Decomposition Pathways Research Articles

Snag decomposition following stand‐replacing wildfires alters wildlife habitat use and surface woody fuels through time

AbstractHigh‐severity wildfires create pulses of snags that serve a variety of functions as they decompose over time. Snag‐related benefits (and hazards) are often linked to specific decomposition stages, but snag decomposition rates and pathways are not well understood in many forest types. We examined temporal patterns of snag decomposition, wildlife cavity creation, and surface woody fuel dynamics in dry coniferous forests of the interior Pacific Northwest region of North America by sampling 159 forest stands within a 39‐year chronosequence of stand‐replacing wildfires in dry coniferous forests dominated by ponderosa pine and Douglas‐fir. We found that most snags broke or fell during the first 15 years after wildfire; small‐diameter snags mostly broke off at or near ground level, while many large‐diameter snags initially broke off above a height of 2 m and then remained standing for an extended period. Ponderosa pine and lodgepole pine snags fell earlier than Douglas‐fir and true fir snags of comparable diameter classes. Wildlife cavities were most common in stands surveyed 8–20 years after fire and in snags with broken tops but were not limited to large diameter snags. Cavity snag diameters ranged from 17 to 98 cm, with 64% of cavity snags having diameters between 30 and 60 cm and 22% of cavity snags having diameters >60 cm. Surface woody fuels increased as snags broke and fell, reaching maximum levels in all size classes 15–20 years after fire. The percentage of large diameter rotten woody fuels increased steadily beginning about 15 years after fire, with implications for fuel management and subsequent wildfire behavior and severity. Our study supports the proposition that fire‐killed snags represent a transient resource pulse in which the relative contribution of snags to different ecological functions varies with snag diameter, species, time since fire, and landscape position.

Global numerical simulation of chemical reactions in phosphate-buffered saline (PBS) exposed to atmospheric-pressure plasmas

Abstract When a phosphate-buffered saline (PBS) solution is exposed to atmospheric-pressure plasmas generated in air, hydrogen peroxide H 2 O 2 in the solution is known to be decomposed by hypochlorite O C l − , which is formed in the solution from reactions between chlorine ions C l − present in the PBS solution and plasma-generated reactive oxygen species. Global numerical simulations of liquid-phase chemical reactions were performed to identify the reaction mechanisms of H 2 O 2 decomposition by solving known liquid-phase chemical reactions self-consistently. It has been confirmed that the decomposition of H 2 O 2 is indeed mostly due to the presence of O C l − in the solution. However, this study has also found that, in the presence of abundant hydroxyl ( O H ) radicals, the most efficient H 2 O 2 decomposition pathway can be a series of reactions that we call a chlorine monoxide cycle, where O C l − first reacts with O H to generate chlorine monoxide C l O , which then decomposes H O C l , rather than O C l − directly decomposing H 2 O 2 . The chlorine monoxide cycle generates O H as one of its byproducts, so once this cycle is initiated, it continues until either C l O − or H 2 O 2 runs out, as long as none of the intermediates are scavenged by other reactions.

Modelling of NO Reduction on CeO2-Supported Pt and Pd Nanoclusters

ABSTRACT The reduction mechanism of NO to N2 on CeO2-supported Pt and Pd nanoclusters (Pt/CeO2 and Pd/CeO2) is analyzed using density functional theory. Different NO decomposition and N2 formation pathways are evaluated, and the thermodynamically preferable paths are identified. The energy barrier of NO decomposition on Pt/CeO2 indicates that the rate of reaction via metallic cluster sites and the ceria oxygen vacancies are comparable. In contrast, the cluster metallic sites of the Pd/CeO2 induce a lower energy barrier of NO decomposition relative to the oxygen CeO2 vacancy sites. The N2 formation on the Pt/CeO2 preferentially occurs via the N–N association, whereas the N2O deoxidation is energetically preferred on the Pd/CeO2.

Direct C(sp3)-H Acylation by Mechanistically Controlled Ni/Ir Photoredox Catalysis.

