Decomposition Rate Constants Research Articles

Photocatalytic degradation of organophosphorus pesticide (terbufos) in aqueous solutions using 3D-printed TaSe2/g-C3N4 nanocomposites

The combination of transition metal dichalcogenide of TaSe2 with a composite of graphitic carbon nitride (g-C3N4) and 3D printing technology enhanced the photocatalytic degradation of organophosphorus pesticide, terbufos from aqueous solutions using the 3D-printed TaSe2/g-C3N4 nanocomposites. The 3D-printed TaSe2/g-C3N4 composites efficiently degrade terbufos upon exposure to UV light, reaching more than 95% degradation of 10 ppm terbufos with a decomposition rate constant of 0.3305 min-1. This rate is 37% more enhanced than that of TaSe2/g-C3N4 (0.2409 min-1) and 57.98% more than that of g-C3N4 (0.2092 min-1). Under visible light, terbufos degradation was achieved in 90 min at a slower rate of 0.0492 min−1, and 6.72 times less efficient than under UV light, emphasizing the superior efficiency of UV light for this system. Additionally, the mechanism, degradation pathway, and reusability of the materials are explored, underscoring the potential of 3D-printed TaSe2/g-C3N4 as a potential nanocomposite for photocatalytic applications.

Unraveling Chain Branching in Cool Flames.

In cool flames, autoxidation of organic compounds forms alkyl hydroperoxides and ketohydroperoxides, and this controls the critical rate of chain branching, but there have been large uncertainties in the decomposition rate constants. We synthesized a series of hydroperoxides and measured their decomposition rate constants in pyrolysis experiments by spray-vaporization jet-stirred-reactor synchrotron vacuum ultraviolet photoionization mass spectrometry. Structural variation of the hydroperoxides, including alkyl, cycloalkyl, aromatic, and heterocyclic functionalities, has only a slight effect on their decomposition rate constants. Calculated rate constants are in good agreement with the experiment. The rate constant of ketohydroperoxide decomposition was obtained by theoretical calculation of 3-hydroperoxy butanal and tested by the pyrolysis of synthesized 3-hydroperoxy-3-phenylpropionate. The rate constant of ketohydroperoxide decomposition is close to that of alkyl hydroperoxides. The new chain-branching rate constants improves the cool-flame kinetic model, which is essential for removing discrepancies in model predictions and for the design of high-efficiency and low-emission engines.

Adsorption and decomposition of perfluorinated compounds using NiSBA-15 and CuSBA-15 catalysts for greenhouse gas reduction

BackgroundThe persistence of the environmental effects of perfluorinated compounds (PFCs) and fluorinated compounds (FCs) has raised concerns due to their widespread use and long-term impact on ecosystems and human health. MethodsIn this study, we investigated the use of NiSBA-15 and CuSBA-15 catalysts for the adsorption and decomposition of PFCs/FCs (CF₄, SF₆, NF₃, C₃F₈, and C₄F₈) by varying parameters such as weight percentage and contact time. The catalysts were synthesized through an impregnation method with stirring at 300 rpm for 24 h, followed by calcination at 550 °C for 6 h. The catalytic decomposition of NF₃ was conducted using a glass reactor with precise flow rate control and FT-IR monitoring. Variations in acid concentration during synthesis led to structural changes, transitioning from elongated rods to doughnut-like shapes and eventually spherical structures. Impregnation with nickel and copper nitrates successfully modified SBA-15, forming NiSBA-15 and CuSBA-15, as confirmed by HR-TEM images displaying black spots. Catalytic PFC decomposition experiments using unmodified SBA-15 showed limited efficiency, achieving only 15 % NF₃ removal at 500 ppm and 500 °C over 1000 min. Subsequent modification with nickel and copper significantly improved NF₃ removal efficiency. Significant ResultsCuSBA-15 exhibited superior performance compared to NiSBA-15, reaching a remarkable 95 % removal efficiency of NF3. Kinetic analysis using a pseudo-first-order reaction model demonstrated the enhanced catalytic efficiency of the modified SBA-15 catalysts, with increased reaction rate constants (K) for NF3 decomposition. This study reveals the potential of NiSBA-15 and CuSBA-15 catalysts for the adsorption and decomposition of specific PFCs/FCs, offering valuable insights into the underlying mechanisms and practical applications of these catalysts.

