CH3 Radicals Research Articles

Plasma Etch of IGZO Thin Film and IGZO/SiO2 Interface Diffusion in Inductively Coupled CH4/Ar Plasmas

ABSTRACTIn this work, the etching characteristics of InGaZnO4 (IGZO) thin films were systemically investigated in inductively coupled CH4/Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH4/Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH4/Ar plasmas with CH4 ratios below 80%, the IGZO etch rate increases with a higher CH4 proportion, aligning with the ascending trend of CH3 radical density, which suggests that CH3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO2 during CH4/Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH4/Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO2 etch by introducing BCl3 into the SiO2 etching chemistry.

Optimizing the reaction pathway of methane photo-oxidation over single copper sites.

Direct photocatalytic conversion of methane to value-added C1 oxygenate with O2 is of great interest but presents a significant challenge in achieving highly selective product formation. Herein, a general strategy for the construction of copper single-atom catalysts with a well-defined coordination microenvironment is developed on the basis of metal-organic framework for selective photo-oxidation of CH4 to HCHO. We propose the directional activation of O2 on the mono-copper site breaks the original equilibrium and tilts the balance of radical formation almost completely toward •OOH. The synchronously generated •OOH and •CH3 radicals rapidly combine to form HCHO while inhibiting competing reactions, thus resulting in ultra-highly selective HCHO production (nearly 100%) with a time yield of 2.75 mmol gcat-1 h-1. This work highlights the potential of rationally designing reaction sites to manipulate reaction pathways and achieve selective CH4 photo-oxidation, and could guide the further design of high-performance single-atom catalysts to meet future demand.

Mathematical Modelling of the Impact of IR Laser Radiation on an Oncoming Flow of Nanoparticles with Methane

Introduction. The study is devoted to the numerical investigation of laser radiation’s effect on an oncoming two-phase flow of nanoparticles and multicomponent hydrocarbon gases. Under such exposure, the hydrogen content in the products increases, and methane is bound into more complex hydrocarbons on the surface of catalytic nanoparticles and in the gas phase. The hot walls of the tube serve as the primary source of heat for the reactive two-phase medium containing catalytic nanoparticles. Materials and Methods. The main method used is mathematical modelling, which includes the numerical solution of a system of equations for a viscous gas-dust two-phase medium, taking into account chemical reactions and laser radiation. The model accounts for the two-phase gas-dust medium’s multicomponent and multi-temperature nature, ordinary differential equations (ODEs) for the temperature of catalytic nanoparticles, ODEs of chemical kinetics, endothermic effects of radical chain reactions, diffusion of light methyl radicals CH3 and hydrogen atoms H, which initiate methaneconversion, as well as absorption of laser radiation by ethylene and particles. Results. The distributions of parameters characterizing laminar subsonic flows of the gas-dust medium in an axisymmetric tube with chemical reactions have been obtained. It is shown that the absorption of laser radiation by ethylene in the oncoming flow leads to a sharp increase in methane conversion and a predominance of aromatic compounds in the product output. Discussion and Conclusion. Numerical modelling of the dynamics of reactive two-phase media is of interest for the development of theoretical foundations for the processing of methane into valuable products. The results obtained confirm the need for joint use of mathematical modelling and laboratory experiments in the development of new resource-saving and economically viable technologies for natural gas processing.

Thermal stability of MDM and oxidative decomposition mechanism under the condition of air infiltration: A combined experimental, ReaxFF-MD and DFT study

When siloxanes are used as the working fluids of organic Rankine cycle systems, there is a possibility of air infiltration due to the large vacuum present in the condenser. To address this issue, experimental and simulation studies were conducted on the thermal stability and pyrolysis product characteristics of octamethyltrisiloxane (MDM) in the presence of air. The results indicated that air significantly promotes the decomposition of MDM at the temperatures above 250 °C. Air was helpful in increasing the formation of CH2O, CO, and CO2, and also enhanced polymerization of decomposition product of siloxane, leading to higher yields of MD2M, MD3M, MD4M, D3, D4, and D5. By combining reactive force field molecular dynamics (ReaxFF-MD) simulations with density functional theory (DFT) calculations, the microscopic mechanisms of MDM's oxidative decomposition by O2 in air and H2O under humid conditions were elucidated. O2 can easily combine with unsaturated Si atoms to form Si-O bonds, combine with CH3 radicals to form C-O bonds, and undergoes hydrogen extraction reactions to initiate decomposition. H2O mainly undergoes initial decomposition through CH3 radical hydrogenation and binding with unsaturated Si atoms. The generated O2H, O, and OH radicals tend to bind with Si atoms in molecules and radicals, facilitating polymerization reactions.

