Decomposition Mechanism Research Articles

Inverse kinetic isotope effect of ammonia decomposition over Ru/CeO2 using deuterated ammonia.

This study investigated the ammonia decomposition mechanism over Ru/CeO2. Isotopic tests using ND3 revealed that the rate-determining step involves adsorbed nitrogen atoms on Ru. Moreover, an inverse kinetic isotope effect where ND3 decomposition was faster than NH3 was clearly observed. The origin of the inverse effect was explained by the lower D coverage on the catalyst surface compared to H coverage for mitigating the inhibition of ND3 activation.

Evaluating the thermal stability of chemicals and systems: A review

AbstractIn the realm of chemical processing, particularly at the industrial scale, safety is of utmost importance. A predominant factor causing accidents within the chemical industry is runaway phenomena, primarily initiated by uncontrolled exothermic reactions. This review critically examines the often‐overlooked decomposition mechanisms as a significant contributor to thermal energy release, necessitating a comprehensive revision and understanding of both experimental and theoretical strategies for assessing thermal degradation. Key to this discourse is the explication of calorimetry as the principal experimental technique, alongside ab initio quantum chemistry simulations as a robust theoretical framework for quantifying the most relevant properties. However, more than mere cognisance of these methodologies is required for a meticulous thermal stability assessment. The review emphasizes identifying and quantifying fundamental parameters through experimental and theoretical investigations. Only upon acquiring these parameters, including kinetic, thermodynamic, onset, and peak characteristics of the exothermic decomposition reactions, can one effectively mitigate risks and hazards in designing and optimizing chemical processes and apparatus. Furthermore, this review delineates qualitative and quantitative methodologies for hazard assessment, proffering strategies for estimating safe operational conditions and sizing relief devices. The paper culminates in exploring future trajectories in thermal stability assessments, focusing on emerging applications in lithium‐ion batteries, electrolyzers, electrified reactors, ionic liquids, artificial intelligence and machine learning approaches. Thus, the paper underlines the evolving landscape of thermal risk management in contemporary and future chemical industries.

The impact of struvite presence on the thermal decomposition of sewage sludge, including formation of NOx emissions

Monoincineration of sewage sludge (SS) is becoming a prevailing type of SS treatment due to its contamination and the ability to achieve enriched concentration of valuable inorganics in the end ash. In order to improve the recovery potential, particularly of inorganic, phosphorous (P) bearing species, thermal transformations of organic as well as inorganic SS compounds have to be considered. While important gains in predictive capability have already been made through extensive description of organic part decomposition, P is mostly present in the inorganic part of SS, together with notable amount of nitrogen (N). Current models consider these species in a simplified manner, making the ability to predict P and N fate during thermal treatment limited. The present work focuses on development and implementation of a one step reaction kinetics mechanism for struvite, a common P and N bearing compound in SS, which also presents an important route for P and N recovery. The new mechanism is implemented into an existing SS organic fraction decomposition mechanism and validated using 0D multiphase reactor simulations in Chemkin software. Results reveal up to 10 s faster temperature increase and decomposition of SS with the presence of struvite due to emission of NH3 and H2O occurring already from 350 °C onwards. The NH3 emissions are especially important as they lead to higher NOx formation. The work presents large potential for improving thermal decomposition prediction as well as emission mitigation strategies if struvite is included in the thermal decomposition models of SS. The developed methodology allows efficient implementation of also other P and N bearing species in the inorganic part of kinetic mechanism.