ConspectusSynthetic chemists have consistently aimed to develop efficient methods for synthesizing ketones, which are essential building blocks in organic chemistry and play significant roles in bioactive molecules. Recent efforts have focused on using photoredox catalysis, which enables previously inaccessible activation modes, to synthesize ketones through the cross-coupling of an acyl electrophile and simple C(sp3)-H bonds. Over the past few years, we have worked on developing effective and versatile approaches for directly acylating activated hydrocarbons to forge ketones.Initially, thioesters were explored as the acyl source to achieve the direct acylation of ethers, but an unexpected thioesterification reaction was observed instead. To gain insights into this reactivity, we conducted the optimization of reaction conditions, substrate scope evaluation, and mechanistic studies. Drawing from our understanding of Ni/Ir photocatalysis obtained in this study, we subsequently developed a method for the direct acylation of simple hydrocarbons. The use of less-reactive amides as the acyl electrophiles was found to be critical for suppressing undesired pathways. This seemingly counterintuitive reactivity was carefully studied, revealing a substrate-assisted reaction mechanism in which the suppressed oxidative addition leads to early-stage nickel oxidation and C-H activation.To address the drawbacks of this method, which primarily arose from decarbonylative and transmetallative side pathways, we employed N-acyllutidiniums as the acyl electrophile. This prevented undesired decomposition pathways, enabling the use of α-chiral acyl substrates with the retention of their stereochemistry, particularly those derived from α-amino acids. The developed versatile methodology allowed us to access a diverse range of α-amino ketones and their homologues.Despite the elegant utility of Ni/photoredox catalysis in developing new synthetic methodologies, the precise behavior of nickel catalysts under redox conditions is incompletely understood. To gain insight into this behavior and develop new chemical reactions, we used a combination of experimental and computational methods. Our investigations revealed that devised adjustments to the reaction conditions in nickel/photoredox catalysis can result in significant differences in the reaction outcomes, providing chemists with opportunities to tailor reactions through carefully designed mechanistic strategies. We believe that continued efforts to study and apply nickel redox modulation will lead to the discovery of additional organic transformations.

Investigation of the thermal hazard and decomposition mechanism of 1,1-di(tert-butylperoxy) cyclohexane by experiment and DFT simulation

1,1-Di (tert-butylperoxy) cyclohexane (1, 1-DTBCH), as an important organic peroxide, is commonly used as initiator, curing agent and crosslinking agent in the chemical industry. Due to the presence of peroxy bonds, the thermal instability of 1, 1-DTBCH may incur a decomposition reaction and cause further thermal runaway. The thermal decomposition characteristics and runaway reaction characteristics of 1, 1-DTBCH were investigated by differential scanning calorimetry (DSC) and accelerated rate calorimetry (ARC). The kinetic triplet and thermal safety parameters were calculated by using non-isothermal method. The gaseous products and pyrolysis products of 1, 1-DTBCH was investigated by thermogravimetric and infrared spectroscopy (TG-FTIR) and gas chromatography/mass spectrometry (GC/MS). The thermal decomposition pathway of 1, 1-DTBCH was explored with density functional theory (DFT). The exothermic dominant reaction in the thermal decomposition process of 1, 1-DTBCH was explored by combining experiment and theoretical calculation. The corresponding safety control measures were provided to reduce the thermal runaway hazard of 1, 1-DTBCH.

Experimental and theoretical studies on the kinetics of thermal decomposition and decomposition mechanism of CF3I in oxidizing environments

CF3I, as a novel “Halon” replacement fire-extinguishing agent, has the characteristics of low fire-extinguishing concentration, high efficiency, and safety. However, there are still some gaps in its thermal decomposition studies when it is released into the high-temperature fire, so the thermal decomposition of CF3I in oxidizing environments was studied to simulate its diffusive decomposition. The decomposition of CF3I was demonstrated to be accelerated by O2 through experiments in the temperature range of 100°C-800°C in air and N2 atmosphere. The effects of initial concentration, temperature, and residence time on the decomposition rate of CF3I and decomposition characteristics were investigated by tube furnace simulation. The kinetics of thermal decomposition was calculated using the Arrhenius equation in which activation energy Ea is 15.18 kJ/mol and pre-exponential factor (A) is 13.87s−1. Additionally, the thermal decomposition products were examined by GC-MS and FTIR. The experimental results showed that the pyrolysis gas products were mainly CF4, C2F6, and CF2O. Using quantum chemistry and density flooding theory (DFT) calculations, it was concluded that the main decomposition pathway was the reaction of CF3I with singlet oxygen. The reaction pathway of the thermal decomposition of CF3I under a high-temperature fire oxidation environment was proposed based on the products.

