Reaction Mechanism Research Articles

Revolutionizing Cybersecurity with AI: Predictive Threat Intelligence and Automated Response Systems

The sophistication and breadth of cyber threats are continuously expanding, making it more difficult for traditional security measures to keep up. Artificial intelligence is revolutionizing cybersecurity by equipping businesses to proactively counter threats with automated reaction systems and predictive threat intelligence. Data analytics, behavioral analysis, and machine learning enable AI-powered systems to anticipate cyber assaults, enabling more efficient and rapid threat detection. By automating reaction mechanisms and mitigating threats in real-time, AI systems can minimize human error and maximize damage mitigation. AI techniques, such as anomaly detection, predictive modeling, and real-time threat analysis; data privacy, ethics, and the risks of hostile attacks are among the subjects covered, as are the benefits and drawbacks of utilizing AI in cybersecurity. This article provides the framework for future intelligent, automated cyber defense methods and illustrates how AI may alter cybersecurity using real-life examples and case studies.

A Detailed Reaction Mechanism for Thiosulfate Oxidation by Ozone in Aqueous Environments.

The ozone oxidation, or ozonation, of thiosulfate is an important reaction for wastewater processing, where it is used for remediation of mining effluents, and for studying aerosol chemistry, where its fast reaction rate makes it an excellent model reaction. Although thiosulfate ozonation has been studied since the 1950s, challenges remain in developing a realistic reaction mechanism that can satisfactorily account for all observed products with a sequence of elementary reaction steps. Here, we present novel measurements using trapped microdroplets to study the pH-dependent thiosulfate ozonation kinetics. We detect known products and intermediates, including SO32-, SO42-, S3O62-, and S4O62-, establishing agreement with the literature. However, we identify S2O42- as a new reaction intermediate and find that the currently accepted mechanism does not directly explain observed pH effects. Thus, we develop a new mechanism, which incorporates S2O42- as an intermediate and uses elementary steps to explain the pH dependence of thiosulfate ozonation. The proposed mechanism is tested using a kinetic model benchmarked to the experiments presented here, then compared to literature data. We demonstrate good agreement between the proposed thiosulfate ozonation mechanism and experiments, suggesting that the insights in this paper can be leveraged in wastewater treatment and in understanding potential climate impacts.

Cobalt-Catalyzed Divergence in C(sp3)-H Functionalization of 9H-Fluorene: A Streamlined Approach Utilizing Alcohols.

Sustainable chemical production demands the creation of innovative catalysts and catalytic technologies. While the development of coherent and robust catalytic systems using earth-abundant transition metals is essential, it remains a significant challenge. Herein, an expedient divergence strategy for tandem dehydrogenative C(sp3)-H alkylation and cyclization reactions of 9H-fluorene using a newly developed N,N-bidentate cobalt catalytic system is developed. This method capitalizes on the use of abundant and readily accessible alcohol. Demonstrating wide-ranging applicability, the catalytic protocol successfully integrated a diverse array of fluorenes and alcohols. This includes benzylic, heteroaromatic, and aliphatic primary and secondary alcohols, amassing a total of 75 distinct examples. When applied to sterically bulky alcohols, the reaction preferentially undergoes alkenylation, yielding a tetrasubstituted olefin as the main product. In the case of diols, the expected outcome is Dual-fluorescence at both terminal positions. This process leads to difluorination, followed by a cyclization step, culminating in the formation of a relatively unprecedented spiro compound. The scalability of this method has been validated through gram-scale synthesis. Control experiments have shed light on the reaction mechanism, indicating that it progresses through an unsaturated intermediate and adheres to the borrowing hydrogen pathway.

The Performance of Ethylene Partial Oxidation on Group IB Metal Stepped Surfaces

Group IB metal catalysts, particularly Ag, Au, and Cu, exhibit particular selectivity for ethylene oxide (EO) formation, while Ag demonstrating the highest performance so far. Previous studies have explored the EO formation mechanism on (100) and (111) surfaces of group IB metals, but the reaction mechanism on the (211) facet (analogous to the edge sites of a catalyst particle) remains poorly understood. Herein, we fill in the knowledge gap by analyzing ethylene partial oxidation to EO on the (211) surfaces of Ag, Au, and Cu through density functional theory (DFT) calculations, scaling relationship analysis, and microkinetic modeling. Our study demonstrates that the (211) surface decreases the energy barrier for the dissociation of oxygen molecules into oxygen atoms, while unfavorable for the production of EO. Therefore, we should preserve an appropriate concentration of (211) surface on the nanoparticles when designing catalysts for the ethylene epoxidation reaction.

