase the CO conversion and C₅⁺ selectivity,but added too much Mn would reduce the activity of catalyst.(d) Take l%Mn-3%Fe-15%Co/γ-Al₂O₃ catalyst as the example, the relation of the CO conversion and selectivity of product with F-T synthesis operating condition was studied. The results showed that the most appropriate conditions were: P=2.0MPa, T=497K, H₂/CO=2.0, GOSV=600h^-1.