A simple synthesis method converts iron oxide to a highly pure form of iron carbide, yielding a catalyst for industrial carbon-coupling reactions that produces exceptionally low quantities of CO2, according to a study (Sci. Adv. 2018, DOI: 10.1126/sciadv.aau2947). The finding may improve efficiency and may also reduce the energy consumption and cost of operating Fischer-Tropsch (FT) reactors, which convert synthesis gas, or syngas (CO + H2), to liquid hydrocarbons such as diesel fuel. Iron- and cobalt-based catalysts both drive FT chemistry. Iron catalysts are less expensive, but they convert up to 30% of the CO in syngas to unwanted CO2, which lowers process efficiency and is costly to separate. So a team led by Emiel J. M. Hensen of Eindhoven University of Technology examined conventional iron FT catalysts and found that in addition to containing iron carbide, the desirable component, they also contain metallic iron and iron oxides, the CO2-forming culprits. The team evaluated preparation methods and found they could make highly pure iron carbide from low-cost iron oxide by fully reducing the starting material in hydrogen and then treating it with nitrogen-diluted syngas. Under industrial conditions, the new catalysts generated as little as 5% CO2 and remained stable for more than 150 hours.