Atmospheric Chemistry of Chloroprene Initiated by OH Radicals: Combined Ab Initio/DFT Calculations and Kinetics Analysis.

Chloroprene (CP; CH2═C(Cl)-CH═CH2) is a significant toxic airborne pollutant, often originating from anthropogenic activities. However, the environmental fate of CP is incompletely understood. High level CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ calculations combined with kinetic modeling were employed here to glean new insight into the reaction mechanism, energies, and kinetics of the reaction of CP with OH radical (•OH). We report the energies of four different addition pathways and six different abstraction pathways. The •OH attack on the terminal C1 atom of the =CH2 group (which is directly attached to the =CCl moiety), leading to the formation of HOCH2-•C(Cl)-CH═CH2, was found to be a major path. The barrier height for the formation of the corresponding transition state was found to be -1.9 kcal mol-1 below that of the starting CP + •OH reactants. Rate coefficients were calculated for addition and abstraction pathways involving the CP + •OH reaction under pre-equilibrium approximation conditions, employing a combination of canonical variational transition state theory and small curvature tunneling. The overall rate coefficient for the reaction of CP + •OH at 298 K was found to be 1.4 × 10-10 cm3 molecule-1 s-1. The thermochemistry of the possible channels and atmospheric implications are provided. In addition, the fate of HOCH2-•C(Cl)-CH═CH2 in the presence of 3O2 was investigated. We found the reaction of the CP-derived peroxy radical adduct with HO2 and NO to make contributions to the formation of products such as formaldehyde, HO2 radical, Cl atom, HOCH2C(OOH)(Cl)CH═CH2, HOCH2C(O)Cl, ClC(O)CH═CH2, HOCH2C(O)CH═CH2, and HC(O) radical.

Recent Advances in Photocatalytic Nitrogen Fixation Based on Two‐Dimensional Materials

AbstractUtilizing solar energy for photocatalytic nitrogen fixation has been extensively regarded as a promising avenue towards renewable nitrogen energy production. 2D materials, renowned for their unique structures and properties, have sparked remarkable advancements in the realm of energy and environment sciences. In this review, we delve into the recent advancements pertaining to 2D materials for solar‐driven photocatalytic nitrogen fixation. This encompasses a diverse array of materials, including metal carbides/nitrides (MXenes), transition metal dichalcogenides (TMDs or TMDCs), graphitized carbon nitride (g‐C3N4), metal‐organic frameworks (MOFs), covalent organic frameworks (COFs), and covalent triazine‐based frameworks (CTFs). We offer a fundamental understanding of the functionalities exhibited by various 2D materials in enhancing photocatalytic nitrogen fixation activity. The photocatalytic properties of these 2D materials are meticulously examined from multiple perspectives, including visible light absorption capabilities, charge transfer within the energy band, and reaction mechanisms. Finally, we present an in‐depth discussion on the existing challenges and prospects surrounding the application of 2D materials in photocatalytic nitrogen fixation.

Synthesis of Aryl Naphthoquinones and Maleimides via Pd(II)-Catalyzed Template-Assisted m-C(sp2)-H Functionalization Reaction.

An efficient approach for the synthesis of substituted aryl naphthoquinones via a Pd(II)-catalyzed template-assisted m-C(sp2)-H bond functionalization reaction of arylmethane sulfonates have been demonstrated. The method involves usage of less expensive and abundant pharmacologically important scaffold naphthoquinone. A wide range of arylmethane sulfonates were examined and found to be compatible with the protocol. The protocol has also been further extended to the synthesis of various substituted aryl maleimide scaffolds. A plausible reaction mechanism has also been proposed to account for the selective distal m-C(sp2)-H bond functionalization reaction.

Two-Step Noncatalyzed Hydrolysis Mechanism of Imines at the Air-Water Interface.