Unveiling the reaction mechanism and 1O2 suppression effect of CO2 in Li-CO2/O2 battery through the reacquaintance of discharge products

Li-CO2/O2 battery has been described as an exceptional strategy for CO2 conversion, however, the effect of CO2 is urgently required for development of practical cells. Here, we innovatively unveil the mysterious role of CO2 by comprehensively analyzing the discharge/charge products, the reaction mechanism, the 1O2 yield, and the corrosion of Li anode in batteries. Unlike previous results where Li2CO3 is the sole discharge product, Li2O2 and Li2CO3 are definitely identified as final discharge products of Li-CO2/O2 battery, confirming a chemical reaction between Li2O2 and CO2 during discharge in TEGDME solvent. During charging, CO2 affects the decomposition pathway of Li2O2 by capturing O2•−, thus suppressing the formation of notorious 1O2. Additionally, introduction of CO2 influences the morphology and structure of the discharge products and improves the stability of Li anode. Since the above effects of CO2 are closely related to the CO2/O2 ratio, appropriate CO2/O2 ratio can optimize various effects of CO2 and obtain the best battery performance.

The structural, electronic properties, pressure response and decomposition mechanism of bispentazole (N10) with first principles calculations

Bispentazole (N10) is one of the recently-found full-nitrogen energetic materials, which have remarkable performance in the pursuit of higher energy and greener explosive. Therefore, the structural, electronic properties, pressure response, and decomposition mechanism of four types of N10, namely P21-N10, I-N10, V-N10, and P-N10, are investigated using first-principles calculations. Our results show that all the structures are thermodynamic stability, and P21-N10 and P-N10 are dynamical stability. All N10 structures belong to insulators with indirect band gaps. The results show that the N-N bond on the five-membered cyclic ring, which is on the opposite side of the N-N bond connected to the two five-membered cyclic rings, is relatively weak. From the decomposition pathway of the N10 molecule, it can be observed that the product N2 is gradually separated from two cyclic N5 rings in the molecule. The result demonstrated that the N-N bond in full-nitrogen materials can release energy by breaking of N-N bond to form the stable N2. The calculated three reaction energy barriers means that the decomposition temperature of N10 is lower than that of N8 and N6. Finally, the released energy as 168.0 kcal/mol indicates that the N10 molecule can release a lot of energy when it decomposes.

The Effect of Biochar Addition on Thermal Stability and Decomposition Mechanism of Poly(butylene succinate) Bionanocomposites.

In the present study, poly(butylene succinate) (PBSu) and its bionanocomposites containing 1, 2.5, and 5 wt.% biochar (MSP700) were prepared via in situ melt polycondensation in order to investigate the thermal stability and decomposition mechanism of the materials. X-ray photoelectron spectroscopy (XPS) measurements were carried out to analyze the surface area of a biochar sample and PBSu/biochar nanocomposites. From XPS, it was found that only physical interactions were taking place between PBSu matrix and biochar nanoadditive. Thermal stability, decomposition kinetics, and the decomposition mechanism of the pristine PBSu and PBSu/biochar nanocomposites were thoroughly studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TGA thermograms depicted that all materials had high thermal stability, since their decomposition started at around 300 °C. However, results indicated a slight reduction in the thermal stability of the PBSu biochar nanocomposites because of the potential catalytic impact of biochar. Py-GC/MS analysis was employed to examine, in more detail, the thermal degradation mechanism of PBSu nanocomposites filled with biochar. From the decomposition products identified by Py-GC/MS after pyrolysis at 450 °C, it was found that the decomposition pathway of the PBSu/biochar nanocomposites took place mainly via β-hydrogen bond scission, which is similar to that which took place for neat PBSu. However, at higher biochar content (5 wt.%), some localized differences in the intensity of the peaks of some specific thermal degradation products could be recognized, indicating that α-hydrogen bond scission was also taking place. A study of the thermal stability and decomposition pathway of PBSu/biochar bionanocomposites is crucial to examine if the new materials fulfill the requirements for further investigation for mulch films in agriculture or in electronics as possible applications.