Synchrotron vacuum ultraviolet photoionization mass spectrometry and modeling study of iso-octane low temperature oxidation at varied pressures

Because of its excellent anti-knock properties, iso-octane has been selected as the main component of gasoline surrogates, and a thorough understanding of its low temperature oxidation process is essential for the development of kinetic models. Although iso-octane has been studied for decades, a comprehensive understanding of its low temperature oxidation chemistry has not been realized, and kinetic models were not well developed. In this work, the previously developed, variable pressure jet-stirred reactor-synchrotron vacuum ultraviolet photoionization mass spectrometry system was used to study the low temperature oxidation of iso-octane at five bar, with an initial fuel mole fraction of 0.01, residence time of 2 s, and equivalence ratio of 0.25. Dozens of oxidation intermediates were qualitatively and quantitatively analyzed, helping to reveal the low temperature oxidation reaction processes of iso-octane and examine the kinetic models. Comparing iso-octane studies at high pressure in the literature, a highly detailed species pool was probed, which included H2O2, carbonyl acids, alkyl hydroperoxides, and keto-hydroperoxides (KHP). By combining the atmospheric pressure data in the literature, the recently developed model of iso-octane low temperature oxidation was examined. Further improvement of the kinetic model was achieved by carefully tuning the reaction rate constant of the KHP decomposition. Finally, according to the variation of mole fraction of products at different pressures, the pressure effects on key reaction pathways were discussed, and the selectivity of products at varied pressure conditions clarified.

THERMAL STABILITY STUDY OF METAL CARBOXYLATES OF Cucurbita pepo SEED OIL

The study investigated the thermal stability of Cucurbita pepo seed oil carboxylates in the temperature range of 433, 453 and 473K. The carboxylates, prepared via metathesis in ethanol, exhibited characteristic vibrations (1633-1398 cm⁻¹) conrming formation of the carboxylates. The decomposition rate constants were found to be of the order of 10⁻³ min⁻¹, with activation energy values spanning 12.0- ǂ 18.4 kJ mol⁻¹. The activation enthalpy (ΔH ) was observed in the range of 8.03-14.47 kJ mol⁻¹, indicating ǂ an endothermic behavior. The non-spontaneous decomposition process, indicated by ΔG (113.7-115.7 ǂ kJ mol⁻¹) and -ΔS (0.227-0.244 kJ mol⁻¹ K⁻¹), identied Ba-PSO as the most stable. This suggests the potential use of Cucurbita pepo seed oil for metal carboxylate synthesis thereby, enhancing its commercial value and promoting its cultivation in Nigeria.

Exploring Cu-doped graphitic carbon nitride for treatment of dye pollutants in textile wastewater: Benefits and limitations

This study introduces an innovative method utilizing Cu-doped graphitic carbon nitride (Cu-GCN) photocatalyst for the effective removal of dye pollutants such as methylene blue (D-MB) and Rhodamine B (D-RhB) from textile industry wastewater. The findings demonstrate that Cu-GCN achieves impressive degradation efficiency of 86.9 and 75.1 % for D-MB and D-RhB, respectively. Notably, the decomposition rate constants (k) exhibit an inverse relationship with pollutant concentrations. Specifically, the k value of D-MB and D-RhB using Cu-GCN increased from 0.010 to 0.023 min−1 and 0.009 to 0.022 min−1, respectively, with decreasing concentrations from 100 to 5 mg L−1. Besides, the decomposition efficiency of D-MB and D-RhB by Cu-GCN shows enhancements of 15.2 and 13.5 %, respectively, with a rise in solution pH from 5.0 to 9.0. Within 60 min of reaction time, Cu-GCN exhibits good decomposition efficiency of 69.1 % for D-MB and 55.3 % for D-RhB in textile wastewater samples. We also explore the comparative advantages and limitations of utilizing the photocatalysis process for the degradation of D-MB and D-RhB. This work offers valuable insights into the potential of Cu-GCN as a promising photocatalyst that can be further developed for effectively removing various pollutants from textile wastewater.

