New insights into the catalytic performance of Na-promoted Fe/Al2O3 catalyst in Fischer-Tropsch synthesis

Abstract

Na in Fe-based catalysts can be used to increase CO conversion and C₂-C₄ olefins and decrease the conversion of H₂ and C₁ selectivity, but its behaviour at different reaction temperatures is of importance in Fischer-Tropsch synthesis (FTS). The dependency of the C₁ formation rate, the conversions of H₂ and CO, the water-gas shift reaction, the olefins and paraffins of the C₂-C₄ and C₅-C₁₂ hydrocarbons, and C₁₃₊ hydrocarbons on the reaction temperature for prepared Fe/Al₂O₃ and FeNa/Al₂O₃ catalysts was evaluated in a tubular fixed-bed reactor. This was done to investigate the effects of Na in Fe-based catalyst at different reaction temperatures (250 – 310 °C). The results show that the effects of Na in Fe-based catalysts to increase CO conversion and decrease H₂ conversion are dependent on the reaction temperature in FTS. The Na-promoted Fe-based catalyst (FeNa/Al₂O₃) gave a lower C₁ formation rate at certain lower reaction temperatures (250 °C and 270 °C) compared to the unpromoted Fe-based catalyst (Fe/Al₂O₃). The presence of Na in the Fe-based catalyst improved the C₁ formation rate at certain higher reaction temperatures (290 °C and 310 °C). Na was found to hinder the selectivity towards C₂-C₄ paraffins and C₁₃₊ hydrocarbons, including the oxygenates, and improve the formation of C₂-C₄ olefins and C₅-C₁₂ hydrocarbons at different reaction temperatures.