Degradation of ciprofloxacin by persulfate activated by Fe(III)-doped BiOCl composite photocatalyst.

Fe-BOC-X photocatalyst was successfully prepared by solvothermal method. The photocatalytic activity of Fe-BOC-X was determined by ciprofloxacin (CIP), a typical fluoroquinolone antibiotic. Under sunlight irradiation, all Fe-BOC-X showed better CIP removal performance than original BiOCl. In comparison, the photocatalyst with iron content of 50 wt% (Fe-BOC-3) has excellent structural stability and the best adsorption photodegradation efficiency. The removal rate of CIP (10mg/L) by Fe-BOC-3 (0.6g/L) reached 81.4% within 90min. At the same time, the effects of photocatalyst dosage, pH, persulfate, persulfate concentration, and combinations of different systems (PS, Fe-BOC-3, Vis/PS, Vis/Fe-BOC-3, Fe-BOC-3/PS, and Vis/Fe-BOC-3/PS) on the reaction were systematically discussed. In reactive species trapping experiments, electron spin resonance (ESR) signals revealed that the photogenerated holes (h+), hydroxyl radical (•OH), sulfate radical (•SO4-), and superoxide radical (•O2-) played an important role in CIP degradation; hydroxyl radicals (•OH) and sulfate radicals (•SO4-) play a major role. Various characterization methods have demonstrated that Fe-BOC-X has larger specific surface area and pore volume than original BiOCl. UV-vis DRS indicate that Fe-BOC-X has wider visible light absorption and faster photocarrier transfer and provides abundant surface oxygen absorption sites for effective molecular oxygen activation. Accordingly, a large number of active species were produced and participated in the photocatalytic process, thus effectively promoting the degradation of ciprofloxacin. Based on HPLC-MS analysis, two possible decomposition pathways of CIP were finally proposed. The main degradation pathways of CIP are mainly due to the high electron density of piperazine ring in CIP molecule, which is mainly attacked by various free radicals. The main reactions include piperazine ring opening, decarbonylation, decarboxylation, and fluorine substitution. This study can better open up a new way for the design of visible light driven photocatalyst and provide more ideas for the removal of CIP in water environment.

Soil Nematodes of Northern Meadows and Agrocoenoses as Bioindicators of the Transformation Degree in Soil Ecosystems

This paper examines the effect exercised by agricultural intensity on soil nematode communities inhabiting natural meadows, hayfields, and monocrop agrocoenoses in the Republic of Karelia. The diversity of the soil nematode fauna in natural meadows is similar to that in hayfields, but it significantly decreases in agrocoenoses. The abundance of nematodes reaches the highest values in soils of meadows and decreases as land use intensity goes up. Bacterial feeders predominate in the eco-trophic structure of nematode communities in all types of biocoenoses reaching the maximum share in agrocoenoses. The relative abundance of predators and nematodes associated with plants in agrocoenoses is significantly lower compared to natural meadows and hayfields. Ecological indices computed for nematode communities indicate the presence of a stable and multicomponent soil ecosystem in meadows. The CI index reflecting the predominant pathway of organic matter decomposition indicates an active participation of bacteria in the destruction. Values of the SI and CI indices decrease in agrocoenoses, while the EI index increases. Such a ratio between indices specifies simplified food web and a disturbed soil ecosystem in agrocoenoses. Discriminant analysis shows that, of all studied biocoenoses, only agrocoenoses and natural meadows can be differentiated statistically significantly based on differences in the SI index. However, the identified positive effect of latitude on the SI index in agrocoenoses indicates that the application of this parameter to northern ecosystems has some limitations.

