Kinetic Simulations Research Articles

Steering diffusion selectivity of chemical isomers within aligned nanochannels of metal-organic framework thin film

The movement of molecules (i.e. diffusion) within angstrom-scale pores of porous materials such as metal-organic frameworks (MOFs) and zeolites is influenced by multiple complex factors that can be challenging to assess and manipulate. Nevertheless, understanding and controlling this diffusion phenomenon is crucial for advancing energy-economic membrane-based chemical separation technologies, as well as for heterogeneous catalysis and sensing applications. Through precise assessment of the factors influencing diffusion within a porous metal-organic framework (MOF) thin film, we have developed a chemical strategy to manipulate and reverse chemical isomer diffusion selectivity. In the process of cognizing the molecular diffusion within oriented, angstrom-scale channels of MOF thin film, we have unveiled a dynamic chemical interaction between the adsorbate (chemical isomers) and the MOF using a combination of kinetic mass uptake experiments and molecular simulation. Leveraging the dynamic chemical interactions, we have reversed the haloalkane (positional) isomer diffusion selectivity, forging a chemical pathway to elevate the overall efficacy of membrane-based chemical separation and selective catalytic reactions.

Sonophotocatalytic degradation of rhodamine B dye using Zr doped ZnO nanoparticles: Kinetic study and toxicity assessment

This study investigates sonophotocatalysis for the oxidation of Rhodamine B (RhB) dye using Zr doped ZnO nanoparticles. The synthesized nanoparticles were characterized by scanning electron microscope, Fourier-transform infrared, X-ray diffraction, Brunauer Emmett-Teller, thermogravimetric analysis, and photoluminescence. The hybrid sonophotocatalysis system achieved 98.73 ± 1.25% degradation of RhB under the conditions: RhB dye concentration = 10 ppm, 4 wt% of Zr doped ZnO = 0.1 g, reaction temperature = 30 °C, time = 60 min, pH = 7. A kinetic model was developed to predict the efficiency of RhB degradation through intrinsic elementary chemical reactions. The high coefficient of determination (R2 = 0.96) indicates the model's prediction accuracy in describing the degradation kinetics of RhB within sonophotocatalysis system. The electrical energy per order (EEO) analysis demonstrated that US + UVC + 4 wt% of Zr doped ZnO significantly reduced EEO (1055 kWh m−3 order−1). The synergy index for this combination was approximately 1.60, demonstrating a significant synergistic effect. Density Functional Theory (DFT) studies were utilized to propose the most probable degradation pathway, identifying reactive sites and potential byproducts. The simulations revealed the central carbon atom (1C site) as highly susceptible to radical attacks, indicating potential decolorization pathways such as N-de-ethylation, chromophore cleavage, and ring opening. Toxicity assessments of both the parent dye and its intermediates were conducted using ECOSAR (Ecological Structure Activity Relationship) to evaluate their ecological impacts. The combination of experimental results and kinetic modeling and simulations offers a deep understanding of RhB degradation complexities, driving advancements in sustainable water treatment technologies.

Kinetics simulation of TiB2 layers on the titanium alloy (Ti6Al4V) obtained by liquid boriding process

Kinetics simulation of TiB2 layers on the titanium alloy (Ti6Al4V) obtained by liquid boriding process

High-Frequency Nongyrokinetic Turbulence at Tokamak Edge Parameters

First of a kind 6D-Vlasov computer simulations of high frequency ion Bernstein wave turbulence for parameters relevant to the tokamak edge show transport comparable to sub-Larmor-frequency gyrokinetic turbulence. The customary restriction of magnetized plasma turbulence studies to the gyrokinetic approximation may not be based on physics but only on a practical constraint due to computational cost. Deciphering turbulent transport is crucial since edge turbulence significantly influences the confinement properties of magnetically confined plasmas. Despite the high computational costs, performing 6D kinetic simulations is essential for understanding the limitations of our current models. Published by the American Physical Society 2024

G-C3N4 coupled with GO accelerates carrier separation via high conductivity for photocatalytic MB degradation

