γ-Fe2O3 as the precursor of iron based catalyst prepared by solid-state reaction at room temperature for Fischer-Tropsch to olefins

Abstract

Iron catalyst was fabricated via simple solid-state reaction of metal nitrates mixture (Fe, K, Al, Ca, Mg, Sm) with oxalic acid dihydrate at room temperature. Iron catalysts prepared by conventional methods, such as co-precipitation and fusing, are also included as comparison. The performances of catalysts were evaluated by the Fischer-Tropsch Synthesis (FTS) in a fixed bed reactor. The results indicate that uniform nanoparticles were obtained with surface area as high as 38.7 m2/g prepared by solid-state reaction. Following calcination at 500 °C, γ-Fe2O3 were obtained as the catalyst precursor. By contrast, α-Fe2O3 was the main precursor derived from co-precipitation. In addition, γ-Fe2O3 prepared by solid-state reaction facilitates the formation of active phase, Fe5C2 with the exposure of (021) facet. High Miller index surface (021) facilitates the adsorption and the dissociation of CO, which contributes the high activity and high selectivity to light olefins. Consequently, compared with conventional catalysts, solid-state reaction derived catalysts exhibit much higher FTO reaction activity and selectivity to lower olefins. The FTY value of 5.62 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1 was obtained which is almost two times higher than that of catalyst prepared by co-precipitation (3.19 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1) or 3 times higher than that of catalyst prepared by fusing method (1.98 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1). The selectivity to light olefins of around 40% is obtained which is significantly higher than that of the reference catalysts (25% and 33% respectively). The present study provides a promising pathway to prepare iron based catalysts at room temperature.