Reaction Mechanism Research Articles

An experimental speciation study of DME, OME1, and OME2 in a single-pulse shock tube at high pressures

The pyrolysis of dimethyl ether (DME), oxymethylene ether-1 (OME1), and oxymethylene ether-2 (OME2) and their oxidation with oxygen under three different equivalence ratios (φ = 0.5, 1.0, and 2.0) have been studied experimentally in a customized single-pulse shock tube. The measurements were carried out highly diluted in argon over a wide temperature range between 975 K and 1400 K at initial pressures behind reflected shock waves p5(t = 0) of about 16 bar. The classical single-pulse mode involving a dump tank was not employed. Instead, post-shock gas samples were extracted through a fast-acting solenoid valve located inside the end flange of the driven section of the shock tube, to reduce measurement errors from thermal boundary layers. Thirteen stable species were identified and quantified by three different gas chromatographs simultaneously, in detail, DME, OME1, OME2, methane, ethane, ethene, acetylene, carbon monoxide, carbon dioxide, molecular hydrogen, formaldehyde, methanol, and methyl formate. The temperature dependent, measured, and normalized species concentration profiles were compared with the predicted species profiles obtained by using two different chemical kinetic reaction mechanisms from the literature and an updated version of the in-house reaction model DLR Concise. In addition, speciation data of 1,1,1-trifluoroethane and nitrous oxide at elevated pressures are presented, which were used as external chemical thermometers to validate the calculated temperature behind the reflected shock wave of the single-pulse shock tube. Novelty and SignificanceIn this work, a series of more than 300 single-pulse shock tube experiments have been performed, to investigate the decomposition products of oxygenated fuels at pressures around 16 bar. To the best of our knowledge, no speciation data is yet available for this pressure regime. By comparing the data with chemical-kinetic reaction mechanisms from the literature, opportunities for model improvement have been identified, particularly regarding methanol formation, which could be further developed in the future.The presented high-pressure validation data contributes to the development of chemical-kinetic reaction models for new oxygenated fuels derived from renewable sources. By incorporating these reaction mechanisms into CFD codes, advancements in combustors and engine technology are facilitated, promoting cleaner combustion processes.

The reaction mechanisms of ethylene oxide and propylene oxide with food Simulants: Based on experiments and computational analysis.

Ethylene oxide (EO) and propylene oxide (PO) are widely used as sterilizing agents in the food industry. However, their residues in food packaging can migrate into food and react with it, affecting the accuracy of residue detection in food. This study aims to explore the reaction mechanisms between EO and PO and aqueous food simulants using both experimental and computational methods. Especially to investigate the effects of temperature, pH and material structure on these reactions. Experimentally, the stability of EO and PO in different types of aqueous food simulants at 20°C, 40°C and 70°C was observed. It was found that at 20°C, EO and PO reacted rapidly in 4% EtOH, which 90% has reacted in 72h, and only 10%-20% reacted in other types of food simulants. All reactions accelerated with increasing temperature. At 70°C, all reactions have been completed except for 50% EtOH, which 80% has reacted in 72h. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that EO and PO can form diols or glycol ethers. Computationally, Density Functional Theory (DFT) and Transition State Theory (TST) was used to calculate the energy barriers of the reaction processes. The results showed that the energy barrier for the reaction of EO and PO with water is about 125kJ/mol. The energy barrier can be reduced by about 40kJ/mol with acid catalysis. Reactivity at the binding sites was analyzed through the Fukui function (FF), average local ionization energy (ALIE), and electrostatic potential (ESP) analysis. According to the results, the f+value at C7 in PO is 0.041 higher than it at C5. The ESP value of EO is 0.15kcal/mol higher than that of PO and the ALIE value of EO is also 0.11eV higher. The experimental results show the impact of temperature, and calculation results highlight the effects of pH and material structure on reaction mechanism. These results can help guide the development of safer packaging materials and provide theoretical support for more accurate detection of residues in food.

Influence of electroporation parameters on the reaction and transport mechanisms in electro-chemotherapeutic treatments using Boolean modeling and the Method of Fundamental Solutions.

