Reaction Mechanism Research Articles

Study on Mechanism and Kinetics of the H2O-Abstraction Reactions Between C3H4 Isomers and •OH Radicals

Study on Mechanism and Kinetics of the H2O-Abstraction Reactions Between C3H4 Isomers and •OH Radicals

Sulfide mediated zero valent iron for enhanced nickel removal under neutral condition: reaction kinetic, mechanism, and stability

The application of sodium sulfide (Na2S) as sulfidation reagent of zero valent iron (ZVI) has been well studied, however, the effect of Na2S existence on ZVI reactivity remains obscure. In this study, Ni(II) removal performance, mechanism, and stability by ZVI with Na2S were investigated at neutral condition. The results showed that Ni(II) removal sharply increased from < 5% to 100% by ZVI within 60min with the increase of Na2S concentration, but the subsequent Ni(II) release occurred. In addition to the slight Ni(II) removal by Na2S in aqueous phase, Ni(II) was mainly removed by the adsorption and reduction by Na2S mediated ZVI system. Characterization analysis indicated that Na2S could lead to the severe Fe0 corrosion and the main corrosion product on ZVI was lepidocrocite, which played the dominant role for Ni(II) immobilization. Meanwhile, the formation of iron sulfides on ZVI surface would enhance Ni(II) reduction and partially transform the adsorbed Ni(II) to NiS. Moreover, the higher ionic strength could further enhance the initial Ni(II) removal rate but the stability became poor. Regardless of the additive methods, the Ni(II) removal significantly enhanced in the system of ZVI and Na2S combination. Overall, this work reveals the sulfide mediated Fe0 corrosion and provides a potential method for enhancing the reactivity of ZVI in the treatment of Ni(II) pollution.

The construction of iron-based catalysts encapsulated by graphite for CO2 hydrogenation to light olefins

Developing efficient catalytic materials and unveiling the active factors are significant for selective hydrogenation of CO2 to light olefins (C2–4=). Herein, Fe3O4-FeCx nanoparticles coated by graphite without other doped elements were synthesized successfully. The optimal catalyst exhibited CO2 conversion of 48.0 %, C2–4= space–time yield of 29.0 mmol·g−1·h−1, and a stability of 100 h (3.0 MPa, 320 °C, and GHSV = 12000 mL·g−1·h−1). The core–shell structure derived from the strong interaction between the phenolic hydroxyl group of resin and iron ions, as well as the encapsulation of the copolymer P123. The characterization results revealed that the size of core–shell particles and thickness of graphite layers could be regulated by P123, which affected the conversion of CO2 and products distribution significantly. Moreover, the combined results of quasi in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and Raman spectra suggested small particle size and thin graphite shell strengthen the adsorption and conversion of CO2, playing an important role in the formation of light olefins. This work proposes a simple and feasible synthesis strategy to construct Fe3O4-FeCx particles encapsulated by graphite shell, which provides insights into catalysts design and the reaction mechanism of CO2 conversion to light olefins.

A Novel Battery Model Considering the Battery Actual Reaction Mechanism for Model Parameters and SOC Joint Estimation

A Novel Battery Model Considering the Battery Actual Reaction Mechanism for Model Parameters and SOC Joint Estimation

Revealing the poisoning effect of potassium salts on MnOx catalysts for low-temperature simultaneous removal of NO and CO

Simultaneously elimination of NO and CO in the sintering flue gas is an urgent problem, in which the application of the bifunctional MnOx catalyst has demonstrated its effectiveness in removing NO and CO simultaneously. Potassium salts are frequently found in the sintering flue gas and exert a detrimental influence on the catalytic performance of catalysts. Herein, the primary focus of this study is to investigate different K+ species (K2SO4, KCl, KNO3) poisoning effect on bifunctional MnOx. The findings suggested a deactivation order in the sequence of KNO3 > KCl > K2SO4. Fresh Mn-AC catalyst had finer grains, and poisoning elements were evenly distributed. XPS results revealed an obvious decrease in Mn4+ and Oβ species across all catalysts after K+ species poisoning, hindering redox cycle activation and oxygen species mobility, thus impacting catalytic activity. The in situ DRIFTS results indicated the forbidden of E-R route over KNO3-poisoned catalysts and low reactivity of adsorbed species after poisoning for NO removal. KNO3 severely suppressed surface reaction paths on Mn-AC catalyst and declined the catalytic efficiency, especially in CO activation. Finally, a possible reaction mechanism model for the simultaneous removal of NO and CO was proposed. This study could provide reference for the development of bifunctional catalyst with high resistance to potassium salts.

