Reaction Rate Research Articles

Efficiency analysis of solar radiation on chemical radioactive nanofluid flow over a porous surface with magnetic field

Artificial neural networks have revolutionized machine learning by providing exceptional capabilities for modeling complicated mechanisms and solving various challenges. Backpropagation is an important training technique in the field of artificial neural networks. However, this technique must be optimized when working with complicated fluid dynamics. This study analyzes the three-dimensional radiative flow of a tangent hyperbolic fluid driven by the Cattaneo-Christov flux system across a porous stretching sheet using ANN backpropagation enhanced by Bayesian Regularization approach. Heat and mass transfer analysis includes thermal radiation, chemical reactions and Cattaneo-Christov flux model. Porosity, radiation, chemical reaction rate, and ion slip effect are among the important physical characteristics that are modified to see how they affect fluid dynamics. Using MATLAB's BVP4C solver, the velocity, temperature, and concentration profiles that result from these model equations provide the training dataset for ANNs. The dataset is divided into 80 % for training, 10 % for testing, and 10 % for validation. Performance plots, regression graphs, and error histograms are used to analyze the performance of the LMT-based ANN and demonstrate its high accuracy and efficiency. With an R2 value of 1, the ANN produced a mean squared error of around 10⁻11. Fluid mobility drops as the magnetic parameter grows, while the thermal profile exhibits an increasing trend. Similarly, decreasing fluid velocity is the outcome of raising the porosity parameter. The study's conclusions have great potential for use in sectors that need sophisticated cooling and heating equipment.

Modeling, simulations, and Simulink developments in the analysis of optimal control of temperature and pH in a batch ethanol fermentation process

Transfer of laboratory-scale experiments to production-scale ethanol fermentation is time-consuming and involves expensive prototype systems from complex experimental designs that determine optimal operating conditions for minimal substrate and product inhibitions. The study developed and validated a Simulink-based model for optimal pH and temperature control using fuzzy logic and PID controllers respectively and taking advantage of 2D and 1D substrate and product inhibition models from which suitable ethanol fermentation reaction rates models were selected. Temperature and pH levels and substrate, product, and biomass concentrations were measured. Selected inhibition models were linear-product, linear substrate-sudden stop product, and linear substrate for cassava, maize, and sorghum, respectively. Fuzzy logic controller ascertained optimal flow rate of acid and base as 0.000196 ml/s and 0.000204 ml/s, respectively, and pH error and rate of pH error as 0.00334 and 0.00368, respectively. F-test two-sample for variances showed no significant difference between model and experimental curves (cassava: F critical = 0.9704, F calculated = 0.1905; maize: F critical 0.9704, F calculated = 0.2149; sorghum: F critical = 0.9704, F calculated = 0.2488). PID logic controller showed model curves and experimental curves with good fit. F-test two-sample for variances showed no significant difference between model and experimental curves (cassava: F critical = 0.9704, F calculated = 0.1288; maize: F critical = 0.9704, F calculated = 0.2083; sorghum: F critical = 0.9704, F calculated = 0.2016). The study provided an improved approach as solution for optimal pH and temperature conditions in order to mitigate substrate and product inhibitions during ethanol fermentation. It illustrated that the application of artificial intelligence-based controllers provides satisfactory outcomes that are desirable for implementation in the industrial space.Graphical

Accelerating the Reduction Kinetics of V4+ to V3+ on Atomically Fe─N4 Decorated Carbon Nanotubes for Vanadium Electrolyte Preparation.

The high manufacturing cost of vanadium electrolytes is caused by the sluggish kinetics of V4+ to V3+, which restricts the commercialization of all vanadium flow batteries (VFBs). Here, density functional theory calculations first reveal the detailed reaction pathway and point out the rate-determined step by the desorption of the end product [V(H2O)6]3+. Catalytic site engineering at the molecular level can optimize the adsorption energy of [V(H2O)6]3+ to boost the kinetics. Furthermore, iron single-atoms embedded nitrogen-doped carbon nanotubes (FeSA/NCNT) are designed to decrease the adsorption energy of [V(H2O)6]3+. The reaction rate constant of FeSA/NCNT toward V4+ to V3+ is 1.62 × 10-7cm s-1, 37.5 times that of the commercial carbon catalyst. Therefore, the energy consumption is reduced by 22.5%. Meanwhile, the prepared vanadium electrolyte is of high quality with the ideal oxidation state of + 3.5 without impurities. This work reveals the catalytic mechanism of V4+ to V3+ and proposes a simple but practical strategy to reduce the preparation cost of V3.5+ electrolyte.

