Mechanism Of Oxidation Research Articles

Petrological and geochemical evidences for anaerobic and thermochemical oxidations of methane in petroliferous basins

Methane oxidation affects hydrocarbon accumulation and carbon cycling with important geological and paleoclimatic responses. However, the petrological and geochemical evidences that can clearly discern anaerobic (AOM) and thermochemical (TOM) oxidations in petroliferous basins are unclear, causing the disputes if these two processes can take place in specific conditions. Here, the Baikouquan Formation (T1b) in the Mahu Sag, Junggar Basin, China, was used as the first case study for comprehensive petrological and geochemical analyses to explore this scientific issue. Results indicate that the two main types of T1b calcite cement record different methane oxidation mechanisms. Calcite cements filling intergranular pores were formed during early diagenesis in relatively shallow-burial stages, through AOM with high-valence Mn oxides as electron acceptors, and with compositions of −47.5 ‰ < δ13C < −30.9 ‰, 1.1 wt% < MnO < 5.8 wt%, and 0.02 wt% < FeO < 0.13 wt%. Calcite cements filling intragranular dissolution pores were formed through TOM with high-valence Mn oxides as electron acceptors during mesogenesis during relatively deep-burial stages, with compositions of −39.7 ‰ < δ13C < −14.3 ‰, 0.43 wt% < MnO < 11.00 wt%, and 0.03 wt% < FeO < 0.36 wt%. Thus, methane oxidation underwent a transition from AOM to TOM with increasing depth, as recorded by the calcite cements with different occurrences. This transition may be a common feature of clastic strata in petroliferous basins.

Eugenol's electrochemical behavior, complexation interaction with copper chloride, antioxidant activity, and potential drug molecular docking application for Covid-19

Electrochemical studies were conducted to analyze the behavior of eugenol, CuCl2, and their complex using cyclic voltammetry. The oxidation mechanisms of eugenol and the redox behavior of copper ions were elucidated, showing differences in reversibility and charge transfer coefficients. Various kinetic and solvation parameters were determined. The redox behavior of CuCl2 was found to be more reversible compared to the copper-eugenol complex. The copper-eugenol complex exhibited enhanced antioxidant activity compared to eugenol and standard ascorbic acid. The eugenol was oxidized to form eugenol quinone methide through two postulated irreversible mechanisms. Molecular docking studies suggested higher potential bioactivity of the copper-eugenol complex towards the target protein of COVID-19 than the eugenol ligand.

Ab initio chemical kinetics and shock-tube experimental study on nitrocyclohexane pyrolysis and combustion

Nitrocyclohexane (NCH) is a model nitroalkane compound with naphthenic structural groups for studying the combustion properties of nitro-based energetic fuels, and also demonstrates significant potential applications for advanced engines. However, accurate description of the detailed kinetic mechanisms for pyrolysis and combustion of NCH receives little attentions. Herein, the detailed pyrolysis and oxidation mechanism of NCH is studied by using quantum chemistry calculations and chemical kinetic theory. The potential energy surfaces of the CN bond dissociation reaction, HONO elimination reaction, abstraction reactions of NCH as well as the subsequent β-scission reactions are calculated using G4//M06–2X/6–311++G(d, p) method, which are subsequently employed for reaction rate constant computations via transition state theory (TST) and RRKM/master-equation (RRKM/ME) method. The ab initio chemical kinetic study results are used to develop a detailed kinetic mechanism to predict the pyrolysis experimental results of NCH, which are performed using a single-pulse shock tube (SPST). The SPST experiment is performed at pressure of 10 bar, temperature ranging from 1070 to 1560 K, reaction time of around 1.77 microsecond with fuel concentrations of 0.5 % diluted by Argon gas. The developed detailed kinetic mechanism exhibits reasonable prediction results of the pyrolysis product distributions together with literature ignition delay times across a wide range of temperature, pressure, and equivalence ratio conditions. Rate-of-production analysis is conducted to gain insight into the pyrolysis chemical kinetics of NCH. The present work should be valuable for the study of the combustion chemistry of nitro-alkane energetic fuels.