Study on the mechanism of Na2CO3-roasting decomposition for water leach residue

In the process of treating cerium fluorocarbon-cerium lanthanide mixed rare earth concentrates by sulfuric acid roasting method, a large amount of waste leach residue containing iron, rare earths and phosphorus produced by flood neutralization needs to be solved urgently. In this paper, sodium carbonate roasting decomposition was used to treat the water leach residue, in which iron and rare earths were transformed into oxides, and the phosphorus was transformed into sodium phosphate. The main reactions and thermodynamic mechanisms of the roasting decomposition process were investigated by thermogravimetric analysis, phase analysis and chemical analysis. When the mass ratio of sodium carbonate to water leach residue is 1.5:1, the roasting temperature is 700 °C, and the roasting time is 1.5 h, the leaching rate of phosphorus with the roasted product reaches more than 98%. Meanwhile, the phase of the roasted product after washing mainly consists of iron oxide and rare earth oxides. The combination of sodium carbonate roasting decomposition and water leaching is effective for the treatment of water leach residue, which provides an experimental and theoretical basis for solving the problem of environmental and resource waste caused by the accumulation of a large amount of water leach residue. In addition, because sodium carbonate can achieve the separation of iron and phosphorus, this method also has certain reference value for the recovery and utilization of iron phosphate in lithium iron phosphate battery waste.

Bulk or supported tungstophosphates? Antioxidant and antimicrobial activities following pesticide removal

The study evaluates caesium, potassium, silver, and zinc tungstophosphates synthesized in bulk and Y zeolite-supported forms through a two-step process. Spectral investigation reveals the impact of cation size on tungstophosphates formation. The large cations form ion-ion interaction with the Keggin ion, while smaller cations form hydrogen bonds between the cation hydration sphere and terminal oxygens in the Keggin ion. Supported salts formation proceeds without Keggin ion distortion. Zeta potential showed the absence of particle aggregation for caesium and potassium tungstophosphate. Nicosulfuron removal by the supported salt exhibits enhanced retention, with the exception observed for zinc tungstophosphate suggesting a decomposition mechanism. Antimicrobial evaluations reveal silver salt's potency, especially in zeolite-supported form, emphasizing the role of zeolite support. In the presence of pesticide molecules, the antimicrobial activity of salts lowers, with the exception seen for fungus strain. The antioxidant assessments demonstrate superior inhibition for insoluble bulk salts, with caesium tungstophosphate exhibiting the highest inhibition, while supported silver salt enhances bulk salt performance. The presence of pesticides affects both antimicrobial and antioxidant activities, while a complex relationship with radical scavenging ability in bulk and supported salts is independent of their pesticide adsorption capacities. The study broadens the range of the versatile applications of tungstophosphates, highlighting their specific interactions with pesticides and their impact on bioactivity and environmental remediation.

Preparation of Zn-Co Bimetallic Catalysts and Their Catalytic Properties for Thermal Decomposition of Ammonium Perchlorate.

This research delves into the preparation of heteronuclear bimetallic catalysts and explores their catalytic properties in the thermal decomposition of ammonium perchlorate (AP). The study's central focus is on enhancing the thermal decomposition characteristics of AP and, consequently, the combustion performance of composite solid propellants. The synthesized materials underwent structural characterization by XRD, XPS, SEM, and FTIR. Catalytic properties were examined using DTA tests. Notably, catalysts derived from calcination at 500 °C exhibited heightened catalytic activity. They advanced the pyrolysis temperature by 135.4 °C and reduced the activation energy by 82.38 kJ/mol compared with pure AP. To further elucidate the decomposition mechanism of AP, the investigation also employed a combined approach involving DSC-TG-FTIR-MS analysis.

Statistical Copolymerization-Induced Self-Assembly.

Statistical copolymers have been extensively used in chemical industries and our daily lives, owing to their ease of synthesis and functionalization. However, self-assembly based on statistical copolymers has been haunted by high interfacial energy, poor stability, and low concentration. We proposed the statistical copolymerization-induced self-assembly (stat-PISA) as a general strategy for one-step preparing stable statistical copolymer assemblies with high solids content. The concept was demonstrated through a model dispersion polymerization system comprising a charged hydrophilic monomer and a core-forming monomer, producing spherical micelles via a spinodal decomposition mechanism with an interconnected network intermediate. The stat-PISA was tunable by varying the fraction of charged monomer, the polymer chain length, and the solids content. The statistical copolymer micelles were demonstrated to be a potential Pickering emulsifier with superior stabilizing performances compared to their block copolymer counterparts. The general applicability of stat-PISA was demonstrated by preparing statistical copolymer assemblies with varying surface charges and chemical compositions. Particularly, this strategy is feasible for conventional free radical polymerization, promising for industrial scale-up.