Hybrid plasma catalysis-thermal system for non-oxidative coupling of methane to ethylene and hydrogen

We report a two-stage hybrid plasma catalysis-thermal system for non-oxidative coupling of methane (NOCM) to ethylene (C2H4) and hydrogen (H2), achieving 66 % C2H4 selectivity and 60 % H2 selectivity with 28 % CH4 conversion. This corresponds to a C2H4 yield of 18 %, which is one of the highest reported in literature. The system consists of the first plasma catalysis stage (stage 1) and the second thermal cracking stage (stage 2). Comprehensive analyses using in-situ mass spectrometry (MS) and gas chromatography (GC) reveal that the combination of plasma and Pt/ZrO2 catalyst in stage 1 predominantly facilitates the conversion of methane to ethane. Characterizations employing X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy-scanning transmission electron microscopy-energy dispersive X-ray (HRTEM-STEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR), indicate that the coordinatively unsaturated site of Pt could be the active sites for C–H bond cracking to generate abundant CH3 radicals (CH3·), enhancing the C2 selectivity by inhibiting the non-selective formation of coke and higher hydrocarbons. Subsequently, the products from stage 1 (especially C2H6) undergo pyrolysis reactions at 880 °C in stage 2, which further boosts the C2H4 selectivity and yield. Based on the reaction performance, catalyst characterization, optical emission spectroscopy (OES), and in-situ Fourier transform infrared spectroscopy (FTIR) results, we reveal the reaction mechanism within the hybrid two-stage plasma catalysis-thermal system for converting CH4 to C2H4 and H2.

Design and implementation of a new apparatus for astrochemistry: Kinetic measurements of the CH + OCS reaction and frequency comb spectroscopy in a cold uniform supersonic flow.

We present the development of a new astrochemical research tool, HILTRAC, the Highly Instrumented Low Temperature ReAction Chamber. The instrument is based on a pulsed form of the CRESU (Cinétique de Réaction en Écoulement Supersonique Uniforme, meaning reaction kinetics in a uniform supersonic flow) apparatus, with the aim of collecting kinetics and spectroscopic information on gas phase chemical reactions important in interstellar space or planetary atmospheres. We discuss the apparatus design and its flexibility, the implementation of pulsed laser photolysis followed by laser induced fluorescence, and the first implementation of direct infrared frequency comb spectroscopy (DFCS) coupled to the uniform supersonic flow. Achievable flow temperatures range from 32(3) to 111(9) K, characterizing a total of five Laval nozzles for use with N2 and Ar buffer gases by impact pressure measurements. These results were further validated using LIF and direct frequency comb spectroscopy measurements of the CH radical and OCS, respectively. Spectroscopic constants and linelists for OCS are reported for the 1001 band near 2890-2940cm-1 for both OC32S and OC34S, measured using DFCS. Additional peaks in the spectrum are tentatively assigned to the OCS-Ar complex. The first reaction rate coefficients for the CH + OCS reaction measured between 32(3) and 58(5) K are reported. The reaction rate coefficient at 32(3) K was measured to be 3.9(4) × 10-10cm3molecule-1s-1 and the reaction was found to exhibit no observable temperature dependence over this low temperature range.

Mode-Specific Dynamics Studies for the Multichannel C2H2 + OH Reaction.

The C2H2 + OH reaction is a key elementary reaction in acetylene oxidation, and the products forming in different reaction channels, such as C2H and CH3 radicals, are also important for subsequent reaction processes in the combustion process. In this work, we investigated the dynamics of the C2H2 + OH reaction with specific vibrational mode excitations and analyzed the mode specificity based on quasi-classical trajectory calculations on a recently developed full-dimensional potential energy surface. It is found that exciting OH stretching mode can promote the production of H + OCCH2 and CO + CH3, while the excitation of C-H symmetric/antisymmetric stretching mode of C2H2 can facilitate the H2O + C2H channel. Based on the prediction of vibrationally adiabatic and sudden vector projection models, the mode specificity in the C2H2 + OH reaction can be attributed to the difference in the degree of coupling between the initial motion mode and the reaction coordinate of each reaction path, which ultimately leads to the changes in rate constants and the product branching ratios. These findings can offer theoretical insights to regulate the branching ratio of the multichannel C2H2 + OH reaction.