A complete and sustained organic/inorganic reaction mechanism of Baeyer’s test

The Baeyer’s test for unsaturation has been used in Qualitative Organic Analysis for a long time. However, if an alkaline reagent is used, compounds having an active hydrogen (carbon acids) also give a positive test with potassium permanganate, detracting the test for unsaturation. The first steps of the reaction sequence have been described but the next stages are missing. These are very important because they involve the formation mode of the observed end product, brown manganese dioxide. In this communication, a complete and sustained reaction mechanism is provided for both reaction mediums, neutral and alkaline. It is in accordance with observed experimental facts. The missing steps are a redox reaction between hypomanganate and permanganate ions, and a second cyclic intermediate now formed with manganate ion. The instability of this intermediate leads directly to manganese dioxide and alkalinization of the neutral medium, as observed experimentally.

A mini-review on influence of physical exercise in remodeling the immune mechanism

Exercising on a regular basis has been associated with delay in onset of many lifestyle disorders and chronic conditions. Different types of exercise have varied effects on our innate immune cells, both positively and negatively. Low-intensity exercises like yoga or brisk walking, medium-intensity exercises like swimming or cycling, and long-term high-intensity exercises like playing sports like volleyball or working out in the gym are some examples. The immune system's function is impacted differently by exercise training depending on the type, duration, intensity, and other factors. Exercise training is a double-edged sword that helps the body's immune system by changing the immune cells' post-exercise reaction mechanisms. Regular physical exercise is one of the lifestyle adjustments aimed at minimizing morbidity and mortality associated with contemporary illnesses such as obesity, diabetes, cardiovascular disease, and cancer. Regular leisure exercise training is regarded to be beneficial, but extreme exercise, such as that performed by professional athletes, is thought to have possibly detrimental consequences. This review summarizes current information in the field of exercise-associated alterations of infection susceptibility and indicates knowledge gaps for further investigation. It highlights that long term effects of physical activity shows a positive association with longevity and exercise.

Efficient synthesis of benzyl-protected cyclic lysine on Pt/m-Al2O3 catalysts and its application in functional nylon-6 copolymers production

Functional nylon-6 polymers, particularly those with special properties such as antibacterial, flame retardant, and specialized thermal properties, have a wide range of applications. However, the efficient synthesis of these polymer monomers has long remained a challenge. Benzyl-protected cyclic lysine (BCL) is a potentially functional monomer, and this article proposes an efficient method for the synthesis of benzyl-protected cyclic lysine on a supported platinum catalyst. Compared to existing techniques, this approach offers higher synthesis efficiency and sustainability. Pt/m-Al2O3 (microspherical Al2O3) catalysts were prepared using a vacuum impregnation method and showed good activity and selectivity in the production of benzyl-protected cyclic lysine. The conversion rate of α-amino-ε-caprolactam (α-ACL) was 100%, and the selectivity of BCL was 96.0%. The Pt/m-Al2O3 catalyst maintained good stability over multiple reaction cycles. The reaction mechanism and thermodynamics of functionalized α-ACL were also investigated. The copolymer synthesized with the prepared BCL showed similar structure and thermal stability to pure nylon-6, indicating possible unique functional properties. This study provides a route for the synthesis of cyclic lysine protected with various groups and its potential applications in the field of polymer chemistry.

Charge Redistribution in Mechanochemical Reactions for Solid Interfaces.

Mechanochemical strategies are widely used in various fields, ranging from friction and wear to mechanosynthesis, yet how the mechanical stress activates the chemical reactions at the electronic level is still open. We used first-principles density functional theory to study the rule of the stress-modified electronic states in transmitting mechanical energy to trigger chemical responses for different mechanochemical systems. The electron density redistribution among initial, transition, and final configurations is defined to correlate the energy evolution during reactions. We found that stress-induced changes in electron density redistribution are linearly related to activation energy and reaction energy, indicating the transition from mechanical work to chemical reactivity. The correlation coefficient is defined as the term "interface reactivity coefficient" to evaluate the susceptibility of chemical reactivity to mechanical action for material interfaces. The study may shed light on the electronic mechanism of the mechanochemical reactions behind the fundamental model as well as the mechanochemical phenomena.

