In situ XAFS research on the formation mechanism of (Fe_xCo_y)₂C for higher alcohol synthesis

Higher alcohol synthesis (HAS) via the Fischer–Tropsch process from syngas is a promising technology for advancing renewable energy applications. This method serves as an effective substitute for fossil fuels and contributes to reducing greenhouse gas emissions. The FeCo bimetallic alloy carbide (Fe_xCo_y)₂C has been shown to optimize the dual active interface and promote the production of higher oxygenates. However, understanding the dynamic interactions between metallic components under reaction conditions remains a significant challenge. In this study, we evaluate FeCoK and FeCo catalysts produced through precipitation, as well as the FeK/CoK catalyst created via physical mixing, for their performance in HAS. These catalysts exhibit notable differences in activity and product selectivity. Our investigation into the structure–performance relationship indicates that FeCoK, with (Fe_xCo_y)₂C as its active site, demonstrates the highest activity and selectivity for alcohol production. To further elucidate the formation mechanism of the FeCo alloy carbide, we conduct in situ X-ray absorption fine structure (XAFS) tests. The results reveal that Co in the FeCo alloy adopts a body-centered cubic structure, differing from the more common Fischer–Tropsch catalyst structures (face-centered cubic or hexagonal close-packed). Further research into the carburization of the FeCo alloy proposes two essential conditions for the formation of (Fe_xCo_y)₂C via the regular thermochemical method: The carburization must originate from the alloy, and an alkali promoter must be present.