惰性气体影响反应速率的文献

The influences of incident energy magnitude and the thermal and transport properties of inert gases on the ignitability and combustion strength of ammonia/oxygen/inert-gas mixtures have been experimentally investigated. Laser-induced spark ignition was adopted because it allows easy adjustment of incident energy and generates plasma without requiring electrode contact. The influences of inert gas and incident energy on minimum ignition energy (MIE), flammable range, peak overpressure (), the time to reach after the laser was fired (), pressure increasing rate (), and index of combustion strength ( value) were systematically investigated. The thermal diffusivity primarily influences ignition characteristics (MIE and flammable range), because a certain period of retention of a hot kernel immediately after the incident energy is provided is required to initiate ignition. Since incident energy compensates for the lacking energy needed to initiate the combustion reaction, its influence becomes more apparent in mixtures with high thermal diffusivity or large specific heat. On the other hand, specific heat primary influences the maximum pressure rise value and the flame temperature. If sufficient energy to sustain the combustion reaction is provided, thermal diffusivity contributes to the rapid increase in the pressure rise because it facilitates the quick transport of heat generated by the combustion reaction throughout the entire the premixed gas. The influence of inert gas on fluid-dynamic phenomena, such as the formation of a third lobe and transient flame velocity behavior, was also explained based on the aforementioned mechanism. The dependence of pressure rise on the equivalence ratio was closely related the adiabatic flame temperature for each composition. In summary, the key properties affecting the ignition and combustion characteristics are thermal diffusivity and specific heat. However, which of these physical properties has a more dominant influence depends on whether it affects ignitability or combustion strength.

To study the effect of the inert gas mixture concentration and ratio on the spontaneous combustion reaction of gas coal, a combination of experimental research and theoretical analysis was used to study the pyrolysis and combustion kinetics characteristics of gas coal and further explore the influence of inert gas on the inerting characteristics of gas coal. Research has shown that during the entire heating reaction process of gas coal, the concentration of inert gases has little effect on the drying and desorption stages, but there is a significant lag phenomenon in the characteristic temperature points of active decomposition and degassing stages. Under the same concentration of mixed inert gases, the higher the relative percentage content of CO2, the more significant the change and the better the inhibitory effect. The higher the volume fraction of the inert gas, the higher the cross-temperature point. In the late stage of rapid heating of coal samples, when the volume fraction of inert gas is 40%, the rate of temperature rise increases rapidly. In a pure air environment, CO begins to be released at 80 °C, and when the temperature rises to 130 ∼ 140 °C, the concentration of CO begins to rapidly increase. Under inert conditions, the higher the relative percentage content of inert gas is, the higher the temperature point at which CO is generated. When the experimental conditions are a mixture of 30% N2 and 10% CO2 as inert gas, the optimal inerting effect has been achieved. The research results provide a theoretical basis for determining the optimal ratio of inert gas inerting concentrations to achieve fire prevention and extinguishing.

Monocrystalline graphene growth has always been an intriguing research focus. Argon (Ar) is merely viewed as a carrier gas due to its inert chemical properties throughout the whole growth procedure by the chemical vapor deposition method. In this work, the influence of Ar on temperature and flow fields was investigated in consideration of its physical parameter difference among all involved gases. Results by experimental characterization and fluid dynamics simulation showed that the temperature elevated, and the velocity of the mixed gas increased as the Ar flow rates rose. Furthermore, the deposition rate of C on the Cu surface, representing graphene generation rate, was studied as the Ar flow rate changed in combination with CH4 decomposition reaction. Based on the effects made by Ar, a method was proposed, where the Ar flow rate was dynamically regulated to break monocrystalline graphene growth cessation. The graphene size was enlarged, and the nucleation site density was reduced remarkably compared with a common consistent Ar flow. It is believed that this work would provide a new perspective in two-dimensional material preparation by combining basic properties with temperature and field distribution in the whole reaction system.

Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, , demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of ∼1 × 1018 molecule m-2. Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.

A mathematical model for thermal explosion in a combustible dusty gas containing fuel droplets with general Arrhenius reaction-rate laws, convective and radiative heat losses, and interphase heat exchange between gas and inert solid particles is investigated. The objective of the study is to examine the effects of interphase heat exchange between the gas and solid particles on (i) ignition of reacting gas, (ii) accumulation of heat by the solid particles during combustion process (iii) evaporation of the liquid fuel droplets, and (iv) consumption of reacting gas concentration. The equations governing the physical model with realistic assumptions are stated and nondimensionalised leading to an intractable system of first-order coupled nonlinear differential equations, which is not amenable to exact methods of solution. Therefore, we present numerical solutions as well as different qualitative effects of varying interphase heat exchange parameter. Graphs and Table feature prominently to explain the results obtained.

2D Metal-Organic Chalcogenolates (MOChas) are an emerging class of materials with high potential in hydrogen generation, storage, and catalysis research, particularly demonstrated by their use in photocatalytic and electrocatalytic hydrogen gas production. Among them, mithrene AgSePh based two-dimensional layered structure, holds significant promise as a catalyst for hydrogen gas storage and generation due to its large surface area. However, conventional synthesis methods have been limited in producing high-quality thin films due to difficulties in controlling the reaction rate, chemical contamination from solvents, and poor reproducibility.In this study, we present a novel synthesis strategy for highly crystalline mithrene thin films using a custom-designed stainless steel reaction chamber under an inert, high-pressure, and solvent-free environment. By precisely controlling the internal vapor pressure through the regulation of the reaction temperature, the reaction kinetics were optimized. This resulted in continuous, stoichiometric, and highly oriented thin films. This research establishes a reliable and reproducible pathway for synthesizing high-quality mithrene thin films without the chemical intervention of solvents, suggesting that MOChas-based thin films fabricated via this method can be expanded to next-generation catalysts, and hydrogen gas storage and other related applications.

No abstract available

Photocatalytic hydrogen production from water is a promising way to fulfill energy demands and attain carbon emission reduction goals effectively. In this study, a loop photoreactor with a total volume of around 500 mL is presented for the photocatalytic hydrogen evolution using a Pt-loaded polymeric carbon nitride photocatalyst under 365 nm irradiation in the presence of sacrificial reducing agents. The fluid flow pattern of the developed photoreactor was characterized experimentally and the photon flux incident to the loop photoreactor was measured by chemical actinometry. The system displayed exceptional stability, with operation sustained over 70 hours. A design of experiment (DOE) analysis was used to systematically investigate the influence of key parameters – photon flux, photocatalyst loading, stirring speed, and inert gas flow rate – on the hydrogen generation rate. Linear relationships were found between hydrogen evolution rate and photon flux as well as inert gas flow rate. Photocatalyst loading and stirring speed also showed linear correlations, but could not be correctly described by DOE analysis. Instead, linear single parameter correlations could be applied. Notably, the loop photoreactor demonstrated an external photon efficiency up to 17 times higher than reported in literature studies, while scaling the reactor size by a factor of 10.

In this work, the influence of different N2/CO2 contents (up to 60% in fuel volume) on combustion features of laminar-premixed CO/CH4/H2 flame with various equivalence ratios (0.6–1.6) at standard conditions was numerically calculated using ANSYS CHEMKIN-PRO with the GRI-Mech 3.0 mechanism. The mole fraction profiles of the major species and the rate of production of dominant elementary reactions in the flames of CO/CH4/H2/N2/CO2/air were obtained. The effect of inert gas addition on the formation of NOX, H, O, and OH was analyzed, and the sensitivity coefficient of the active radical mole fraction was obtained. The results suggest that the addition of inert gas of the fuel mixture with various equivalence ratios reduces laminar burning velocity and adiabatic temperature, which have always had a good positive correlation and the maximum peak point shifted left. CO2 has obvious inhibitory effect on the formation of NO by reducing the amount of O radicals and obstructing the conduct of the reaction of NNH + O ⇔ NH + NO, but it promotes the formation of NO2 mainly through the reaction HO2 + NO ⇔ NO2 + OH. The reactions H + O2 + H2O ⇔ HO2 + H2O, H + O2 ⇔ O + OH, and OH + CO ⇔ H + CO2 are three very important reactions for the molar fractions of H, O, and OH that decrease significantly with an increase of inert gas concentration.

No abstract available

Predicting the reaction kinetics, that is, how fast a reaction can happen in a solution, is essential information for many processes, such as industrial chemical manufacturing, refining, synthesis and separation of petroleum products, environmental processes in air and water, biological reactions in cells, biosensing, and drug delivery. Collision theory was originally developed to explain the reaction kinetics of gas reactions with no dilution. For a reaction in a diluted inert gas solution or a diluted liquid solution, diffusion often dominates the collision process. Thus, it is necessary to include diffusion in such a calculation. Traditionally, the classical Smoluchowski rate is used as a starting point to predict the collision frequency of two molecules in a diluted solution. In this report, a different collision model is derived from the adsorption of molecules on a flat surface. A surprising result is obtained, showing that the reaction order for bimolecular reactions should be 2 and 1/3 instead of 2, following a fractal reaction kinetics.

