Reaction Kinetics Research Articles

Sorption-enhanced intensified CO2 hydrogenation via reverse water–gas shift reaction: Kinetics and modelling

Intensification of CO2 hydrogenation via the reverse water–gas shift (RWGS) reaction for CO production can be achieved through in situ removal of water when hydrophilic adsorbents are incorporated alongside the catalyst in the reaction bed. In this work, seeking to move a step closer to the industrial implementation of this innovative CO2 valorization process, a comprehensive reactor model, validated by experimental data obtained in a fixed-bed reactor, was developed to simulate the behavior of this sorption-enhanced (SE) RWGS process. Simulation and experimental data matched with good accuracy, demonstrating the striking benefits brought by the adsorbent addition, such as an almost doubling of the CO yield at 300 °C. The kinetics of RWGS reaction over a Cu-based catalyst and H2O adsorption on a 13X zeolite adsorbent were studied both experimentally and theoretically and the kinetic models were integrated into the reactor model to assess the performance of SE-RWGS process. Fitting of the RWGS reaction rates by a Langmuir-Hinschelwood-Hougen-Watson-type heterogeneous kinetic model suggested that the rate-determining step of the reaction is the surface interaction between an adsorbed CO2 molecule and a H* species on catalytic sites of different nature. Meanwhile, the dynamic behavior of water adsorption was effectively simulated by a semi-empirical double-stretched exponential model combined with the Sips isotherm model. The results of this work could be applied to the design and scale-up of the SE-RWGS process, which offers considerable improvements over the thermodynamically constrained conventional process. The intensified approach represents a promising avenue for the effective conversion of carbon dioxide into CO, as well as into other value-added chemicals as part of a multi-stage CO2 reduction process.

How Humans Run Faster: The Neuromechanical Contributions of Functional Muscle Groups to Running at Different Speeds.

How the neuromechanics of the lower limb functional muscle groups change with running speed remains to be fully elucidated, with implications for our understanding of human locomotion, conditioning, and injury prevention. This study compared the neuromechanics (ground reaction and joint kinetics, kinematics and muscle activity) of middle-distance athletes running on an instrumented treadmill at six wide-ranging speeds (2.78-8.33 m·s-1). Ground reaction forces and kinematics were analyzed using inverse dynamics to calculate flexor and extensor joint torques, and positive and negative work done by these torques. Contributions of each functional muscle group to the total positive and negative work done by the limb during stance, swing, and the whole stride were quantified. During stance, the ankle plantar flexors were the major energy generator and absorber (>60%) at all speeds, but their contribution to whole stride energy generation and absorption declined with speed. Positive work by the hip extensors rose superlinearly with speed during stance (3-fold) and especially during swing (12-fold), becoming the biggest energy generator across the whole stride at >5 m·s-1. Knee flexor and extensor negative work also rose superlinearly with speed during swing, with the knee flexors becoming the greatest energy absorber over the whole stride at >7.22 m·s-1. Across speeds, plantar flexor peak moment and positive work accounted for 97% and 96% of the variance in step length, and swing hip extension peak moment and positive work accounted for 98% and 99% of the variance in step frequency. There were pronounced speed, phase (stance/swing), and work (positive/negative) dependent contributions of the different functional muscle groups during running, with extensive implications for conditioning and injury prevention.

Modeling of Micro Aluminum Particle Flames Using Particle Burning Time

ABSTRACT This work presents a Lagrangian model, referred to as the integral model in this study, for aluminum-dust combustion, with the intent to reduce the computational burden and numerical stiffness. A comparison with available experimental data and a detailed model explicitly resolving chemical kinetics is presented for the canonical case of a planar flame. The influence of particle diameter, dust concentration and fresh-gases temperature on the flame speed and flame temperature is presented. Most results are within experimental uncertainties, unfortunately significant for aluminum-dust flames. Paths for improvements are proposed when needed. Regarding computational burden, it is shown that the integral model is faster and more robust than its counterpart using chemical kinetics. Insights on polydisperse flows and validation with constant volume combustion cases are provided. This study paves the way for a use in more complex cases such as turbulent flames or afterburning in energetic materials.

Low-Cost Self-Reconstructed High Entropy Oxide as an Ultra-Durable OER Electrocatalyst for Anion Exchange Membrane Water Electrolyzer.