Wavelength-Dependent Activity of Oxygen Species in Propane Conversion on Rutile TiO2(110).

Photocatalytic oxidative dehydrogenation of propane (C3H8) into propene (C3H6) under mild conditions holds great potential in the chemical industry, but understanding how active species participate in C3H8 conversion remains a significant challenge. Here, the wavelength-dependent activities of bridging oxygen (Ob2-) and the Ti5c-bound oxygen adatom (OTi2-) of model rutile (R) TiO2(110) in C3H8 conversion have been investigated. Under 257 and 343 nm irradiation, hole-trapped OTi- and Ob- can abstract the hydrogen atom of C3H8, forming the CH3CH•CH3 radical and C3H6. However, the rate of C3H8 conversion with hole-trapped Ob- is strongly dependent on the wavelength, primarily producing the C3H7• radical. In the case of hole-trapped OTi-, C3H6 is the main product, which is nearly independent of wavelength. The differences in the wavelength-dependent activity and product selectivity are likely due to dynamic control rather than thermodynamic control. The result provides a deeper understanding of the dynamic processes involved in the conversion of light alkanes in TiO2 photocatalysis.

Photofragmentation laser-induced fluorescence imaging of CH3 by structured illumination in a plasma discharge

Methyl is crucial in plasma-assisted hydrocarbon chemistry, making precise in situ imaging essential for understanding various plasma applications. Its importance in methane chemistry arises from its role as a primary byproduct during the initial phase of methane dehydrogenation. Detecting the CH3 radical is challenging due to its high reactivity and the prevalence of strongly pre-dissociative electronically excited states. To address this, photofragmentation planar laser-induced fluorescence (PF-LIF) techniques have been developed. These involve laser-induced photodissociation of the CH3 radical into CH fragments, which are then probed using another laser. This method allows for both temporally and spatially resolved measurements. However, quantifying the signal from photofragmented species is complicated by the overlap with naturally occurring CH fragments. We employ PF-LIF with structured illumination to distinguish photofragmented species from naturally occurring ones using a frequency-sensitive lock-in technique. This methodology is demonstrated in an atmospheric pressure dielectric barrier discharge (DBD) containing argon and methane, enabling spatially and temporally resolved data acquisition of the CH3 radical. This approach facilitates interference-free PF-LIF measurements of methyl in various applications.

Atomistic insights from DFT calculations into the catalytic properties on ceria-lanthanum clusters for methane activation.

Improving the catalytic performance of materials based on cerium oxide (CeO2) for the activation of methane (CH4) can be achieved through the following strategies: mixture of CeO2 with different oxides (e.g., CeO2-La2O3) and the use of particles with different sizes. In this study, we present a theoretical investigation of the initial CH4 dehydrogenation on (La2Ce2O7)n clusters, where n = 2, 4, and 6. Our framework relies on density functional theory calculations combined with the unity bond index-quadratic exponential potential approximation. Our results indicate that chemical species arising from the first dehydrogenation of CH4, that is, CH3 and H, bind through the formation of C-O and H-O bonds with the clusters, respectively. The coordination of the adsorption site and the chemical environment plays a crucial role in the magnitude of the adsorption energy; for example, species adsorb more strongly in the low-coordinated topO sites located close to the La atoms. Thus, it affects the activation energy barrier, which tends to be lower in configurations where the adsorption of the chemical species is stronger. During CH4 dehydrogenation, the CH3 radical can be present in a planar or tetrahedral configuration. Its conformation changes as a function of the charge transference between the molecule and the cluster, which depends on the CH3-cluster distance. Finally, we analyze the effects of the Hubbard effective parameter (Ueff) on adsorption properties, as the magnitude of localization of Ce f-states affects the hybridization of the interaction between the molecule and the clusters and hence the magnitude of the adsorption energies. We obtained a linear decrease in the adsorption energies by increasing the Ueff parameter; however, the activation energy is only slightly affected.