The systemic administration of chemotherapeutic drugs involves some reaction and transport mechanisms (RTMs), including perfusion along the blood vessels, extravasation, lymphatic drainage, interstitial and transmembrane transport, and protein association and dissociation, among others. When tissue is subjected to the controlled application of electric pulses (electroporation), the vessel wall and cell membrane are permeabilized, capillaries are vasoconstricted and tissue porosity is modified, affecting the RTMs during electro-chemotherapeutic treatments. This study is a theoretical investigation about the influence of the electric field magnitude (E), number of electroporation treatments (Nep) and duration of each electroporation protocol (Tep) on the presence, interaction and rates of the RTMs using in-house computational tools. Firstly, the ratios between the extracellular, free intracellular and bound intracellular concentrations are calculated by solving the species conservation equations of a tumor cord domain by the Method of Fundamental Solutions (MFS), which was implemented, calibrated and validated in a previous work. Then, a Boolean model, which is founded on the comparison of the spatio-temporal evolution of concentration ratios, is proposed here to explore the interaction between RTMs. Different combinations of E=[0kV/m,46kV/m,70kV/m], Nep=[6,8,12] and Tep=[5min,10min,15min] are tested here. The MFS results indicate that Nep and Tep do not have a relevant influence on the types and relative importance of RTMs, but only on the rates of these mechanisms. In general, increasing E reduces the radial uniformity of transmembrane transport and association rates regarding the non-electroporated tissue, whereas the axial uniformity is affected in a lower extent.

Investigation on the activation of various coal gangues and the reaction mechanism with portlandite

Investigation on the activation of various coal gangues and the reaction mechanism with portlandite

Degradation of Toluene via DBD: Detailed Kinetic Reaction Mechanism

The degradation of toluene via Dielectric Barrier Discharge(DBD) has been extensively studied experimentally, however, the reaction mechanism remains elusive, with a dearth of theoretical research. This paper focuses the reaction mechanism of toluene degradation by DBD, developing a detailed kinetic model that encompasses 122 species and 688 reactions. Through the inference of intermediate products from experimental, 661 reactions involving heavy species were established. Finding a lowest-energy reaction path for toluene open loops in conjunction with transition state(TS) theory. Detailed kinetic modelling was carried out to explore the factors affecting toluene degradation. The main species degrading toluene was found to be ·OH, followed by ·O. The degradation rate of toluene was substantially increased by humid carrier gas. The main degradation pathway of toluene is dehydrogenation from methyl groups, conversion to six-membered rings, five-membered rings, and finally ring-opening degradation. Simulation to explore species distribution in a reactor. Electron and excited state densities are predominantly in the intermediate region, and contaminant and carrier gas densities are predominantly in the vicinity of the electrodes. Increasing the inlet air temperature makes the plasma discharge more uniform and the toluene degradation more complete.

Genetic improvement of low-lignin poplars: a new strategy based on molecular recognition, chemical reactions and empirical breeding.

As an important source of pollution in the papermaking process, the presence of lignin in poplar can seriously affect the quality and process of pulping. During lignin synthesis, Caffeoyl-CoA-O methyltransferase (CCoAOMT), as a specialized catalytic transferase, can effectively regulate the methylation of caffeoyl-coenzyme A (CCoA) to feruloyl-coenzyme A. Targeting CCoAOMT, this study investigated the substrate recognition mechanism and the possible reaction mechanism, the key residues of lignin binding were mutated and the lignin content was validated by deep convolutional neural-network model based on genome-wide prediction (DCNGP). The molecular mechanics results indicate that the binding of S-adenosyl methionine (SAM) and CCoA is sequential, with SAM first binding and inducing inward constriction of the CCoAOMT; then CCoA binds to the pocket, and this process closes the outer channel, preventing contamination by impurities and ensuring that the reaction proceeds. Next, the key residues in the recognition process of SAM (F69 and D91) and CCoA (I40, N170, Y188 and D218) were analyzed, and we identified that K146 as a base catalyst is important for inducing the methylation reaction. Immediately after that, the possible methylation reaction mechanism was deduced by the combination of Restrained Electrostatic Potential (RESP) and Independent Gradient Model (IGM) analysis, focusing on the catalytic center electron cloud density and RESP charge distribution. Finally, the DCNGP results verified that the designed mutant groups were all able to effectively reduce the lignin content and increase the S-lignin content/ G-lignin content ratio, which was beneficial for the subsequent lignin removal. Multifaceted consideration of factors that reduce lignin content and combined deep learning to screen for favorable mutations in target traits provides new ideas for targeted breeding of low-lignin poplars.

Reaction mechanisms and hydrogen production in the thermal decomposition of simple carboxylic acids in O2/H2O environments

Reaction mechanisms and hydrogen production in the thermal decomposition of simple carboxylic acids in O2/H2O environments

A review of polysorbate quantification and its degradation analysis by liquid chromatography coupled with charged aerosol detection.

