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

Abstract

To explore the influence of the rare earth element neodymium (Nd) on the production of light olefins (C⁼₂–C⁼₄) via high-temperature Fischer–Tropsch synthesis (HTFT), a series of FeMn-based catalysts promoted with Nd and Na were synthesized using a combination of coprecipitation and incipient wetness impregnation techniques. These included Nd-modified FeMnxNd (x = 0, 0.1, 0.4, 0.7, 1, and 2), FeMnNa, and FeMn0.7NdNa catalysts. The results indicate that Nd reduces catalyst particle size and increases the BET specific surface area. Nd enhances surface basicity, increases the electron density around Fe atoms, suppresses hydrogen adsorption, and promotes CO dissociative adsorption, thereby facilitating the formation of χ-Fe₅C₂ and improving Fischer–Tropsch synthesis (FTS) activity. However, excessive Nd loading results in Nd deposition on the catalyst surface, which decreases the BET surface area, induces particle agglomeration and growth, and inhibits catalyst reduction and carburization. These effects collectively reduce the content of χ-Fe₅C₂ and lead to inferior FTS performance. In contrast, the synergistic interaction of Nd–Na suppresses the formation of θ-Fe₃C, prevents particle agglomeration, and enhances the content of χ-Fe₅C₂, thereby significantly increasing CO conversion and light olefin yield. The FeMn0.7NdNa catalyst achieves a light olefin yield of 412.1 g h⁻¹ kg_Cat⁻¹, markedly surpassing that of FeMn0.7Nd and FeMnNa.