Impact of regioisomerism on unimolecular decomposition reactions of energetic materials: Quantum chemistry modeling of ICM-103 and NAPTO

Energetic regioisomers usually behave different physicochemical properties, and the thermal decomposition mechanism might also be different. In this work, the unimolecular decomposition reactions of two novel energetic isomers, ICM-103 and NAPTO, were investigated through quantum chemistry calculations to reveal the decay mechanism of energetic regioisomers. The molecular properties were first explored to reveal their differences in the molecular properties of ICM-103 and NAPTO. Then, six initial decomposition channels were obtained, including N2 release of azide group, H transfer, O transfer, nitro dissociation, nitro-nitrite isomerization, and ring-opening reaction. Thermochemistry results show that the most possible decay reaction is the cleavage of NN bonds of azide group to generate N2, and the energy barrier of ICM-103 is lower than that of NAPTO, which is consistent with the conclusion that NAPTO is more stable form the experiment. Specially, two molecules react differently, and a sequential N2 loss is expected in one, and N2O loss in the other is almost lost in the clutter. Besides, the nitro dissociation, nitro-nitrite isomerization, and ring-opening reaction energy of ICM-103 are also lower than that of NAPTO. However, for the other same reaction, the energy barrier of ICM-103 is higher than that of NAPTO. These findings in the initial decomposition pathways of ICM-103 and NAPTO could gain more understanding of the effect of regiochemical control on the thermal stability of energetic materials.

Thermal stability and pyrolysis mechanism of decamethyltetrasiloxane (MD2M) as a working fluid for organic Rankine cycle

The thermal stability of working fluids is a crucial property studied in the selection of organic Rankine cycle fluids, as they may undergo decomposition at elevated temperatures. In previous studies, siloxanes have been identified as promising choices for ORCs. However, research on the thermal stability of siloxanes in ORCs has been relatively limited. This study investigates the thermal stability and pyrolysis mechanism of MD2M through a combination of experiment, DFT simulation, and ReaxFF-MD calculation. The experiment revealed that MD2M exhibits poor thermal stability, with a decomposition rate of approximately 1.82 % at 200 °C in 72h. Consequently, it is unsuitable for operating in ORCs at temperatures of 200 °C and above. The primary gas products in the pyrolysis of MD2M include CH4, C2H6, C2H4, CO, and CO2, among others. ReaxFF-MD and DFT elucidated the thermal decomposition mechanism of MD2M. The Gibbs free energy barriers for Si–C bond cleavage reactions are relatively lowest, measured at 352.98 and 341.33 kJ mol−1, respectively. Simultaneously, methylation of the terminal Si atom is likely to represent the primary reaction pathway for the initial decomposition.

Effect of water on formic acid and formaldehyde decomposition on the TiO2 (110) surface

The catalytic and photocatalytic performance of TiO2 in air pollutant degradation is significantly influenced by the adsorption of water. Here, we explore the molecular mechanism of formic acid and formaldehyde decomposition and their interaction with water on the TiO2 (110) surface, employing density functional theory (DFT) calculations and reactive molecular dynamics (RMD) simulations. RMD simulations indicate that due to the competitive adsorption of water at the surface Ti site, formic acid predominantly exists in a monodentate dissociative adsorption form on the TiO2 (110) surface. Moreover, on the TiO2 (110) surface, water molecules inhibit the adsorption and dissociation of formic acid, but they facilitate that of formaldehyde, forming methanediol (*CH2OHO) and dioxymethylene (*CH2O2). DFT calculations suggest that the formation pathway of *CH2OHO or *CH2O2 is energetically favorable, but the formation of formate is difficult. This contrasts with the adsorption of formaldehyde on the anatase surface, where formate species are formed.