Polysorbates (PS), as non-ionic surfactants, contribute significantly to the stability of proteins in formulations. However, their lack of chromophore groups makes them difficult to detect with high sensitivity and simplicity. The charged aerosol detector (CAD) is an emerging and universal detector that can provide highly sensitive response signals to non-volatile or semi-volatile substances, such as esters, acids, oxidized aldehydes, and contaminant ions in PS. This article provides a comprehensive review of the qualitative and quantitative analysis of PS, profiling its composition, investigating the reasons for its degradation, and discussing its reaction mechanisms. This review aims to promote the quality control of PS production for the development of stable and safe protein formulations.

Atomically Dispersed Metal Catalysts for Oxygen Reduction Reaction: Two-Electron vs. Four-Electron Pathways.

Developing eco-friendly electrochemical devices for electrosynthesis, fuel cells (FCs), and metal-air batteries (MABs) requires precisely designing the electronic pathway in the oxygen reduction reaction (ORR) process. Understanding the principle of designing low-cost, highly active, and stable catalysts helps to reduce the usage of noble metals in ORR. Atomically dispersed metal catalysts (ADMCs) emerge as promising alternatives to replace commercial noble metals due to their high utilization of active metal atoms, high intrinsic activity, and controllable coordination environments. In this review, the research tendency and reaction mechanisms in ORR are first summarized. The basic principles concerning the geometric size of the catalysts for both two-electron ORR (2e ORR) and four-electron ORR (4e ORR) were then discussed, aiming to outline the material design differences for 2e ORR and 4e ORR. Subsequently, the recent advances concentrated on the ADMCs, including coordination numbers, light heteroatom doping, dual-metal atoms-based coordination, and interaction between nanoparticle (NPs)/nanoclusters (NCs) and ADMs are documented. Finally, the key challenges and opportunities in the future design of ADMCs for the ORR are highlighted.

Polycarbosilane-derived Ti3SiC2 and its reaction mechanism

Polycarbosilane-derived Ti3SiC2 and its reaction mechanism

Insights from multiple stable isotopes (C, N, Cl) into the photodegradation of herbicides atrazine and metolachlor.

Many processes can contribute to the attenuation of the frequently detected and toxic herbicides atrazine and metolachlor in surface water, including photodegradation. Multi-element compound-specific isotope analysis has the potential to decipher between these different degradation pathways as Cl is a promising tool for both pathway identification and a sensitive indicator of degradation for both atrazine and metolachlor. In this study, photodegradation experiments of atrazine and metolachlor were conducted under simulated sunlight in buffered solutions (direct photodegradation) and with nitrate (indirect photodegradation by OH radicals) to determine kinetics, transformation products and isotope fractionation for C, N and for the first time Cl. For metolachlor, the C-Cl dual isotope slope (ΛC/Cl=0.46±0.19) is identical to previously reported values for hydrolysis and biodegradation in soils, suggesting the same reaction mechanism (C-Cl bond breakage by SN2 nucleophilic substitution). For atrazine, both direct and indirect photodegradation resulted in a pronounced inverse isotope effect for chlorine (εCl=6.9±3.3 ‰, and εCl=2.3±1.2 ‰, respectively), leading to characteristic dual isotope slopes (ΛC/Cl=-0.49±0.17 and ΛC/Cl=-0.31±0.10, respectively). These values are distinct from those previously reported for abiotic hydrolysis, biotic hydrolysis and oxidative dealkylation which are all relevant processes in surface water, opening the path for pathway identification in future field studies.

Kinetics, reaction mechanism and product distribution of lignocellulosic biomass pyrolysis using triple-parallel reaction model, combined kinetics, Py-GC/MS, and artificial neural networks

Kinetics, reaction mechanism and product distribution of lignocellulosic biomass pyrolysis using triple-parallel reaction model, combined kinetics, Py-GC/MS, and artificial neural networks

Ternary Cu–Fe–Al spinel catalyst for hydrogen production via water gas shift reaction: Electron transfer enhancement and reaction mechanism

Ternary Cu–Fe–Al spinel catalyst for hydrogen production via water gas shift reaction: Electron transfer enhancement and reaction mechanism

Temperature dependence of hydrogen yields from the radiolysis of reprocessing solutions: The dissolved solution of spent nuclear fuel

ABSTRACT To assess the temperature dependence of hydrogen yields from the radiolysis of dissolved solution of spent nuclear fuel, experiments were conducted to measure hydrogen yields and calculate dose rates as functions of solution temperature. The results indicated a decrease in G(H2) values with increasing solution temperature under static conditions. Comparison of the experimental values with the simulated values of G(H2) considering the previously reported reactions of hydrogen consumption by a catalytic effect of palladium ions showed a similar pattern of decreasing G(H2) values with increasing temperature. The results suggest that palladium ions have a catalytic effect in the dissolved solution, inhibiting the release of hydrogen produced by radiolysis from the liquid phase to the gas phase. This effect follows the Arrhenius law and increases with increasing solution temperature. On the other hand, the experimental values were lower than the simulated values of G(H2). This discrepancy suggest that the dissolved solution may have another mechanism for hydrogen consumption reactions in addition to a catalytic effect of palladium ions.