The effective conversion of carbon dioxide (CO2) and nitrogen (N2) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90%:10%) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2-500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2-500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

The problem of using gaseous extinguishants to eliminate fire sources is to inhibit the active radicals of the flame, but at the same time it is necessary to take into account the change in the concentration of oxygen. Therefore, the object of research was the value of the extinguishing concentrations of both individual extinguishants and binary mixtures of halocarbons and inert gases during the elimination of heptanes burning. It has been proven that when nitrogen was supplied, gaseous combustion products were diluted and the relative radiation intensity of hydroxyl radicals decreased to 80 %; on the contrary, when pentafluoroethane (HFC-125) and heptafluoropropane (HFC-227ea) were supplied, the process of chemical inhibition of the combustion reaction took place which led to a significant reduction of the burning rate and, accordingly, the intensity of radiation of hydroxyl radicals by more than 4 times. The joint action of the inert gas and the combustion inhibitor in different ratios did not exceed the intensity of the radiation of hydroxyl radicals of the flame of the inhibitor itself. However, when an inert gas was introduced, the flame was being enriched with fuel and the number of hydroxyl radicals decreased, and the additional introduction of an inhibitor led to a more effective reduction of hydroxyl radicals in the flame. On the basis of the derived results of the experimental studies on the elimination of the fire source of a cup burner with binary mixtures of a halocarbon and an inert gas, it was established that a relatively small dilution of air with nitrogen led to a significant decrease in the extinguishing concentration of the combustion inhibitor. In particular, the extinguishing concentration of heptafluoropropane HFC-227ea for extinguishing n-heptane can be reduced by 2.0 times if, by adding nitrogen, the concentration of oxygen in the air is reduced from 20.5 to 19 % by volume, that is, by only 7 % (relative). The practical value lies in the fact that the derived results of determining the extinguishing concentration of halocarbons, nitrogen and their binary mixtures make it possible to establish the conditions for the elimination of fire sources.

ABSTRACT Injecting CO2 and N2 to reduce the concentration of O2 in the air is a commonly used measure to prevent coal spontaneous combustion (CSC). To study the difference in inhibitory effects of CO2 and N2 on coal oxidation, experiments in this study were conducted using a setup of self-developed gas-bath coal oxidation for low temperatures. The oxidation process of the coal-oxygen system was then analyzed using reaction kinetics. Two different coal samples were tested in experiments under two inert gas environments, i.e. CO2 and N2 with various O2 concentrations, respectively. The changes in O2 and CO concentrations were measured during the oxidation process. By studying the standard oxygen consumption rate (SOCR) and the apparent activation energy of the coal-oxygen reaction system, inhibitory effects of CO2 and N2 on CSC were analyzed and compared. The results showed that the SOCR of the same coal sample remained consistent and independent of the O2 concentration within the same inert gas environment although under different O2 levels. In both CO2-O2 and N2-O2 environments, the SOCR of the coal sample exhibits exponential growth with temperature. The SOCR was found to have a functional connection with temperature, it can be represented as $y = a\cdot {e^{bT}}$y=a⋅ebT, and the R2 (determination coefficients) of the fitting formulas are all greater than 0.94. In the correlation, the inert gas environment has minimal impact on coefficient “b,” while in the CO2-O2 environment, reducing the value of coefficient “a” can effectively lower the coal sample’s SOCR. The GBMK sample and YMWK sample have an “a” value that is 20% of the value in the N2-O2 environment when oxidizing in the CO2-O2 environment. The SOCR in the CO2-O2 environment showed a decrement of between 26.0% and 52.1% when compared to that in the N2-O2 environment, whereas the activation energy showed an increment between 1.4% and 18.6%. The findings in this work provide an in-depth understanding of the prevention of CSC in the gob for risk mitigation.

Understanding the aging behavior of Fe electrolytes is critical in designing electrochemical experiments to achieve reproducible electrodeposition results. In this presentation, we will introduce the natural oxidation rate of the simplest aqueous Fe electrodeposition electrolytes in a common lab setting. The aging trend was measured with both solution pH and the open-circuit potential (OCP) of the solution at the glassy carbon electrode, with the trend adequately reflected by the theoretical curves estimated from the mass-conservation and solution thermodynamics. Beyond the aging kinetics of the Fe electrolytes, the effects of Ar purging and the anodic reaction were evaluated. We believe that inert gas purging has a very limited effect on the Fe(II) solution aging if the experiment is conducted in the open air, and Fe(III) cannot be limited and controlled during the electrodeposition process if the cathode is not separated from the anode using a 2-compartment cell. Figure caption: (a) Impact of natural oxidation on pH and OCP drift of 20mL Fe(II) solution stored in a sealed glass vial in air. (b) observed and estimated pH-OCP aging trajectory for 1.0M FeSO4 solution at its natural pH or with pH adjusted to 2.0. (c) the estimated trajectory of Fe solution aging at natural pH or with pH adjusted to 2.0. Figure 1

This study investigates the microscale suppression mechanisms of four powder explosion suppressants on coal dust/methane (CH4) mixed system explosions. Combining experimental and numerical simulation methods, we explore the gas-phase reaction processes and the role of free radicals in the explosion suppression. Results show that all suppressants reduce the maximum explosion pressure and pressure rise rate, with MPP being the most effective, reducing pressure by 38%. Suppressants inhibit explosions through physical (heat absorption) and chemical (free-radical consumption) mechanisms. Phosphorus-containing intermediates from NH4H2PO4 and MPP react with free radicals, while NaHCO3 and MCA decompose to produce inert gases and consume O• and H• radicals. This work provides a theoretical foundation for optimizing explosion suppressants in mining safety applications.

Photocatalytic nitrogen fixation reaction can harvest the solar energy to convert the abundant but inert N2 into NH3. Here, utilizing metal-organic framework (MOF) membranes as the ideal assembly of nanoreactors to disperse and confine gold nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic nitrogen fixation under ambient conditions. Upon visible irradiation, the hot electrons generated on the AuNPs can be directly injected into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but evanescently localized surface plasmon resonance field, resulting in a supralinear intensity dependence of the ammonia evolution rate with much higher apparent quantum efficiency and lower apparent activation energy under stronger irradiation. Moreover, the gas-permeable Au@MOF membranes, consisting of numerous interconnected nanoreactors, can ensure the dispersity and stability of AuNPs, further facilitate the mass transfer of N2 molecules and (hydrated) protons, and boost the plasmonic photocatalytic reactions at the designed gas-membrane-solution interface. As a result, an ammonia evolution rate of 18.9 mmol gAu-1 h-1 was achieved under visible light (>400 nm, 100 mW cm-2) with an apparent quantum efficiency of 1.54% at 520 nm.

No abstract available

The reaction of Co with gaseous BBr3 in a temperature range of 700 to 1000 °C was studied using the hot-wire method with an experimental set-up reminiscent of the van Arkel-de Boer method. The borides Co2B und CoB form as layers on the surface of elemental cobalt. The influence of pressure, temperature and time on the reaction rate and on the composition of the borides was investigated. The reaction rate is significantly decreased by small amounts of an inert gas. The adjustment of reaction conditions allows to obtain single-phase and well-crystallized bulk materials of Co2B or CoB.

Capturing the dynamic character of metal nanoparticles under the reaction conditions is one of the major challenges within heterogeneous catalysis. The role of nanoparticle dynamics is particularly important for metal alloys as the surface composition responds sensitively to the gas environment. Here, a first-principles-based kinetic Monte Carlo method is developed to compare the dynamics of dilute PdAu alloy nanoparticles in inert and CO-rich atmospheres, corresponding to reaction conditions for catalyst deactivation and activation. CO influences the dynamics of the activation by facilitating the formation of vacancies and mobile Au-CO complexes, which are needed to obtain CO-stabilized Pd monomers on the surface. The structure of the catalyst and the location of the Pd monomers determine the rate of deactivation. The rate of catalyst deactivation is slow at low temperatures, which suggests that metastable structures determine the catalyst activity at typical operating conditions. The developed method is general and can be applied to a range of metal catalysts and reactions.

In this study, by proposing a comprehensive multi-step model, the combustion of magnesium particles in O2-He, O2-Ar, and O2-N2 is scrutinized. In the current model, both the heterogeneous and homogeneous combustions are considered and the process is divided into four stages solid, liquid, and gas combustion and melting. Moreover, the diffusions of oxygen and unreacted magnesium to droplet and infinity together with surface exothermic reaction are considered. The governing equations are analytically solved and then, the formulas are extracted for combustion time and temperature, flame standoff distance, and evaporation rate as the functions of particle diameter, ambient temperature and pressure, oxygen mass fraction, type of inert gas, and Lewis numbers. For 120 µm particle and oxygen content of 0.05, time contributions of homogeneous and heterogeneous combustions are 85.8% and 14.2%, respectively. The burning time has drastic changes at ambient pressures below l atm, so that the burning time variations relative to the pressure in the environments less than 1 atm and greater than it are equal to 1200–1550 and 70–90 ms/atm, respectively. When the oxygen mass fraction is less than 0.29, combustion in helium-oxygen ends earlier than that in O2-Ar and O2-N2, but for the mass fraction greater than 0.35, it has the longest burning time.

Radon (Rn), a ubiquitous radioactive noble gas, is the main source of natural radiation to human and one of the major culprits for lung cancer. Reducing ambient Rn concentration by porous materials is considered as the most feasible and energy-saving option to lower this risk, but the in-depth Rn removal under ambient conditions remains an unresolved challenge, mainly due to the weak van der Waals (vdW) interaction between inert Rn and adsorbents and the extremely low partial pressure (<1.8 × 10-14 bar, <106 Bq/m3) of Rn in air. Adsorbents having either favorable adsorption thermodynamics or feasible diffusion kinetics perform poorly in in-depth Rn removal. Herein, we report the discovery of a metal-organic framework (ZIF-7-Im) for efficient Rn capture guided by computational screening and modeling. The size-matched pores in ZIF-7-Im abide by the thermodynamically favorable principle and the exquisitely engineered quasi-open apertures allow for feasible kinetics with little sacrifice of sorption thermodynamics. The as-prepared material can reduce the Rn concentration from hazardous levels to that below the detection limit of the Rn detector under ambient conditions, with an improvement of at least two orders of amplitude on the removal depth compared to the currently best-performing and only commercialized material activated charcoal.

