Fischer–Tropsch Synthesis: Effect of Potassium on Activity and Selectivity for Oxide and Carbide Fe Catalysts

Click on the DOI link to access the article (may not be free).The effect of potassium on oxides and carbides of iron for Fischer-Tropsch synthesis (FTS) was investigated by pretreating Fe3O4 and K-promoted Fe catalysts with different gases (H-2/H2O and CO). A freshly activated sample and catalysts that were recovered from the CSTR before, during and after FT synthesis were characterized ex situ using Mossbauer spectroscopy. Iron carbide is found to be active for both FT and water gas shift (WGS) reactions. After H-2/H2O activation, all three catalysts (Fe3O4, low alpha-Fe, and high alpha-Fe) exhibit a steady but low FT activity for a period of FT synthesis. However, both FT and WGS activity for Fe3O4 and low alpha-Fe catalysts were greatly improved after CO activation. In contrast, the high potassium containing catalyst (high alpha-Fe) did not show any further improvement in activity after CO activation. The difference in FT and WGS activity observed after pretreatment conditions using these catalysts may be associated to the amount of potassium and conversely the iron carbide present in the catalysts.This work was supported by the Commonwealth of Kentucky

Hydrocarbons via CO2 Hydrogenation Over Iron Catalysts: The Effect of Potassium on Structure and Performance

We present a study in which the suitability of potassium promoted iron-based Fischer–Tropsch (FT) catalysts for the generation of synthetic natural gas additives via the hydrogenation of carbon dioxide through a combined reverse water gas shift (WGS) and FT reaction is studied. Using novel in situ instrumentation based on XRD and magnetometry techniques the reversible conversion of metallic iron to Hägg carbide under reaction conditions and its decomposition in hydrogen could be monitored. The facilitating effect of potassium in the formation of iron carbide could be exposed as function of time on stream. While the FT reaction was reduced in the presence of high potassium loadings the reverse WGS reaction seemed to be unperturbed. A faster activation of an iron phase obtained via the decomposition of iron carbide, compared to the initial activation of a pristine iron phase obtained via the reduction of iron oxide was witnessed.National Research Foundation (South Africa