Trace-level halogen blocks CO₂ emission in Fischer-Tropsch synthesis for olefins production

Sustainable production of fuels and olefins from syngas (carbon monoxide and hydrogen) through the Fischer-Tropsch synthesis process requires catalysts that deliver high selectivity, industrial productivity, and minimal carbon dioxide (CO₂) emissions. Current industrial iron catalysts form substantial CO₂ by-product that limits carbon efficiency. We report that introducing trace amounts [parts per million (ppm) level] of halogen-containing compounds into the feed gas can suppress CO₂ formation using iron-based catalysts and boost olefin selectivity over paraffin and olefin productivity. Cofeeding 20 ppm bromomethane over an iron carbide catalyst decreased CO₂ selectivity to <1% and increased olefin selectivity to ~85% among all carbon-containing products. Surface-bound halogens modulated the catalyst surface structure and selectively inhibited pathways responsible for CO₂ generation and olefin hydrogenation. This strategy provides a simple, scalable, and broadly applicable route for carbon-efficient syngas conversion.