The paper considers the problem of optimizing gas-discharge sources of multiband UV radiation --- excilamps. A method is proposed for estimating the ratio of partial pressures of the components of a gas mixture, which makes it possible to simplify the process of developing a multiband excilamp with the desired power ratio of the emission bands. It is shown that the optimization of a multiband excilamp on a mixture of one noble gas with several halogen carriers can be reduced to the problem of optimizing an excilamp on a two-component mixture. If, in addition to the radiation of exciplex molecules, the radiation of excimer molecules is of importance, then the method makes it possible to control the relative contribution of the powers emitted by these molecules. Keywords: gas discharge, sources of ultraviolet radiation, kinetics of plasma-chemical processes, excimer and exciplex molecules.

No abstract available

No abstract available

Microwave (MW) activated H2/Ar (and H2/Kr) plasmas operating under powers and pressures relevant to diamond chemical vapor deposition have been investigated experimentally and by 2-D modeling. The experiments return spatially and wavelength resolved optical emission spectra of electronically excited H2 molecules and H and Ar(/Kr) atoms for a range of H2/noble gas mixing ratios. The self-consistent 2-D( r, z) modeling of different H2/Ar gas mixtures includes calculations of the MW electromagnetic fields, the plasma chemistry and electron kinetics, heat and species transfer and gas-surface interactions. Comparison with the trends revealed by the spatially resolved optical emission measurements and their variations with changes in process conditions help guide identification and refinement of the dominant plasma (and plasma emission) generation mechanisms and the more important Ar-H, Ar-H2, and H-H2 coupling reactions. Noble gas addition is shown to encourage radial expansion of the plasma, and thus to improve the uniformity of the H atom concentration and the gas temperature just above the substrate. Noble gas addition in the current experiments is also found to enhance (unwanted) sputtering of the copper base plate of the reactor; the experimentally observed increase in gas phase Cu* emission is shown to correlate with the near substrate ArH+ (and KrH+) ion concentrations returned by the modeling, rather than with the relatively more abundant H3+ (and H3O+) ions.

In this perspective we deal with the challenge of investigating nuclear quantum effects in solvated and condensed phase molecular systems in a computationally affordable way. To this end, semiclassical methods are promising theoretical approaches, as we demonstrate through vibrational spectroscopy and reaction kinetics. We show that quantum vibrational features can be found in hydrates of carbonyl compounds and microsolvated amino acids, and we report quantum estimates of the low-temperature reaction rate constant of a unimolecular reaction taking place in a noble-gas matrix. The hallmark of semiclassical methods is their ability to include nuclear quantum effects into classical molecular dynamics simulations. For this reason, unlike other popular methods, semiclassical approaches are able to account also for real-time quantum contributions and are expected to point out the importance of nuclear quantum effects in complex systems for a wider range of chemical properties.

The influence of argon and helium on the rovibrational kinetics of carbon dioxide (CO2) and CO in low-temperature conversion plasma is investigated. With this objective, a combined experimental and computational study is conducted, applying quantum cascade laser infrared absorption spectroscopy to a pulsed DC CO2 glow discharge with varying noble gas admixture and modeling it with a two-term Boltzmann solver. Time-resolved rovibrational temperatures and dissociation fractions are presented, exhibiting an increase in rotational-vibrational non-equilibrium and an increasing CO2 conversion with argon (Ar) and helium (He) admixtures. Results are discussed in the context of energy transfer processes for collisions involving electrons, corroborated by electron-kinetic modeling, and heavy particle collisions. With noble gas addition, an increase in the electron number density, promoting excitation, and the high-energy tail of the electron energy distribution function are found. Penning ionization processes are proposed as an explanation for the increase in conversion, showing higher conversion for Ar due to the lower excitation thresholds and, therefore, larger state population. In the context of rovibrational kinetics, processes leading to the gain or loss of vibrational energy of CO2 are analyzed, pointing out subtle differences in, for example, relaxation rate coefficients between Ar and He. However, the cooling of the gas through conductive heat transfer is identified as the most important influence of the Ar and He admixture, as it keeps the relaxation rate for vibrational quenching low.

The importance of quantum-mechanical tunneling becomes increasingly recognized in chemical reactions involving hydrogen as well as heavier atoms. Here we report concerted heavy-atom tunneling in an oxygen-oxygen bond breaking reaction from cyclic beryllium peroxide to linear dioxide in cryogenic Ne matrix, as evidenced by subtle temperature-dependent reaction kinetics and unusually large kinetic isotope effects. Furthermore, we demonstrate that the tunneling rate can be tuned through noble gas atom coordination on the electrophilic beryllium center of Be(O2), as the half-life dramatically increased from 0.1 h for NeBe(O2) at 3 K to 12.8 h for ArBe(O2). Quantum chemistry and instanton theory calculations reveal that noble gas coordination notably stabilizes the reactants and transition states, increases the barrier heights and widths, and consequently reduces the reaction rate drastically. The calculated rates and in particular kinetic isotope effects are in good agreement with experiment.

Plasma-catalysis has attracted significant interest in recent years as an alternative for the direct upgrading of methane into higher-value products. Plasma-catalysis systems can enable the electrification of chemical processes; however, they are highly complex with many previous studies even reporting negative impacts on methane conversion. The present work focuses on the non-oxidative plasma-catalysis of pure methane in a Dielectric Barrier Discharge (DBD) reactor at atmospheric pressure and with no external heating. A range of transition and noble metals (Ni, Fe, Rh, Pt, Pd) supported on γ-Al2O3 are studied, complemented by plasma-only and support-only experiments. All reactor packings are investigated either with pure methane or co-feeding of helium or argon to assess the role of noble gases in enhancing methane activation via energy transfer mechanisms. Electrical diagnostics and charge characteristics from Lissajous plots, and electron temperature and collision rates calculations via BOLSIG+ are used to support the findings with the aim of elucidating the impact of both active metal and noble gas on the reaction pathways and activity. The optimal combination of Pd catalyst and Ar co-feeding achieves a substantial improvement over non-catalytic pure methane results, with C2+ yield rising from 30% to almost 45% at a concurrent reduction of energy cost from 2.4 to 1.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\text{M}\text{J}\:{\text{m}\text{o}\text{l}}_{\text{C}{\text{H}}_{4}}^{-1}$$\end{document} and from 9 to 4.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\text{M}\text{J}\:\text{m}\text{o}{\text{l}}_{{\text{C}}_{2+}}^{-1}$$\end{document}. Pd, along with Pt, further displayed the lowest coke deposition rates among all packings with overall stable product composition during testing.

No abstract available

No abstract available

ABSTRACT Coal bed methane (CBM) is a clean energy resource, CH4 and various blends of C2H6, C2H4, CO, and H2 in different proportions were chosen to formulate a surrogate fuel for coal bed methane. The objective was to study the explosion characteristics of coal bed methane while alleviating the computational complexity associated with intricate reaction mechanisms. The explosion properties (peak explosion pressure (Pmax) and the maximum pressure rise rate (dp/dt)max) of the mixtures were tested. The unstretched laminar burning velocity (Ul) of the surrogate components was determined under a range of initial temperatures (Tu) (298–373 K) and blended fuel concentrations (0.4–2.0%). Two simplified kinetics models for the surrogate fuel were developed using the GRI Mech 3.0 and USC Mech II mechanisms. These models were constructed through the application of a direct relation graph with error propagation (DRGEP) and full species sensitivity analysis (FSSA). To assess the accuracy of the models, simulations based on these simplified mechanisms were compared with both the detailed mechanism and experimental data. Additionally, sensitivity analyses, utilizing the simplified mechanism, were conducted in order to identify precisely the reactions that govern the interaction dynamics between blended fuel and methane. Within the range of the experimental conditions, the results indicated that Pmax decreased linearly and with increasing initial temperature. (dp/dt)max was only slightly sensitive to the variation in the initial temperature. However, Ul increased with increasing initial temperature, as expected. When blended fuel was added to a 7% CH4-air mixture, Pmax, (dp/dt)max, and unstretched Ul exhibited increasing trends. An equation was derived using the experimental data, to forecast changes in Ul across elevated temperatures and blended gas concentrations. The simplified mechanism model successfully replicated the results of the detailed mechanism model and demonstrated good agreement with experimental data concerning species concentrations, ignition delay times, and the Ul of the coal bed methane surrogate fuel. Compared to sample 2, the chemistry of sample 1 exhibits greater sensitivity toward intermediate temperature reactions, particularly at higher temperatures.

ABSTRACT In this paper, the inhibition effects of Ar/He/N2 on the H2-O2 system near the extended second explosion limit were investigated by ReaxFF simulations. It was found that all three inert gases can inhibit the reactions, delaying the initiation reaction, and prolonging ignition delay since the generation and consumption of free radicals such as HO2 and OH were suppressed. Further, the inhibitory effect has the correlation of Ar > He > N2. The inhibitory effect of Ar is more pronounced compared to He due to the bigger effective radius and physical mass. Moreover, the addition of N2 introduced extra initiation reaction (H2 + N2 → NNH + H) and generated additional intermediate products such as NNH and N2OH, which result in the weakest inhibitory effect. Compared to diatomic inhibitors (e.g., N2), the monatomic inhibitors such as Ar and He exhibit stronger inhibitory effects on the hydroxide reaction under high pressure.