Ligand-Engineered Hydrophilic Perovskite Enabling Surface Potential-Driven Anions Exchange for Multicolor Biosensing.

The difficulty in designing zwitterionic ligands impedes the water-dispersed CsPbX3 perovskite nanocrystals (NCs) and their application as fast anion exchange (FAE) probes in biosensing. This study proposes a design paradigm for zwitterionic ligands predicated upon revealing the mechanism of the SN2 reaction between unsaturated alkylamines (Cn') and haloalkanoic acids (HAAs). Among them, the C=C bond can enhance the nucleophilicity of Cn' and promote the electrostatic adsorption of HAAs onto Cn', i.e., the geometric preorganization process, thereby initiating the SN2 reaction. Moreover, an appropriate "bridge" length enables HAAs to balance the geometric preorganization process and the Sigma hole intensity of the C-Br bond. Zwitterionic ligands derived from oleylamine (C18') and 5-bromovaleric acid (5-BVA) endow CsPbBr3 NCs with water dispersibility, an almost 100% photoluminescence quantum yield, and enhanced surface potential, facilitating the capture of halide ions and driving the FAE reaction. Using AgI nanoparticles (NPs) as latent anion exchangers, a third FAE strategy is presented for multicolor biosensing. Such a robust biosensing strategy can generate wavelength shift and chromatic difference for biological target molecules, exemplified by H2S, and is ultimately applicable to multicolor assay in biological, environmental and food samples, demonstrating the immense potential of perovskite-based FAE probes in biosensing.

A Comparative Study of CH and mCH Mechanisms in Hydrosilylation Reactions

The cyclic process of Si-H oxidation addition, olefin insertion, and reductive elimination was discussed by density functional theory (DFT) and high-precision quantum chemical calculations. All the calculations were performed at the B3LYP-D3/def2-TZVP level. Two fundamental mechanisms of Chalk-Harrod (CH) and modified Chalk-Harrod (mCH) were explored, in the perspective of computational chemistry. Pt(PH3)2 was used as model for the renowned Speier's catalyst, while HSiR (R=(CH3)3 and CH3(OSi(CH3)3)2 and CH2=CHR’ (R’=H, CH2OH and CH2OCH2CH2OH) were used as the reactant models. Significant findings include the identification of the olefin insertion as the rate-determining step in both mechanisms.The energy barrier of rate-determining step was 27.6 kcal/mol and 41.0 kcal/mol, respectively, according to the CH mechanism and the mCH mechanism, when HSi(CH3)3 and CH2=CH2 were used as the reactant models. But the barrier of rate-determining step become to 27.2 kcal/mol and 28.4 kcal/mol, when HSiCH3(OSi(CH3)3)2 and CH2=CHCH2OCH2CH2OH were used as the reactant models. The difference in energy barriers betweeen the CH and mCH mechanisms become closer as the reactant models increase. The reaction between polyhydrosiloxane and allyl polyether may very potentially follow the mCH mechanism rather than CH mechanism.

Storage stability evaluation of chicken seasoning by accelerating oil oxidation under different storage conditions.

The effects of temperature, humidity, and UV irradiation on the accelerated oil oxidation of chicken seasoning (CS) were investigated, aiming to establish a method for evaluating its storage stability. Key oxidation indicators, such as peroxide value (POV), fatty acid profile, and volatile aldehydes, were measured to assess the degree of oil oxidation. The results indicated that oil oxidation of CS is not significantly accelerated by temperatures of 50-80 °C due to the inhibitory effects of the Maillard reaction. The effect of humidity on accelerating oil oxidation of chicken seasoning was insignificant, either, due to the high barrier properties of the packaging material. The oil oxidation rate was greatly accelerated by UV irradiation. However, the mechanism of photosensitive oxidation reaction is inconsistent with that of auto-oxidation reaction under actual storage conditions. Ultimately, UV irradiation combined with constant temperature storage was used to induce auto-oxidation of CS, and the suitable accelerating conditions were 18h of UV irradiation, followed by 50 °C of constant temperature storage. The storage stability of 6 commercially available CS was successfully evaluated using this method. The established method provides a reliable approach for assessing the storage stability and shelf life of CS.

