Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2

Abstract

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives^1-3. Their conversion first generates syngas, a mixture of CO and H₂, which is then processed further using Fischer-Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present^4-8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO₂ waste that leads to a low carbon utilization efficiency^9-14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C₅-C₁₀ LAOs than are found in the C₂-C₄ olefins that dominate the product mixtures^9-14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1-2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. ^12-15), is stable for 200 h, and produces desired C₂-C₁₀ LAOs and unwanted CO₂ with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250-320 °C), demonstrates the potential of the system for developing a practically relevant technology.