The hydrolysis of imines has long been assumed to be their main atmospheric fate, based on early studies in the field of organic chemistry. However, the hydrolysis mechanism and kinetics of atmospheric imines remain unclear. Here, an advanced Born-Oppenheimer molecular dynamics method was employed to investigate the noncatalyzed hydrolysis mechanism and kinetics at the air-water interface by selecting CH2NH as a model molecule. The results indicate that CH2NH exhibits a pronounced surface preference. The noncatalyzed hydrolysis of CH2NH follows a unique two-step reaction mechanism involving first proton transfer and then OH- transfer through the water bridge at the air-water interface, in contrast to the traditional one-step mechanism. The calculated reaction rate for the rate-determining step is 3.32 × 105 s-1, which is 2 orders of magnitude greater than that of the bulk phase. In addition, the involvement of the interfacial electric field further enhances the reaction rate by approximately 3 orders of magnitude. The noncatalyzed hydrolysis rate at both the air-water interface and the bulk phase is higher than that of the possible acid-catalyzed one, clarifying noncatalyzed hydrolysis as the dominant mechanism for CH2NH. This study elucidates that the noncatalyzed hydrolysis of atmospheric imines is feasible at the air-water interface and that the revealed unique two-step hydrolysis mechanism has significant implications in atmospheric and water environmental chemistry.

State-of-the-Art Light-Driven Hydrogen Generation from Formic Acid and Utilization in Enzymatic Hydrogenations.

A concept of combining photocatalytically generated hydrogen with green enzymatic reductions is demonstrated. The developed photocatalytic formic acid (FA) dehydrogenation setup based on Pt(x)@TiO2 shows unprecedented hydrogen generation activity, which is two orders of magnitude higher than reported values of state-of-the-art systems. Mechanistic studies confirm that hydrogen generation proceeds via a photocatalytic pathway, which is entirely different from purely thermal reaction mechanisms previously reported. The viability of the presented approach is demonstrated by the synthesis of value-added compounds 3-phenylpropanal and (2R, 5S)-dihydrocarvone at ambient pressure and room temperature, which should be applicable for many other hydrogenation processes, e.g., for the preparation of flavours and fragrance compounds, as well as pharmaceuticals.

MnO2@Fe2O3 Cathode for Aqueous Zinc/Manganese Batteries: Enhanced Discharge Capacity and Stability through Forming FeMnO3

Abstract Rechargeable Zn/MnO2 batteries suffer from limited cycle life and low capacity. We utilized MnO2@Fe2O3 as the cathode material, achieving a discharge capacity of 290mAh g-1 at 1A g-1. The Zn/MnO2@Fe2O3 battery maintained over 90% coulombic efficiency after 1800 cycles at 1A g-1. Even at 5 A g-1, it reached 154mAh g-1. The addition of Fe2O3 changed the reaction mechanism and realized the MnO2@Fe2O3 transformation between MnO2@Fe2O3 and MnOOH, FeMnO3 based on the co-doping and conversion of H+/Fe(III). This study underscores the immense potential of the MnO2@Fe2O3 electrode in energy storage applications and highlights the significance of Fe2O3 in enhancing cathode cycling stability and discharge capacity.

Chiral Sodium Glycerophosphate Catalyst for Enantioselective Michael Reactions of Chalcones

A chiral sodium glycerophosphate is successfully exploited as a catalyst in the Michael addition of methyl malonate to a number of chalcones. The reactions supplied the target adducts in satisfactory yields and good enantiomeric excesses. A tentative computational study is presented, aiming to understand the reaction mechanism.

Unveiling high-temperature stability and growth dynamics of CVD-SiOC coatings across different deposition conditions and environments

Abstract In this study, we systematically investigated the high-temperature protection performance and evolution behavior of three different SiOC coatings (1050SiOC, 1100SiOC, 1150SiOC) under different atmospheres. The coatings were prepared by the organometallic chemical vapor deposition (CVD) method and characterized using scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS) techniques. It was found that the composition and microstructure of SiOC coatings, environmental atmosphere, and heat treatment temperature can affect the thermal stability and high-temperature reaction mechanism of SiOC coatings. Further, it was revealed that the three SiOC coatings only exhibit the same high-temperature evolution behavior and reaction mechanism in an air environment while exhibiting different high-temperature evolution behavior and reaction mechanisms in both an inert atmosphere and a reduced air atmosphere. Among the coatings prepared, the 1050SiOC coating demonstrated the highest on-set oxidation temperature under identical oxygen content conditions. This characteristic may contribute to the coating’s excellent resistance to high-temperature oxidation.

Photoelectrochemical Ethylene Glycol Oxidization Coupled with Hydrogen Generation Using Metal Oxide Photoelectrodes.

