Abstract
Metal sulphides constitute cheap, naturally abundant, and environmentally friendly materials for energy storage applications and chemistry. In particular, iron (II) monosulphide (FeS, mackinawite) is a material of relevance in theories of the origin of life and for heterogenous catalytic applications in the conversion of carbon dioxide (CO2) towards small organic molecules. In natural mackinawite, Fe is often substituted by other metals, however, little is known about how such substitutions alter the chemical activity of the material. Herein, the effect of Ni doping on the structural, electronic, and catalytic properties of FeS surfaces is explored via dispersion-corrected density functional theory simulations. Substitutional Ni dopants, introduced on the Fe site, are readily incorporated into the pristine matrix of FeS, in good agreement with experimental measurements. The CO2 molecule was found to undergo deactivation and partial desorption from the doped surfaces, mainly at the Ni site when compared to undoped FeS surfaces. This behaviour is attributed to the energetically lowered d-band centre position of the doped surface, as a consequence of the increased number of paired electrons originating from the Ni dopant. The reaction and activation energies of CO2 dissociation atop the doped surfaces were found to be increased when compared to pristine surfaces, thus helping to further elucidate the role Ni could have played in the reactivity of FeS. It is expected that Ni doping in other Fe-sulphides may have a similar effect, limiting the catalytic activity of these phases when this dopant is present at their surfaces.
Highlights
The production of fuels and organic molecule feedstock from captured CO2 and a hydrogen source, e.g., water, using renewable energy sources is considered a promising route towards achieving a sustainable and green future [1]
B FeS surfaces doped with Ni exhibit weaker binding as well as deactivation of ada Ni is readily incorporated substitutionally at the Fe site into the FeS matrix, where low formation energies indicate that it may be difficult to control the dopant concentration
B FeS surfaces doped with Ni exhibit weaker binding as well as deactivation of adsorbed CO2 molecules, when compared to the same process on undoped mackinawite surfaces
Summary
The production of fuels and organic molecule feedstock from captured CO2 and a hydrogen source, e.g., water, using renewable energy sources is considered a promising route towards achieving a sustainable and green future [1]. Iron sulphides constitute a distinct group of solids and complexes that play a key role in marine systems and global biogeochemical sulphur cycles, which are central to fundamental concepts about the evolution of the Earth surface environment [11] They have been associated as catalysts in a number of key biochemical reactions related to Origin of Life theories [11,12,13,14,15,16,17], and more recently, as a potential electron source for autotrophic denitrification [18], as well as chromium [19] and vanadium removal [20]. Due to the variety in composition and structure of iron sulphides, a broad range of oxidation states is possible for both the iron and sulphur, which makes these minerals remarkably reactive [8,21]
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