Temperature-Dependent Oxidation Behavior of Silicon Carbide Surface: Reactive Molecular Dynamics Simulations.

The high-temperature oxidation mechanism of silicon carbide (SiC) is crucial for designing thermal protection systems in aircraft. This study explored the oxidative chemical reaction processes and mechanism on SiC surface and interfaces within the temperature range of 300-2300 K by using reactive molecular dynamics simulation. The oxygen impact on the silica (SiOx) growth of the SiC surface was analyzed, which shows a progressive increase of silica thickness. The simulation results indicated that the oxidation process of SiC was a typical passive oxidation mechanism. With the environmental temperature rising and oxygen impact, the increase of oxidation thickness on the SiC surface undergoes three oxidizing reaction processes: little chemical adsorption of oxygen molecules on the initial surface, rapid oxidation of silicon and carbon, and dramatic oxidation of the interface between the oxidation layer and SiC. Additionally, this work studied the mechanism of oxidation thickness growth and chemical diffusion of oxygen. The oxidation rate is weakened according to the oxygen atom diffusion barrier effect of silica repulsion. Moreover, the kinetic parameters were statistically calculated by fitting the growth of Si-O bonds and their reaction rate constants. Subsequently, the activation energy and pre-exponential factors were derived by using the Arrhenius equation to model the chemical reaction kinetics of the thermal oxidation process. The chemical reaction behaviors of the two stages could be concluded as follows: (i) in stage I, the initial oxidation is reaction rate limiting; (ii) in stage II, SiC oxidation is limited by both the oxidation reaction rate and the oxygen diffusion coefficient of the oxidation layer. The activation energy of stage II increased compared with stage I due to the oxygen atoms diffusion barrier between the oxidation layers. This study on the oxidation and ablation mechanism of the SiC surface at the atomic scale would provide insight into understanding thermal oxidation behavior and the design of ceramic materials.

Harnessing the potential of Type-II heterostructures: NiO/TiO2/ZnO fibers for enhanced photocatalytic and electrochemical performance in asymmetric supercapacitors

A novel two-step approach, electrospinning followed by wet chemical route, was used for the synthesis of NiO/TiO2/ZnO heterostructure fibers. Structural, morphological, and elemental analyses confirmed the single-phase formation with a unique, one-dimensional furry insect-like morphology, free of impurities. BET analysis revealed a significant increase in the specific surface area from 12.64 to 54.50 m2/g for NiO/TiO2/ZnO heterostructure fibers, indicating the existence of more active sites for catalytic and redox activities. Optical studies demonstrated a reduction in the band gap of NiO in the presence of TiO2 and ZnO, enhancing the photocatalytic properties. The Langmuir-Hinshelwood kinetic model was employed to measure the reaction rate constant, showing improved photocatalytic performance of NiO by enhancing the separation rate of photo-generated electrons and holes on its surface. Furthermore, the electrochemical performance of the prepared fibers-based asymmetric supercapacitors (ASCs) showed a low polarization, attributed to low charge transfer resistance. The NiO/TiO2/ZnO fibers-based ASCs exhibited higher specific capacitance (108 F/g), with a maximum specific energy density of 9.6 Wh/kg at a specific power density of 2000 W/kg indicating excellent performance suitable for finding potential uses in energy storage applications. Various practical and physical tests further certified the efficient performance of the prepared NiO/TiO2/ZnO heterostructure fibers-based asymmetric supercapacitors. The contribution of NiO and TiO2 to the inner surface were ∼52.02 and ∼47.08 %, respectively. In contrast, the NiO/TiO2/ZnO fibers showed a notable difference, with ZnO-NWs contributing ∼4.99 % to the overall surface. This increase in the inner surface contribution to around 95.01 % indicates that the growth of ZnO-NWs provides additional channels for electrochemical reactions during redox processes and enhances adhesion between the ZnO-NWs and NiO/TiO2 heterostructure, facilitating OH− ions transportation.

