Imagine turning the culprit behind global warming into building blocks for everyday essentials. Through certain chemical processes, carbon dioxide (CO2)—a growing threat to our planet—can be converted into fuels, plastics and other chemicals that power our modern lives.
One such promising process is the Modified Fischer-Tropsch (MFT), which turns CO2 and hydrogen gas into valuable chemical feedstocks through a pair of sequential reactions. However, despite MFT’s potential, it faces a major hurdle that impedes its long-term industrial use: the iron (Fe)-based catalysts that currently power its reactions gradually lose their potency over time.
According to Juan Manuel Arce-Ramos, a Senior Scientist at A*STAR’s Institute of High Performance Computing (IHPC), a deeper understanding of how these catalysts are deactivated and regenerated can help researchers develop more durable and efficient strategies for industrial CO2 reduction.
To explore this, a team comprised of Arce-Ramos and colleagues from IHPC, the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), and industry partner IHI Corporation combined benchtop experiments with density functional theory (DFT) simulations to take a close look at Fe-based catalysts for MFT.
“Like a super-powered microscope, DFT allows us to zoom in to the atomic level and see what’s happening inside catalysts during chemical reactions,” said Arce-Ramos. “By combining simulations with experimental data, we can observe how atoms interact and chemical bonds break and form under different conditions. This lets us paint a more complete picture of why these catalysts stop working, and how we can undo that.”
(a) A simplified model of a reactor that converts CO2 and H2 into hydrocarbons (CxHy). Inside, the iron-based catalyst transitions from active iron carbide (Fe5C2, in blue) into deactivated iron oxide (Fe3O4, in red) as it moves from the reactor’s entrance to its exit. These changes, which affect the catalyst’s activity, occur as the reactant gas mixture evolves in the reactor, consuming some compounds and producing others. (b) An illustration of CxHy production from CO2 and H2 within the reactor. As oxygen (red spheres) from CO2 accumulates on the catalyst’s surface, it eventually forms Fe3O4, which can still aid the conversion of CO2 and H2 into carbon monoxide (CO) and water (H2O), but cannot then convert CO into CxHy.
Their research showed that an Fe-based catalyst which begins as a carbide (an iron-carbon compound) undergoes progressive oxidation during MFT reactions. Oxygen atoms from CO2 slowly replace carbon atoms in the catalyst, leading to its eventual deactivation. “It’s a bit like how rust gradually weakens and changes the colour of iron,” Arce-Ramos added.
In search of solutions, the team found that spent catalysts, which had turned into iron oxide, could be revived for reuse through a two-stage process. The team first used hydrogen to remove oxygen from the catalysts, reducing them back to their metallic state, then reintroduced carbon to them through a process called carburisation.
These insights can pave the way for developing more resilient and efficient MFT catalysts. “By modifying the catalyst’s surface properties to make it easier to shake off oxygen, or increasing the presence of specific iron oxides that are more effective in certain reactions, we can enhance the catalyst’s performance and durability,” said Arce-Ramos.
The team plans to continue advancing decarbonisation technologies, with future work focusing on data-driven techniques, such as machine learning, to study more complex catalytic systems.
“Besides thermochemical processes like MFT, we’re actively exploring electrocatalytic methods to transform CO2 into valuable chemicals,” said Arce-Ramos.
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing (IHPC) and the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2).
