Atomistic Analysis of Sulphonamides as a Microbial Influenced Corrosion (MIC) Inhibitor

Four sulfonamide-type microbial inhibitors were studied using density functional theory (DFT) to assess their effectiveness in controlling microbial corrosion. The experimental techniques (FTIR, SEM, EIS, EFM, and AFM) are beneficial for measuring properties such as chemical composition, bond formation, electrochemical behavior, and surface topography; however, DFT can be useful as a new method for understanding microbial corrosion. Sulfacetamide (SFC), sulfamerazine (SFM), sulfapyridine (SFP), and sulfathiazole (SFT) uniformly adsorb onto the iron surface and block the active site, reducing the corrosion rate. To study the effect on microbial activity, a 0.6 eV electric field was applied. The absolute increase in the interaction energy indicates that sulfonamides are effective microbial inhibitors. Electronic SFC, SFM, SFP, and SFT descriptors agree with the experimental inhibition efficiency. The shift of the density of state (DOS) toward a low energy level for sulfonamides indicates the stabilization of these molecules at the Fe (100) surface. The population analysis combined with atomic and molecular parameters further explains the anticorrosive mechanism of sulphonamides.

Reaction Dynamics of CO2 Hydrogenation on Iron Catalysts Using ReaxFF Molecular Dynamics Simulation

The conversion of CO2 to hydrocarbons using catalysts is a promising route to utilize CO2 and produce more valuable chemicals in a sustainable manner. Recent studies have shown that iron-based catalysts perform well for the hydrogenation of CO2. While the hydrogenation reaction mechanism in the gas phase is straightforward, when catalyzed by iron it has been demonstrated to involve various chemical transformations, and the selectivity and conversion are strongly dependent on the particle size. To further investigate the dependence of the reactivity of iron catalysts on cluster size, we performed reactive molecular dynamics simulations using the ReaxFF force field (ReaxFF-MD) for iron nanoclusters of various sizes in a CO2 and H2-rich environment. We demonstrated that the homogeneous hydrogenation of CO2 was correctly described by this ReaxFF model. The dissociation mechanism of CO2 on the Fe4, Fe16 clusters, and the bcc(100) Fe slab agrees with previous DFT results. The ReaxFF-MD simulations suggest a strong dependence of reactivity on the cluster size, with the Fe4 cluster having the highest reactivity. We show that ReaxFF-MD provides a route to understand reaction mechanisms in these nonequilibrium reactive processes where fast processes and local minima are important.

Sulfide (H2S) Corrosion Modeling of Cr-Doped Iron (Fe) Using a Molecular Modeling Approach

This work presents the use of density functional theory to study the adsorption/dissociation mechanism of the H₂S molecule at the Cr-doped iron (Fe(100)) surface. It is observed that H₂S is weakly adsorbed on Cr-doped Fe; however, the dissociated products are strongly chemisorbed. The most feasible path for disassociation of HS is favorable at Fe compared to Cr-doped Fe. This study also shows that H₂S dissociation is a kinetically facile process, and the hydrogen diffusion follows the tortuous path. This study helps better understand the sulfide corrosion mechanism and its impact, which would help design effective corrosion prevention coatings.

Effect of Impurity Atoms on the Adsorption/Dissociation of Hydrogen Sulfide and Hydrogen Diffusion on the Fe(100) Surface

In the actual environment, impurity atoms significantly affect the adsorption/dissociation of gas molecules on the substrate surface and in turn promote or impede the formation of subsequent products. In this study, we investigate the effects of three kinds of impurity atoms (H, O, and S) on the adsorption/dissociation of hydrogen sulfide (H₂S) and hydrogen (H) diffusion processes by using the density functional theory method. We found that impurity atoms can change the charge density distribution of the surface and thus affect the adsorption/dissociation process of H₂S. The existence of a H atom reduces the dissociation barrier of H₂S. The adsorption site of H₂S near the O atom is transferred from the bridge site to the adjacent top site and the first-order dissociation barrier of H₂S is 0.07 eV, which is prominently lower than that of the pristine surface (0.28 eV). The presence of a S atom transfers the adsorption site of H₂S to a farther bridge site and effectively affects the dissociation process of H₂S. Both O and S atoms hinder the dissociation process of HS. Moreover, the diffusion process of H atoms to the subsurface can be slightly impeded by the O atom. Our work theoretically explains the influence mechanism of impurity atoms on the adsorption/dissociation of H₂S and H diffusion behavior on the Fe(100) surface.

Theoretical study on water adsorption and dissociation on the nickel surfaces

Using density functional theory methods, H₂O dissociation was investigated on the Ni(111), Ni(100), and Ni(110) surfaces. H and O atom as well as OH species adsorb stably at the high coordination sites. While on the Ni(110) surface, the OH species prefers at the twofold short bridge site because the adsorption on the fourfold hollow site is less feasible due to the increased distances between the nickel atoms. The amount of charge transfer is related to the adsorption stability. The more charge transfer, the more stable the adsorption. The charge transfer decreases in the order of O > OH > H. H₂O molecule adsorbs at the top site in a configuration parallel to the surface. The final products are different for H₂O dissociation due to the different mechanisms. On the Ni(111) surface, the final product is the O atom. On the Ni(100) and Ni(110) surfaces, the most abundant species are OH and H, but the reaction mechanisms were different. It is not necessary to linear BEP relationship for a given reaction on different surfaces. These results could provide fundamental insights into water behaviors and a favorable theoretical basis for further understanding and research on the interaction between water and metal surfaces.

Exploring direct and hydrogen-assisted CO activation on iridium surfaces – surface dependent activity

To understand CO activation on iridium surfaces, direct dissociation, H-assisted activation and hydrogenation to methanol were computed on the flat Ir(111) and Ir(100), corrugated Ir(110) and Ir(210), and stepped Ir(311) and Ir(221) surfaces.

Photochemistry of Fe:H2O Adducts in Argon Matrixes: A Combined Experimental and Theoretical Study in the Mid-IR and UV-Visible Regions

The photochemistry of Fe:H₂O adducts is of interest in fields as diverse as catalysis and astrochemistry. Industrially, iron can be used as a catalyst to convert H₂O to H₂, whereas in the interstellar medium it may be an important component of dust grains, influencing the chemistry on their icy surfaces. This study consisted of the deposition and spectral characterization of binary systems of atomic iron with H₂O in cryogenic argon matrixes. In this way, we were able to obtain information about the interaction of the two species; we observed the formation of adducts of iron monomers and dimers with water molecules in the mid-IR and UV-visible spectral domains. Upon irradiation with a UV radiation source, the iron species were inserted into the water molecules to form HFeOH and HFe₂OH, leading in some cases to the formation of FeO possibly accompanied by the production of H₂. DFT and correlated multireference wave function calculations confirmed our attributions. This combination of IR and UV-visible spectroscopy with theoretical calculations allowed us to determine, for the first time, the spectral characteristics of iron adducts and their photoproducts in the UV-visible and in the OH stretching region of the mid-IR domain.