Graphitic carbon nitride (g-C3N4) is widely utilized in photocatalysis due to its responsiveness to visible light, low cost, and non-toxicity. However, its efficiency is limited by factors such as the rapid recombination of photogenerated electron-hole pairs, slow electron transfer rates, and a limited number of active surface sites. In this study, g-C3N4 was synthesized through thermal polymerization, and varying amounts of graphene oxide (GO) were incorporated via physical blending to fabricate composite photocatalysts. The results indicated that the incorporation of GO not only increased the specific surface area and modified the pore size distribution of g-C3N4 but also affected the heptazine ring structure through chemical bonding, thereby enhancing the density of active sites. Photocatalytic degradation experiments with methylene blue (MB) indicated that g-C3N4 containing 2% GO exhibited photocatalytic activity 2.84 times greater than that of pristine g-C3N4. Kinetic simulations indicated that the Kapp value for the 2% GO-g-C3N4 composite was 0.00469min-1, which is 4.34 times higher than that of pure g-C3N4 (0.00108min-1). Furthermore, this composite maintained high photocatalytic activity after four cycles of reuse. An analysis of the photocatalytic degradation mechanism revealed that the incorporation of GO effectively promoted the separation and transfer of photogenerated electron-hole pairs, enhanced photocurrent density, and improved carrier separation efficiency. Electron spin resonance (ESR) and free radical scavenging experiments confirmed that the primary active species involved in the degradation of MB by the composite photocatalyst were ·O2- and h+. This study presents a novel approach for enhancing the photocatalytic performance of g-C3N4 by modifying its electronic structure and surface properties.

A modified phosphorus-based inhibitor for dry water inhibitor and its chemical mechanisms in preventing benzoyl peroxide explosion

Dust explosions caused by benzoyl peroxide (BPO) pose a significant risk to the chemical industry, making the development of high-performance inhibitors essential. The effect of a novel inhibitor on the explosion behavior of BPO dust was studied through experiments and simulations. The chemical mechanism behind the suppressed BPO dust explosion was clarified. The primary explosion hazard of BPO stems from the instability of the oxygen–oxygen bond. To address this, a novel phosphorus-based dry water powder inhibitor, MAP-DW, was prepared which effectively captures key reactive radicals involved in the chain reaction. At the optimal explosion concentration of BPO, a concentration of 400 g/m3 of MAP-DW reduced the maximum explosion pressure and the maximum explosion pressure rise rate by 96.48 % and 99.58 %, respectively. The suppression effects of MAP-DW on the explosion of BPO dust include heat absorption, oxygen dilution, thermal insulation, and capture of key free radicals. The kinetic simulation results showed that the suppression cycle between phosphorus-containing substances captured key chain reaction radicals, and the coupled suppression among NH3, H2O, and phosphorus-containing substances dominated the suppression mechanism of MAP-DW on BPO dust explosion. This study provides new insights into the characterization and suppression of BPO dust explosion, while also supplying crucial data for the safe utilization of peroxides.

Soot formation and laminar combustion characteristics of anisole: ReaxFF MD simulation and kinetic analysis

The application of biomass energy is one of the important ways to achieve carbon neutrality and deal with global warming. The study on the combustion mechanism of anisole, an oxygen-containing fuel, is helpful for biofuel large-scale application. In this study, the soot formation and laminar combustion characteristics of anisole were analyzed by reactive force field molecular dynamics (ReaxFF MD) and kinetic simulation, respectively. ReaxFF MD simulation studies had shown that soot formation of anisole combustion occurred in three stages, stage 1 (0–1 ns), stage 2 (1–2.5 ns), stage 3 (2.5–6 ns). The three stages represented the pyrolysis of the fuel, the developmental stage of the soot, and the graphitization stage of the soot, respectively. During the combustion of anisole, primary mechanisms for the soot formation were as follows: H-abstraction-C2H2-addition, carbon-addition-hydrogen-addition, internal ring formation and long carbon chain link. The formation of soot graphitization exhibited different morphologically behaviors: from flakes to onions to spheres with fewer branched chains. From the study of the laminar combustion characteristics of anisole, it can be found that the laminar burning velocities increased along with the increase of temperature, while the opposite trend was shown along with the increase of pressure. The sensitivity coefficient of naphthalene, the main soot precursor, revealed that the main promotional reactions for soot formation were R5 (O2 + H < = > O + OH), R36 (CO + OH < = > CO2 + H).