Future energy loss can be minimized to a greater extent via developing highly active electrocatalysts for alkaline water electrolyzers. Incorporating an innovative design like high entropy oxides, dealloying, structural reconstruction, in situ activation can potentially reduce the energy barriers between practical and theoretical potentials. Here, a Fd-3m spinel group high entropy oxide is developed via a simple solvothermal and calcination approach. The developed (FeCoMnZnMg)3O4 electrocatalyst shows a near equimolar distribution of all the metal elements resulting in higher entropy (ΔS≈1.61R) and higher surface area. The self-reconstructed spinel high entropy oxide (S-HEO) catalyst exhibited a lower overpotential of 240mV to reach 10mA cm-2 and enhanced reaction kinetics (59mV dec-1). Noticeably, the S-HEO displayed an outstanding durability of 1000h without any potential loss, significantly outperforming most of the reported OER electrocatalysts. Further, S-HEO is evaluated as the anode catalyst for an anion exchange membrane water electrolyzer (AEMWE) in 1m, 0.1m KOH, and DI water at 20 and 60°C. These results demonstrate that S-HEO is a highly attractive, non-noble class of materials for high active oxygen evolution reaction (OER) electrocatalysts allowing fine-tuning beyond the limits of bi- or trimetallic oxides.

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions.

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

The Influence of Acetone on the Kinetics of Water Electrolysis Examined at Polycrystalline Pt Electrode in Alkaline Solution

This study investigated the impact of acetone on the electrochemical behavior of polycrystalline platinum electrodes in 0.1 M NaOH solution, with respect to the kinetics of hydrogen and oxygen evolution reactions (HER and OER) and indirectly to the underpotential deposition of hydrogen (UPDH). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to analyze these processes for acetone concentrations ranging from 1.0 × 10−6 to 1.0 × 10−3 M. The addition of (CH3)2C=O enhanced the catalytic efficiency of alkaline water splitting, which was believed to be a result of a significant reduction in the surface tension phenomenon (due to mutual interaction of acetone and water molecules), thus considerably facilitating hydrogen bubble detachment from the Pt electrode. Key findings in this work are described with respect to facilitation of both the HER and the OER reactions’ kinetics by the presence of acetone (also undergoing Pt electroreduction over the potential range for UPDH) in the working solution, without an electrode surface poisoning effect. The latter implies significant opportunities for traces of organic additives into alkaline electrolyte to improve the industrial alkaline water electrolysis process.

Anisotropic Heterobimetallic Nanomaterials with Controlled Composition for Efficient Oxygen Reduction at Ultralow Loading

AbstractHydrogen fuel cells represent a leading technology in developing green energy targeting net‐zero emissions goals by mid‐century. However, the sluggish kinetics of the oxygen reduction reaction (ORR) have hitherto demanded substantial quantities of expensive platinum (Pt) group metals. Advances in catalyst design, including the controllable fabrication of highly branched morphologies to increase the surface area‐to‐volume ratio, intermixing Pt with more affordable transition metals, and controlling composition, offer solutions that can further enhance activity and reduce expense. In this context, Pt/M (M = Fe, Ni, Co) nanopods and nanodendrites with precise composition control using more affordable starting materials are designed and crafted. The method is highly efficient, taking only 30 min and avoiding the need for high‐pressure equipment, making it highly scalable. These catalysts show superior ORR performance at an electrode loading as low as 0.0022 mgPt cm−2. One, nanodendritic Pt/Ni, achieves a mass activity of at 0.9 V versus RHE, making it 87 times more efficient in terms of Pt‐content than a commercial 10 wt% Pt/C nanoparticle standard. These findings provide new opportunities for developing next‐generation, cost‐efficient Pt‐based catalysts, by potentially advancing hydrogen fuel cell technology through performance enhancement and addressing cost challenges through catalyst design.

DNA Dissipative System for Controlled Release of Immunostimulatory CpG Oligodeoxynucleotides

Herein, a dissipative system tailored for the controlled loading and release of CpG oligodeoxynucleotides (CpG ODNs), known for their pharmacological immunostimulatory properties, is reported. The approach involves multiple cycles of deactivation and activation of the CpG ODNs via its hybridization with a complementary fuel strand, followed by its selective release mediated by the enzymatic activity of T7 exonuclease. The autonomous and temporal behavior of this dissipative system can be tuned by three factors: the design of the fuel strand and its concentration that governs the kinetics of the forward hybridization reaction, as well as the concentration of T7 exonuclease, which regulates the backward energy dissipation reaction. Furthermore, the enzyme's tolerance toward waste accumulation is demonstrated, and the system's robust performance when utilizing various fuel strands in alternating fashion is showcased. The findings underscore the potential of this approach for precise and programmable delivery of therapeutic nucleic acids in multiple cycles, with implications for enhancing immunotherapeutic strategies in which controlled kinetics of the nucleic acid is highly desired.

