Comparative Study of Iron-Based Fischer-Tropsch Synthesis Catalysts Promoted with Strontium or Potassium

摘要

The effect of strontium as a chemical promoter on iron-based Fischer-Tropsch synthesis (FTS) catalysts was investigated and compared with that of potassium. Strontium was chosen for study because of its relationship to potassium through the Diagonal relationship in the Periodic Table. The catalysts were characterized by N-2 physisorption, X-ray diffraction, laser Raman spectroscopy, Mossbauer effect spectroscopy, H-2/CO temperature programmed reduction and temperature programmed hydrogenation. FTS reaction was tested in a fixed-bed reactor. It was found that strontium and potassium strengthened Fe-O bonds of iron oxides species, which is not favorable for the reduction of the catalysts in H-2. Both of them enhanced the reduction and carbonization of the catalysts in CO and syngas atmosphere, suppressed the hydrogenation of surface carbon species, however, strontium is less effective than potassium. Besides, strontium improved the dispersion of iron oxide. Strontium did not significantly affect the activity of FTS and water gas shift (WGS), but facilitated the oxidation of iron carbides to Fe3O4 during FTS reaction process, while potassium significantly improved the FTS and WGS activity and inhibited the oxidation of iron carbide. Both of strontium and potassium decreased the selectivity of methane while facilitated the formation of heavy hydrocarbons and olefin, whatever, strontium exhibited a weaker effect compared to potassium.