Kinetic rate constants for the oxidation reactions of OH radicals with CH3SH (1), C2H5SH (2), n-C3H7SH (3) and iso-C3H7SH (4) under inert conditions (Ar) over the temperature range 252−430 K have been studied using the CBS-QB3 composite method. Kinetic rate constants under atmospheric pressure and in the fall-off regime have been estimated using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Comparison with experiment confirms that in the OH-addition pathways 1−4 leading to the related products, the first bimolecular reaction step has effective negative activation energies around −2.61 to 3.70 kcal mol−1. Effective rate coefficients have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a result of the negative activation energies, pressures larger than 104 bar would be required to restore to some extent the validity of this approximation for all the channels. By comparison with experimental data, all our calculations for both the OH-addition and H-abstraction reaction pathways indicate that from a kinetic viewpoint and in line with the computed reaction energy barriers, the most favourable process is the OH-addition pathway to n-C3H7SH to yield the [n-C3H7SH−OH]• species, whereas under thermodynamic control of the bimolecular reactions (R−SH+OH•), the most abundant product derived from the H-abstraction pathway will be the [n-C3H7 S•+H2O] species.

In this study, the effects of water addition on ethanol/air flames with high water content at elevated temperature and pressure are numerically investigated, and a novel correlation for their laminar burning velocity (LBV) is proposed based on experimental results. The dependence of the temperature and pressure exponents on thermodynamic parameters is numerically analyzed and considered in the new correlation to optimize the existing correlation. The fitting results of LBV correlations based on experimental measurements using a constant-volume method demonstrate that incorporating high-order and cross terms into the correlation enhances the overall performance, particularly under fuel-rich conditions where existing correlations exhibit significant discrepancies. The new LBV correlation of hydrous ethanol/air mixtures performs well over a wide range of elevated temperatures and pressures and agrees well with experimental data in the literature at high temperatures and pressures. The calculated LBV using the new correlation is also in good agreement with simulations using various mechanisms, except for fuel-rich mixtures with high water content, where the LBV is underpredicted by all mechanisms considered, suggesting further development of chemical mechanisms is needed. A sensitivity analysis suggests that under high water content, the dominant reactions of fuel-rich flames are different from those in stoichiometric and fuel-lean mixtures, highlighting that fuel-rich hydrous ethanol/air flames are very sensitive to water addition. The results also suggest that water addition leads to a reduction in the LBV. Both the burnt gas temperature and the peak heat release rate decrease with the water content, with a stronger influence on fuel-rich ethanol/air mixtures. Furthermore, the dilution effect of water addition constitutes the single largest effect in reducing the LBV, while chemical and thermophysical effects are found to be comparatively minor. The findings are helpful in understanding the fundamental combustion properties of hydrous ethanol and optimizing the LBV correlation under engine-relevant conditions.

Considerable increase in global coffee consumption has resulted in a marked increase in the amount of spent coffee grounds (SCG). To examine the applicability of SCG as a renewable energy source this study evaluated the pyrolysis characteristics of SCG. Elemental and proximate analyses were conducted on SCG, and kinetic analysis was performed using thermogravimetric analysis to identify the activation energy for the pyrolysis reaction. The experiment was performed in a nitrogen atmosphere using a fixed-bed reactor to analyze the gas and liquid products as well as the solid residues produced from the pyrolysis reaction by varying the reaction temperature and heating rate. The activation energy for the pyrolysis reaction of coffee hemicellulose and cellulose was higher than that for the pyrolysis reaction of lignin. With regard to gaseous products, CO and CO2 began to occur at a lower temperature than hydrocarbons, and hydrocarbons began to occur at approximately 330 °C. The yield of the liquid products was highest at 500 °C, and it increased with the heating rate. Moreover, most of the liquid products were components containing oxygen, and the compound composition of the liquid products depended on the reaction temperature and heating rate. The yield of the solid residues decreased according to the reaction temperature and heating rate, and it was confirmed through infrared and X-ray diffraction spectrum analysis that gradual carbonization occurred according to reaction conditions.

The study presents a comprehensive experimental and numerical investigation of the autoignition kinetics of a hydrogen–air mixture under elevated pressures relevant to modern energy systems. Experiments were conducted using high-pressure constant-volume and constant-pressure reactors as well as a flow reactor to evaluate induction periods across a wide range of temperatures, pressures, and gas compositions. The results demonstrated that increasing pressure from 2.9 to 8 MPa reduced the induction period by more than half, with measured times varying from 1.21 seconds at 550 K and 3 MPa to 0.21 seconds at 750 K and 6 MPa. The addition of inert gases, dilution, and heat-absorption effects. A new global kinetic equation was derived, characterized by an activation energy of approximately 170,000 J/mol and reaction orders of 1.1 for oxygen and 0.3 for hydrogen. Validation against detailed kinetic mechanisms and literature data confirmed deviations within 10–12%, demonstrating high predictive accuracy. The proposed equation for modelling hydrogen oxidation in engineering applications operating at high pressures.

Metal organic chalcogenolates (MOCs) constitute a promising class of materials for optoelectronic applications owing to their unique 2D layered hybrid structure and inherent environmental stability. Among these materials, mithrene (silver phenylselenolate, AgSePh) is particularly compelling because of its sharp blue emission and notable anisotropic excitonic properties. However, conventional solvent-assisted mithrene synthesis methods are often associated with the introduction of chemical complexities as well as compromised film quality. Addressing these limitations, this study provides a robust solvent-free strategy for synthesizing high-quality mithrene thin films through precise pressure and temperature control in an inert gas environment, leading to optimized reaction kinetics. Comprehensive characterization through grazing incidence wide-angle X-ray scattering (GIWAXS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis absorption, and photoluminescence (PL) spectroscopy revealed that the resulting films possess greatly improved crystallinity, enhanced excitonic absorption, and significantly greater PL emission than their solvent-processed counterparts. Notably, a previously unreported excitonic feature (Xα) was identified, possibly originating from the high structural coherence along the out-of-plane direction achieved through our method. This study not only provides an advanced solvent-free route for high-quality MOC thin film fabrication but also unlocks avenues for their broader integration into next-generation optoelectronic devices, semiconductors, and catalysts.

Understanding and controlling the evolution of pressure during thermal events of Li-ion batteries is a key aspect when assessing the safety of Li-ion batteries. In this study we evaluate the impact of solvent composition, gas solubility, and conductive salts on the pressure build-up during the exposure of the Li-ion battery electrolytes to high temperatures. We employ a vapour–liquid equilibrium model based on the statistical associating fluid theory (SAFT)- 𝛾 Mie equation of state, extended to include an ion-pairing model to account for low degrees of salt dissociation in solvents with a low dielectric constant, such as linear carbonates. The effect of the degradation gases is accounted for by implementing a gas source mimicking a CO 2 evolving reaction. We find that argon or nitrogen are good choices as inert gases during solvent storage and cell assembly, as they only gas out slightly during heating, i

The kinetics of the reaction of hydroxyl radical (OH) with dimethyl methylphosphonate (DMMP, (CH3O)2CH3PO) (reaction 1) OH + DMMP → products (1) was studied at the bath gas (He) pressure of 1 bar over the 295–837 K temperature range. Hydroxyl radicals were produced in the fast reaction of electronically excited oxygen atoms O(1D) with H2O. The time-resolved kinetic profiles of hydroxyl radicals were recorded via UV absorption at around 308 nm using a DC discharge H2O/Ar lamp. The reaction rate constant exhibits a pronounced V-shaped temperature dependence, negative in the low temperature range, 295–530 K (the rate constant decreases with temperature), and positive in the elevated temperature range, 530–837 K (the rate constant increases with temperature), with a turning point at 530 ± 10 K. The rate constant could not be adequately fitted with a standard 3-parameter modified Arrhenius expression. The data were fitted with a 5-parameter expression as: k1 = 2.19 × 10−14(T/298)2.43exp(15.02 kJ mol−1/RT) + 1.71 × 10−10exp(−26.51 kJ mol−1/RT) cm3molecule−1s−1 (295–837 K). In addition, a theoretically predicted pressure dependence for such reactions was experimentally observed for the first time.

Criegee intermediates exert a crucial influence on atmospheric chemistry, functioning as powerful oxidants that facilitate the degradation of pollutants, and understanding their reaction kinetics is essential for accurate atmospheric modeling. In this study, the kinetics of CH2OO and syn-CH3CHOO reactions with acetaldehyde (CH3CHO) were investigated using a flash photolysis reaction tube coupled with the OH laser-induced fluorescence (LIF) method. The experimental results indicate that the reaction of syn-CH3CHOO with CH3CHO is independent of pressure in the range of 5-50 Torr when using Ar as the bath gas. However, the rate coefficient for the reaction between CH2OO and CH3CHO at 5.5 Torr was found to be lower compared to the near-constant values observed between 10 and 100 Torr. Furthermore, the reaction of syn-CH3CHOO with CH3CHO demonstrated positive temperature dependence from 283 to 330 K, with a rate coefficient of (2.11 ± 0.45) × 10-13 cm3 molecule-1 s-1 at 298 K. The activation energy and pre-exponential factor derived from the Arrhenius plot for this reaction were determined to be 2.32 ± 0.49 kcal mol-1 and (1.66 ± 0.61) × 10-11 cm3 molecule-1 s-1, respectively. In comparison, the reaction of CH2OO with CH3CHO exhibited negative temperature dependence, with a rate coefficient of (2.16 ± 0.39) × 10-12 cm3 molecule-1 s-1 at 100 Torr and 298 K and an activation energy and a pre-exponential factor of -1.73 ± 0.31 kcal mol-1 and (1.15 ± 0.21) × 10-13 cm3 molecule-1 s-1, respectively, over the temperature range of 280-333 K.

