Effect of Ca Promoter on the Structure and Catalytic Behavior of FeK/Al₂O₃ Catalyst in Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) to olefins is an alternative route for lower olefins production. The role of alkaline-earth metals as promoters in FTS was not so clear. Herein, we prepared a series of FeKCa/Al₂O₃ catalysts by excessive co-impregnation method to elucidate the promotion effect of Ca on catalytic performance. Characterization technologies of N₂ physisorption, XRD, Raman spectrum, TEM and CO chemisorption were used to study the textural properties, phase composition and dispersion of Fe species. The results showed that the addition of Ca promotes dispersion of iron species thus leads to much smaller crystallite size. Meanwhile, no electron donation effect was observed upon Ca introduction, as evidenced by XPS and H₂-TPR. A maximum of FTY is achieved at 1.0 wt.% Ca, followed by a decline when adding excessive Ca due to less exposed active sites. Notably, the product distribution is almost unchanged. The nearly constant TOF values with and without Ca addition indicates Ca works only as a structural promoter rather than chemical promoter.