Development of the adjoint of the unified tropospheric–stratospheric chemistry extension (UCX) in GEOS-Chem adjoint v36

Abstract. Atmospheric sensitivities (gradients), quantifying the atmospheric response to emissions or other perturbations, can provide meaningful insights on the underlying atmospheric chemistry or transport processes. Atmospheric adjoint modeling enables the calculation of receptor-oriented sensitivities of model outputs of interest to input parameters (e.g., emissions), overcoming the numerical cost of conventional (forward) modeling. The adjoint of the GEOS-Chem atmospheric chemistry-transport model is a widely used such model, but prior to v36 it lacked extensive stratospheric capabilities. Here, we present the development and evaluation of the discrete adjoint of the global chemistry-transport model (CTM) GEOS-Chem unified chemistry extension (UCX) for stratospheric applications, which extends the existing capabilities of the GEOS-Chem adjoint to enable the calculation of sensitivities that include stratospheric chemistry and interactions. This development adds 37 new tracers, 273 kinetic and photolysis reactions, an updated photolysis scheme, treatment of stratospheric aerosols, and all other features described in the original UCX paper. With this development the GEOS-Chem adjoint model is able to capture the spatial, temporal, and speciated variability in stratospheric ozone depletion processes, among other processes. We demonstrate its use by calculating 2-week sensitivities of stratospheric ozone to precursor species and show that the adjoint captures the Antarctic ozone depletion potential of active halogen species, including the chlorine activation and deactivation process. The spatial variations in the sensitivity of stratospheric ozone to NOx emissions are also described. This development expands the scope of research questions that can be addressed by allowing stratospheric interactions and feedbacks to be considered in the tropospheric sensitivity and inversion applications.

An Electron-Coupled Co-ZrO2 Nanodot Heterojunction Electrocatalyst with Lewis Acid-Base Site Pairs Enables High Redox Reaction Kinetics of Li-S Batteries.

Using electrocatalysts is effective in solving the slow reaction kinetics of polysulfides in Li-S batteries, but designing stable electrocatalysts with an integrated adsorption-catalysis-desorption system is challenging. Here, we report a stable metal-semiconductor (Co-ZrO2) heterojunction electrocatalyst fabricated by assembling electron-coupled Co-ZrO2 nanodots into macroporous carbon nanofibers. The Co-ZrO2 contact causes interfacial electron enrichment and electron transfer from Co to ZrO2, which creates abundant Lewis-acid sites on Co that can adsorb polysulfides. Simultaneously, the enriched interfacial electrons can activate the S-S bond and boost the catalytic conversion of long-chain polysulfides, while the ZrO2 with Lewis-base sites facilitate the desorption of short-chain polysulfides from the electrocatalyst. Moreover, the nanodot heterojunctions show great chemical stability and high redox reaction kinetics of polysulfides. Li-S batteries show high discharge capacities of 954.5 mA h·g-1 at 0.5 C with a retention of 84.9% over 200 cycles, and 710.2 mA hg-1 at 1 C with a retention of 98.6% over 200 cycles. This study provides an effective strategy for developing active and durable electrocatalysts for Li-S batteries.

A Nitrogen/Oxygen Dual-Doped Porous Carbon with High Catalytic Conversion Ability toward Polysulfides for Advanced Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) have attracted widespread attention due to their high theoretical energy density and low cost. However, their development has been constrained by the shuttle effect of lithium polysulfides and their slow reaction kinetics. In this work, a nitrogen/oxygen dual-doped porous carbon (N/O-PC) was synthesized by annealing the precursor of zeolitic imidazolate framework-8 grown in situ on MWCNTs (ZIF-8/MWCNTs). Then, the N/O-PC composite served as an efficient host for LSBs through chemical adsorption and providing catalytic conversion sites of polysulfides. Moreover, the interconnected porous carbon-based structure facilitates electron and ion transfer. Thus, the S/N/O-PC cathode exhibits high cycling stability (a stable capacity of 685.9 mA h g−1 at 0.2 C after 100 cycles). It also demonstrates excellent rate performance with discharge capacities of 1018.2, 890.2, 775.1, 722.7, 640.4, and 579.6 mAh g−1 at 0.2, 0.5, 1.0, 2.0, 3.0, and 5.0 C, respectively. This work provides an effective strategy for designing and developing high energy density, long cycle life LSBs.

Heterogeneous Solid Electrolyte Interphase Interactions Dictate Interface Instability in Sodium Metal Electrodes.

Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro-chemo-mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity-induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms-mechanical, transport, and kinetic-that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.

