Abstract
We present a theoretical investigation of the prismatic (0110) surface of troilite in an oxidizing environment, which aims to elucidate the presence of oxygen detected experimentally in the pyrrhotite Fe1–xS nanoparticles. We find that atomic oxygen adsorbs in Fe–O–Fe bridging motifs, which are thermodynamically stable under ambient conditions. During the first oxidation steps, the formation of the S–O bond is less favored than Fe–O, suggesting that the sulfur oxides detected experimentally form only subsequently. We predict, moreover, that substitution of sulfur for oxygen can occur. The appearance of Fe–O–Fe–O–Fe bridging motifs due to successive adsorptions points toward a clustering growth of the oxidic units. In agreement with the experimental observations, the oxidation of troilite is exothermic, where the equilibrium between adsorption and substitution is influenced by the presence of Fe vacancies.
Highlights
Iron sulfide surfaces play a pivotal role in a number of significant environmental processes
They can adsorb heavy metals and radionuclides, thereby providing an effective solution to the remediation of polluted water.[2−7] Considerable interest has been devoted to the role of iron sulfides as possible catalysts in the formation of the first organic compounds at hydrothermal vents,[8−11] where the formation of mackinawite FeS has been revealed in experiments simulating chimney growth under early Earth conditions.[12]
Pyrrhotites are very reactive toward molecular oxygen, which is incorporated into their surfaces.[17−21] In order for the catalytic mechanisms to be understood properly, we need to achieve a detailed knowledge of the oxidized substrate available to the reactants after exposure to ambient air
Summary
Iron sulfide surfaces play a pivotal role in a number of significant environmental processes. Pyrrhotites Fe1−xS (0 ≤ x ≤ 0.125), the most common iron sulfides in nature after pyrite FeS2, hold great potential as catalysts. Both molecular hydrogen[14] and oxygen[15] evolution, as well as the hydrogenation of azobenzenes,[16] have recently been shown to occur on their surfaces. Pyrrhotites are very reactive toward molecular oxygen, which is incorporated into their surfaces.[17−21] In order for the catalytic mechanisms to be understood properly, we need to achieve a detailed knowledge of the oxidized substrate available to the reactants after exposure to ambient air. We discuss how Fe vacancies affect the oxidation mechanism
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