Domino Sequence of Ketimization and Electrophilic Amination for an Inverse Aza Intramolecular Morita-Baylis-Hillman Adduct.

Morita-Baylis-Hillman (MBH) reaction, typically catalyzed by a Lewis base, is a popular and useful method for C-C bond formation. Unfortunately, it is limited by a slow reaction rate and has sensitivity toward steric and electronic parameters. Despite tremendous efforts, the versatility of the reaction keeps the quest open for new mechanistic and catalytic pathways. Here, we have reported a Bro̷nsted acid-catalyzed, electrophilic amination (Umpolung of imine) as a method for an inverse Aza Intramolecular MBH adduct in the form of 2-acylindole. Umpolung of imine with nitrogen acting as an electrophilic center has been achieved. Interestingly, the reaction was also shown to occur under catalyst-free conditions also. The expected products of ketimine formation, 6π electrocyclization, or quinoline formation were least/not observed. A large number of examples have demonstrated the reaction strength. β-aryl-substituted acrylate and acrylamide (cinnamates and cinnamides), which are extremely sluggish in conventional MBH chemistry, are the highlights of the developed methodology. The annulated product exhibited keto-enol tautomerism, which was proven by 1H NMR integrals. As an application, another tandem reaction in the form of Michael addition on a highly complex amine was carried out to provide spiro-annulated indole.

Kinetic modelling and mechanism elucidation of catalyst-free dimethyl terephthalate hydrolysis process intensification by reactive distillation

Polyethylene terephthalate (PET) is a widely used thermoplastic polymer in the packaging and materials industries, and is predicted to have continuous market growth in the future. Methods such as glycolysis and methanolysis of PET have been identified as promising approaches in sustainable chemical recycling of PET. The latter produces dimethyl terephthalate (DMT), which can be easily hydrolyzed to terephthalic acid (TPA) at elevated temperatures and pressures, and further reused for PET production. The aim of this study was to develop a kinetic model for the hydrolysis of dimethyl terephthalate, using the experimental data. Various reaction conditions (temperature, pressure, time) have been investigated and used to calculate the activation energies and reaction rate constants, while the variation in reactor setup with methanol (MeOH) removal was conducted to show its detrimental effect on the efficiency of the reaction and selectivity towards terephthalic acid. The first reaction step of DMT to monomethyl terephthalate (MMT) is relatively irreversible, while the second reaction step of MMT to TPA ceases, as soon as the equilibrium is reached. Highest yields of TPA (76.7 %) were obtained after 40 min at 265 °C, with MeOH removal, and the activation energy was calculated to be 95 and 64 kJ mol−1 for the first and second hydrolysis reaction step, respectively.

High-Valence Mn MOF Inspired by Laccase Mediators Enables Versatile Nature-Mimicking Catalysis.

In nature, active Mn3+ -ligand complexes produced by laccase catalyzed oxidation can act as the low-molecular mass, diffusible redox mediators to oxidize the phenolic substrates overcoming the limitations of natural enzymes. Learning from the metal-ligand coordination of natural functional units, high-valence Mn metal-organic framework (Mn MOF) is constructed to simulate the catalysis in natural mediator system. Benefiting from the characteristics of nanoscale size, rich metal coordination unsaturated sites, and mixed valence state dominated by Mn(III), Nano Mn(III)-TP exhibits superior laccase-mimicking activity, whose Vmax (maximal reaction rate) is much higher than that of natural laccase. Referring to natural systems, relevant free radical experiments prove that the material induces the production of active oxygen species with the assistance of carboxylic acid, and active oxygen species further oxidize phenolic substrates. Based on its robust performances, the primary oxidative degradation of an emerging pollutant triclosan (TCS) is creatively applied, an important antiasthmatic medicine terbutaline sulfate (TBT) detection, and the synthesis of non-toxic and black near-natural dyes for dyeing. By simulating the essential mediators of natural enzymatic catalysis, an Mn MOF-based material that demonstrates multiple novel applications is successfully developed, which introduces a new reliable strategy for achieving versatile nature-mimicking catalysis.