Investigating the influence of pressure on the ignition and oxidation behavior of EV33 alloy

The study investigates ignition and oxidation behavior of Mg-3Nd-3Gd-0.2Zr-0.2Zn (wt.%) (EV33 alloy) in air and varying pressure. EV33 exhibits easy ignition in air but not under specific pressure conditions. Surface microstructure evolution and detailed discussion of ignition mechanisms using oxidation mechanism and residual stress of oxide film are presented. Findings suggest a correlation between alloy ignition and oxide film rupture. Surface oxidation film rupture is the direct cause of ignition in magnesium alloys, and this phenomenon has been observed and documented for the first time. The residual stresses calculated under atmospheric conditions and at pressures of 0.05 MPa, 0.1 MPa, and 0.15 MPa (with air as the pressure medium) are as follows: 0.282 GPa, 0.561 GPa, 2.271 GPa, and 5.242 GPa.

Probing the Mechanism and Impact of Light Oil Oxidation on In Situ Hydrogen Production from Petroleum Reservoirs: A Combined SARA-Based Experimental and Numerical Investigation

Probing the Mechanism and Impact of Light Oil Oxidation on In Situ Hydrogen Production from Petroleum Reservoirs: A Combined SARA-Based Experimental and Numerical Investigation

Study on the oxidation mechanism of Al-SiC composite at elevated temperature

Study on the oxidation mechanism of Al-SiC composite at elevated temperature

Performance and mechanism of electrocatalytic oxidation of urea based on carbon-doped FeCoNiCrMn high entropy alloy film

The application and research of high entropy alloy electrodes in urea oxidation reactions (UOR) are significant. In this study, FeCoNiCrMn, FeCoNiCrMnO, and FeCoNiCrMnC high entropy alloy thin films were prepared by magnetron sputtering by controlling the sputtering power, varying the sputtering atmosphere, and using double target co-sputtering, respectively. The microstructure and surface morphology of the electrode were observed and analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and atomic force microscope. In addition, the chemical state of the elements on the electrode surface was analyzed by X-ray photoelectron spectroscopy (XPS) to clarify the mechanism related to the excellent UOR performance of the electrode. The study found that a small amount of carbon doping can greatly improve the UOR performance of this type of electrode. The amorphous FeCoNiCrMnC electrode has more potential UOR active sites than the face-centered cubic FeCoNiCrMn electrode. After cyclic voltammetry (CV), the potential active sites of the electrode are activated, and the active substances of these electrodes are increased, furthermore, the UOR performance of these electrodes has improved. Since it has 200 cycles of CV, the 10 mA cm−2 potential of FeCoNiCrMnC electrode for UOR is only 1.337 V. After 100 days of natural aging, the catalytic ability of the electrode not only did not decrease but slightly improved, with a potential of 1.321 V at 10 mA cm−2, reflecting the good stability of the catalytic electrode.

Understanding of the irradiation response of Cr-based ATF coatings using in-situ TEM

Although CrNb coated zirconium alloy materials are considered as ATF candidates with excellent oxidation resistance and mechanical properties, the irradiation response behavior under harsh and complex service conditions is still unrevealed. Here, we report the evolution of the microstructure of pure Cr and CrNb coatings with different Nb contents under simultaneous irradiation with Cr+-He+-H2+ triple ion beams at 633 K by using an advanced in-situ transmission electron microscope (TEM). The results show that CrNb coatings with high Nb content have better irradiation stability. Under high-temperature irradiation conditions, irradiation-induced oxidation and grain growth or crystallization are observed for both Cr-8 Nb with a nanocrystalline structure and Cr-18 Nb coatings with an almost amorphous structure, whereas Cr-37 Nb coatings maintains relatively intact in the amorphous phase after irradiation at a dose of 10 dpa. Based on the in-situ tracking of the microstructural evolution, it is revealed that the mechanism of irradiation-accelerated oxidation and crystallization of coatings originates from displacement cascades enhancing local atomic diffusion and rearrangement.

Insights from Ca2+→Sr2+ substitution on the mechanism of O-O bond formation in photosystem II.

In recent years, there has been a steady interest in unraveling the intricate mechanistic details of water oxidation mechanism in photosynthesis. Despite the substantial progress made over several decades, a comprehensive understanding of the precise kinetics underlying O-O bond formation and subsequent evolution remains elusive. However, it is well-established that the oxygen evolving complex (OEC), specifically the CaMn4O5 cluster, plays a crucial role in O-O bond formation, undergoing a series of four oxidative events as it progresses through the S-states of the Kok cycle. To gain further insights into the OEC, researchers have explored the substitution of the Ca2+ cofactor with strontium (Sr), the sole atomic replacement capable of retaining oxygen-evolving activity. Empirical investigations utilizing spectroscopic techniques such as XAS, XRD, EPR, FTIR, and XANES have been conducted to probe the structural consequences of Ca2+→Sr2+ substitution. In parallel, the development of DFT and QM/MM computational models has explored different oxidation and protonation states, as well as variations in ligand coordination at the catalytic center involving amino acid residues. In this review, we critically evaluate and integrate these computational and spectroscopic approaches, focusing on the structural and mechanistic implications of Ca2+→Sr2+ substitution in PS II. We contribute DFT modelling and simulate EXAFS Fourier transforms of Sr-substituted OEC, analyzing promising structures of the S3 state. Through the combination of computational modeling and spectroscopic investigations, valuable insights have been gained, developing a deeper understanding of the photosynthetic process.

