Effects of Initial Phase on Activity and Selectivity in Fischer-Tropsch Synthesis over Precipitated Iron Catalysts

摘要

The Fischer-Tropsch synthesis (FTS) offers the feasible way of converting syngas (H_2+CO) into clean hydrocarbons. The application of slurry bubble column reactor (SBCR) makes it possible to carry out the conversion at lower investment. Iron-based catalyst is regarded as one of the most effective catalysts in slurry FTS, due to its high water-gas-shift (WGS) reaction activity especially for coal-derived syngas. It is well known that the iron catalysts undergo phase transformations after pretreated by syngas, and these new phases have remarkable effects on FTS activity and WGS activity. In present work, two novel Fe/Cu/K/SiO_2 catalysts with different initial iron phases were prepared from an iron sulfate precursor (FeSO_4·7H_2O). The catalysts were characterized by BET, H_2-TPR, XRD and Mossbauer spectroscopy. A fixed bed reactor (FBR) and a continuous stirred tank reactor (CSTR) were used to study the effects of initial phases on FTS activity and selectivity over the two catalysts. The results show that a small quantity of Fe_3O_4 in initial catalyst facilitates the reduction of Fe_2O_3, and may correlate with an improved WGS activity. Less olefin selectivity were obtained in FTS over the catalyst both in FBR and CSTR.