Controlling Oxide-to-Carbide Transformation Enables Highly Active and Carbon-Efficient Fe-Carbide Fischer-Tropsch Catalysts from Flame Spray Pyrolysis

Abstract

Achieving high activity while suppressing undesired methane and CO2 formation remains a central challenge in Fischer–Tropsch (FT) synthesis over iron catalysts. Here, we demonstrate that precise control over the oxide-to-carbide transformation enables highly active and carbon-efficient FT catalysts. A well-defined γ-Fe2O3 precursor synthesized by flame spray pyrolysis (FSP) provides uniform, nanosized particles that facilitate low-temperature carburization. Complete conversion to iron carbide is achieved at 275 °C under mild conditions, while minimizing residual oxides, particle sintering, and excessive carbon deposition. By combining in situ wide-angle X-ray scattering (WAXS), quasi-in situ X-ray photoelectron spectroscopy (XPS), and Mössbauer spectroscopy, we elucidate the phase evolution and surface dynamics during carburization. Rapid formation of χ-Fe5C2 is observed without detectable accumulation of metallic Fe, whereas prolonged treatment primarily results in surface carbon buildup rather than further carbide formation. The optimized catalyst exhibits high CO conversion with a combined CH4 and CO2 selectivity below 20%, demonstrating a promising balance between catalytic activity and product selectivity. Comparative studies reveal that the superior performance originates from enhanced carbide phase purity, suppressed carbon deposition, and improved dispersion. These findings highlight precursor engineering coupled with mild carburization as a general strategy for designing efficient iron-based FT catalysts.