Voltage-Driven Molecular Photoelectrocatalysis of Water Oxidation.

Molecular photocatalysis and photoelectrocatalysis have been widely used to conduct oxidation-reduction processes ranging from fuel generation to electroorganic synthesis. We recently showed that an electrostatic potential drop across the double layer contributes to the driving force for electron transfer (ET) between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. In this article, we report voltage-driven molecular photoelectrocatalysis with a prevalent homogeneous water oxidation catalyst, (bpy)Cu (II), which was covalently attached to the carbon surface and exhibited photocatalytic activity. The strong potential dependence of the photooxidation current suggests that the electrostatic potential drop across the double layer contributes to the driving force for ET between a water molecule and the excited state of surface-bound (bpy)Cu (II). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine the faradaic efficiencies for the generation of oxygen and hydrogen peroxide. Unlike electrocatalytic water oxidation by (bpy)Cu (II) in the dark, which produces only O2, the voltage-driven photooxidation includes an additional 2e- pathway generating H2O2. DFT calculations show that the applied voltage and the presence of light can alter the activation energy for the rate-determining water nucleophilic attack steps, thereby increasing the reaction rate of photo-oxidation of water and opening the 2e- pathway. These results suggest a new route for designing next-generation hybrid molecular photo(electro)catalysts for water oxidation and other processes.

Микронизация в технологии минорного компонента консервирующего действия

Natural preservatives are a global trend in the food industry. As a rule, they are traditional herbs or spices. Flavonoids inhibit microbial activity. However, they are effective only when their distribution in the food matrix is uniform. This uniformity is achieved by increasing their solubility, e.g., by micronization. The research assessed the feasibility and effectiveness of micronization of a plant preservative using a purified flavonoi d fraction obtained from defatted sea-buckthorn meal. The study featured samples of purified flavonoid fraction of sea-buckthorn meal with different dispersions. Their solubility, antioxidant properties, antimicrobial activity, and fungicidal effect were assessed by standard methods. Micronization under ultrasonic conditions and cryogenic grinding increased the solubility in water, ethyl, and oil. Ultrasonic micronization proved efficient as it produced particles of 1,400 nm under rational conditions, i.e., 50 W ultrasonic vibration in a 0.5% suspension for 10 min. The sample obtained in this way increased the rate of catalase reaction by 19% relative to the control sample while maintaining a constant rate of glutathione reduction. Its antioxidant activity increased fourfold. The samples demonstrated bacteriostatic activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, as well as fungistatic activity against Candida albicans. Purified flavonoid fraction of sea-buckthorn meal micronized under ultrasonic conditions can be recommended as a natural preservative in various food systems.

A-083 Performance evaluation of Sentinel Diagnostics’ ACE assay on the Abbott Alinity c system and ARCHITECT c16000 System

Abstract Background The analytical performances of the Angiotensin Converting Enzyme (ACE) assay for quantitative determination of ACE activity in human serum and plasma have been evaluated on the Abbott Alinity c system and ARCHITECT c16000 System. ACE (dipeptidyl carboxypeptidase) is a glycoprotein peptidyldipeptide hydrolase that cleaves histidylleucine dipeptide from angiotensin I, a relatively inactive decapeptide. The latter is converted to the potent vasoconstrictor, angiotensin II. ACE also inactivates bradykinin. Elevated levels of ACE activity occur in serum of patients with active sarcoidosis, and occasionally in premature infants with respiratory distress syndrome, in adults with tuberculosis, Gaucher’s disease, leprosy, and in many other pathologic conditions involving lung and liver diseases. Methods ACE hydrolyses urylacryloylphenylalanine-glycylglycine (FAPGG) to furylacryloylphenylalanine (FAP) and glycylglycine. Hydrolysis of FAPGG results in a decrease in absorbance at 340 nm. The ACE activity in the sample is determined by comparing the sample reaction rate to that obtained with the Sentinel ACE calibrator. Performances evaluation have been done following the latest CLSI guidelines protocols available. Results Summary of the analytical performances for the tested assay is reported in table below. Conclusions Analytical performances of Sentinel Diagnostics’ ACE assay demonstrate that quantitative determination of ACE activity in human serum and plasma are suitable for the routine measurement of the analyte on Abbott Alinity c system and ARCHITECT c16000 System.