An experimentally validated model for anodic H2O2 production in alkaline water electrolysis and its implications for scaled-up operation

The anodic co-production of hydrogen peroxide (H2O2) during alkaline water electrolysis has gained interest as a sustainable alternative for anthraquinone oxidation. However, electrochemical H2O2 production is often studied with idealized laboratory setups to determine the H2O2 formation kinetics. In this work, we perform the reaction with industrially relevant operating principles using a flow cell with separately recirculating anolyte and catholyte. We then fit the data to an analytical model that we derive based on mole balances that accounts for anodic generation, anodic oxidation, and bulk disproportionation of H2O2, as well as electrolyte volumes and electrode surface area. We performed experiments at 100, 200, and 300 mA cm-2 to derive values for the reaction system. At 200 mA cm-2, we found a generation rate of 0.037 mmol min-1 cm-2 (FEH2O2 = 59%) and an anodic decomposition rate constant of 0.304 cm min-1, with a bulk disproportionation rate constant of 1.85 × 10-3 min-1. We successfully applied our model to two sources in literature to derive values for their systems as well. In all cases, the contribution of anodic oxidation of H2O2 was found to be the larger loss mechanism in comparison to bulk disproportionation. Using the analytical model, we show that decreasing the reservoir volume is a simple way to increase the H2O2 concentration over time. Further refinement of the model can be achieved through the use of mass transfer relationships based on electrolyzer geometries to describe the anodic oxidation of H2O2 in the mole balance equations.

UV photolysis of oxalyl chloride: ClCO radical decomposition and direct Cl2${\rm Cl}_2 {\rm }$ formation pathways

AbstractOxalyl chloride, , is widely used as a photolytic source of Cl atoms in reaction kinetics studies. photolysis is typically assumed to produce Cl atoms with an overall yield of 2 via three‐body dissociation, , followed by fast subsequent ClCO unimolecular decomposition of either the energetically excited fragment, , or the thermalized ClCO radical, . However, a study by Huang et al. (J. Phys. Chem. A 121 (2017) 2888–2895) found that UV photolysis of at directly yields with a photolysis quantum yield of . This new product pathway may complicate the use of as a clean source of Cl atoms and challenges the previously accepted photodissociation scheme. The purpose of the present work was 2‐fold. Firstly, the unimolecular decomposition of and ClCO radicals has been investigated in / gas mixtures after UV photolysis at and . Cl atoms were captured by added in excess such that concentration‐time profiles of HCl measured by means of mid‐infrared frequency modulation spectroscopy reflect the temporally separated Cl formation pathways. The low‐pressure thermal ClCO decomposition rate constant was determined to be at , which is in very good agreement with previously reported literature values. Secondly, the photolysis quantum yield of direct formation from photofragmentation was studied with time‐of‐flight mass spectrometry using a photoelectron photoion coincidence setup. Calibrated concentration‐time profiles were recorded and analyzed using kinetic simulations accounting for both direct and secondary formation of from photolysis and reactions involving Cl, ClCO, and , respectively. Direct formation could be confirmed, where wavelength‐dependent quantum yields of , , and at , , and were determined. Complementary quantum‐chemical calculations of the potential energy diagram for ground‐state photodissociation reveal a low‐lying energy barrier for the formation of phosgene, . We suggest that subsequent and Cl formation from energetically excited may actually play a role for the overall photodissociation of .

Investigation on UV Degradation and Mechanism of 6:2 Fluorotelomer Sulfonamide Alkyl Betaine, Based on Model Compound Perfluorooctanoic Acid

