Reactivity of CO₂ on the surfaces of magnetite (Fe₃O₄), greigite (Fe₃S₄) and mackinawite (FeS)

The growing environmental, industrial and commercial interests in understanding the processes of carbon dioxide (CO₂) capture and conversion have led us to simulate, by means of density functional theory calculations, the application of different iron oxide and sulfide minerals to capture, activate and catalytically dissociate this molecule. We have chosen the {001} and {111} surfaces of the spinel-structured magnetite (Fe₃C₄)and its isostructural sulfide counterpart greigite (Fe₃S₄), which are both materials with the Fe cations in the 2+/3+ mixed valence state, as well as mackinawite (tetragonal FeS), in which all iron ions are in the ferrous oxidation state. This selection of iron-bearing compounds provides us with understanding of the effect of the composition, stoichiometry, structure and oxidation state on the catalytic activation of CO₂. The largest adsorption energies are released for the interaction with the Fe₃C₄ surfaces, which also corresponds to the biggest conformational changes of the CO₂ molecule. Cur results suggest that the Fe₃S₄ surfaces are unable to activate the CO₂ molecule, while a major charge transfer takes place on FeS{111}, effectively activating the CO₂ molecule. The thermodynamic and kinetic profiles for the catalytic dissociation of CO₂ into CO and O show that this process is feasible only on the FeS{111} surface. The findings reported here show that these minerals show promise for future CO₂ capture and conversion technologies, ensuring a sustainable future for society. This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'. http://dx.doi.org/10.1098/rsta.2017.0065.