Comprehensive Study of CoCrCuNi High-Entropy Alloys: Effects of Preparation, Heat Treatment, Computational Simulation, and Alloying Elements

High-entropy alloys have attracted widespread attention from researchers worldwide due to their unique microstructure and outstanding mechanical properties, making them a prominent focus in the field of metallurgy. Among the various high-entropy alloys, the CoCrCuNi system was among the first alloys discovered, and it has shown significant progress in development. By employing different preparation and heat treatment processes, researchers have obtained alloys with diverse performances. The addition of various alloying elements or other components can lead to pronounced variations in the properties of CoCrCuNi high-entropy alloys. This work provides a comprehensive review of recent research progress on CoCrCuNi high-entropy alloys. It covers the preparation methods, thermodynamic and kinetic simulation calculations, as well as discussions on heat treatment processes and the influence of alloying elements on the microstructure and mechanical properties of CoCrCuNi high-entropy alloys. Finally, the review concludes with a prospective analysis and predictions for the potential applications and future directions in developing novel high-entropy alloys.

Thermal oxidation kinetic simulation of ignition and combustion of B–Mg–Al ternary metal alloy particles in alternating atmosphere

Thermal oxidation kinetic simulation of ignition and combustion of B–Mg–Al ternary metal alloy particles in alternating atmosphere

Real Case Study of 600 m3 Bubble Column Fermentations: Spatially Resolved Simulations Unveil Optimization Potentials for l-Phenylalanine Production With Escherichia coli.

Large-scale fermentations (»100 m³) often encounter concentration gradients which may significantly affect microbial activities and production performance. Reliably investigating such scenarios in silico would allow to optimize bioproduction. But related simulations are very rare in particular for large bubble columns. Here, we pioneer the spatially resolved investigation of a 600 m³ bubble column operating for Escherichia coli based l-phenylalanine fed-batch production. Microbial kinetics are derived from experimental data. Advanced Euler-Lagrange (EL) computational fluid dynamics (CFD) simulations are applied to track individual bubble dynamics that result from a recently developed bubble breakage model. Thereon, the complex nonlinear characteristics of hydrodynamics, mass transfer, and microbial activities are simulated for large scale and compared with real data. As a key characteristic, zones for upriser, downcomer, and circulation cells were identified that dominate mixing and mass transfer. This results in complex gradients of glucose, dissolved oxygen, and microbial rates dividing the bioreactor into sections. Consequently, alternate feed designs are evaluated splitting real feed rates in two feeds at different locations. The opposite reversed installation of feed spots and spargers improved the product synthesis by 6.24% while alternate scenarios increased the growth rate by 11.05%. The results demonstrate how sophisticated, spatially resolved simulations of hydrodynamics, mass transfer, and microbial kinetics help to optimize bioreactors in silico.

Fully Kinetic Simulations of Proton-beam-driven Instabilities from Parker Solar Probe Observations

The expanding solar wind plasma ubiquitously exhibits anisotropic nonthermal particle velocity distributions. Typically, proton velocity distribution functions (VDFs) show the presence of a core and a field-aligned beam. Novel observations made by the Parker Solar Probe (PSP) in the innermost heliosphere have revealed new complex features in the proton VDFs, namely anisotropic beams that sometimes experience perpendicular diffusion. In this study, we use a 2.5D fully kinetic simulation to investigate the stability of proton VDFs with anisotropic beams observed by PSP. Our setup consists of a core and an anisotropic beam population that drift with respect to each other. This configuration triggers a proton beam instability from which nearly parallel fast magnetosonic modes develop. Our results demonstrate that before this instability reaches saturation, the waves resonantly interact with the beam protons, causing perpendicular heating at the expense of the parallel temperature.

Experimental and Kinetic Simulations of Technetium-Catalyzed Hydrazine Oxidation in Nitric Acid Solution

The catalytic reaction of Tc plays a significant role in the chemical separation process during spent fuel reprocessing. However, few studies have been conducted on the chemical reaction mechanism between Tc and hydrazine. Moreover, the instability of Tc(V) and Tc(VI) makes their measurement difficult, rendering many aspects of the reaction process and mechanism unclear. This study investigates the catalytic reaction between Tc and hydrazine in a nitric acid solution. To this end, we obtained the kinetic laws of the reaction under various conditions of acidity, hydrazine concentration, and Tc concentration by monitoring the concentrations of hydrazine and Tc(VII) over time. The reaction kinetics model demonstrated that numerical simulations could effectively predict the reaction process. Results indicated that hydrazine promotes the reduction of Tc(VII) to Tc(IV), constituting the basis for establishing the Tc(IV, V, VI, VII) catalytic cycle. Among these, Tc(V) and Tc(VI) were important active intermediates and the main consumers of hydrazine. The research results may be useful for actinide separation processes based on valence control.