Personal data strategies in digital advertising: Can first-party data outshine third-party data?

As Google explores new personal data strategies, it aims to strike a balance between enhancing privacy and maintaining personalization, ensuring that consumers' data is handled responsibly while still delivering relevant and personalized advertising. This study, based on the privacy calculus framework, employs a mixed-methods approach to address two key objectives: 1) understanding how different levels of personalization impact advertising performance based on the type of data utilized, and 2) exploring the underlying mechanism of consumer reactions to personalized advertising using different types of personal data. To achieve the first research goal, Study 1 integrates Analytic Hierarchy Process (AHP) analysis of survey data from 25 advertisers with econometric analysis of advertising data from a European beauty company. To achieve the second research objective, Study 2 explores consumer perceptions through in-depth interviews and an online survey. The key findings of this study are as follows. The AHP analysis revealed that advertisers prioritize first-party data, especially purchase history, for enhancing personalized targeting. The econometric analysis suggested that while third-party data is currently most effective for enhancing advertising performance, first-party data emerges as a promising alternative in light of evolving advertising policies. Qualitative and quantitative analyses revealed complex interactions between personalization levels, data types, and consumer responses, highlighting the tension between personalization benefit and risk. These insights provide valuable guidance for advertisers, platforms, and policymakers in navigating the changing landscape of digital advertising and personal data privacy.

Boosting bio-lipids hydrodeoxygenation via highly dispersed and coking-resistance bimetallic Ni-La/SiO2 catalyst

A highly dispersed and coking-resistance bimetallic Ni-La/SiO2 catalyst was prepared for the selective hydrodeoxygenation (HDO) of fatty acid methyl esters (FAMEs) and non-edible bio-lipids to hydrocarbon compounds. Under optimum conditions, full conversion of methyl palmitate (MP) and 97.6% selectivity for pentadecane (PD) were achieved. The catalyst also exhibited high conversion and excellent desired product selectivity for the HDO of various model FAMEs, fatty acids, trilaurin, jatropha oil (JO) and waste cooking oil (WCO). Multiple characterizations show that the embedding effect (metal−support or metal−metal interaction) associated with the introduction of metallic La not only contributes to the formation of well-dispersed Ni particles and abundant active Niδ+−OV−LaOx species, but also prevents the migration and sintering of metallic Ni particles at high temperatures. Furthermore, the mutual transformation of the La2O3 and La2O2CO3 crystal phases effectively inhibits coke deposition on the catalyst surface during the reaction process, resulting in remarkable stability and reusability of the catalyst. A plausible reaction network and mechanism for the catalytic HDO of MP over Ni-La/SiO2 catalyst were proposed. This method of constructing a catalytic system can provide a basis for the development of efficient catalysts for the HDO of non-edible bio-lipids.

Enhanced oxidative bioleaching for nickel and metal recovery from arsenic ores moves toward efficient and sustainable extraction.

The research focuses on extracting nickel and other valuable elements through oxidative bioleaching from two distinct arsenic-rich ores of varying grades. This process involved utilizing a mix of mesophilic and moderately thermophilic bacteria in shake flasks with different pulp density levels to bio-leach nickeline. Mesophilic bacteria achieved over 99% nickel dissolution from both low- and high-grade ores within 10 and 28 days, respectively, at pulp densities of 0.5% and 1%. In contrast, abiotic control and chemical tests showed significantly lower nickel dissolution rates (approximately 6.9% and 26.1% for low-grade; 10.3% and 45% for high-grade samples). Moderately thermophilic bacteria achieved complete nickel dissolution from the low-grade ore at a 0.5% pulp density, while dissolution from the high-grade ore reached approximately 63%. In comparison, abiotic controls and chemical achieved only 19% and 39% dissolution for the high-grade ore, and 21.9% and 45% for the low-grade ore, respectively. X-ray diffraction (XRD) analysis confirmed the formation of scorodite as a secondary phase due to arsenic solubilization from primary minerals in the presence of iron. Kinetic modelling revealed that the bioleaching of the low-grade ore was predominantly controlled by a mixed reaction mechanism, whereas chemical factors limited the bioleaching rate of the high-grade ore. This research underscores the efficacy of oxidative bioleaching using mixed bacterial cultures and highlights its potential for efficiently extracting nickel and other valuable metals (cobalt and copper) from arsenic-bearing ores under controlled pulp density conditions.