The kinetics of the reaction of hydroxyl radical (OH) with trimethyl phosphate (CH3O)3PO (TMP) (reaction (1)) OH + TMP → products (1) was studied at the bath gas (He) pressure of 1 bar over the 273–837 K temperature range. Hydroxyl radicals were produced in fast reactions of electronically excited oxygen atoms O(1D) with either H2O or H2. Excited oxygen atoms O(1D) were produced by photolysis of ozone, O3, at 266 nm (4th harmonic of Nd:YAG laser) over the 273–470 K temperature range and by photolysis of N2O at 193 nm (ArF excimer laser) over the whole temperature range including the elevated temperature range 470–837 K. The reaction rate constant exhibits a V-shaped temperature dependence, negative in the low temperature range, 273–470 K (the rate constant decreases with temperature), and positive in the elevated temperature range, 470–837 K (the rate constant increases with temperature), with a turning point at 471 K. The rate constant could be fairly well fitted with the three parameter modified Arrhenius expression, k1 = 7.52 × 10−18 (T/298)9 exp(34 367 J mol−1/RT) cm3 per molecule per s (273–837 K). Previously, only one indirect experimental measurement at a single (ambient) temperature was available. The temperature dependence over an extended temperature range obtained in this study together with the peculiar V-shaped temperature dependence will have an impact on the modelling of the flame inhibition by phosphates as well on the further understanding of the mechanisms of elementary chemical reactions.

The combustion kinetics of three symmetric diesel-boiling-range ether isomers were investigated experimentally using a plug flow reactor. The isomers were di-n-butyl ether (DNBE), diisobutyl ether (DIBE), and di-sec-butyl ether (DSBE). The flow reactor experiments employed oxygen as the oxidizer and helium as the diluent, with oxidation carried out at atmospheric and elevated pressure conditions and temperatures from 400 to 1000 at 20 K intervals. The fuel, oxidizer, and diluent flow rates were varied at different temperatures to maintain a constant initial fuel mole fraction of 1000 ppm under stoichiometric conditions and a residence time of 2 s. Reaction products were analyzed by gas chromatography (GC). Depending on the structure, ethers showed different degrees of negative temperature coefficient (NTC) behavior. Speciation results from the GC analysis were then compared to simulations using existing and newly developed chemical kinetic models. Most of the simulated product concentrations showed reasonable agreement with the experimental data. The chemical kinetic models were utilized to elucidate key features of the reactivity and NTC behavior of the different isomers. The chemical kinetic analysis indicates that the combustion behaviors of the three isomers are influenced by the key species formed at the low-temperature reaction regime. The key species identified for DNBE, DIBE, and DSBE at atmospheric pressure are n-butanal, isobutanal, and sec-butanol, respectively.

A priori rate predictions for gas phase reactions have undergone a gradual but dramatic transformation, with current predictions often rivaling the accuracy of the best available experimental data. The utility of such kinetic predictions would be greatly magnified if they could more readily be implemented for large numbers of systems. Here, we report the development of a new computational environment, namely, EStokTP, that reduces the human effort involved in the rate prediction for single channel reactions essentially to the specification of the methodology to be employed. The code can also be used to obtain all the necessary master equation building blocks for more complex reactions. In general, the prediction of rate constants involves two steps, with the first consisting of a set of electronic structure calculations and the second in the application of some form of kinetic solver, such as a transition state theory (TST)-based master equation solver. EStokTP provides a fully integrated treatment of both steps through calls to external codes to perform first the electronic structure and then the master equation calculations. It focuses on generating, extracting, and organizing the necessary structural properties from a sequence of calls to electronic structure codes, with robust automatic failure recovery options to limit human intervention. The code implements one or multidimensional hindered rotor treatments of internal torsional modes (with automated projection from the Hessian and with optional vibrationally adiabatic corrections), Eckart and multidimensional tunneling models (such as small curvature theory), and variational treatments (based on intrinsic reaction coordinate following). This focus on a robust implementation of high-level TST methods allows the code to be used in high accuracy studies of large sets of reactions, as illustrated here through sample studies of a few hundred reactions. At present, the following reaction types are implemented in EStokTP: abstraction, addition, isomerization, and beta-decomposition. Preliminary protocols for treating barrierless reactions and multiple-well and/or multiple-channel potential energy surfaces are also illustrated.

We designed and constructed a whole-cell biosensor capable of detecting the presence and quantity of carbon monoxide (CO) using the CO regulatory transcription factor. This biosensor utilizes CooA, a CO-sensing transcription regulator that activates the expression of carbon monoxide dehydrogenase (CODH), to detect the presence of CO and respond by triggering the expression of a GUS reporter protein (β-glucuronidase). The GUS reporter protein is expressed from a CO-induced CooA-binding promoter (PcooF) by CooA and enables the effective colorimetric detection of CO. An Escherichia coli strain used to validate the biosensor showed growth and GUS activity under anaerobic conditions; this study used the inert gas (Ar) to create anaerobic conditions. The pBRCO biosensor could successfully detect the presence of CO in the headspace. Moreover, the GUS-specific activity of pBRCO according to the CO strength as partial pressure followed Michaelis-Menten kinetics (R2 = 0.98). It was confirmed that the GUS-specific activity of pBRCO increased linearly up to 30.39 kPa (R2 = 0.98), and thus, a quantitative analysis of CO concentration (i.e., partial pressure) was possible.

Atmospheric pressure plasmas generated from a helium gas with admixtures of water vapor have numerous applications in biomedicine. It is important that the chemistry of such plasmas can be tightly controlled so that they may be tailored for their intended use. In this study, computational modeling is used to vary the pulse repetition frequency of a nanosecond-pulsed, pin-to-pin He + 0.25% H2O discharge in the range of 1–100 kHz to determine the influence of the pulse repetition frequency on the resulting densities of reactive oxygen species and the rates of dominant reaction pathways involving them. The plasma is simulated using the 0D plasma-chemical kinetics model GlobalKin. The pulse shape is kept constant. The afterglow duration is, therefore, dependent on the repetition frequency. Analysis of the bulk plasma chemistry after the plasma has reached equilibrium shows that the peak electron density is only weakly dependent on the pulse repetition frequency. Increasing the pulse repetition frequency is shown to increase the density of H, O, and OH radicals, while the relationship between the repetition frequency and the densities of species with longer lifetimes, namely, H2O2 and O3, is found to be more complex. These are formed throughout the afterglow, and their density depends on the availability of reactant species, the afterglow duration, and the background gas temperature. This work concludes that the pulse repetition frequency is not a simple control parameter, especially for species that are predominantly produced in the afterglow. Detailed modeling is required for accurate control of species densities using the pulse repetition frequency.

Low-pressure-limit microcanonical (collisional activation) and thermal rate constants are predicted using a combination of automated ab initio potential energy surface construction, classical trajectories, transition state theory, and a detailed energy- and angular-momentum-resolved collision kernel. Several systems are considered, including CH4 (+M) and HO2 (+M), with an emphasis on systems where experimental information is available for comparison. The a priori approach involves no adjustable parameters, and we show that the predicted thermal rate constants are in excellent agreement with experiments, with average deviations of less than 25%. Notably, the a priori approach is shown to perform equally well for atomic, diatomic, and polyatomic baths, including M = H2O, CO2, and "fuel" baths like M = CH4 and NH3. Finally, the utility of microcanonical rate constants for interpreting trends and inferring mechanistic details in the thermal kinetics is demonstrated.

Abstract. The termolecular reactions of hydroxyl radicals (OH) with carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxides (NO2) and the termolecular reaction of hydroperoxy radicals (HO2) with NO2 greatly impact the atmospheric oxidation efficiency. Few studies have directly measured the pressure-dependent rate coefficients in air at 1 atm pressure and water vapour as third-body collision partners. In this work, rate coefficients were measured with a high accuracy (<5 %) at 1 atm pressure, at room temperature, and in humidified air using laser flash photolysis and detection of the radical decay by laser-induced fluorescence. The rate coefficients derived in dry air are (2.39±0.11)×10-13 cm3 s−1 for the OH reaction with CO, (7.3±0.4)×10-12 cm3 s−1 for the OH reaction with NO, (1.23±0.04)×10-11 cm3 s−1 for the OH reaction with NO2, and (1.56±0.05)×10-12 cm3 s−1 for the HO2 reaction with NO2. For the OH reactions with CO and NO, no dependence on water vapour was observed for the range of water partial pressures tested (3 to 22 hPa), and for NO2, only a weak increase of 3 % was measured, in agreement with the study by Amedro et al. (2020). For the rate coefficient of HO2 with NO2 an enhancement of up to 25 % was observed. This can be explained by a faster rate coefficient of the reaction of the HO2–water complex with NO2 having a value of (3.4±1.1)×10-12 cm3 s−1.

ABSTRACT A comprehensive and hierarchical optimization of a joint hydrogen and syngas combustion mechanism has been carried out. The Kéromnès et al. (Combust Flame, 2013, 160, 995–1011) mechanism for syngas combustion was updated with our recently optimized hydrogen combustion mechanism (Varga et al., Proc Combust Inst, 2015, 35, 589–596) and optimized using a comprehensive set of direct and indirect experimental data relevant to hydrogen and syngas combustion. The collection of experimental data consisted of ignition measurements in shock tubes and rapid compression machines, burning velocity measurements, and species profiles measured using shock tubes, flow reactors, and jet‐stirred reactors. The experimental conditions covered wide ranges of temperatures (800–2500 K), pressures (0.5–50 bar), equivalence ratios (ϕ = 0.3–5.0), and C/H ratios (0–3). In total, 48 Arrhenius parameters and 5 third‐body collision efficiency parameters of 18 elementary reactions were optimized using these experimental data. A large number of directly measured rate coefficient values belonging to 15 of the reaction steps were also utilized. The optimization has resulted in a H2/CO combustion mechanism, which is applicable to a wide range of conditions. Moreover, new recommended rate parameters with their covariance matrix and temperature‐dependent uncertainty ranges of the optimized rate coefficients are provided. The optimized mechanism was compared to 19 recent hydrogen and syngas combustion mechanisms and is shown to provide the best reproduction of the experimental data.