Conditions for enhancement of gas phase chemical reactions inside a dark microwave cavity

The ability to slow down or enhance chemical reactions, by a seemingly simple setup of reactions inside a cavity made of two parallel mirrors is fascinating. Unfortunately, currently, theory and experiment have not yet fully converged. Since theory and experiment perfectly match for atom/molecular collisions in gas phase the enhancing chemical reactions in gas phase through its coupling to quantized electromagnetic modes in a dark cavity is investigated. Here the conditions and guidelines for selecting the proper type of reactions that can be enhanced by a dark cavity are provided. Showing that the asymmetric reaction rates of O + D2 → [ODD]# → OD + D and H + ArCl → [ArHCl]# → H + Ar + Cl can be enhanced by a dark cavity. On the other hand, an effect of the dark cavity on the symmetric reaction of hydrogen exchange in methane is predicted to be negligible. Notice that the theory is not limited to microwave cavities only.

Impact of Nuclear Motion on Light-Induced Bimolecular Interaction Dynamics

In chemical reactions, the nuclear motion of the molecules plays a crucial role in determining the reaction rates and outcomes. Employing the cold target recoil ion momentum spectroscopy and femtosecond pump-probe techniques, we perform a molecular-level study into the influence of nuclear vibrations on light-induced bimolecular reactions within H2−D2 dimers. The study focuses on the formation dynamics of D2H+ and H2D+ cations, shedding light on the interplay between translational and vibrational motions of the nuclei steering the bimolecular reactions. Our observations reveal a notable yield ratio of 1:1.6 between H2D+ and D2H+ channels, accompanied with a faster formation of D2H+ compared to H2D+. Molecular dynamics simulations unveil that the faster vibrational motion of H2+ than that of D2+ upon single ionization within the dimer accounts for these differences. Our findings provide new insight into the time-resolved kinetic isotope effect on the bimolecular reactions, highlighting the critical relationship between nuclear vibrational motions and reaction dynamics. Published by the American Physical Society 2024

Effects of Arrhenius activation energy and melting heat transfer on Carreau fluid through a stretching sheet

ABSTRACT This article investigates the effect of activation energy on Carreau fluid flow in the presence of variable thermal conductivity, inclined magnetic field, melting heat transfer, and Soret and Dufour phenomena. A set of suitable similarity transformations is applied for transforming the governing partial differential equations (PDEs) considered for the physical phenomena into non-linear ordinary differential equations (ODEs). We obtained the results by solving the non-linear ODEs numerically which describe the behavior of the velocity, temperature, and concentration profiles of the fluid against the governing parameters and illustrated these graphically. The velocity distribution decreases for angle of inclination while it is increasing against higher melting parameter. The temperature distribution enhances with higher modified Dufour parameter and Prandtl number while it declines for thermal conductivity, activation energy, and melting parameters. The concentration distribution increases for melting parameter, Soret number, and activation energy parameter while decreasing for temperature difference parameter, Schmidt number, and reaction rate parameter. Skin friction, Nusselt and Sherwood numbers are evaluated numerically against the various governing parameters. Accuracy of the present work is illustrated and established through comparison carried out for skin friction versus magnetic parameter with existing results in the literature.

Variable density and heat generation impact on chemically reactive Carreau nanofluid heat-mass transfer over stretching sheet with convective heat condition

The present study focuses on the physical significance of heat generation and chemical reaction on Carreau nanofluid with convective heat conditions. Heat transfer is characterized using convective boundary conditions. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) by using well define stream functions and similarity transformations. Using a shooting methodology, the Keller-box method with Newton Raphson scheme is used to elaborate the numerical solutions of physical phenomena. Utilizing a similar technique to find the impact of physical parameter such as the production of heat , the rate of reaction , Biot numbers , Brownian motion variable , the thermophoresis parameters , the Weissenberg quantity , Prandtl number , and Lewis number on velocity profile, temperature profile and mass transmission profile are determined graphically. The skin-friction coefficient , local Nusselt , and Sherwood numbers are analyzed numerically. Increment in fluid velocity and slip temperature are depicted with high Biot number. Maximum magnitude of fluid temperature and fluid concentration function are depicted at high value of temperature dependent density. The magnitude of heat and mass transportation enhanced with maximum choice of Brownian motion.