Bibliometric Analysis of Research Status, Hotspots, and Prospects of UV/PS for Environmental Pollutant Removal

There are various methods for environmental organic pollutant degradation and removal, among which ultraviolet/persulfate has drawn significant attention due to its excellent oxidizing properties, high maneuverability, and less formation of by-products. To comprehensively assess the development of ultraviolet/persulfate, a bibliometric analysis was conducted based on relevant literature indexed by Web of Science from 2002 to 2024. The findings revealed a growing number of publications, with China, Iran, and the United States being the top three countries with the highest total number of publications. Robust regional collaborations were evident. Additionally, Chinese and American scholars presented more significant activity in this field, and their publications exhibited higher quality. Furthermore, the current research hotspots, as indicated by keywords, primarily focused on the degradation mechanism of ultraviolet/persulfate and the reaction kinetic model simulation. Bibliometric results underscored that ultraviolet/persulfate, as an effective and environmentally friendly disinfection technology, possessed substantial potential for controlling diverse environmental pollutants, such as antibiotics, dyes, natural organic substances, heavy metals, microorganisms, and so on. Future research might concentrate on developing new catalytic composites and optimization of the photoactivation system. The practical application still needs to be investigated due to the complexity of the water matrix. The revival of microorganisms and the variation of toxicity should be considered further.

Soft-gluon exchange matters: Isotropic screening in QCD kinetic theory

QCD kinetic theory simulations are a prominent tool for studying the nonequilibrium initial stages in heavy-ion collisions. Despite their success, all implementations rely on approximations of the hard thermal loop (HTL) screened matrix elements in the collision terms. In this paper, we present our results for different isotropic screening prescriptions in the elastic collision term for gluons. In particular, we go beyond the simple Debye-like screening form that is used in all current implementations and apply the isotropic HTL matrix element instead. For isotropic systems, the evolution is nearly unchanged, but when studying the equilibration process in a Bjorken expanding plasma, we find qualitative and quantitative differences in a range of moments of the distribution function, such as a decrease in the maximum pressure anisotropy by up to 50%. In contrast, we find no significant qualitative impact on the jet quenching parameter or on the late-time hydrodynamization dynamics of anisotropic plasmas, but observe systematically smaller values of η/s by about 10% that coincide with perturbative calculations at small couplings. Our study reveals that the choice of the screening prescription can lead to large corrections at early times, but is less important close to equilibrium. Published by the American Physical Society 2024

Kinetic simulation and experimental study of steel material removal by the diamond bead

Kinetic simulation and experimental study of steel material removal by the diamond bead

Enhanced syngas production through dry reforming of methane with Ni/CeZrO2 catalyst: Kinetic parameter investigation and CO2-rich feed simulation

Natuna's natural gas reserve, which contains 70 %–v CO2 and 30 %–v CH4, opens a prospective method for producing syngas through the dry reforming of methane (DRM). This study used the equation and determination of kinetic parameters in a fixed-bed reactor to develop the operating conditions for the DRM process. The catalyst used was 10 %Ni/CeZrO2 and followed the Langmuir-Hinshelwood mechanism, with CH4 dissociation (activation of C–H bonds) on the Ni catalyst as the rate-determining step. According to the results, the simulation and experimental data have error values of ≤ 5 % and RMSE < 0.046. This indicates that the equation and kinetic parameters used in the simulation are valid for reactor modeling. Steady-state modeling was then conducted using a 1D quasihomogeneous model. The feed composition of CO2:CH4 = 70:30 (Natuna gas field composition) has optimized results with temperature 700 °C, CH4 conversion at 92 %, CO2 conversion at 28 %, and H2/CO ratio 1.42, and carbon formation at 7.1 mgC/gcat. This study also found that a higher CO2:CH4 feed ratio could reduce carbon formation during DRM.

