Effect of the Zr promoter on precipitated iron-based catalysts for high-temperature Fischer-Tropsch synthesis of light olefins

FeMnxZr and FeMnxZr2Na catalysts prepared by coprecipitation and impregnation methods were applied to investigate the promoting effects of Zr on iron-based catalysts for high-temperature Fischer-Tropsch synthesis (HTFT). Ar physisorption and TEM demonstrated that Zr-promoted catalysts have a larger BET surface area and larger pore volume, which are more conducive to the distribution of active phases. Zr promoted the dispersity of iron particles and reduced the grain size of iron particles, resulting in the improvement of the FTS activity. The CO-TPD and MES results revealed that the introduction of Zr promoted the dissociative adsorption of CO, thereby promoting the formation of the active phase chi-Fe5C2 while suppressing the formation of epsilon '-Fe2.2C and further improving the FTS activity and the selectivity to C-2(=)-C-4(=) in the hydrocarbon distribution. However, the addition of an excessive amount of Zr caused the excess ZrO2 to cover the surface of the active site, inhibiting the CO dissociative adsorption and the formation of chi-Fe5C2, resulting in a decrease in the CO conversion and the selectivity to C-2(=)-C-4(=). The XPS and H-2-TPR results proved the interaction between Fe2O3 and ZrO2. And the Fe-ZrO2 interaction inhibited the coke deposition and aggregation of the Fe species, as confirmed by XRD and TEM, respectively. The FeMn5Zr2Na catalyst exhibited the highest C-2(=)-C-4(=) selectivity of 34.4% at a CO conversion of 96.3%. And FeMn5Zr2Na displayed the highest production of light olefins (441.6 g h(-1) kg(Cat)(-1)), which was significantly higher than FeMn2Na (162.2 g h(-1) kg(Cat)(-1)).

Automated summary

FeMnxZr and FeMnxZr2Na catalysts with larger BET surface area and pore volume showed improved FTS activity and selectivity to C-2(=)-C-4(=) due to the promotion of Zr on dispersity of iron particles, dissociative adsorption of CO and formation of active phase chi-Fe5C2. However, excessive Zr addition inhibited CO dissociative adsorption and chi-Fe5C2 formation. The interaction between Fe-ZrO2 also inhibited coke deposition and aggregation of Fe species.