Chemistry across dust and gas gaps in protoplanetary disks. Modelling the co-spatial molecular rings in the HD 100546 disk

Nearby extended protoplanetary disks are commonly marked by prominent rings in dust emission, possibly carved by forming planets. High-resolution observations show that both the dust and the gas are structured. These molecular structures may be related to radial and azimuthal density variations in the disk and/or the disk chemistry. The aim of this work is to identify the expected location and intensity of rings seen in molecular line emission in gapped disks while exploring a range of physical conditions across the gap. In particular, we aim to model the molecular rings that are, in contrast with most other gapped disks, co-spatial with the dust rings at sim 20 and sim 200 au in the HD 100546 disk using the thermochemical code DALI. We modelled observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of CO isotopologues C I HCN, CN C2H NO, and HCO+ in the HD 100546 disk. An axisymmetric 3D thermochemical model reproducing the radial profiles of the CO isotopologue observations and the double ring seen in continuum emission was used to make predictions for various emission lines. The effect of the amount of gas in the dust gap, the C/O ratio, an attenuated background UV radiation field, and the flaring index on the radial distribution of different molecules were investigated. The fiducial model of a gapped disk with a gas cavity at $0-15$ au, a dust cavity at $0-20$ au, and a gas and dust gap at $40-175$ au provides a good fit to the continuum and the CO isotopologues in the HD 100546 disk. In particular, the CO isotopologue emission is consistent with a shallow gas gap with no more than a factor of approximately ten drop in gas density at $40-175$ au. Similar to the CO isotopologues, the HCN and HCO+ model predictions reproduce the data within a factor of a few in most disk regions. However, the predictions for the other atom and molecules C I CN C2H and NO, neither match the intensity nor the morphology of the observations. An exploration of the parameter space shows that, in general, the molecular emission rings are only co-spatial with the dust rings if the gas gap between the dust rings is depleted by at least four orders of magnitude in gas or if the C/O ratio of the gas varies as a function of radius. For shallower gaps the decrease in the UV field roughly balances the effect of a higher gas density for UV tracers such as CN C2H and NO. Therefore, the CN C2H and NO radicals are not good tracers of the gas gap depth. In the outer regions of the disk around 300 au, these UV tracers are also sensitive to the background UV field incident on the disk. Reducing the background UV field by a factor of ten removes the extended emission and outer ring seen in CN and C2H respectively, and reduces the ring seen in NO at 300 au. The C/O ratio primarily effects the intensity of the lines without changing the morphology much. The C I HCN, CN, and C2H emission all increase with increasing C/O, whereas the NO emission shows a more complex dependence on the C/O ratio depending on the disk radius. CO isotopologues and HCO+ emission trace gas gaps and gas gap depths in disks. The molecular rings in HCN, CN C2H and NO predicted by thermochemical models do not naturally coincide with those seen in the dust, contrary to what is observed in the HD 100546 disk. This could be indicative of a radially varying C/O ratio in the HD 100546 disk with a C/O above one in a narrow region across the dust rings, together with a shallow gas gap that is depleted by a factor of approximately ten in gas, and a reduced background UV field. The increase in the C/O ratio to approximately greater than one could point to the destruction of some of the CO, the liberation of carbon from ice and grains, or, in the case of the outer ring, it could point to second generation gas originating from the icy dust grains.

New Estimates of Nitrogen Fixation on Early Earth.

Fixed nitrogen species generated by the early Earth's atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth's N2/CO2-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NOx species (i.e., no HCN formation) via the thermochemical dissociation of N2 and CO2 in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth's early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN2, inspired by the experimental results which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN2 reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe.

First-Principles Study of Adsorption of CH4 on a Fluorinated Model NiF2 Surface.

Electrochemical fluorination on nickel anodes, also known as the Simons' process, is an important fluorination method used on an industrial scale. Despite its success, the mechanism is still under debate. One of the proposed mechanisms involves higher valent nickel species formed on an anode acting as effective fluorinating agents. Here we report the first attempt to study fluorination by means of first principles investigation. We have identified a possible surface model from the simplest binary nickel fluoride (NiF2). A twice oxidized NiF2(F2) (001) surface exhibits higher valent nickel centers and a fluorination source that can be best characterized as an [F2]- like unit, readily available to aid fluorination. We have studied the adsorption of CH4 and the co-adsorption of CH4 and HF on this surface by means of periodic density functional theory. By the adsorption of CH4, we found two main outcomes on the surface. Unreactive physisorption of CH4 and dissociative chemisorption resulting in the formation of CH3F and HF. The co-adsorption with the HF gave rise to four main outcomes, namely the formation of CH3F, CH2F2, CH3 radical, and also physisorbed CH4.

Breaking the Activity-Selectivity Trade-off for CH4-to-C2H6 Photoconversion.