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In low-temperature flash photolysis of NH3/O2/N2 mixtures, the NH2 consumption rate and the product distribution is controlled by the reactions NH2 + HO2 → products (R1), NH2 + H (+M) → NH3 (+M) (R2), and NH2 + NH2 (+M) → N2H4 (+M) (R3). In the present work, published flash photolysis experiments by, among others, Cheskis and co-workers, are re-interpreted using recent direct measurements of NH2 + H (+N2) and NH2 + NH2 (+N2) from Altinay and Macdonald. To facilitate analysis of the FP data, relative third-body collision efficiencies compared to N2 for R2 and R3 were calculated for O2 and NH3 as well as for other selected molecules. Results were in good agreement with the limited experimental data. Based on reported NH2 decay rates in flash photolysis of NH3/O2/N2, a rate constant for NH2 + HO2 → NH3 + O2 (R1a) of k1a = 1.5(±0.5) × 1014 cm3 mol-1 s-1 at 295 K was derived. This value is higher than earlier determinations based on the FP results but in good agreement with recent theoretical work. Kinetic modeling of reported N2O yields indicates that NH2 + HO2 → H2NO + O (R1c) is competing with R1a, but perturbation experiments with addition of CH4 indicate that it is not a dominating channel. Measured HNO profiles indicate that this component is formed directly by NH2 + HO2 → HNO + H2O (R1b), but theoretical work indicates that R1b is only a minor channel. Based on this analysis, we estimate k1c = 2.5 × 1013 cm3 mol-1 s-1 and k1b = 2.5 × 1012 cm3 mol-1 s-1 at 295 K, with significant uncertainty margins.

We present theory and a simulation framework to model three-body collisions and gas phase recombination in dilute atom/diatom mixtures of pure oxygen (O/O2) and nitrogen (N/N2) using the Quasi-Classical Trajectory method. We formulate a three-body collision rate constant based on the lifetimes of binary collisions and initialize three-body collisions by sampling the arrival time of a third body within the lifetimes of pre-simulated binary collisions. We use this method to calculate distributions of recombined product energies, probabilities of recombination, and recombination rate constants through different collision pathways. Long-lived binary atom-diatom collisions are observed, but are too rare to play a dominant role in the recombination process for shock-heated air near the equilibrium conditions studied. The resulting recombination rate constants are within an order of magnitude of the predictions of detailed balance. Notably, the recombination simulation framework does not appeal to the principle of detailed balance and could be useful for studying conditions far from equilibrium.

We present the first-principles determination of the three-body polarizability and the third dielectric virial coefficient of helium. Coupled-cluster and full configuration interaction methods were used to perform electronic structure calculations. The mean absolute relative uncertainty of the trace of the polarizability tensor, resulting from the incompleteness of the orbital basis set, was found to be 4.7%. Additional uncertainty due to the approximate treatment of triple and the neglect of higher excitations was estimated at 5.7%. An analytic function was developed to describe the short-range behavior of the polarizability and its asymptotics in all fragmentation channels. We calculated the third dielectric virial coefficient and its uncertainty using the classical and semiclassical Feynman-Hibbs approaches. The results of our calculations were compared with experimental data and with recent Path-Integral Monte Carlo (PIMC) calculations [Garberoglio et al., J. Chem. Phys. 155, 234103 (2021)] employing the so-called superposition approximation of the three-body polarizability. For temperatures above 200 K, we observed a significant discrepancy between the classical results obtained using superposition approximation and the ab initio computed polarizability. For temperatures from 10 K up to 200 K, the differences between PIMC and semiclassical calculations are several times smaller than the uncertainties of our results. Except at low temperatures, our results agree very well with the available experimental data but have much smaller uncertainties. The data reported in this work eliminate the main accuracy bottleneck in the optical pressure standard [Gaiser et al., Ann. Phys. 534, 2200336 (2022)] and facilitate further progress in the field of quantum metrology.

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The utilization of hydrogen-enriched liquefied petroleum gas (LPG) is an effective means of reducing carbon emissions, but the special physical and chemical properties of hydrogen have raised concerns among the public. To delve into the intricate chemical kinetic mechanisms governing the inhibitory effect of CO2 on the explosion of hydrogen-enriched LPG, this study systematically investigated the influence of varying CO2 concentrations (3%, 6%, and 9%) on the explosion characteristics of hydrogen-enriched LPG (hydrogen ratio ranging from 0 to 0.5) within a 20 L spherical explosion chamber. Subsequently, a chemical kinetic analysis was conducted, focusing on the explosion reaction dynamics of the H2/LPG/CO2/Air mixture, encompassing temperature sensitivity assessments and the production rates of key free radicals. The findings reveal that although hydrogen incorporation does not significantly alter the maximum explosion pressure of LPG, it markedly accelerates the explosion reaction rate, posing a challenge for CO2 in effectively inhibiting the explosion of hydrogen-enriched LPG. CO2 functions as a stabilizing third body within the reaction system, diminishing the collision frequency among free radicals, hydrogen molecules, hydrocarbon molecules, and oxygen molecules, thereby slowing down the reaction rate. As the proportion of hydrogen increases, the concentration of ·H radicals, known for their high reactivity, escalates, rapidly completing the propagation phase of the chain reaction and intensifying the overall generation rates of critical free radicals, including ·H, ·O, and ·OH. Notably, the key reaction H+O2⇋O+OH, which governs the reaction temperature, undergoes significant enhancement, further accelerating the explosion reaction rate and ultimately diminishing the inhibitory efficacy of CO2 against the hydrogenated LPG explosion. Furthermore, as the amount of hydrogen added increases, hydrogen’s competitiveness for oxygen within the reaction system markedly improves, attenuating the oxidation of hydrocarbons. Concurrently, the alkane recombination reaction, exemplified by C3H6+CH3(+M)⇋sC4H9(+M), is strengthened. These insights provide valuable understanding of the complex interactions and mechanisms during the explosion of hydrogen-enriched LPG in the presence of CO2, with implications for the safe application of hydrogen-enriched LPG.

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Rovibrationally excited ephemeral complexes AB**, formed from the association of two molecules A + B, are generally considered to undergo collisions only with an inert bath gas M that transfer energy-inducing termolecular association reactions A + B (+M) → AB (+M). Recent studies have demonstrated that reactive collisions of AB** with a third molecule C-inducing chemically termolecular reactions A + B + C → products-can also be significant in combustion and planetary atmospheres. Previous studies on systems with reactive collisions have primarily focused on limited ranges of reactive collider mole fraction, XC, and pressure, P, specific to the chosen application. Yet, it remains to be established how such systems, and the rate constants of their emergent phenomenological reactions, behave over the wide XC and P ranges of potential interest-a gap in the present understanding that has impeded the development of broadly applicable rate laws and general treatment of such systems in kinetic modeling. Here, we present results from master equation calculations for HO2** formed from H + O2 and its reactions with H to advance understanding and explore representations of systems with reactive colliders across wide ranges of XC and P. With regard to understanding, we demonstrate that reactive collisions can both (1) increase the overall rate of conversion of reactants to products and (2) alter the branching ratio among final products. With regard to representations in kinetic models, we find that rate constants of all emergent phenomenological reactions-termolecular association A + B (+M), chemically termolecular A + B + C, and bimolecular AB + C-exhibit a rich XC and P dependence. We also present analyses to explore the existence of a unique phenomenological representation (or lack thereof) and assess ways for the distinct effects of reactive collisions to be represented in kinetic models.

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Understanding how the H2 molecule is formed under the chemical conditions of the interstellar media (ISM) is critical to the whole chemistry of it. Formation of H2 in the ISM requires a third body acting as a reservoir of energy. Polycyclic aromatic hydrocarbons (PAHs) are excellent candidates to play that role. In this work we simulated the collisions of hydrogen atoms with coronene to form H2 via the Eley-Rideal mechanism. To do so, we used Born-Oppenheimer (ab initio) Molecular Dynamics simulations. Our results show that that adsorption of H atoms and subsequent release of H2 readily happen on coronene for H atoms with kinetic energy as large as 1 eV. Special attention is paid to dissipation and partition of the energy released in the reactions. The capacity of coronene to dissipate collision and reaction energies depends varies with the reaction site. Inner sites dissipate energy easier and faster than edge sites, thus evidencing an interplay between the potential energy surface around the reaction center and its ability to cool the projectile. As for the the recombination of H atoms and the subsequent formation of H2, it is observed that $\sim 15~{{\ \rm per\ cent}}$ of the energy is dissipated by the coronene molecule as vibrational energy and the remaining energy is carried by H2. The H2 molecules desorb from coronene with an excited vibrational state (υ ≥ 3), a large amount of translational kinetic energy (≥ 0.4 eV) and with a small activation of the rotational degree of freedom.