Hydrogenation process intensification of 2-nitro-4-acetylamino anisole by HiGee technology

The catalytic hydrogenation of 2-nitro-4-acetylamino anisole (NMA) is the main path to synthesize 2-amino-4-acetylamino anisole (AMA), belonging to a typical gas-liquid-solid system. However, the small mass transfer rate of traditional hydrogenation reactor can't match its intrinsic fast reaction rate, resulting in the low hydrogenation efficiency. In this work, a rotating packed bed (RPB) reactor with excellent mass transfer performance was applied for the hydrogenation process intensification of NMA. The characterization analysis of the commercial Raney-Ni catalyst shows that the liquid-solid mass transfer resistance during the reaction process can be ignored, and improving the gas-liquid mass transfer rate is the key to improve the macroscopic reaction rate. The effects of operating conditions (solvent, rotational speed, hydrogen pressure, temperature, and catalyst dosage) on NMA conversion and AMA selectivity were investigated. A macro-kinetic equation of NMA catalytic hydrogenation in the RPB reactor was proposed. Under optimized conditions, the NMA was completely converted in the RPB reactor within 30 min, while it took 4 h in the stirred tank reactor. The overall reaction efficiency of RPB reactor was increased by 87.5% in comparison with STR. This study provides practical guidance for the industrial application of RPB reactor for gas-liquid-solid hydrogenation.

Insights into the crucial role of pH to achieve the dual goals of efficient fluoride removal and resource recovery from the photovoltaic manufacturing wastewater

Fluoride-containing wastewater arose from the rapid development of photovoltaic manufacturing, and caused many environmental and health concerns. Chemical precipitation is commonly applied for fluoride removal, in which pH plays a crucial role while lacking systematic and in-depth research. In this study, the effect of pH on fluoride removal was investigated from both theoretical and experimental views, and the recovered precipitates with pH control were characterized. Theoretical analysis illustrated the quantitative relationship between reaction rate and pH, which indicated an optimal pH of about 8 for fluoride removal. This result was further validated by the batch and continuous experiments. In the batch experiments, the highest fluoride removal efficiency of 99.00 ± 0.01 % and lowest fluoride residual of 19.93 ± 0.16 mg/L were achieved at pH 8.00. In the continuous experiments, the fluoride residual was controlled under 10 mg/L with a fluoride removal rate of 2298.3 ± 0.5 kg F/(m3·d) in the optimal pH range of 6.95 to 8.47. The precipitate characteristics in terms of morphology, elements composition, and crystallization property showed a close correlation with reaction pH. Furthermore, a multidimensional system involving CaF2 content, precipitant saving, particle size, crystallinity, and fluoride residual was established to assess the fluoride removal and precipitate recovery with pH control. A neutral condition was recommended to achieve the above dual goals. This work provided systematical and deep insights into the pH role in fluoride removal and precipitates recovery, and could offer guidelines for the development of industrial fluoride-containing wastewater treatment.

Selective methanol production via CO2 reduction on Cu2O revealed by micro-kinetic study combined with constant potential model

