Highly Selective Bifunctional Iron-Zeolite Catalysts for the Production of Liquid-Range Hydrocarbons Via Fischer-Tropsch Synthesis: Correlation between Acidity and Hydrocarbon Distribution

Fischer-Tropsch synthesis (FTS) was carried out over bifunctional catalysts prepared by physically mixing precipitated iron-based FTS catalysts (P-Fe) and H-ZSM-5. We adjusted the acidity of bifunctional catalysts by varying the ratio of P-Fe/H-ZSM-5 and the ratio of Si/Al in the H-ZSM-5. The physical mixing of H-ZSM-5 was adequate to supply the Brønsted acid sites (BAS), which are nonexistent in the P-Fe, to the bifunctional catalysts without deteriorating the catalytic activity of P-Fe. As a result, the bifunctional catalysts showed high CO conversion (73–78%), comparable to that of P-Fe (73%), and improved C 5 –C 20 selectivity with increased BAS concentration. The highest C 5 –C 20 selectivity obtained in this study (72 wt%) was twice higher than that obtained in the P-Fe (36 wt%). Furthermore, we found a linear correlation between the cracking rate and the BAS concentration in the bifunctional process of FTS and cracking for the first time.