Effect of gas pre-decomposition device on the growth of GaN epitaxial layer

In previous studies, the influence of gas phase and surface reactions on the growth of GaN was mainly calculated through simulations. In this study, a novel gas pre-decomposition device (GPDD) was designed to experimentally investigate the effects of gas phase and surface reactions on GaN growth by changing the length and height of the isolation plates (IPs). By varying the structure of the GPDD, the effects on the growth rate and thickness uniformity of the GaN films were studied. The growth rate of the GaN sample slowed with the extension of the IPs because the longer partition plates led to insufficient gas mixing and premature consumption of the precursor trimethylgallium (TMG). The use of GPDD simultaneously achieves high crystal quality and smooth surface morphology of the GaN film. Owing to the use of GPDD, the decomposition of TMG in the pyrolysis pathway was promoted, which suppressed Ga vacancies and C impurities, resulting in weak yellow luminescence bands in the photoluminescence. This study provides a comprehensive understanding of the chemical reaction mechanism of GaN and plays an important role in promoting the development of metal-organic chemical vapor deposition equipment.

Mixture optimization for mechanical, environmental, and economic objectives in grouting slurry for repairing earthen sites

Anchor and fissure grouting are used to repair earthen sites. However, the common method to obtain the compressive strength of grouting slurry would cause material, labor, and time losses. In addition the material properties, environmental and economic benefits have gained increasing attention. This study proposes a design framework for multi-objective proportioning optimization based on machine learning and metaheuristics. The results indicated that the eXtreme Gradient Boosting (XGBoost) model, whose hyper-parameters were optimized by a genetic algorithm, can accurately predicted the compressive strength of the slurries. The impact of the variables on development of compressive strength can explain the internal reaction mechanisms. The analytical framework based on meta-heuristic and technique for order of preference by similarity to an ideal solution (TOPSIS) provided Pareto-optimal solutions in design scenario of each sub-dataset. The framework proposed in this study can efficiently achieve mechanical, environmental, and economic design objectives of anchor grouting and fissure grouting slurries for repairing earthen sites.

Development of an Elementary Reaction-Based Kinetic Model to Predict the Aqueous-Phase Fate of Organic Compounds Induced by Reactive Free Radicals.

ConspectusAqueous-phase free radicals such as reactive oxygen, halogen, and nitrogen species play important roles in the fate of organic compounds in the aqueous-phase advanced water treatment processes and natural aquatic environments under sunlight irradiation. Predicting the fate of organic compounds in aqueous-phase advanced water treatment processes and natural aquatic environments necessitates understanding the kinetics and reaction mechanisms of initial reactions of free radicals with structurally diverse organic compounds and other reactions. Researchers developed conventional predictive models based on experimentally measured transformation products and determined reaction rate constants by fitting with the time-dependent concentration profiles of species due to difficulties in their measurements of unstable intermediates. However, the empirical treatment of lumped reaction mechanisms had a model prediction limitation with respect to the specific parent compound's fate. We use ab initio and density functional theory quantum chemical computations, numerical solutions of ordinary differential equations, and validation of the outcomes of the model with experiments. Sensitivity analysis of reaction rate constants and concentration profiles enables us to identify an important elementary reaction in formating the transformation product. Such predictive elementary reaction-based kinetics models can be used to screen organic compounds in water and predict their potentially toxic transformation products for a specific experimental investigation.Over the past decade, we determined linear free energy relationships (LFERs) that bridge the kinetic and thermochemical properties of reactive oxygen species such as hydroxyl radicals (HO•), peroxyl radicals (ROO•), and singlet oxygen (1O2); reactive halogen species such as chlorine radicals (Cl•) and bromine radicals (Br•); reactive nitrogen species (NO2•); and carbonate radicals (CO3•-). We used literature-reported experimental rate constants as kinetic information. We considered the theoretically calculated aqueous-phase free energy of activation or reaction to be a kinetic or a thermochemical property, and obtained via validated ab initio or density functional theory-based quantum chemical computations using explicit and implicit solvation models. We determined rate-determining reaction mechanisms involved in reactions by observing robust LFERs. The general accuracy of LFERs to predict aqueous-phase rate constants was within a difference of a factor of 2-5 from experimental values.We developed elementary reaction-based kinetic models and predicted the fate of acetone induced by HO• in an advanced water treatment process and methionine by photochemically produced reactive intermediates in sunlit fresh waters. We provided mechanistic insight into peroxyl radical reaction mechanisms and critical roles in the degradation of acetone and the formation of transformation products. We highlighted different roles of triplet excited states of two surrogate CDOMs, 1O2, and HO•, in methionine degradation. Predicted transformation products were compared to those obtained via benchtop experiments to validate our elementary reaction-based kinetic models. Predicting the reactivities of reactive halogen and nitrogen species implicates our understanding of the formation of potentially toxic halogen- and nitrogen-containing transformation products during water treatment processes and in natural aquatic environments.