Environmental water-mediated dual-mechanism regulation of PtCuδ-MnOx-catalyzed acetone oxidation: Enhancement of MvK and inhibition of L-H mechanism

Environmental H2O has a significant effect on the reaction mechanism and process of VOC oxidation, of which the intrinsic mechanism is hardly reported. Herein, a series of PtCuδ-MnOx catalysts with different strong metal-supported interactions were constructed by replacing some Pt species with Cu species. Among them, the PtCu3-MnOx catalyst exhibited superior catalytic performance (T90 = 170 ℃), high water resistance, and long-term stability. Furthermore, in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTs) showed that the acetone oxidation followed synergistic cooperation of the Langmuir-Hinshelwood (L-H) and Mars van Krevelen (MvK) mechanism. Acetone oxidation over PtCu3-MnOx occurred via the L-H mechanism producing surface acetate and formate species intermediate. Above 100 °C, adsorbed acetone (i.e., acetate and formate species) reacts with MnOx lattice oxygen according to the MvK mechanism to form CO2 and H2O. When water vapor was present, the L-H mechanism was impaired, inhibiting the deep oxidation of acetone. This research provides an in-depth exploration of how water vapor impacts the reaction mechanism of acetone oxidation. It offers valuable insights for creating dependable catalysts suitable for use in various industrial settings.

Oxidation behavior of SiC‐AlN ceramics exposed to dry oxygen and water oxygen environments at 1100–1300°C

AbstractThe corrosion of SiCf/SiC composites in gas environment threatens their long‐term service in aeroengines as hot‐end structure components. Addition of corrosion‐resistant phases into SiC matrix is a potential strategy to improve the service performance of SiCf/SiC materials. Here, AlN added SiC ceramics were prepared by reactive melt infiltration, and the effect of AlN phase on the oxidation resistance of the ceramics was emphasized. The oxidation tests were performed in dry oxygen and water oxygen atmospheres at 1100°C–1300°C, respectively. The oxidation mechanism was discussed based on the microstructure evolution of the oxide layer. The results show that the oxide layer is composed of aluminum silicate glass and Al2O3 flakes dispersedly distributed in the glass phase. As the temperature rises, the oxide layer gradually grows and thickens. Finally, a smooth and dense protective layer could be formed on the surface of ceramics to resist oxidation. This study can provide a profound insight to construct SiCf/SiC composites with excellent oxidation resistance.

The beginning of iron corrosion - high-resolution visualization with 3D electron tomography

Understanding the genesis and early-phase reactions of iron corrosion is essential for the early detection, mitigation and prevention of metal degradation. In this work, high-resolution 3D tomography of metallic iron oxidation was acquired using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In particular, dendritic capillaries (<0.5 nm) were observed during the initial oxidation of fresh nanoscale zero-valent iron due to the differential oxygen diffusion and iron atoms migration. This observation led to the proposal of a nanoscale “pothole” model for early-phase corrosion, wherein hollowing out of the metal nanoparticle and formation of nanovoids beneath the iron/oxide interface through Kirkendall effect. Coalescence of the nanocapillaries results in the ultimate collapse of metal structure and/or functional failure. Using nanoscale zero-valent iron as a research model, this work provides unprecedented insights into the nano- and atomic-scale mechanisms of iron oxidation, paving the way for advanced detection and prevention strategies for iron corrosion.