Efficient removal of alkali and alkaline earth metals from biodiesel using Ion-exchange resin: Performance and mechanism

Raw materials, production process, and other factors cause several metal ions to exist in biodiesel. Furthermore, the existence of alkali and alkaline earth metals seriously affects the quality and performance of biodiesel. To improve fuel quality, a 732 ion-exchange resin was used to reduce the contents of alkali and alkaline earth metal ions in Jatropha biodiesel. The adsorption efficiency of the ion-exchange resin for alkali and alkaline earth metal ions in biodiesel was evaluated using ion chromatography, while the adsorption mechanism of ion change resin on alkali and alkaline earth metal ions in biodiesel was elucidated via FTIR and XPS. In addition, the effects of ion-exchange resin on several key physiochemical properties of biodiesel, including oxidation stability, corrosivity, heat value and kinematic viscosity, were also explored. The results showed that the total content of alkali and alkaline earth metal ions in biodiesel was reduced by 88.19%, and the K+, Na+, Mg2+, and Ca2+ contents were reduced to 0.11 mg/kg, 0.89 mg/kg, 0.53 mg/kg, and 0.78 mg/kg, respectively, after removing the ion-exchange resin. In the removal process, the hydroxyl group of sulfonic acid group on the ion-exchange resin is broken, and the substitution adsorption reaction between H+ and the alkali and alkaline earth metal ions in biodiesel is carried out. Moreover, the oxidation induction period of biodiesel was prolonged by 40.8% owing to the reduction in the content of alkali and alkaline earth metal ions, which significantly blocked the decomposition pathways of unstable oxidation intermediates in biodiesel. The degree of copper corrosion in biodiesel did not change significantly before and after ion-exchange resin adsorption during short-term corrosion (3 h); however, the copper corrosion grade decreased from 2c to 1b after ion-exchange resin adsorption during long term corrosion (240 h). Nevertheless, the heat value and kinematic viscosity of biodiesel were observed to be independent of the ionic metal content.

Photocatalytic degradation performance and mechanism of tetracycline by Pd-loaded titanium dioxide

The development of effective and environmentally safe photocatalysts for the removal of antibiotics from aquatic environments remains an important issue. In this work, materials with different metal Pd mass loading ratios were prepared by loading TiO2 with noble metal Pd after the introduction of oxygen vacancies. After the photocatalytic degradation of TC, it was found that the 0.5% Pd/TiO2-Vo photocatalyst showed good photocatalytic activity in the degradation of tetracycline, with a degradation efficiency of 95.04% in 2 h and a reaction rate constant 2.18 times higher than that of TiO2. It was found that the introduction of oxygen vacancies and Pd loading could enhance the visible light response to overcome the drawback that TiO2 could only be irradiated by UV while increasing the free carrier density and inhibiting electron-hole recombination to improve its photocatalytic degradation efficiency. Finally, the possible decomposition pathways and degradation products of TC were inferred by combining liquid chromatographymass spectrometry (LCMS). The findings of this work may provide a new approach to improving the photocatalytic activity of TiO2.

Light-Fueled Primitive Replication and Selection in Biomimetic Chemical Systems.

The concept of chemically evolvable replicators is central to abiogenesis. Chemical evolvability requires three essential components: energy-harvesting mechanisms for nonequilibrium dissipation, kinetically asymmetric replication and decomposition pathways, and structure-dependent selective templating in the autocatalytic cycles. We observed a UVA light-fueled chemical system displaying sequence-dependent replication and replicator decomposition. The system was constructed with primitive peptidic foldamer components. The photocatalytic formation-recombination cycle of thiyl radicals was coupled with the molecular recognition steps in the replication cycles. Thiyl radical-mediated chain reaction was responsible for the replicator death mechanism. The competing and kinetically asymmetric replication and decomposition processes led to light intensity-dependent selection far from equilibrium. Here, we show that this system can dynamically adapt to energy influx and seeding. The results highlight that mimicking chemical evolution is feasible with primitive building blocks and simple chemical reactions.

Low-Temperature Oxidation Reaction Processes of Cyclopentanone Unraveled by In Situ Mass Spectrometry and Theoretical Study.