Effect of polymer crosslinking to the failure behavior of thermoplastic composite remelting interface: Molecular dynamics simulation and experimental verification

AbstractThe forming interface is the weak link of thermoplastic composite complex structures. To explore the effect of polymer crosslinking on the failure behavior of thermoplastic composite remelting interface using “Preforming + Remelting bonding” process, the all‐atom models of different types of interfaces were established, and a molecular dynamics (MD) simulation was conducted on the uniaxial tensile failure process of the remelting interface. The failure behavior of the remelting interface with different preforming processes was tested to verify the correctness of MD simulation, and the influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified. The results showed that the yield stress of the uncrosslinked interface reaches 283.2 MPa and 16.0% and 50.6% higher than that of the unilateral and bilateral crosslinked interfaces respectively. The polymer crosslinking reaction during the preforming stage will reduce the interlaminar bonding performance. The interlaminar shear strength (ILSS) of the uncrosslinked interface is 87.46 MPa and 7.21% and 27.36% higher than that of the unilateral and bilateral crosslinked interface respectively, and only 3.95% lower than that of the non‐remelting sample formed by standard process. This research provides a new approach for predicting and analyzing the effect of polymer crosslinking on remelting interface properties of thermoplastic composite using “Preforming + Remelting bonding” process.Highlights The failure behavior of different thermoplastic composite remelting interfaces was studied. MD simulation was conducted on the uniaxial tensile failure process of the remelting interface. The influencing mechanism of polymer crosslinking reactions in the preforming stage to the remelting interface properties was clarified. It is effective to explore the failure mechanism of thermoplastic remelting interface by MD simulation.

Unveiling the Selectivity of Ru(II)-Catalyzed C-H Activation for Defluorinative Cyclization of 2-Arylbenzimidazole and Trifluoromethyl Diazo: A DFT Study.

The synthesis of monofluorinated heterocyclic compounds by C-H activation combined with defluorination is useful. Studies on the reaction mechanism and selectivity have shown that these processes play a positive role in promoting the development of monofluorinated reactions. Density functional theory (DFT) calculations were performed to investigate the mechanism and selectivity of Ru(II)-catalyzed 2-arylbenzimidazole with trifluoromethyl diazo. DFT calculations showed that C-H activation occurs through a concerted metalation/deprotonation (CMD) mechanism. After that, deprotonation and defluorinative cyclization are assisted by acetate and trifluoroethanol (TFE). Further mechanistic insights through noncovalent interaction (NCI) analysis were also obtained to elucidate the origin of the selectivity in the defluorination process.

Understanding the Ageing Processes of Electrolytes in Aqueous Magnesium Batteries Using Radiation Chemistry

Manufacturing aqueous batteries based on the magnesium cations is an important step towards more sustainable and safer energy storage solutions. Thus, it is important to understand how these systems age and which species are formed throughout numerous charge/discharge cycles. To this end, we have used radiolysis to induce accelerated aging in concentrated solutions of magnesium bistriflimide Mg(TFSI)2 (also called “water‐in‐salt electrolytes” or WISEs). We demonstrate in this work that the degradation products formed, whether in the gas or liquid phase, are very similar to those formed in concentrated LiTFSI aqueous solutions. In fact, the behavior under ionizing radiation is driven by the anion/water molar ratio regardless of whether the cation is Li+ or Mg2+. This is because both cations are non‐reactive, and the bond strengths in the TFSI‐ anion do not vary with the nature of the cation. Reaction mechanisms are proposed to explain the formation of several species under ionizing radiation.

Visible-Light-Mediated [2+2] Photocycloadditions of Alkynes.