Photoelectrochemical (PEC) water splitting represents a promising approach for harnessing solar energy and transforming it into storable hydrogen. However, the complicated 4-electron transfer process of water oxidation reaction imposes kinetic limitations on the overall efficiency. Herein, we proposed a strategy by substituting water oxidation with the oxidation of ethylene glycol (EG), which is a hydrolysis byproduct of polyethylene terephthalate (PET) plastic waste. To achieve this, we developed and synthesized BiVO4/NiCo-LDH photoanodes capable of achieving a high Faradaic efficiency (FE) exceeding 85% for the oxidation of EG to formate in a strongly alkaline environment. The reaction mechanism was further elucidated using in-situ FTIR spectroscopy. Additionally, we successfully constructed an unassisted PEC device for EG oxidation and hydrogen generation by pairing the translucent Mo:BiVO4/NiCo-LDH photoanode with a state-of-the-art Cu2O photocathode, resulting in an approximate photocurrent density of 2.3 mA/cm2. Our research not only offers a PEC pathway for converting PET plastics into valuable chemicals but also enables simultaneous hydrogen production.

Photoelectrochemical Ethylene Glycol Oxidization Coupled with Hydrogen Generation Using Metal Oxide Photoelectrodes

Photoelectrochemical (PEC) water splitting represents a promising approach for harnessing solar energy and transforming it into storable hydrogen. However, the complicated 4‐electron transfer process of water oxidation reaction imposes kinetic limitations on the overall efficiency. Herein, we proposed a strategy by substituting water oxidation with the oxidation of ethylene glycol (EG), which is a hydrolysis byproduct of polyethylene terephthalate (PET) plastic waste. To achieve this, we developed and synthesized BiVO4/NiCo‐LDH photoanodes capable of achieving a high Faradaic efficiency (FE) exceeding 85% for the oxidation of EG to formate in a strongly alkaline environment. The reaction mechanism was further elucidated using in‐situ FTIR spectroscopy. Additionally, we successfully constructed an unassisted PEC device for EG oxidation and hydrogen generation by pairing the translucent Mo:BiVO4/NiCo‐LDH photoanode with a state‐of‐the‐art Cu2O photocathode, resulting in an approximate photocurrent density of 2.3 mA/cm2. Our research not only offers a PEC pathway for converting PET plastics into valuable chemicals but also enables simultaneous hydrogen production.

Electrochemical Construction of C−F Bonds: Recent Advances and Future Perspectives

AbstractIdeal pathways to synthesize fluorinated compounds were pursued for over 100 years, due to wide application of organofluorides in materials, agrochemicals and pharmaceuticals. In this regard, electro‐organic synthesis, evolved as a sustainable and scalable approach in various synthetic protocols, stands out as a promising strategy. As a result, many novel and attracting applications of introduction of fluorine items into organic compounds by direct and redox‐mediated electrochemical methods has been reported, especially in recent five years. In this review, we are aim to highlight the reaction scopes, reaction mechanism, the fundamental aspects and the fluorine source variation in electrochemcial fluoriation transformation.

Kinetics study of pyrolysis of petroleum sludge and characterization of char

Thermochemical conversion (or pyrolysis) has emerged as an effective technique for the disposal of sludge generated in process industries. This paper reports physicochemical characterization and kinetic analysis of pyrolysis of sludge from a petroleum refinery and characterization of resultant char. The sludge had high volatile matter (>70 wt%) and low ash content (15 wt%). Pyrolysis of sludge was studied using a thermo-gravimetric analyzer (TGA). The TGA data was analyzed using two isoconversional models, viz. KAS and Vyazovkin AIC are used for the deduction of kinetic triplets, viz. activation energy, pre-exponential factor, and reaction mechanism. The activation energy (Ea ) of sludge pyrolysis varied in the 64.79–190.37 kJ/mol range. The pre-exponential factor varied from 1.18E + 07 to 4.29E + 12 s−1. The predominant solid-state mechanism of thermal conversion was an order-based reaction (F2/F3). The thermodynamic factors (viz. ΔH, ΔS, ΔG) of sludge pyrolysis were also determined. Relatively small values of (Ea – ΔH) ∼ 5 kJ/mol revealed high susceptibility of sludge for thermal conversion. Residual char after pyrolysis was characterized for physicochemical properties. The char properties were fixed carbon = 54.37%, calorific value = 22.48 MJ/kg, and BET surface area = 18.35 m2/g. These properties make char suitable for numerous applications.