Although cyclopentanone (CPO) is a promising bio-derived fuel, thermodynamic data of its low-temperature oxidation under high-pressure conditions are lacking. In this work, the low-temperature oxidation mechanism of CPO is investigated in a flow reactor in the temperature range of 500-800 K and at a total pressure of 3 atm by a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer. The electronic structure and pressure-dependent kinetic calculations are carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+G(d,p) level to explore the combustion mechanism of CPO. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPO radicals with O2 is HO2 elimination, yielding 2-cyclopentenone. The hydroperoxyalkyl radical (•QOOH) generated by 1,5-H-shifting is easily reacted with second O2 and forms ketohydroperoxide (KHP) intermediates. Unfortunately, the third O2 addition products are not detected. In addition, the decomposition pathways of KHP during the low-temperature oxidation of CPO are further assessed, and the unimolecular dissociation pathways of CPO radicals are confirmed. The results of this study can be used for future research on the kinetic combustion mechanisms of CPO under high pressure.

A detailed chemical kinetic mechanism of 1,1-diamino-2,2-dinitroethylene (FOX-7) initial decomposition in the gas phase

1,1-Diamino-2,2-dinitroethylene (FOX-7 or DADNE) is a promising ingredient of the low-vulnerability propellants. However, one of the major concerns in its further development and applications is the lack of detailed kinetic mechanism for its initial decomposition in the gas phase. In this study, a detailed chemical kinetic mechanism consisting of 38 species and 131 reactions was developed to describe the initial decomposition process of FOX-7. At first, a comprehensive reaction network was established with the aid of reactive molecular dynamics (MD) simulation. Then, the potential energy surfaces (PES) for both unimolecular and bimolecular reactions were identified at the QCISD(T)/CBS//M062X/6-311++G(d,p) level of theory. The rate coefficients were obtained by solving RRKM/ME, and the thermochemical properties of relevant species were calculated at CBS-APNO/G3/G4 levels with the atomization method. Finally, these kinetic and thermochemistry data were processed into a kinetic mechanism and used to simulate the initial decomposition process of FOX-7. The results demonstrated that the H-atom transfer to the beta carbon atom (enamino-imino isomerization) followed by the nitro group elimination dominates the initial decomposition, and the reaction FOX-7 = R3a + NO2 becomes the most significant one under high temperatures (Channel C3). Besides, bimolecular reactions also play a role as the decomposition goes on. Overall, this work provides quantitative predictions of the reaction pathways of gas-phase FOX-7 initial decomposition, and it would serve as a solid foundation for the development of a fully detailed combustion kinetic mechanism for FOX-7.

Thermal Behavior and Decomposition Pathway for Nitrophenols and Sodium Nitrophenolates

Nitrophenols and corresponding sodium nitrophenolates are the main side products in the production of mononitrobenzene (MNB). These side products are hazardous due to their thermal instability nature. In this article, the thermal decomposition behaviors of nitrophenols and sodium nitrophenolates were first characterized by differential scanning calorimeter and accelerating rate calorimetry techniques. Then, the influence of phenol and sodium phenolate on the thermal decomposition of MNB was studied to clarify the effect of phenolic hydroxyl groups on the thermal stability of nitrophenols. It was found that compared to nitrophenols, the exothermic peaks of sodium nitrophenolates were more intense and presented strongly autocatalytic features. Sodium phenolate could significantly decrease the decomposition temperature of MNB. Aniline was detected as the unique product in the decomposition processes of pure MNB and MNB/sodium phenolate mixtures, and the nitrosobenzene was verified as the intermediate product. It was experimentally proven that sodium phenolate could catalyze the decomposition of nitrosobenzene (the decomposition intermediate of MNB). The violent decomposition of sodium nitrophenols was caused by the intermolecular catalysis effect of phenoxy groups.