Visible-light-mediated [2+2] photocycloaddition reaction can be considered an ideal solution due to its green and sustainable properties, and is one of the most efficient methods to synthesize four-membered ring motifs. Although research on the [2+2] photocycloaddition of alkynes is challenging because of the diminished reactivity of alkynes, and the more significant ring strain of the products, remarkable achievements have been made in this field. In this article, we highlight the recent advances in visible-light-mediated [2+2] photocycloaddition reactions of alkynes, with focus on the reaction mechanism and the late-stage synthetic applications. Advances in obtaining cyclobutenes, azetines, and oxetene active intermediates continue to be breakthroughs in this fascinating field of research.

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

Organic photocatalysts frequently possess dual singlet and triplet photoreactivity and a thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox catalyst in the sulfonylation/arylation of styrenes and as a triplet sensitizer in energy transfer catalysis. The singlet lifetime is sufficiently long to exploit the exceptional excited state reduction potential for the activation of 4-cyanopyridine. Photoinduced electron transfer generating the radical cation was directly observed confirming the previously proposed mechanism of a three-component reaction. Several steps of the photoredox cycle were investigated separately, providing deep insights into the complex mechanism. The triplet-excited Aza-H, which was studied with quantitative LFP, is formed with a quantum yield of 0.34. The pronounced triplet formation was exploited for the isomerization reaction of (E)-stilbene to the Z-isomer and the cyclization of cinnamyl chloride. Catalyst degradation mainly occurs through the long-lived Aza-H triplet (28 µs), but the photostability is greatly increased when the triplet efficiently reacts in a catalytic cycle such that turnover numbers exceeding 4400 are achievable with this organocatalyst.

Phase Evolution and Reaction Mechanism of LiFePO4 During NaHSO4·H2O-Assisted Roasting Process

Phase Evolution and Reaction Mechanism of LiFePO4 During NaHSO4·H2O-Assisted Roasting Process

A Strategic NH3-Dosing Approach for the Minimization of N2O Production During NH3-SCR Reactions over Cu-SSZ-13 Catalysts

AbstractThe undesired production of N2O during NH3-SCR reactions is investigated over a reference commercial Cu-CHA catalyst. Steady-state experiments performed in the 150–500 °C temperature range exhibit a bimodal trend in the N2O formation profile, confirming the existence of two different reaction mechanisms occurring at low and high temperatures. Focusing on a low-to-medium T-range, N2O production, usually ascribed to NH4NO3 formation and decomposition, increases with the NO2/NOx ratio. However, an excess of NO2 leads to a decrease in the N2O release due to ammonium nitrate deposition and catalyst clogging phenomena. Steady-state and dynamics experiments show the promoting effect of both NH3 feed concentration and NH3 storage on N2O production at T &gt; 200 °C. Surprisingly, N2O decreases with increasing NH3/NOx ratio at lower temperature. A novel approach based on the strategic injection of NH3 is also applied to mitigate the N2O formation while maintaining high deNOx activity. Remarkably, complete NOx conversion and ~ 11% N2O saving are achieved (with inlet NO2/NOx = 0–0.5) at temperatures exceeding 200 °C; in addition, a peculiar behavior is observed in the N2O profile, which increases and decreases when adding and removing NH3 from the feed, respectively. Notably, the opposite trend is observed in the N2O profile at 200 °C. When under Standard SCR conditions, this so far unreported observation challenges the NH4NO3 formation route for N2O and suggests the existence of different controlling phenomena at different temperature regimes: i) the Cu/redox chemistry at T ≤ 200 °C and ii) the NH3 storage at higher temperature, ideally up to 300 °C.

Study of fusion and one-neutron stripping process for 6Li + 94Zr system around the Coulomb Barrier

Abstract The complete and incomplete fusion cross section as well as one-neutron stripping process of 6Li + 94Zr system were measured at the energies around the Coulomb barrier by online γ-ray method. In addition to a 30% suppression factor compared with the measured total fusion process, the complete fusion cross section in 6Li + 94Zr system was observed to be significantly lower than those in the nearby 6Li + 90,96Zr system.The new experimental result implies that the coupling with breakup channel in the 6Li-induced fusion processes would be affected by the inner structure of the target, which is still not clear in any available model calculation.For the one-neutron stripping process, the direct production cross sections for each level in 95Zr were extracted and compared with the coupled reaction channel calculation, offering a unique opportunity to study the single-particle nature of the produced excited states. Due to the fact that an overall overestimation of the production cross section for 954-keV and 1618-keV levels was observed in the comparison, further investigation is highly demanded in order to understand the full reaction mechanism for the one-neutron stripping process induced by 6Li.