High efficiency electrocatalysis of greenhouse gas CO2 to liquid fuel methanol attracts great attentions that allows energy transformation from renewable electric energy to storable chemical energy. Catalytically converting CO2 to methanol using green hydrogen is a promising pathway to achieve carbon neutrality. In this work, the catalytic activity and product selectivity of the electrochemical CO2 reduction reaction on Cu2O were studied using a micro-kinetic model based on Marcus charge transfer theory. The constant potential model under the grand-canonical ensemble enables the accurate description of binding energies and ground-state charge transfer upon surface adsorption as a function of electrode potential. Firstly, the potential-dependent activation energies and rate constants of all possible elementary reactions involved in CO2 reduction are calculated. Then, the surface coverage and its derivative can be obtained in a steady-state approximation. Finally, the total reaction rate and partial reaction rate can be deduced, allowing for direct comparison with catalytic activity (current density) and product selectivity (Faradaic efficiency). It is found that CH3OH is the dominant product on the Cu2O(111) surface, while CO is the main product on the Cu2O(110) surface. Based on the derived total and partial reaction rates under the steady-state approximation, it is demonstrated that Cu2O(111) exhibits the highest electrocatalytic activity and methanol selectivity at U = − 0.6 V vs. SHE. This research presents a methodology for predicting apparent electrocatalytic performance from microscopic reaction energy calculations, which can be applied to other important electrocatalytic reaction mechanisms and performance predictions.

Implications of 1.5 K climate warming on warm-season ozone exposure and atmospheric oxidation capacity in China

Surface ozone (O3) poses significant threats to public health, agricultural crops, and plants in natural ecosystems. Global warming is likely to increase future O3 mainly by altering atmospheric photochemical reactions and enhancing biogenic volatile organic compound (BVOC) emissions. To assess the impacts of the future 1.5 K climate target on O3 concentrations and ecological O3 exposure in China, numerical simulations were conducted using the CMAQ (Community Multiscale Air Quality) model during April–October 2018. Ecological O3 exposure was estimated using six indices (i.e., M7, M24, N100, SUM60, W126, and AOT40f). The results show that the temperature rise increases the MDA8 O3 (maximum daily eight-hour average O3) concentrations by ∼3 ppb and the number of O3 exceedance days by 10–20 days in the North China Plain (NCP), Yangtze River Delta (YRD), and Sichuan Basin (SCB) regions. All O3 exposure indices show substantial increases. M24 and M7 in eastern and southern China will rise by 1–3 ppb and 2–4 ppb, respectively. N100 increases by more than 120 h in the surrounding regions of Beijing. SUM60 increases by greater than 9 ppm h−1, W126 increases by greater than 15 ppm h−1 in Shaanxi and SCB, and AOT40f increases by 6 ppm h−1 in NCP and SCB. The temperature increase also promotes atmospheric oxidation capacity (AOC) levels, with the higher AOC contributed by OH radicals in southern China but by NO3 radicals in northern China. The change in the reaction rate caused by the temperature increase has a greater influence on O3 exposure and AOC than the change in BVOC emissions.

Enhanced anisotropy of Pr-Nd-Fe-B HDDR magnetic powders by regulating the hydrogen decrepitated process

The evolution of microstructures for different hydrogen decrepitated routes was investigated in hydrogenation-disproportionation-desorption-recombination (HDDR) magnetic powders, with particular focus on the fracture of the SC heat-treated alloy during two-step hydrogen decrepitation (HD) and the influence of the first step temperature on magnetic properties. As the temperature increases, the properties of the magnetic powders increase and then decrease, the optimized performance of HDDR magnetic powders was obtained with Br=1.45T, (BH)max=393kJ·m-3, DOA=0.79 when the first HD temperature is 65°C. The microscopic analysis shows that there are two problems in the one-step HD route: one is that the particle size is larger ~150 μm and there are incomplete fractured cracks, the particle surface is more PrNd-rich phase, which leads to different reaction rates between the surface and center in HDDR particles, and the texture orientation of the fine grains at the edge of surface and crack is disordered. The second issue is that HD grains have significant angular difference with the c-axis orientation in incomplete fractured grain clusters, which is directly inherited by the HDDR magnetic powder, resulting in a misalignment texture. In comparison, the two-step HD process effectively addresses the issues derived from one-step HD process. Not only is the grain size of HDDR magnetic powders uniform and the width of the thin grain boundary phases (GBs) is less than the exchange coupling length, but also (Fe+Co) content exceeding 30at.% in GBs with weak magnetism. This is beneficial for enhancing exchange coupling effect between adjacent grains. Moreover, magnetic powder particle exhibits single-domain characteristics, which improves the grain texture orientation. This research provides a new insight for the development of high-orientation and high-performance HDDR magnetic powders.