Efficiently activating peroxymonosulfate by CoFe-LDHs/MoS2 for rapid degradation of tetracycline

A series of CoFe-LDHs@MoS2-x (x = 0.1, 0.2 and 0.5) samples were successfully synthesized to activate peroxymonosulfate (PMS) for tetracycline (TC) removal. With the introduction of MoS2 could promote the catalytic performance via accelerating the Fe2+/Fe3+ and Co2+/Co3+ cycle. About 98.8 % of TC could be removed over 12 min under a neutral condition in the CoFe-LDHs@MoS2-0.2/PMS system, which was 4.4 times higher than that of CoFe-LDHs/PMS system. The main reactive oxygen species (ROS) in CoFe-LDHs@MoS2-0.2/PMS system were also explored by using quenching and free radical capture experiments. The singlet oxygen (1O2) played a major role for the TC removal. Besides, the decomposition pathways of TC were deduced by UPLC-QTOF/MS, and the stability of catalysts had also been studied. This work provided theoretical and experimental basis for designing and preparation more effective heterogeneous catalysts for PMS activation.

Investigation of thermal decomposition of nitrobenzene: An energetic material

Oxidation and pyrolysis mechanisms of energetic materials shape their macro properties such as autoignition and detonation. The high reaction-enthalpy, microsecond order reaction time, and toxicity necessitate investigation of their detailed chemical kinetics. A shock tube combined with laser absorption diagnostic provides time-resolved, high-sensitivity, and homogeneous environment to study thermal degradation of energetic and hazardous materials. In this work, we investigated the thermal fragmentation of nitrobenzene (C6H5NO2), a prototypical energetic material and nitro-aromatic representative, behind reflected shock waves. We studied its pyrolysis and decomposition branching channels over temperatures of 1155–1434 K and pressures of 0.82–1.78 bar. Channel-specific branching ratio was determined by employing a two-color laser absorption diagnostic. Two decomposition pathways are found to be significant under our experimental conditions. The first channel (k1) produces phenyl radical (C6H5) and NO2 while the second channel (k2) generates phenoxy radical (C6H5O) and NO. We monitored the reaction progress by tracing channel-specific products, i.e., phenyl radical (C6H5) and NO, using ultraviolet–visible (UV–vis) and infrared (IR) absorption diagnostics. UV–vis light at 445 nm for phenyl radical detection came from the frequency doubling of 890 nm light, generated by a titanium–sapphire laser, which was pumped by a green (532 nm) Nd:YAG laser. IR light at 5.517 μm for NO detection was generated by an external-cavity quantum cascade laser. We extracted the rate coefficients of the two decomposition channels and fitted them in Arrhenius form (units of s−1):k1=8.49×1014exp(−30476KT)k2=2.31×1013exp(−27618KT)Rate coefficients of both channels show positive temperature dependence while we did not observe discernible pressure dependence over 0.82–1.78 bar. Our measurements agree with a previous theoretical work qualitatively that, under these high-temperature conditions, the decomposition channel producing phenyl radicals and NO2 (k1) prevails over the NO-producing channel. Quantitatively, however, the theoretical work overestimates the importance of k1 channel, particularly at low temperatures. Our rate of production analysis shows that most of the phenyl radicals are consumed through their self-recombination while N atoms are mainly converted to NO2. This work benefits high-fidelity chemical modeling of the relevant safety and ignition aspects of nitrogen-containing energetic/hazardous materials.

Chemical Reaction Networks Explain Gas Evolution Mechanisms in Mg-Ion Batteries.

Out-of-equilibrium electrochemical reaction mechanisms are notoriously difficult to characterize. However, such reactions are critical for a range of technological applications. For instance, in metal-ion batteries, spontaneous electrolyte degradation controls electrode passivation and battery cycle life. Here, to improve our ability to elucidate electrochemical reactivity, we for the first time combine computational chemical reaction network (CRN) analysis based on density functional theory (DFT) and differential electrochemical mass spectroscopy (DEMS) to study gas evolution from a model Mg-ion battery electrolyte─magnesium bistriflimide (Mg(TFSI)2) dissolved in diglyme (G2). Automated CRN analysis allows for the facile interpretation of DEMS data, revealing H2O, C2H4, and CH3OH as major products of G2 decomposition. These findings are further explained by identifying elementary mechanisms using DFT. While TFSI- is reactive at Mg electrodes, we find that it does not meaningfully contribute to gas evolution. The combined theoretical-experimental approach developed here provides a means to effectively predict electrolyte decomposition products and pathways when initially unknown.