Structural and Electronic Rearrangements in Fe2S2, Fe3S4, and Fe4S4 Atomic Clusters under the Attack of NO, CO, and O2

First-Principles Perspective on Gas Adsorption by [Fe4S4]-Based Metal-Organic Frameworks

[Fe₄S₄] or [4S-4Fe] clusters are responsible for storing and transferring electrons in key cellular processes and interact with their microenvironment to modulate their oxidation and magnetic states. Therefore, these clusters are ideal for the metal node of chemically and electromagnetically tunable metal-organic frameworks (MOFs). To examine the adsorption-based applications of [Fe₄S₄]-based MOFs, we used density functional theory calculations and studied the adsorption of CO₂, CH₄, H₂O, H₂, N₂, NO₂, O₂, and SO₂ onto [Fe₄S₄]⁰, [Fe₄S₄]²⁺, and two 1D MOF models with the carboxylate and 1,4-benzenedithiolate organic linkers. Our reaction kinetics and thermodynamics results indicated that MOF formation promotes the oxidative and hydrolytic stability of the [Fe₄S₄] clusters but decreases their adsorption efficiency. Our study suggests the potential industrial applications of these [Fe₄S₄]-based MOFs because of their limited capacity to adsorb CO₂, CH₄, H₂O, H₂, N₂, O₂, and SO₂ and high selectivity for NO₂ adsorption.

Interaction Study of Oxygen and Iron-Sulfur Clusters Based on the Density Functional Theory

For the petrochemical industry, the spontaneous burning of iron sulfide compounds has been a major issue. In this study, XRD characterization of samples of iron sulfide compounds with spontaneous combustion tendency revealed that amorphous FeS was the primary constituent of the samples. A molecular simulation was used to build an amorphous FeS cluster model, and the density functional theory was used to examine the adsorption and reactivity characteristics of Fe4S4 clusters with O2. Different adsorption structures are generated by considering different adsorption sites and the electronic characteristics of each adsorption structure are evaluated. The results show that O2 prefers to adsorb around Fe atoms and has repulsion with S atoms, and the adsorption energy is maximum when two O atoms are co-adsorbed around Fe atoms, which is 198.13 kJ/mol. After adsorption charge, oxygen is in the superoxide state. The calculation of the reaction path divides the reaction process into different stages and considers different reaction routes. A thorough evaluation of the energy barriers and reaction energies of the two exothermic reactions leads to the conclusion that reaction path 1 is the optimal reaction path, and the reaction can release a total of 582.76 kJ/mol of heat. According to calculations, dimeric sulfur S2 must absorb a large part amount of energy in order to conduct the oxidation process. However, because S2 is present in the Fe4S4 reaction system, it may start the oxidation reaction by absorbing heat from the system and releasing 470.94 kJ/mol of heat. As a result, we conclude that this spontaneous exothermic reaction is a major cause of iron sulfide compounds spontaneous combustion. The thermal oxidation of the dimeric sulfur S2 generated in the reaction system releases heat that aggregates with the heat from the Fe4S4 cluster’s oxidation reaction system, eventually causing spontaneous combustion as a result of the heat’s continual buildup. In this study, we explore the reason for the extremely easy oxidation and spontaneous burning of iron sulfide compounds from a microscopic perspective to provide a theoretical foundation for the prevention and control of iron sulfide compound spontaneous combustion in the petrochemical sector.