Fischer-tropsch synthesis: Effect of potassium on activity and selectivity for oxide and carbide fe catalysts

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 (H₂/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 Mössbauer spectroscopy. Iron carbide is found to be active for both FT and water gas shift (WGS) reactions. After H₂/H₂O activation, all three catalysts (Fe₃O₄, low α-Fe, and high α-Fe) exhibit a steady but low FT activity for a period of FT synthesis. However, both FT and WGS activity for Fe₃O₄ and low α-Fe catalysts were greatly improved after CO activation. In contrast, the high potassium containing catalyst (high α-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. Graphical Abstract: [Figure not available: see fulltext.]