Thermal decomposition kinetics and spectral analysis of mixed ester propellants

Mixed ester propellants are extensively used in artillery weapons due to their superior mechanical properties. This study investigates the decomposition kinetics and mechanism of mixed ester propellants using Differential Scanning Calorimetry (DSC) and Thermogravimetry-Fourier Transform Infrared Spectroscopy-Mass Spectrometry (TG-FTIR-MS). Kinetic parameters were determined via a model-free approach, while laser diagnostic technology captured radicals and molecular fragments during the decomposition-combustion process. Results indicate a single exothermic peak during decomposition, with apparent activation energy (Ea) increasing initially (0.01 ≤ α ≤ 0.4) and stabilizing around 278.43 kJ/mol later. The thermal decomposition behavior of mixed ester propellants follows the Sestak-Berggren equation, consistent with an autocatalytic reaction. NO2 generated during decomposition acts as a catalyst, accelerating the decomposition process. CN* radicals were detected throughout the combustion stages, indicating the resilience of the CN bond against breaking. This study can provide a theoretical basis for predicting fire development and for the selection or design of fire sensors.

Mechanism insight into the conversion between COS and thiophene during CO2 gasification of carbon-based fuels

Thiophene is the organic sulfur with good thermal stability in carbon-based fuel, clarifying the conversion mechanism between thiophene and COS is beneficial for achieving in-situ sulfur fixation during CO2 gasification of carbon-based fuels, but the mechanism has rarely been reported. Therefore, calculations based on density functional theory were performed and 16 reaction paths were proposed in this research, clarifying the decomposition mechanism of thiophene and re-fixation mechanism of COS. The attachment of CO2 will lead to the destruction of the thiophene ring and the generation of COS, and CO2 adsorption is the rate-determined step, while the carbon atom that adjacent sulfur atom is the reaction active site. However, the energy barriers of CO2 addition reactions are lower than those of CO2 adsorption reactions, and the energy barrier of reactions occurring on the aliphatics are lower than that occurring on the aromatics. The combination of CO2 and thiophene will thermodynamically lead to the generation of COS and CO. Moreover, gaseous sulfur generated from thiophene decomposition will be converted mutually, while H2S will not be converted into COS. Furthermore, COS will be captured by char, forming solid organic sulfur. The re-fixation of COS will occur on aliphatic chains from the decomposition of aromatics.

Synthesis and characterization of new 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (MMTP) Schiff base for spectrophotometric detection of iron(III) and copper(II) ions in laboratory and different water samples: A biological and molecular docking exploration

New spectrophotometric techniques were introduced for the determination of Fe(III) and Cu(II) in many different analyzed samples. The concentrations of Fe(III) and Cu(II) ions were measured in the existence of a novel Schiff base (Z)-6-(3-mercapto-5-methyl-4H-1,2,4-triazol-4-ylimino)-2-thioxotetrahydropyrimidin-4(1H)-one (MMTP). The new chelates were formed rapidly at the room temperature at 510 and 550 nm in presence of triton X-100 and CPB surfactants for Fe(III) and Cu(II), respectively. Linear calibrated graphs were obtained at concentration ranges of 1.0–130 µg mL-1 for Fe(III) and 0.5–90 µg mL-1 for Cu(II). LOD were calculated to be 1.05, 1.98 µg mL-1 and LOQ were 3.18 and 6.02 µg mL-1 for Fe(III) and Cu(II), respectively. A large number of foreign ions were not interfering in the present method. The stoichiometric composition of the chelates was studied by molar ratio and job´s methods to be found 1:2 (metal ion: ligand) ratio. The Fe(III) and Cu(II) solid chelates were prepared and characterized using IR, UV–Vis., 1HNMR , 13CNMR TG-DTG, and XRD spectroscopy. The IR spectral revealed that MMTP chelated as a bidentate ligand via NO atoms. Thermal analysis revealed the decomposition mechanism of MMTP and its chelates. A suggested octahedral geometry encompasses all of the chelates. The UV–visible spectra and magnetic moment analyses confirm the octahedral geometrical geometries. The band gap (Eg) values are 1.53 and 1.56 for Fe(III) and Cu(II) respectively. The smallest band gaps imply that these chelates are semiconductors belonging to solar materials. The in-vitro antioxidant activity of the individual chelates was evaluated using the DPPH radical scavenging assay. All compounds showed antioxidant activity with IC50 values of 0.316, 0.186 and 0.124 mg/mL for MMTP, Fe(III) and Cu(II), respectively. MMTP and its chelates were tested for their antimicrobial activity against various types of bacteria and fungi using the disc diffusion method. The Cu(II) complex showed the greatest biological activity.