Nickel Single‐Atoms Modified Organic Anodes with Enhanced Reaction Kinetics for Stable Potassium‐Ion Batteries

AbstractThe redox‐active organic compounds including potassium 1,1′‐biphenyl‐4,4′‐dicarboxylate (K‐BPDC) are attracting considerable attention as anodes for potassium‐ion batteries (PIBs). Nevertheless, the practical applications of K‐BPDC organic anodes are severely hindered by short cycle life due to their relatively sluggish redox kinetics and instability. In this work, Ni single atoms (up to 6 wt.%) are implanted into K‐BPDC (NiSA@K‐BPDC) by using an electrochemical‐induced reconstruction (EIR) strategy to enhance the reaction kinetics and stability of PIBs. During the EIR process, Ni‐based metal‐organic framework (Ni‐BPDC) is in situ reconstructed into K‐BPDC by replacing Ni2+ with K+ to make the rest nickel species exist in the form of single atoms in K‐BPDC. By kinetic analysis and theoretical calculations, it is uncovered that the Ni single atoms supported on K‐BPDC efficiently redistribute the local charge of K‐BPDC to accelerate the K+ transport rate, and thermodynamically reduce the redox energy barrier. As a result, the NiSA@K‐BPDC anode exhibits outstanding cycle stability with 88.5% capacity retention during 4000 cycles at 1 A g−1 and an excellent rate capability (114 mAh g−1 at 2 A g−1). This study opens up a new door to the design of organic anodes with single atoms for high‐performance PIBs.

Evaluating the physico-chemical properties of water-based and 2% lidocaine hydrochloride-based aluminum-free glass polyalkenoate cements for distal radius fixation.

Lidocaine hydrochloride is used as an anesthetic for clinical applications. This study considers the effects of the substitution of 2% lidocaine hydrochloride for deionized (DI) water on the rheological, mechanical, ion release, pH and injectable properties of two formulations of aluminum-free glass polyalkenoate cements (GPCs) using two distinct poly(acrylic) acids (PAA), E9 and E11, which have different molecular weights (Mw). The substitution of 2% lidocaine hydrochloride demonstrated increased injectability, but did not affect mechanical properties. The mechanical properties increased with time, as expected, and, in general, E9-based GPCs displayed significantly higher strengths over E11-based GPCs. With respect to ion release, which includes calcium (Ca), strontium (Sr), zinc (Zn) and silicon (Si); all ions displayed a steady and consistent increased release over time. Ca and Sr showed similar ion release patterns, whereby the GPC made with E11 PAA and lidocaine hydrochloride released significantly more ions than all other compositions likely due to similar chemical kinetics. However, Zn is also divalent in nature, but displayed only one significant difference across the GPC series at all time points, which was attributed to its higher electronegativity allowing for increased participation in the setting reaction. Finally, an analysis of the pH confirmed an increase in pH with time, suggesting that H+ ions were attacking the glass structure to allow for ion release. After 1 and 7 days, water-based GPCs environments achieved a higher pH than lidocaine hydrochloride-based GPCs, indicating that the lidocaine hydrochloride may be releasing additional protons upon bond formation with PAA.

Thermo-rheological and kinetic characterization and modeling of an epoxy vitrimer based on polyimine exchange.

The present study describes the development of cure kinetics and chemo-rheological models for an epoxy vitrimer based on polyimine exchange to elucidate the potential in terms of processing and accurate process selection. Reaction kinetics is investigated using differential scanning calorimetry. A good agreement between the model and data can be demonstrated for different stoichiometries by selecting a parallel reaction approach consisting of an nth-order and an autocatalytic approach. The suggested chemo-rheological model captures the intrinsically high viscosity of the resin over a broad temperature and curing range, even after the gelation point. The Di-Benedetto equation represents the glass transition temperature advancement with cure while combining the rheological Winter-Chambon criterion and the kinetic model determines the degree of cure at the gelation. These results give important advice for improved process modeling of vitrimeric resins, facilitate accurate process selection, and pave the way towards the development of composites based on the matrix system investigated in this work.

Constructed Mott–Schottky Heterostructure Catalyst to Trigger Interface Disturbance and Manipulate Redox Kinetics in Li-O2 Battery

HighlightsA carbon free self supported Mott-Schottky heterostructure was constructed as an efficient cathode catalyst for lithium oxygen batteries, achieving homogeneous contact between the two materials for strong interfacial interactions.The heterostructure triggered interfacial perturbations and band structure changes, which accelerated oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, resulting in an extremely long cycle life of 800 cycles and an extremely low overpotential of 0.73 V.Combined with advanced characterization techniques and density functional theory calculations, the underlying mechanism behind the boosted ORR/OER activities and the electrocatalytic mechanism were revealed.