OH+NO is an important termolecular association reaction in the troposphere and stratosphere that influences the atmospheric ozone budget. In this study, rate coefficients for the reaction of OH + NO + M → HONO + M were measured under conditions relevant to the troposphere/lower stratosphere over a temperature range of 228-298 K and pressure range of 50-750 Torr using N2 as a bath gas. Time-resolved kinetics were studied by pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) detecting OH by laser-induced fluorescence. Data for the temperature range 258-298 K were fit to two falloff expressions, with the JPL expressions (k1,0N2 = 7.37 × 10-31(T/300 K)-2.90 cm6 molecule-2 s-1 and k1,∞ = 3.44 × 10-11(T/300 K)-0.1cm3 molecule-1 s-1) and IUPAC expression (k1,0N2 = 6.80 × 10-31(T/300 K)-2.81 cm6 molecule-2 s-1, FC = 0.81, k1,∞ = 1.96 × 10-11(T/300 K)-0.3 cm3 molecule-1 s-1). At temperatures T < 258 K, the measured rate coefficients were significantly higher than the IUPAC and JPL fits. To accommodate the rate coefficient deviation from the two expressions, data across the entire temperature range (228-298 K) was fit with two approaches. First, rate coefficients were fit with an empirical modification by adding a second falloff term to the JPL expression with a second low-pressure rate coefficient of k1,0N2 = 5.20 × 10-35(T/300 K)-30.4 cm6 molecule-2 s-1. Second, k1,0N2, k1,∞, and n were fit globally to the entire temperature data set, but FC was varied for each individual temperature, which increased with decreasing temperature. In the second portion of the study, the influence of H2O on the reaction rate was investigated using a N2-H2O mixture as the bath gas at 50 Torr and 273 and 298 K. The JPL and IUPAC falloff expressions were modified to include H2O as a third-body collisional partner consistent with a nonlinear mixture model. Fits to the data yielded the low pressure termolecular rate coefficients in H2O, k1,0H2O = 3.81 × 10-30(T/300 K)-6.04 and k1,0H2O = 3.31 × 10-30(T/300 K)-5.81 cm6 molecule-2 s-1, respectively. Experimental data were fit using MESMER give energy relaxation parameters of = 170 ± 10 cm-1 and = 634 ± 20 cm-1, indicating that H2O is a 4× more efficient collisional quencher than N2 alone. The modified JPL expressions with the newly derived low pressure rate coefficients were implemented into a STOCHEM-CRI atmospheric model. Predictions of HONO concentrations with the new rates were up to 15% higher in remote tropical regions.

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To explore the mechanism of inhibiting spontaneous combustion of coal by mixed gases, the low-temperature oxidation characteristics of coal under different components of mixed gases were analyzed. ESR and FTIR experiments were used to investigate the effects of different gas mixtures on the activity of coal during low-temperature oxidation and the oxidation reaction of coal surface functional groups. The mechanism of chemical oxygen inhibition of mixed gas was studied by density functional theory. The results show that the larger the CO2 component in the mixed gas, the higher the ability to inhibit coal oxidation. The concentration of free radicals in coal under dry air condition is higher than that under inert mixed gas condition during oxidation heating at 30–230 °C. The oxidation ability of –CH3, –OH and oxygen-containing functional groups in the mixed gas reaction is inhibited. Through quantum chemistry calculation, it is found that the mixed gas increases the activation energy of free radicals and reduces the heat release of the reaction. This study provides theoretical reference for coal mine thermal disaster.

No abstract available

ABSTRACT The oxidation behavior of IG-110, a graphite core component, was investigated at temperatures ranging from 400 to 1000°C in a 10 ppm Ar/O2 flow to simulate the oxidation process between the graphite core component and helium coolant with low O2 concentrations employed in advanced High-Temperature Gas-cooled Reactors (HTGRs). The results reveal that IG-110 undergoes significant mass loss at temperatures above 700°C, resulting in total mass changes of −1.5%, −5.3%, and −9.0% at 700, 800, and 1000°C, respectively, during a 10-hour oxidation period. No significant mass loss is observed below 600°C. To understand the oxidation mechanism of IG-110 under low O2 concentrations, we propose a kinetic model as the current chemical kinetic-controlled model does not fully explain the oxidation behavior observed in our research. Our analysis shows lower estimated reaction rates compared to studies at higher O2 concentrations; the activation energy values exhibit good agreement. The proposed kinetic model sheds light on the oxidation mechanism of IG-110 under 10 ppm Ar/O2 flow. This study provides new insights into the oxidation behavior of graphite core components in HTGRs and highlights the importance of controlling the O2 concentration in the helium coolant to prevent severe degradation of SiC-matrix fuel compacts.

A comparative study of both plasma parameters and regularities of ZrO2 reactive-ion etching kinetics in BCl3 + Ar and BCl3 + He mixtures with variable initial compositions was carried out. The combination of plasma diagnostics and modeling tools allowed one a) to figure out key physical and chemical processes determining effects of type and content of inert carrier gas on densities of plasma active species and b) to eliminate most realistic mechanisms of heterogeneous processes responsible for phenomenological etching kinetics.

No abstract available

Synthesis of magnetic nanoparticles is relevant to many applications in the fields of catalysis, energy storage, and biomedicine. Understanding the growth mechanisms and morphology of nanoparticles during inert gas condensation is crucial to rationally improve the performance of the final nanoparticles. In this work, molecular dynamics simulations are carried out to study the structural and thermodynamic behavior of Ni–Fe nanoparticles from homogenous vapor phase in Ar atmosphere. It is revealed that the final morphology of the resulting nanoparticles presents a spherical shape by cluster coalescence at high temperatures where the small clusters are liquid droplets prior to their collisions. However, probabilistic nucleation and cluster growth indicate that the occurrence of spherical shape is more controlled by the probability limits for different Fe concentrations. Meanwhile, a larger inert gas density induces a more efficient cooling effect leading to a larger probability control of the cluster formation with non-spherical shape by agglomeration. Furthermore, the solidification of the as-formed Ni–Fe clusters is examined by evaluating the evolution of crystalline and amorphous structure. The linear scaling-down dependence of the solidification temperature on the reciprocal of the nanoparticle size clearly signifies a linear size-depression effect for the liquid-to-solid phase change of Ni–Fe nanoparticles. Our findings thus extend the current understanding of inert gas condensation behavior and mechanisms of Ni–Fe nanoparticles from an atomic/molecular perspective.

ABSTRACT The purpose of this study is to study the effect of CO2-N2 composite gas on coal spontaneous combustion index gas and the mechanism of inhibiting coal spontaneous combustion through a competitive adsorption process and to provide theoretical guidance for adopting inert injection fire prevention and control technology in goaf to prevent coal spontaneous combustion. The programmed temperature experiment and gas chromatography were used to analyze the indicator gas after injecting different mixed ratios of CO2 and N2 inert gas. In the whole oxidation heating process (25–300 ℃), the generation of indicator gas and the peak point of gas ratio showed an apparent “Hysteresis phenomenon” and the more significant the proportion of CO2 in the composite inert gas, the more pronounced the “Hysteresis phenomenon.” Even in the CO2-dry air environment, the peak point disappears, indicating that with the injection of N2 and CO2, the coal body is in a more complex gas atmosphere, and a variety of gases are in the process of adsorption and desorption on the inner and outer surfaces of the coal body. The characteristics of the evolution of the spontaneous combustion oxidation process of coal are more complex, directly affecting the coal-oxygen interaction, thus affecting the intuitive combustion oxidation process. Molecular simulation studies the characteristics of coal molecules on CO2, N2, and O2. The results show that the adsorption capacity and adsorption energy of coal molecules on CO2 molecules are more significant than O2 and N2, and there is a competitive adsorption relationship between CO2 and N2 molecules and O2 molecules, and the competitive adsorption capacity of CO2 is more significant than N2. It shows that the composite inert gas can inhibit the coal-oxygen adsorption by competitive adsorption to displace oxygen and achieve the combustion inhibition effect. The experimental and theoretical basis for developing and improving inert gas fire extinguishing technology is provided by studying the index gas after CO2-N2 composite inert gas action and the adsorption capacity and energy in the competitive adsorption process.

This study introduces a novel method for synthesizing carbon nanotube (CNT) fibers using floating catalyst chemical vapor deposition (FC-CVD) in an open-atmosphere without the need for hydrogen as a carrier gas. Traditional FC-CVD techniques depend on hydrogen gas and require a harvest box with inert gas purging, which restricts scalability. Our approach utilizes nitrogen gas as the sole carrier, allowing for CNT fiber production without a harvest box. To understand the spinning process mechanism in an open-atmosphere, we conducted thermodynamic and computational fluid dynamics (CFD) analyses. Methanol was selected as the carbon source based on thermodynamic calculations, which revealed that at high temperatures, methanol forms CO and H2 as thermodynamically stable species instead of carbon (C), thereby preventing soot formation. Moreover, methanol undergoes catalytic cracking exclusively in the presence of catalysts, further preventing soot formation. This approach allows operation at high partial pressure, even above the upper explosive limit (UEL), effectively preventing combustion. A 600 mm cooling zone was incorporated into the reactor to lower the outlet gas temperature below methanol's auto-ignition point, mitigating combustion risks. CFD calculations were employed to determine the necessary cooling zone length. Additionally, we developed a predictive model using the XGBoost machine learning method to efficiently map the parameter space for CNT fiber spinning, achieving an accuracy of 95.24%. The resulting CNT fibers demonstrate high electrical conductivity (240 ± 24 S/cm) and a low ID/IG ratio, indicating a high degree of crystallinity.

At present, lead-containing wastes have increasingly become the raw materials together with primary lead concentrate for lead production to meet the ever-increasing lead demand market. PbSO4 is the dominant component in the lead-containing wastes, nevertheless, its reaction behavior during lead smelting is not sufficiently investigated. This study investigated PbSO4 decomposition behaviors and phase transformation mechanisms at oxidizing and reductive atmospheres and various gas flow rates. The investigations reveal that increasing the temperature and decreasing the oxygen partial pressure of the decomposition atmosphere can accelerate PbSO4 decomposition degree. PbSO4 decomposition intensity under different atmospheres follows the order of reducing atmosphere > inert atmosphere > oxidizing atmosphere. PbSO4 decomposition path was identified: at a non-reductive atmosphere, the decomposition of PbSO4 belongs to a multi-step decomposition process, PbSO4 gradually decompose into xPbO·PbSO4 (x = 1, 2, 4 in turn) and finally PbO. At a reductive atmosphere, the multi-step decomposition process was accelerated significantly, at the same time, the reduction decomposition path PbSO4 → PbS was increasingly dominant with the extension of decomposition time. PbS and Pb were generated successively. Therefore, a suitable reducing atmosphere is suggested to co-smelt PbSO4-bearing wastes in primary lead smelting furnace.

