Catalytic water dissociation by greigite Fe3S4surfaces: density functional theory study.
The iron sulfide mineral greigite, Fe3S4, has shown promising capability as a hydrogenating catalyst, in particular in the reduction of carbon dioxide to produce small organic molecules under mild conditions. We employed density functional theory calculations to investigate the {001},{011} and {111} surfaces of this iron thiospinel material, as well as the production of hydrogen ad-atoms from the dissociation of water molecules on the surfaces. We systematically analysed the adsorption geometries and the electronic structure of both bare and hydroxylated surfaces. The sulfide surfaces presented a higher flexibility than the isomorphic oxide magnetite, Fe3O4, allowing perpendicular movement of the cations above or below the top atomic sulfur layer. We considered both molecular and dissociative water adsorption processes, and have shown that molecular adsorption is the predominant state on these surfaces from both a thermodynamic and kinetic point of view. We considered a second molecule of water which stabilizes the system mainly by H-bonds, although the dissociation process remains thermodynamically unfavourable. We noted, however, synergistic adsorption effects on the Fe3S4{001} owing to the presence of hydroxyl groups. We concluded that, in contrast to Fe3O4, molecular adsorption of water is clearly preferred on greigite surfaces.
School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, UK.
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Roldan
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK; Department of Earth Sciences, Utrecht University, Princetonplein 9, Utrecht 3584 CC, The Netherlands.
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de Leeuw
electronic structure; iron sulfide; magnetite; solid–water interface; synergistic adsorption