Cost‐Effective Synthesis of Fe₅C₂ Catalyst From Nanosized Zero‐Valent Iron to Achieve Efficient Photothermocatalytic CO Hydrogenation to Light Olefins

Abstract Fe‐based catalysts are commonly applied in the process of Fischer−Tropsch synthesis (FTS) to olefins, with Hägg iron carbide (Fe₅C₂) recognized as the primary active phase. However, iron carbonyls, the raw materials for wet chemical synthesis of Fe₅C₂, are expensive and toxic, which limits large‐scale preparation. Here, a cost‐effective and versatile method is proposed for the synthesis of Fe₅C₂ nanoparticles (NPs) with nanosized zero‐valent iron (abbreviated as NZVI, prepared by reducing iron salts or ball‐milling iron powder) instead of iron carbonyls, achieving a cost reduction of 76.8%. Experimental characterizations revealed that NZVI obtained from the reduction of iron salts can catalyze the cracking of octadecylamine to form a carbonized atmosphere, thus realizing the phase transition of Fe into Fe₅C₂. The optimized Fe₅C₂ catalyst is employed in the photothermocatalytic FTS process, achieving a light olefins selectivity of 54.2% in hydrocarbons, with a CO conversion of 24.3%. Furthermore, it is proved that the particle size and surface oxide state of NZVI can impact the synthesis of Fe₅C₂. This study demonstrates a cost‐effective method for the large‐scale preparation of the Fe₅C₂ catalyst.