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Fossil Fuels

Catalyst drives carbon-coupling chemistry without making CO2

Highly pure form of iron carbide may improve efficiency and lower cost of Fischer-Tropsch process

by Mitch Jacoby
October 14, 2018 | A version of this story appeared in Volume 96, Issue 41


This molecular model shows an iron carbide catalyst making hydrocarbons from CO and hydrogen.
Credit: Robin J.P. Broos, Emiel J. M. Hensen
A pure iron carbide catalyst makes hydrocarbons from CO and H2 while producing almost no CO2. Orange = Fe. Black = C. Red = O. White = H.

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.


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