Activation of Peroxymonosulfate by Fe, O Co-Embedded Biochar for the Degradation of Tetracycline: Performance and Mechanisms

In recent years, pollution stemming from pharmaceuticals has garnered widespread global concern, which exacerbates the ecological risk to both surface and groundwater. In the current study, Fe and O co-embedded biochar (Fe-O-BC) was synthesized through a one-step pyrolysis procedure with corncob serving as the feedstock. The fabricated Fe-O-BC catalysts were characterized by various techniques and were employed for the activation of peroxymonosulfate (PMS) to degrade tetracycline (TC). TC was rapidly degraded within 40 min, with a degradation rate of 0.1225 min−1, which was much higher than those for O-BC/PMS (0.0228 min−1) and Fe-BC/PMS (0.0271 min−1) under the same conditions. The effects of PMS dosage, Fe-O-BC dose, initial pH value and coexisting anions for TC degradation were investigated. Finally, the mechanism of TC oxidation in the catalytic system was implored through experiments of determining the active sites and radical scavenging experiments. The C-O-Fe bond in the catalyst was confirmed to be the dominant active sites accelerating TC degradation. Free diffused HO•, the surface-bound HO• and SO4•− and O2•−participated in the reaction and absorbed SO4•−, and HO• predominantly contributed to TC degradation. This study provides an efficient and green alternative for pharmaceutical wastewater treatment by Fe and O co-doped catalyst-induced heterogeneous process.

Wear behaviour analysis of thermo-mechanically processed AA7075 and AA7075/SiC/Graphite composite

The current work focuses on investigating the tribological performance of AA7075 alloy and AA7075 hybrid composite with SiC and graphite reinforcements of 2 and 0.5 wt percentages, respectively. The alloy and hybrid composite are fabricated through stir casting and thermo-mechanically processed through hot rolling routes. Dry sliding wear characterization has been carried out using a pin-on-disc wear testing setup for alloy and composite under various processing conditions using experiments designed according to Taguchi's L9 orthogonal array. The technique for order preference by similarity to ideal solution (TOPSIS) method has been adopted to achieve a single multi-response index (MRI) considering the minimization of multiple objective functions for specific wear rate (SWR) and coefficient of friction (COF). The analysis of variance (ANOVA) results of the MRI indicated that sample processing condition and load were the most significant parameters. The wear mechanism at different experimental conditions was studied using Scanning electron microscope (SEM) micrographs, energy dispersive spectroscopy analysis and 3D surface profile of wear track. The AA7075 composites are found to be comparatively good in all experimental conditions compared to the base alloy due to load-bearing SiC particles and solid lubricant graphite as reinforcing elements. The mechanically mixed layer (MML) formation in hybrid composites helped achieve good tribological properties. The AA7075 alloy and hybrid composites cross rolled at 350 °C yielded better results than other samples. The wear mechanism was abrasive and adhesive at low temperature and low load conditions in both alloy and hybrid composites. Whereas, at higher temperatures and high loads oxidative wear mechanism with delamination was prevalent. The transition of SWR from mild to severe value occurs at 250 °C in all experimental cases. The specific wear rate was improved by 85.64 % between worst and best conditions, i.e., annealed alloy and cross rolled composite.

Efficient degradation of haloacetic acids by vacuum ultraviolet-activated peroxymonosulfate: Kinetics, mechanisms and theoretical calculations

Efficient degradation of haloacetic acids (HAAs) is crucial due to their potential risks. This study firstly proposed vacuum ultraviolet - activated peroxymonosulfate (VUV/PMS) to remove HAAs (i.e., monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), etc). VUV/PMS achieved 99.51 % MCAA and 63.29 % TOC removal within 10 min. Electron paramagnetic resonance (EPR), quenching and probe experiments demonstrated that •OH was responsible for MCAA degradation. MCAA degradation followed pathways of dehalogenation (major) and decarboxylation (minor). VUV/PMS showed application potential under various reaction parameters. Broad spectrum of VUV/PMS on various HAAs was further explored. Chlorinated HAAs (Cl-HAAs) were primarily degraded by oxidation reactions, while brominated HAAs (Br-HAAs) by direct VUV photolysis. The density functional theory-based calculations (DFT) revealed that reaction rates of HAAs correlated with the highest occupied molecular orbital (HOMO) and energy gap (ΔE), indicating that HAAs degradation depends on their chemical structures. The Fukui function (f0 values) and bond length showed vulnerability of the halogen atom in Cl-HAAs and C–Br bond in Br-HAAs. Overall, this study provides an in-depth perspective on the oxidation performance and mechanism of HAAs using VUV/PMS. It not only demonstrates a green and efficient method but also inspires new strategies for HAAs remediation.