Photocatalytic conversion of methane (CH4) to ethane (C2H6) has attracted extensive attention from academia and industry. Typically, the traditional oxidative coupling of CH4 (OCM) reaches a high C2H6 productivity, yet the inevitable overoxidation limits the target product selectivity. Although the traditional nonoxidative coupling of CH4 (NOCM) can improve the product selectivity, it still encounters unsatisfied activity, arising from being thermodynamically unfavorable. To break the activity-selectivity trade-off, we propose a conceptually new mechanism of H2O2-triggered CH4 coupling, where the H2O2-derived ·OH radicals are rapidly consumed for activating CH4 into ·CH3 radicals exothermically, which bypasses the endothermic steps of the direct CH4 activation by photoholes and the interaction between ·CH3 and ·OH radicals, affirmed by in situ characterization techniques, femtosecond transient absorption spectroscopy, and density-functional theory calculation. By this pathway, the designed Au-WO3 nanosheets achieve unprecedented C2H6 productivity of 76.3 mol molAu-1 h-1 with 95.2% selectivity, and TON of 1542.7 (TOF = 77.1 h-1) in a self-designed flow reactor, outperforming previously reported photocatalysts regardless of OCM and NOCM pathways. Also, under outdoor natural sunlight irradiation, the Au-WO3 nanosheets exhibit similar activity and selectivity toward C2H6 production, showing the possibility for practical applications. Interestingly, this strategy can be applied to other various photocatalysts (Au-WO3, Au-TiO2, Au-CeO2, Pd-WO3, and Ag-WO3), showing a certain universality. It is expected that the proposed mechanism adds another layer to our understanding of CH4-to-C2H6 conversion.

Tuning Properties of Layered Materials Based on Hexagonal Boron Nitride by Methylation: A Density Functional Theory Study.

In this work, the rational design of optoelectronic properties of two-dimensional materials based on hexagonal boron nitride (h-BN) by functionalization by methyl (CH3) groups is proposed. Using density functional theory, we examine the functionalization of single- or double-layer systems with either CH3 radicals alone or with both CH3 (cations) and chlorine (anions), i. e., under conditions of homolytic or heterolytic splitting of CH3Cl precursor molecules, respectively. Different degrees of methylation (coverages) are considered. The methylation of pure h-BN leads to a reduction of the band gap, while in h-BN/G heterostructures (with methylated graphene layer), methylation increases the band gap. As a consequence, h-BN/G heterostructures offer a high tunability of their optoelectronic properties. To guide possible experiments, vibrational properties and spectra of methylated h-BN and methylated h-BN/G are determined.

Structure, dissociation pathways and thermochemistry of some nitrogen-containing astrophysical molecules: a theoretical study

The structure, relative energies, dissociation pathways and thermochemistry of acetonitrile (CH3CN or methyl cyanide), acrylonitrile (CH2CHCN or vinyl cyanide), propionitrile (CH3CH2CN or ethyl cyanide) and their stable isomers have been studied in detail using density functional B3LYP, B3PW91 and ab initio MP2, QCISD and CCSD(T) methods. Several space missions have already confirmed the abundance of these molecules in different interstellar mediums (ISMs). The existence of related radicals, atoms and molecules are also confirmed using various IR-spectrometric techniques and that may be evolved in solar irradiation in the cold dark core TMC-1 or massive star-forming regions such as Sagittarius B2 or Oion-KL. Possible ways of fragmentation of ground state CH3NC, CH2CHNC and CH3CH2NC through different dissociation channels and their link to other isomers have been considered to justify the presence of such observed radicals in the interstellar cloud. Cyanide(-C≡N), iso-cyanide (-N = C) and imine (-C = N-H) isomeric forms have been considered here and out of these, cyanide isomers are more stable species compared to its iso-nitrile and imine form. Favourable product molecules, such as CH2 radical, C2H2, C2H4 and HCN/HNC, are considered in the dissociation channels.