Controllable decomposition/recrystallization of water-sensitive CsPbBr3 glass ceramics for dynamic anti‐counterfeiting with high security

Due to the sensitivity to water, the all-inorganic CsPbBr3 nanocrystals have been widely applied in information encryption with spatial dimensions. However, the absence of time-dimension information limits the information capacity for the application of CsPbBr3. In this work, the CsPbBr3 nanocrystal was combined with water-sensitive borophosphate glass, achieving decomposing/recrystallization of CsPbBr3 nanocrystal with multi-dimension. The addition of SiO2 confirms that the collapse of the borophosphate glass network structure causes the exposure of the CsPbBr3 nanocrystals. The decomposition and recrystallization mechanism of CsPbBr3 nanocrystals in glass-ceramics upon encountering water has been verified. Finally, an information encryption strategy, using the mixture of CsPbBr3 glass ceramic and sodium carboxymethylcellulose as ink, is designed via adopting screen-printing technology, which not only provides a new idea for the preparation of CsPbBr3 nanocrystals, but also establish a new avenue for the information encryption technology.

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid (MA) derivatives has been studied with focus on two key mechanisms analysing their energy barrier diagrams using the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for MA, monomethyl Meldrum’s acid (MMA), dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. The barrier to initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found to be endothermic requiring activation energies (∼180 – 230 kJ/mol) at decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. Transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Calculation of the Structure and Reaction Potential Barrier of the Decomposition Products of SF6/N2 Mixed Gases

Abstract The greenhouse effect caused by SF6 gas in the power system cannot be ignored, and N2 has enormous industrial potential to replace pure SF6 by mixing with SF6 due to its advantages of low environmental pollution, low price, and stable chemical performance. This article combines density functional theory (DFT) and transition state theory (TST) to calculate the molecular structure and vibrational frequency information of various reactants, products, and transition states involved in SF6/N2 gas mixtures containing water and oxygen. The single point energy of each component is calculated using the CCSD (T)/cc pvtz theory level, and all reaction barrier energies are obtained. The calculated molecular structure and vibration frequency results are in good agreement with the experimental data of NIST, proving the reliability of the calculation method in this paper. The difficulty of the reaction can be determined by obtaining all the reaction barrier energies. It was found that SF5 molecules are unstable and prone to decomposition. SF4 is very important in the SF6/N2 reaction system, and further decomposition will produce a large number of stable by-products. The calculation method in this article helps to deeply understand the decomposition reaction mechanism of SF6/N2 mixed gas, and is of great significance for the research of decomposition experiments.

Investigation of phase separation mechanism in AlCoCrFeMo0.05Ni2 high-entropy alloy by first-principles calculations

AlCoCrFeMo0.05Ni2 high-entropy alloy (HEA) has great potential for high-temperature applications. However, its FCC matrix will decompose during annealing, which seriously limits its high-temperature applications. Here, the lattice distortion, Gibbs free energy change, phonon spectra, density of states, and bond length distribution of the FCC matrix were calculated by first-principles calculations. The findings indicate that the primary barrier to the formation of a single homogeneous solid solution in the alloy is more closely associated with Gibbs free energy rather than the degree of lattice distortion. The vibration frequency of Al is not in sync with the overall structure, making it prone to desolvation at elevated temperatures. Furthermore, an analysis of bond lengths reveals that the Al–Ni bond length is significantly shorter than the theoretical value, facilitating the formation of a (Ni, Al)-rich phase. In contrast, the longer bond lengths of Al–Cr and Al–Mo facilitate the detachment of Cr and Mo from the (Ni, Al)-rich phase, resulting in the formation of (Cr, Mo)-rich phase. This in-depth investigation sheds light on the phase decomposition mechanism of high-entropy alloys, offering valuable insights for future research in this field.