High-throughput preparation and quick characterization of oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W–based superalloy prepared using multi-arc ion plating technology

The early oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W substrate prepared by multi-arc ion plating technology (MIPT) at 1000 °C for 20–60 min were rapidly characterized. The as-deposited coatings with compositions ranging from (55%–90%Al, 45%–10%Cr) exhibited the laminated structure α-Al + Al80Cr20+Al8Cr5+α-Cr. After annealing at 640 °C for 40 h, a two-layered coating composed of (Co(Al, Cr) + Al8Co18Cr4) and IRL formed, and the thickness of the coating increased from the 14–18 μm of the as-deposited state to 25–35 μm. During oxidation at 1000 °C for 20–60 min, a three-layer structure consisting of an outer α-Al2O3+α-Cr2O3+CoCr2O4 layer, a central unoxidized Al–Cr layer, and an inner μ-Co7(W0.55Cr0.45) 6+B2–CoAl layer formed on the substrate. The Al–Cr coatings with higher Cr content had a looser oxide layer due to the CoCr2O4 phase, which might degrade the intended protective effect of the Al–Cr coatings. Thus, the Al–Cr coatings with higher Al content were suitable for preventing oxidation behavior. This work proposes a high-throughput screening method for rapid characterization of the early oxidation mechanism of the complex Al–Cr compositional gradient coatings.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Scavenging of reactive oxygen species in Candidatus Brocadia fulgida through nanocompartments

The antioxidant defense mechanisms for anaerobic ammonia oxidation (anammox) bacteria are still unclear. In this study, the potential antioxidant ability of nanocompartments in Candidatus Brocadia fulgida to typical reactive oxygen species (ROS) was investigated. The results showed that the copies of genes involved in anammox central metabolism were inhibited with hydrogen peroxide (H2O2), while the genes encoded putative anti-oxidative protein (nanocompartments and cargo HAO) up-regulated. The genetically engineered bacteria grew better and maintained the lower ROS levels (65.60 %-78.07 %) and higher electron transport activities (∼5–21 times) than the wild bacteria under H2O2 stimulus. Molecular docking confirmed that nanocompartment proteins could provide diverse sites to bind with H2O2 based on heme as the redox center. Additionally, the nanocompartments induced up-regulation of multiple protective pathways for coping with oxidative stress from H2O2, including antioxidant enzymes and other non-enzymatic pathways. Thus, the heme-containing nanocompartments presented great potential in preventing and relieving oxidative stress.

Mechanism and In Situ Prevention of Oxidation in Coal Gangue Piles: A Review Aiming to Reduce Acid Pollution

The acid pollution produced from coal gangue piles is a global environmental problem. Terminal technologies, such as neutralization, precipitation, adsorption, ion exchange, membrane technology, biological treatment, and electrochemistry, have been developed for acid mine drainage (AMD) treatment. These technologies for treating pollutants with low concentrations over a long period of time in coal gangue piles appear to be costly and unsustainable. Conversely, in situ remediation appears to be more cost-effective and material-efficient, but it is a challenge that coal producing countries need to solve urgently. The primary prerequisite for preventing acidic pollutants is to clarify the oxidation mechanisms of coal gangue, which can be summarized as four aspects: pyrite oxidation, microbial action, low-temperature oxidation of coal, and free radical action. The two key factors of oxidation are pyrite and coal, and the four necessary conditions are water, oxygen, microorganisms, and free radicals. The current in situ remediation technologies mainly focus on one or more of the four necessary conditions, forming mixed co-disposal, coverage barriers, passivation coatings, bactericides, coal oxidation inhibitors, microorganisms, plants, and so on. It is necessary to scientifically and systematically carry out in situ remediation coupled with various technologies based on oxidation mechanisms when carrying out large-scale restoration and treatment of acidic coal gangue piles.

Study on the effect and mechanism of polyethylene oxide and alum in flotation separation of fine smithsonite/calcite

The flotation separation of fine smithsonite and calcite has always been a challenging issue in the mineral processing industry. Both minerals are microfine particle distribution in nature, requiring ultra-fine grinding to maximize their liberation, which makes their flotation separation difficult. This study investigated the effects of PEO (Polyethylene oxide) and alum as combination agent on the flotation separation of fine smithsonite and calcite. The research results showed that using PEO and alum as combination agent can effectively separate fine smithsonite and calcite. PEO has a flocculation effects on both minerals, and Alum has better selective adsorption and flocculation effects on calcite, thereby effectively reducing the recovery of calcite. After treatment with PEO and alum, soluble starch tends to adsorb on the surface of calcite more than smithsonite, selectively depressing calcite in flotation separation, thus allowing for the effective flotation separation of fine smithsonite and calcite.