New Insights into the Catalytic Performance of Na-Promoted Fe/Al2O3 Catalyst in Fischer-Tropsch Synthesis

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