Volatile matter characterization of birch biochar produced under pressurized conditions

The volatile matter (VM) content and composition of birch biochars produced at 320 °C under elevated pressure (0.1–11 MPa) and constant pressure or constant volume reactor conditions were characterized by thermogravimetry/mass spectrometry (TG/MS) and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). Some of the thermal properties of the biochars and the composition of the VMs varied as a function of the maximal pressure applied during carbonization. The samples prepared at higher pressures released more volatiles up to 320 °C, while the maximal rate of thermal decomposition at around 440 °C showed decreasing tendency with the carbonization pressure. In terms of VM composition, the most apparent effect was the significant increase of the amounts of apoallobetulins from biochars prepared at elevated pressures, which were formed by dehydration, ring closure and rearrangement from the betulin content of birch. The change in the ratio of the evolved guaiacol and 4-methylguaiacol as well as that of syringol and 4-methylsyringol as a function of the maximal pressure of carbonization indicated a modification of the lignin decomposition mechanism.

Kinetic modelling of non-equilibrium plasma enhanced catalytic ammonia decomposition

It is important for the usage of ammonia as energy carrier to achieve ammonia decomposition at low temperature. In the present study, a reactor model of plasma catalytic ammonia decomposition over Fe catalyst at atmospheric pressure is developed in the aspect of plasma and chemical synergies kinetics. The plasma catalytic model accounted for multiple physical mechanisms in electronic and vibrational plasma kinetics and detailed ammonia decomposition mechanisms on the catalyst surface. In addition, a novel view that identify the surface chemisorption enhancement by plasma attributed to charge transfer via EMSI (electronic metal-support interaction) effect is highlighted. The result shows that the synergetic effect of plasma and thermal-catalyst is much greater than that of plasma or catalyst alone on ammonia decomposition, especially at low temperature. It is revealed that the surface desorption of nitrogen is still the rate-limiting step. Moreover, the numerical results also indicate that Langmuir-Hinshelwood reaction via 2 N(s)=>N2 is more likely to dominate the surface desorption of nitrogen in the presence of plasma rather than Eley-Rideal reaction via N + N(s)=>N2. At low electric field, there are infrequent free radicals (NH2, NH and N) and few vibrational ammonia (NH3(v)) generated by the plasma, thus considering that the adsorbed ammonia only undergoes a three-step dehydrogenation reaction. As a consequence, the rate of surface nitrogen desorption with plasma is greater than that with catalyst alone since plasma promotes the chemisorption process of ammonia. This work provides new fundamental insights into the synergistic effect of plasma and catalyst, as well as the direction for the ammonia decomposition catalyst design in plasma.

The growth-promoting and disease-suppressing mechanisms of Trichoderma inoculation on peanut seedlings.

Trichoderma spp. is known for its ability to enhance plant growth and suppress disease, but the mechanisms for its interaction with host plants and pathogens remain unclear. This study investigated the transcriptomics and metabolomics of peanut plants (Arachis hypogaea L.) inoculated with Trichoderma harzianum QT20045, in the absence and presence of the stem rot pathogen Sclerotium rolfsii JN3011. Under the condition without pathogen stress, the peanut seedlings inoculated with QT20045 showed improved root length and plant weight, increased indole acetic acid (IAA) production, and reduced ethylene level, with more active 1-aminocyclopropane-1-carboxylate acid (ACC) synthase (ACS) and ACC oxidase (ACO), compared with the non-inoculated control. Under the pathogen stress, the biocontrol efficacy of QT20045 against S. rolfsii was 78.51%, with a similar effect on plant growth, and IAA and ethylene metabolisms to the condition with no biotic stress. Transcriptomic analysis of peanut root revealed that Trichoderma inoculation upregulated the expression of certain genes in the IAA family but downregulated the genes in the ACO family (AhACO1 and AhACO) and ACS family (AhACS3 and AhACS1) consistently in the absence and presence of pathogens. During pathogen stress, QT20045 inoculation leads to the downregulation of the genes in the pectinesterase family to keep the host plant's cell wall stable, along with upregulation of the AhSUMM2 gene to activate plant defense responses. In vitro antagonistic test confirmed that QT20045 suppressed S. rolfsii growth through mechanisms of mycelial entanglement, papillary protrusions, and decomposition. Our findings highlight that Trichoderma inoculation is a promising tool for sustainable agriculture, offering multiple benefits from pathogen control to enhanced plant growth and soil health.