Biologically inert gases play important roles in the biological functionality of proteins. However, researchers lack a full understanding of the effects of these gases since they are very chemically stable only weakly absorbed by biological tissues. By combining X-ray fluorescence, particle sizing and molecular dynamics (MD) simulations, this work shows that the aggregation of these inert gases near the hydrophobic active cavity of pepsin should lead to protein deactivation. Micro X-ray fluorescence spectra show that a pepsin solution can contain a high concentration of Xe or Kr after gassing, and that the gas concentrations decrease quickly with degassing time. Biological activity experiments indicate a reversible deactivation of the protein during this gassing and degassing. Meanwhile, the nanoparticle size measurements reveal a higher number of “nanoparticles” in gas-containing pepsin solution, also supporting the possible interaction between inert gases and the protein. Further, MD simulations indicate that gas molecules can aggregate into a tiny bubble shape near the hydrophobic active cavity of pepsin, suggesting a mechanism for reducing their biological function.

Molecular nitrogen (N2) is widely used as a carrier or protective gas in many catalytic reactions because of its chemical inertness and large availability in nature. Up to now, N2 has not been recognized as a promoter or an active component to enhance catalytic performance. However, the textbook description of inert N2 has been rewritten in a recent paper published in Nature Catalysis by Duan et al., reporting that N2 can dramatically promote biomass hydrodeoxygenation (HDO) over ruthenium (Ru)based catalysts [1]. As exemplified by the HDO of p-cresol to toluene, a representative model reaction for upgrading the lignin-rich biomass, the presence of N2 led to a 4.3-fold increase in HDO activity over Ru clusters (with an average diameter of 1.2 nm) dispersed on titaniumoxide (Ru/TiO2) in a batch reactor (at 160◦C, 1 bar H2 and 6 bar N2). Similar promoting effects of N2 were also observed when applying other Ru catalysts in theHDOreaction, confirming the ability of N2 to unprecedentedly act as a catalytic promoter. Detailed studies [1], collaboratively carried out by the research groups of Jun Li from Tsinghua University and Edman Tsang and Dermot O’Hare from University of Oxford with complementary expertise in computational catalysis, surface catalysis and biomass conversion, have clarified the mechanism of N2 promotion (Fig. 1). In situ X-ray absorption near edge structure and in situ Fourier-transform infrared spectroscopy show that hydrogenated nitrogen species (NxHy, x = 1, 2, y = 1, 2) form on the Ru surface under the aforementioned H 2

Chlorpyrifos (CPF) is a widely used pesticide; however, limited experimental work has been completed on its thermal decomposition. CPF is known to decompose into 3,5,6-trichloro-2-pyridinol (TCpyol) together with ethylene and HOPOS. Under oxidative conditions TCpyol can decompose into the dioxin-like 2,3,7,8-tetrachloro-[1,4]-dioxinodipyridine (TCDDPy). With CPF on the cusp of being banned in several jurisdictions worldwide, the question might arise as to how to safely eliminate large stockpiles of this pesticide. Thermal methods such as incineration or thermal desorption of pesticide-contaminated soils are often employed. To assess the safety of thermal methods, information about the toxicants arising from thermal treatment is essential. The present flow reactor study reports the products detected under inert and oxidative conditions from the decomposition of CPF representative of thermal treatments and of wildfires in CPF-contaminated vegetation. Ethylene and TCpyol are the initial products formed at temperatures between 550 and 650 °C, although the detection of HOPOS as a reaction product has proven to be elusive. During pyrolysis of CPF in an inert gas, the dominant sulfur-containing product detected from CPF is carbon disulfide. Quantum chemical analysis reveals that ethylene and HOPOS undergo a facile reaction to form thiirane (c-C2H4S) which subsequently undergoes ring opening reactions to form precursors of CS2. At elevated temperatures (>650 °C), TCpyol undergoes both decarbonylation and dehydroxylation reactions together with decomposition of its primary product, TCpyol. A substantial number of toxicants is observed, including HCN and several nitriles, including cyanogen. No CS2 is observed under oxidative conditions - sulfur dioxide is the fate of S in oxidation of CPF, and quantum chemical studies show that SO2 formation is initiated by the reaction between HOPOS and O2. The range of toxicants produced in thermal decomposition of CPF is summarised.

The pyrolysis of acetylene was studied experimentally in a cyclic compression reactor in an atmosphere of buffer inert gases (argon, neon, helium). A significant difference in the thermodynamic conditions for the complete pyrolysis of the precursor for various buffer gases was revealed. The reaction products of acetylene in neon and helium contained up to 20% of the part soluble in organic solvents. The study of the ethanol-soluble part of the product using time-of-flight mass spectrometry with matrix-assisted laser desorption/ionization made it possible to distinguish even and odd branches in the spectrum of substances by the number of carbon atoms. A mechanism is proposed for the formation of larger particles by merging smaller ones. Keywords: cyclic compression reactor, acetylene pyrolysis, buffer inert gas, growth mechanism, carbon nanoparticles.

Elemental mercury and mercury (Hg)-bearing particles may be present in gas and condensate from specific geologic reservoirs and be coproduced with them. In this study, we found that over 70% of the Hg mass in field monoethylene glycol (MEG) is present as 100–200 nm particulate β-HgS, and it is therefore important to understand the decomposition behavior of β-HgS in MEG to determine the partitioning of mercury species in liquid natural gas (LNG) plants. Thermal decomposition studies in MEG and MEG-water solutions showed that β-HgS decomposition to elemental mercury started at around 100 °C, which is significantly lower than the 200 °C required for β-HgS decomposition in an inert gas. Density functional theory calculations supported the experimental observations that β-HgS has a lower decomposition temperature in solvents than its counterpart without a solvent because the solvent interactions decrease the Hg–S bond strength. Thermal decomposition studies at 130 °C showed that increased water content and decreased β-HgS particle size significantly increased the decomposition rate, while some common additives in field MEG did not have a significant effect. Experiment results suggest the decomposition pathway of β-HgS in MEG/water includes dissolution to form dissolved Hg(II) ions, followed by reduction to form elemental mercury by reaction with MEG. This study highlights the strong effect of solvent on the thermal decomposition mechanism of β-HgS, improving our understanding of the fate and species of Hg in petrochemical processing.

No abstract available

A clean energy revolution is occurring across the world. As iron and steelmaking have a tremendous impact on the amount of CO2 emissions, there is an increasing attraction towards improving the green footprint of iron and steel production. Among reducing agents, hydrogen has shown a great potential to be replaced with fossil fuels and to decarbonize the steelmaking processes. Although hydrogen is in great supply on earth, extracting pure H2 from its compound is costly. Therefore, it is crucial to calculate the partial pressure of H2 with the aid of reduction reaction kinetics to limit the costs. This review summarizes the studies of critical parameters to determine the kinetics of reduction. The variables considered were temperature, iron ore type (magnetite, hematite, goethite), H2/CO ratio, porosity, flow rate, the concentration of diluent (He, Ar, N2), gas utility, annealing before reduction, and pressure. In fact, increasing temperature, H2/CO ratio, hydrogen flow rate and hematite percentage in feed leads to a higher reduction rate. In addition, the controlling kinetics models and the impact of the mentioned parameters on them investigated and compared, concluding chemical reaction at the interfaces and diffusion of hydrogen through the iron oxide particle are the most common kinetics controlling models.

No abstract available

CO2 utilization has been an emerging technology of increasing global interest due to its direct impact in limiting greenhouse gas emissions. In this contribution, the fluid dynamic behavior of a CO2 conversion non-thermal plasma (NTP) in a dielectric barrier discharge (DBD) reactor is studied through computational fluid dynamics (CFD) simulations. Calculations are provided in conjunction with experimental results and the thermodynamic characterization of the compounds and mixtures involved. This CFD study utilizes a well-established methodology that allows the optimization of fluid flow with limited computational burden. Firstly, results are presented for an Example Case, in which several variables are studied both at the final iteration as well as across iterations. Secondly, a range of Study Cases, changing the inlet composition and volume rate, are presented. Average velocity is one of the most significant variables to predict the reactor’s yield, while the temperature, density and pressure in the reactor remain, in most cases, almost constant. The resulting CFD computations describe the behavior of the fluids in the reactor in a predictive manner for future experimental results. Limitations in the fluid’s characterization occur due to not explicitly including the plasma reaction, which will be aimed at in future contributions.

Non-thermal plasma (NTP) conversion applications have become an emerging technology of increasing global interest due to their particular ability to perform at atmospheric pressure and ambient temperature. This study focuses on a specific case of a dielectric barrier discharge NTP reactor for carbon dioxide conversion with the usage of argon as diluent gas. The plasma computations in COMSOL® Multiphysics are compared to experimental results and coupled with previous thermodynamic characterization of argon species and fluid dynamic calculations. The model is defined as a time-dependent study with a 2D-Geometry of pure argon, with both fluid flow and plasma phenomena. Firstly, the model showcases an accurate understanding of the plasma physics involved, in the form of electron density, excited argon, argon ions, and mean electron energy. It also allows a direct comparison of the velocity, vorticity, pressure, and dynamic viscosity results with fluid flow computations. Secondly, the impact of several variables is studied, notably the inlet volumetric rate, dielectric barrier thickness and material, and reactor length. Limitations in the plasma characterization can occur by not including packed material or all relevant species in experimental CO2 conversion and their respective reactions, which should be aimed at in future contributions.

No abstract available