Real-Time Simulation of the Reaction Kinetics of Supported Metal Nanoparticles.

A common issue with supported metal catalysts is the sintering of metal nanoparticles, resulting in catalyst deactivation. In this study, we propose a theoretical framework for realizing a real-time simulation of the reactivity of supported metal nanoparticles during the sintering process, combining density functional theory calculations, microkinetic modeling, Wulff-Kaichew construction, and sintering kinetic simulations. To validate our approach, we demonstrate its feasibility on α-Al2O3(0001)-supported Ag nanoparticles, where the simulated sintering behavior and ethylene epoxidation reaction rate as a function of time show qualitative agreement with experimental observation. Our proposed theoretical approach can be employed to screen out the promising microstructure feature of α-Al2O3 for stable supported Ag NPs, including the surface orientation and promoter species modified on it. The outlined approach of this work may be applied to a range of different thermocatalytic reactions other than ethylene epoxidation and provide guidance for the development of supported metal catalysts with long-term stability.

Variance-reduction kinetic simulation for characterization of surface and corner effects in low-speed rarefied gas flows through long micro-ducts

Variance-reduction kinetic simulation for characterization of surface and corner effects in low-speed rarefied gas flows through long micro-ducts

Can ZnO/Cu catalyst provide promising activity for glycerol direct dehydrogenation? A combined density functional theory and coverage-dependent microkinetics study

Non-oxidative dehydrogenation (NODH) reaction of glycerol is a perfect atom economical technical route to produce higher-value 1,3-dihydroxyacetone (DHA). Cu-based catalyst (especially ZnO/Cu system), is known as active species for alcohol dehydrogenation, which may be also promising one for glycerol NODH. In this study, we combine coverage-dependent free energy profile using first-principle calculation, and microkinetic model, to investigate the NODH of glycerol on the ZnO/Cu(111) surface, and a detailed comparison is made with Cu (111) surface. The coverage-dependent microkinetic model takes into account the lateral adsorbate–adsorbate self-interactions and cross-interactions, and their effect on binding energy of both intermediate and transition state. Besides, it guarantees the reaction kinetics is based on the coverage self-consistent between surface model and microkinetic result under practically reaction conditions. Compared with coverage-dependent kinetics simulation (20 %–30 %), coverage-independent model overestimates the DHA selectivity on Cu (111) (over 90 %). Our coverage-dependent kinetics simulation illustrates that both glycerol conversion and DHA selectivity are most determined by the first dehydrogenation step (OH bond scission) of glycerol on Cu (111). However, when ZnO cluster adsorbed on the Cu (111) surface, ZnO cluster promotes the electron transferring between glycerol and Cu sites, which accelerates OH bond scission process of glycerol. Under coverage-dependent microkinetic model, the turnover frequency and selectivity of DHA on ZnO/Cu(111) get much improvement compared with Cu (111). Finally, the superior of ZnO/Cu(111) is further proved by continuous stirred tank reactor simulation, where NODH of glycerol need shorter residence times or lower temperature to reach 100 % conversion, as well as keep higher DHA selectivity.

Mesoscale chromatin confinement facilitates target search of pioneer transcription factors in live cells.

Pioneer transcription factors (PTFs) possess the unique capability to access closed chromatin regions and initiate cell fate changes, yet the underlying mechanisms remain elusive. Here, we characterized the single-molecule dynamics of PTFs targeting chromatin in living cells, revealing a notable 'confined target search' mechanism. PTFs such as FOXA1, FOXA2, SOX2, OCT4 and KLF4 sampled chromatin more frequently than non-PTF MYC, alternating between fast free diffusion in the nucleus and slower confined diffusion within mesoscale zones. Super-resolved microscopy showed closed chromatin organized as mesoscale nucleosome-dense domains, confining FOXA2 diffusion locally and enriching its binding. We pinpointed specific histone-interacting disordered regions, distinct from DNA-binding domains, crucial for confined target search kinetics and pioneer activity within closed chromatin. Fusion to other factors enhanced pioneer activity. Kinetic simulations suggested that transient confinement could increase target association rate by shortening search time and binding repeatedly. Our findings illuminate how PTFs recognize and exploit closed chromatin organization to access targets, revealing a pivotal aspect of gene regulation.