A Cascade Reaction Triggered by H‐H Steric Hindrance: Dimeric Covalent Organic Frameworks on Au(111) and Dimeric Nanoribbons on Ag(111)

Comprehensive SummaryIn on‐surface synthesis, dimers are typically utilized to explore reaction mechanisms or as intermediates in the formation of final products. However, constructing the innovative nanostructures with dimers as building blocks remains challenging. Here, using non‐planar 2,2′,7,7′‐tetrabromo‐9,9′‐biflurenyliden molecules, we have successfully synthesized dimeric covalent organic frameworks (COFs) on the Au(111) surface through a temperature‐controlled cascade reaction. Notably, the H‐H steric hindrance within precursors caused by double bonds leads to selective stepwise debromination during the thermal annealing, which promotes the dimerization through intermolecular Ullmann coupling and cyclodehydrogenation reaction to form COFs primarily constituted by dimer building blocks. Combining scanning tunneling microscopy/spectroscopy and density functional theory calculations, we have precisely confirmed the structural evolution and reaction mechanism. Furthermore, by introducing Ag adatoms to form C−Ag−C intermediates, we have successfully regulated the reaction path and synthesized one‐dimensional nanoribbons with dimers as building blocks. This work not only validates the strategy of synthesizing dimeric nanostructures on different surfaces through cascade reactions induced by precursor design, but also enriches the research field of surface synthesis of COFs and nanoribbons.

In‐situ Monitoring of Photocatalysis on Polymeric Carbon Nitride Thin Films

Polymeric carbon nitride has attracted significant interest in heterogeneous photocatalysis due to its activity under visible‐light irradiation. Herein, we report on using carbon nitride‐coated NMR tubes for in‐situ studies of photocatalytic reaction mechanisms. In a first step, we exploited carbon nitride‐coated crimp vials as batch photoreactors for visible photocatalytic fluorinations of unactivated C(sp3)‐H bonds, with moderate to excellent yields and reusability over multiple cycles. Eventually, carbon nitride‐coated NMR tubes were used as a photoreactor by coupling them with optical fiber irradiation directly inside the spectrometer. This enabled us to follow the reaction with in‐situ NMR spectroscopy identifying reactive intermediates otherwise elusive in conventional analyses. The method provides advantages for the study of photocatalytic mechanisms of complex reactions and substantially reduces the need of comparative tests for depicting reaction intermediates and conversion pathways.

In-situ Monitoring of Photocatalysis on Polymeric Carbon Nitride Thin Films.

Polymeric carbon nitride has attracted significant interest in heterogeneous photocatalysis due to its activity under visible-light irradiation. Herein, we report on using carbon nitride-coated NMR tubes for in-situ studies of photocatalytic reaction mechanisms. In a first step, we exploited carbon nitride-coated crimp vials as batch photoreactors for visible photocatalytic fluorinations of unactivated C(sp3)-H bonds, with moderate to excellent yields and reusability over multiple cycles. Eventually, carbon nitride-coated NMR tubes were used as a photoreactor by coupling them with optical fiber irradiation directly inside the spectrometer. This enabled us to follow the reaction with in-situ NMR spectroscopy identifying reactive intermediates otherwise elusive in conventional analyses. The method provides advantages for the study of photocatalytic mechanisms of complex reactions and substantially reduces the need of comparative tests for depicting reaction intermediates and conversion pathways.

Theoretical insight into the mechanism of Li-mediated nitrogen reduction reaction by density functional theory

Lithium-mediated electrochemical nitrogen reduction reaction (NRR) as an alternative to the Haber-Bosch process has attracted increasing attention because of its high faradaic efficiency and reproducibility. However, the limited understanding of the mechanism has hampered further improvement of its catalytic performance. This work has endeavored to study the process of Li-mediated NRR and its underlying mechanism using density functional theory. It is founded that the Li6N2, Li7N2 atom groups, Li3N (001) and Li3N (110) layer stably exist on the deposited Li (001) layer. The replacing model has been established to describe the hydrogenation process with ethanol as a proton source, revealing that the replacement between Li and H atom is a spontaneously thermal process. Based on the replacing mechanism, the structure of interface and coverage rate of reactive sites are the two main factors that determine the ammonia formation. These findings further our understanding of Li-mediated NRR mechanism and will be helpful for the rational design of experiments of Li-mediated NRR.