Theoretical kinetics of H-transfer and β-scission reactions following H-abstraction in n-butylamine during fuel-nitrogen combustion

Aliphatic amines are a significant nitrogenous fuel. To better understand the combustion of n-butylamine (CH3CH2CH2CH2NH2, N), the CBS method was used to compute the potential energy surfaces of the primary H-abstraction of n-butylamine by H, CH3 radicals, and NO2 radicals, as well as the H-transfer and β-scission reactions of n-butylamine radicals. The rate constants for the mentioned reactions were predicted between 300 and 2000 K based on transition state theory (TST) and RRKM theory. The results showed that the abstraction process for the H-atom by the addition of H radicals was more favored by the reaction kinetic. The yield of the cis-HONO by the addition of NO2 is highest. In the subsequent reactions, the breakage of the C–H bond was most competitive between 300 and 800 K, especially the H-transfer of int1 to int5, with the lowest forward energy of 15.81 kcal mol−1. The β-scission reactions became the main pathway for radical consumption with the increase in temperature. Subsequently, the rate constants with temperature and pressure have been fitted by the modified Arrhenius equation. The present work provides a theoretical basis and kinetic parameters for further development of the combustion model of n-butylamine.

Study on combustion mechanism of methanol/nitromethane based on reactive molecular dynamics simulation

Oxygenated fuels and nitro fuels are effective strategies for addressing incomplete combustion by increasing the oxygen-fuel ratio. A computational approach based on reactive molecular dynamics simulations reveals oxidation mechanisms of temperature-induced effects on a mixed fuel of methanol and nitromethane. The method enables the demonstration of the initial reaction scheme of a binary fuel mixture, even for complicated interplay and coupling reactions. The results showed that the first reaction step of nitromethane was homolysis in poor-oxygen conditions, mainly via CH3NO2 → CH3 + NO2 (Net flux = 183, ratio = 92.89%). Methanol undergoes dehydrogenation reaction with the assistance of active radicals (OH, HO2, CH3, NO, and NO2), and the participation rates of these active groups are 60%, 17.14%, 8.57%, 7.62%, and 6.67%, respectively. The decomposition of nitromethane provided NO2 and CH3 radicals and significantly increased the amount of OH and NO via a reaction of NO2 + H → HNO2 → OH + NO. By fragment analysis, the main C1 intermediates are formed by pyrolysis of methanol/nitromethane such as formaldehyde, hydroxymethyl radical, and formyl radical. The CH3OH and CH2O are relatively stable, and the dehydrogenation is mainly highly active groups such as OH and NO. In contrast, the dehydrogenation of CH2OH and CHO free radicals is completed by self-cleavage or with the help of O2, NO2, etc. Our findings shed light on the oxidation behaviors of methanol/nitromethane mixed fuel in combustion.

Water Radiocatalysis for Selective Aqueous-Phase Methane Carboxylation with Carbon Dioxide into Acetic Acid at Room Temperature.

Methane (CH4) carboxylation with carbon dioxide (CO2) into acetic acid (CH3COOH) is an ideal chemical reaction to utilize both greenhouse gases with 100% atom efficiency but remains a great challenge under mild conditions. Herein, we introduce a concept of water (H2O) radiocatalysis for efficient and selective aqueous-phase CH4 carboxylation with CO2 into CH3COOH at room temperature. H2O radiolysis occurs under γ-ray radiation to produce ·OH radicals and hydrated electrons that efficiently react with CH4 and CO2, respectively, to produce ·CH3 radicals and ·CO2- species facilely coupling to produce CH3COOH. CH3COOH selectivity as high as 96.9 and 96.6% calculated respectively from CH4 and CO2 and a CH3COOH production rate of as high as 121.9 μmol·h-1 are acquired. The water radiocatalysis driven by γ-rays is also applicable to selectively produce organic acids from other hydrocarbons and CO2.

Laminar flame speed measurement and combustion mechanism optimization of methanol–air mixtures

AbstractLaminar flame speeds of methanol/air mixtures at 338–398 K are measured by the heat flux method, extending the range of equivalence ratio up to 2.1. And a new optimized methanol mechanism with 94 reactions is proposed by using the particle swarm algorithm, adjusting 20 Arrhenius pre‐exponential factors in their uncertainty domains. The optimized model is compared with eight methanol combustion mechanisms and experimental data published in recent years, covering a wide range of initial temperatures (298–1537 K), pressures (0.04–50 atm) and equivalence ratios (0.5–2.1). The results show that the optimized mechanism not only improves the accuracy of ignition delay time with rapid compression machine at low temperature but also moderately improve the description of laminar flame speed in lean and stoichiometric conditions. Meanwhile, the optimized model significantly enhances the prediction accuracy of CH3 and CH2O radical, and perfectly captures the evolution trend of HCO radical in laminar flat flame. Overall, the optimized mechanism provides the best overall description of the currently available measurements, leading to more accurate and comprehensive prediction of ignition delay time, laminar flame speed and species concentration.