A Novel Iron-Based Catalyst For Forming Light Olefins Via Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) is an important technology in production of hydrocarbon compounds and oxygen containing organic compounds from syngas. Due to the rapid of fossil energy consumption and the limitation of crude oil supplement, FTS has been paid great attention, because it can efficiently and cleanly use various energy resources, such as coal, natural gas and biomass, to produce various chemical feedstock and fuel oil to alleviate the oil crisis. The production of FTS has a widely distribution, following Anderson-Schultz-Flory (ASF) distribution. The selectivity of products have a certain limitation except for methane and wax. In this study, We prepared iron-based catalysts by adding promoters or carbon fibers to break the ASF distribution of FTS products.The iron-based catalysts, with high stability, high activity and high selectivity of light olefins C2=～C4=), were prepared using coprecipitation method to investigate the influence of Cr promoter. The iron-based catalysts mixed with carbon nanofiber were also developed, and the Na promotional effects were investigated. Meanwhile, the calcination temperature and reduction temperature were further investigated.The obtained iron-based catalysts were characterized by X-ray diffraction (XRD), N2 adsorption (BET-PSD), H2 and CO temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscope (TEM).The results show that the right amount of Cr can improve the activity of the catalyst, promoting the reducibility and the formation of light olefins, inhibiting the production of methane. The catalyst of Cr5 realized the best catalytic performance, as the CO conversion was 63.15%, and the light olefins selectivity was up to 53.42% and O/P is reached 4.35.For Fe-Mn-Na-CNF catalysts, it was found that a moderate amount of Na can improve the activity of catalyst, inhibiting the formation of methane, promoting the selectivity of light olefins.200Fe10Mn5Na-CNF exhibited the best reaction performance, as CO conversion is 65.72% and light olefins selectivity reached 51.47%, which is 1.25 times higher than 200Fe10Mn. Meanwhile, O/P is 2.3 times higher than 200Fe10Mn.By changing the calcination temperature and reduction temperature, it is found that the higher the calcination temperature resulted in weaker water gas shift (WGS) reaction and higher O/P.