Identification of the Female Sex Pheromone of Grammodes Geometrica (Lepidoptera: Erebidae: Erebinae).

The female sex pheromone of Grammodes geometrica (Lepidoptera: Erebidae: Erebinae) was identified as a 2:100:4 mixture of (3Z,6Z,9Z)-3,6,9-icosatriene (T20), (3Z,6Z,9Z)-3,6,9-henicosatriene (T21), and (3Z,6Z,9Z)-3,6,9-tricosatriene (T23) through chemical and electrophysiological analyses of female gland extracts. T23 is a novel sex pheromone component in Erebinae species. Field trapping tests demonstrated optimal male captures in attractant-baited traps when using a 2:100:4 blend of T20, T21 and T23, with a significant decrease in captures observed when T20 or T23 were removed from the full blend. Traps were set in early August, but males began to be captured in early September. The seasonal prevalence showed a bimodal peak, occurring on September 11 and October 9. These findings provide valuable insights into the chemical communication and ecological dynamics of this species within the subfamily Erebinae.

DNA nanosensor based on bipedal 3D DNA walker-driven proximal catalytic hairpin assembly for sensitive and fast TK1 mRNA detection.

Hyperproliferative diseases are the first step for tumor formation; thymidine kinase 1 (TK1) mRNA is closely related to cell proliferation. Therefore, the risk of malignant proliferation can be identified by sensitively detecting the variance in TK1 mRNA concentration, which can be used for tumor auxiliary diagnosis and monitoring tumor treatment. Owing to the low abundance and instability of TK1 mRNA in real samples, the development of a sensitive and fast mRNA detection method is necessary. A DNA nanosensor that can be used for detecting TK1 mRNA based on bipedal 3D DNA walker-driven proximal catalytic hairpin assembly (P-CHA) was developed. P-CHA hairpins were hybridized to a linker DNA strand coupled with magnetic nanoparticles to increase their local concentrations. The bipedal DNA walking on the surface of NPs accelerates reaction kinetics using the proximity effect. Taking advantage of the signal amplification of P-CHA as well as the rapid reaction rate of the DNA walker in 80min, the proposed sensor detects TK1 mRNA with a low detection limit of 14pM and may then be applied toclinical diagnosis.

Exploring the sorption and degradation dynamics of validamycin-A in agricultural soils for environmental management.

Validamycin A (VA) is one of the antibiotics that have been utilized in agriculture in Asia; nevertheless, there haven't been many investigations on what happens to VA in soil. The rate at which pesticides are adsorbed into the soil must be determined, since their usage in agriculture is growing. In order to accomplish this, the current study investigated the sorption and degradation of VA in ten distinct soil samples via batch equilibrium studies while maintaining strict laboratory controls. In thermodynamic analysis with a C-type curve, the negative values of Gibbs free energy (ΔG) are thoroughly evaluated using both linear and Freundlich models. These values vary from - 16.8 to - 22.2kJ/mol. Impact of temperature (18, 23, and 30°C) and pH (5, 7, and 9) on the degradation of this antibiotic in soil was also scrutinized. Our findings demonstrated that, as a result of enhanced microbial activity at higher temperatures, VA deteriorated more quickly at 23°C and 30°C than at 18°C. In comparison to lower pH values, the VA removal efficiencies with sample-4 was significantly greater at pH 7.4 (92.9%) and pH 9 (97.4%). Moreover, first order reaction kinetics were followed in the degradation of VA. The results demonstrated that VA bound to the selected soils, resulting in medium to low persistence as demonstrated by degradation values. In summary, this study provides important information regarding the behavior and fate of VA in different types of soil, information that might be useful in developing workable management strategies and environmental risk assessments.

Simulating Chemistry on Bosonic Quantum Devices.

Bosonic quantum devices offer a novel approach to realize quantum computations, where the quantum two-level system (qubit) is replaced with the quantum (an)harmonic oscillator (qumode) as the fundamental building block of the quantum simulator. The simulation of chemical structure and dynamics can then be achieved by representing or mapping the system Hamiltonians in terms of bosonic operators. In this Perspective, we review recent progress and future potential of using bosonic quantum devices for addressing a wide range of challenging chemical problems, including the calculation of molecular vibronic spectra, the simulation of gas-phase and solution-phase adiabatic and nonadiabatic chemical dynamics, the efficient solution of molecular graph theory problems, and the calculations of electronic structure.