Observation of epsilon iron carbide formation by environmental transmission electron microscopy. Source: Eindhoven University of Technology

New iron-based catalysts are expected to lower the operating costs of coal to liquid fuel conversion (CTL) facilities while enabling the capture of generated carbon dioxide.

The first stage is the conversion of coal to syngas. During CTL, the mixture of carbon monoxide and hydrogen produced by the Fischer-Tropsch process is converted to liquid fuels. Some of the CO is removed from the syngas by converting it to CO₂ in a water-gas shift reaction.

The CTL catalysts used to drive the process are mainly iron-based and convert about 30% of the CO to unwanted CO₂. The carbon dioxide is difficult to capture and is often released in large volumes, consuming a lot of energy without benefit.

Researchers from the National Institute of Clean-and-Low-Carbon Energy in Beijing and Eindhoven University of Technology in the Netherlands determined that the CO₂ release occurs because the iron-based catalysts are not pure, but instead consist of several components. A pure form of a specific iron carbide — epsilon iron carbide — was developed that has a very low CO₂ selectivity. The stable catalyst remains functional even under typical industrial processing conditions of 23 bar and 250° C and eliminates nearly all CO₂ generated in the Fischer-Tropsch reactor. This can reduce the energy needed and slash the operating costs by roughly €25 million ($29 million) per year for a typical CTL plant.

The CO₂ that was previously released in this stage can now be removed in the preceding water-gas shift stage by means of carbon capture, utilization and storage technology.

The research is published in Science Advances.