DFT Study of Oxidation States on Pyrite Surface Sites

Abstract

Density functional calculations have been performed to study the interaction of oxygen with clean and defective pyrite (100) surfaces. Molecular adsorption states are predicted to undergo dissociation because atomic chemisorption is far more favorable thermodynamically for all surfaces. On the defect-free FeS2 surface molecular adsorption takes place on neighboring iron sites in a side-on fashion. S-adatoms react weakly with O2 whereas S-vacancies bind very strongly molecular oxygen. Dissociative chemisorption on clean surface prefers the sulfur atoms to iron in sharp contrast to water adsorption. Reaction with atomic oxygen is thermodynamically preferred on the defect sites when they are available. Oxidation can fully eliminate the S-adatom sites by SO2 formation. The most favorable sites for oxidation are sulfur vacancies where O atoms can occupy the missing sulfur sites. The predicted oxidation states and their relative stabilities are in agreement with experiments and expected to assist the interpretation of XPS measurements.

Photo-Driven Syngas Conversion to Lower Olefins over Oxygen-Decorated Fe5C2 Catalyst

“…This suggests that the surface O atoms can modify the local electronic structure and optical band gap of the surface. 41,42 Under photoirradiation, the domain products are preferred over olefins on oxygen-decorated Fe 5 C 2 (111), whereas for pure Fe 5 C 2 (111), the formation of alkane is more favorable. We believe that (1) the presence of Fe 5 C 2 in the oxygen-decorated catalyst is responsible for the light-heat transformation and (2) the existence of a small amount of FeO x species on Fe 5 C 2 as a heterostructure also absorbed light, was stimulated, and interacted with the reactants, resulting in a different reaction path and different product distribution.…”

Unravelling the early oxidation mechanism of zinc phosphide (Zn3P2) surfaces by adsorbed oxygen and water: a first-principles DFT-D3 investigation

“…At the (101) ) species. A number of earlier ab initio calculations have also identified the formation of a superoxo and peroxo species via electron transfer from iron sulfide mackinawite 39 and pyrite [57][58][59] surfaces. For water adsorption, whereas less charge is transferred from the (001), (101) and (110) surfaces to the molecular water species, a significant amount of charge is drawn by the dissociated species.…”

How Do Surface Defects Change Local Wettability of the Hydrophilic ZnS Surface? Insights into Sphalerite Flotation from Density Functional Theory Calculations

“…In realistic mineral systems, the existence of surface imperfections (e.g., vacancies, impurities, etc.) is inevitable. − The presence of any imperfection alters the interactions between adsorbents and adsorbates. ,− Using a semiempirical quantum-chemical approach, Simpson et al revealed that the degree of wettability of the sphalerite surface depends critically on the impurity levels. Correspondingly, doping the ZnS surface with Cu and Fe atoms altered the hydrophobic nature of the surface with the order of Cu-doped > undoped > Fe-doped ZnS surface.…”

“…Correspond-ingly, doping the ZnS surface with Cu and Fe atoms altered the hydrophobic nature of the surface with the order of Cu-doped > undoped > Fe-doped ZnS surface. In another study, Rozgonyiet and Stirling 42 simulated the oxidation behavior of defect-free and sulfur-deficient pyrite surfaces by DFT. The results showed that for the S-deficient slab, the O 2 molecule prefers to adsorb on the S-vacant site, either in the molecular or dissociative manner.…”