The UV treatment of 6:2 FTAB involves the mitigation of this persistent chemical by the impact of ultraviolet radiation, which is known for its resistance to environmental breakdown. UV treatment of PFOA and/or 6:2 FTAB, and the role of responsible species and their mechanism have been presented. Our investigation focused on the degradation of perfluorooctanoic acid (PFOA) and 6:2 fluorotelomer sulfonamide alkyl betaine (6:2 FTAB, Capstone B), using UV photolysis under various pH conditions. Initially, we used PFOA as a reference, finding a 90% decomposition after 360 min at the original (unadjusted) pH 5.6, with a decomposition rate constant of (1.08 ± 0.30) × 10−4 sec−1 and a half-life of 107 ± 2 min. At pH 4 and 7, degradation averaged 85% and 80%, respectively, while at pH 10, it reduced to 57%. For 6:2 FTAB at its natural pH 6.5, almost complete decomposition occurred. The primary UV transformation product was identified as 6:2 fluorotelomer sulfonic acid (6:2 FTSA), occasionally accompanied by shorter-chain perfluoroalkyl acids (PFAAs) including PFHpA, PFHxA, and PFPeA. Interestingly, the overall decomposition percentages were unaffected by pH for 6:2 FTAB, though pH influenced rate constants and half-lives. In PFOA degradation, direct photolysis and reaction with hydrated electrons were presumed mechanisms, excluding the involvement of hydroxyl radicals. The role of superoxide radicals remains uncertain. For 6:2 FTAB, both direct and indirect photolysis were observed, with potential involvement of hydroxyl, superoxide radicals, and/or other reactive oxygen species (ROS). Clarification is needed regarding the role of eaq− in the degradation of 6:2 FTAB.

Superb enhancement of thermal decomposition of ammonium perchlorate in the presence of methyl viologen salts: A TG-DSC/MS and kinetic study

Different salts of 1,1′-dimethyl-4,4′-bipyridinium which known as methyl viologen compounds (MVX2) (where X= iodide (I‾, MVI2), perchlorate (ClO4‾, MVC2) and tetraphenylborate anion (BPh4‾, MVT2)) were prepared and characterized using 1H NMR, 13C NMR, elemental analysis and mass spectroscopy. The impact of these viologen salts on the thermal decomposition of ammonium perchlorate was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mass spectroscopy. The obtained results revealed that the high-temperature decomposition (HTD) temperature of MVX2:AP mixtures (5:100 (w/w)) significantly decreases by 121 ◦C, 151 ◦C and 112 ◦C compared to pure AP in MVC2, MCI2 and MVT2, respectively. Moreover, the apparent released heat of AP decomposition in these mixtures grows up from 574.2 J g−1 for the pure AP to 2108, 1965 and 1564 J g−1 for MVC2, MCI2 and MVT2, respectively. Furthermore, the calculation of the kinetic parameters confirms that the activation energy of HTD of AP was significantly decreased from 142.9 to 124.9, 138.9 and 131.2 KJ mol−1, upon mixing with MVC2, MVI2 and MVT2 respectively. The rate constant of AP decomposition at the peak temperatures of these mixtures was higher than that at the peak temperature of pure AP. The evolved gas analysis using mass spectrometry shows that the decomposition of pure AP mainly results in ClO3, ClO2, HClO4, ClO, Cl2, HCl, N2O and O2, while the major gaseous products of the 5:100 (w/w) mixture of MVX2 salts with AP were detected as N2, NO, N2O, O2, Cl2, ClO, ClO2, ClO3, HClO4, HCl and 4, 4′-Bipyridine (Bpy). The amounts of Bpy in decomposition products of AP/MVX2 mixtures follow the order of MVC2>MVI2>MVT2, which surprisingly is in accordance with the catalytic activity of these compounds.

Construction of Cnts/calcined Zn-Co-LDHs hydrid to enhanced photocatalytic for ofloxacin decomposition: mechanism, degradation pathway, and toxicity assessment.

This work successfully synthesized the Cnts/calcined Zn-Co-LDHs (xCnts@ZnC) hybrid material using the Zn-Co-LDHs precursor. Using the co-precipitation method, we synthesized Zn-Co-LDHs onto Cnts ranging in mass from 0 to 80 mg. These were subsequently calcined at 550 °C to yield xCnts@ZnC (x = 2, 4, 6, 8). Based on the results, ZnC is found on the surface of Cnts in two phases: ZnO and ZnCo2O4. The photocatalytic activity of xCnts@ZnC is demonstrated by its capacity to degrade ofloxacin antibiotics (OFL) in the visible region; 6Cnts@ZnC (85.8%; k = 0.0099 min-1), shows the best decomposition rate constant, increasing by three times when compared to ZnC (53.3%; k = 0.0048 min-1). The h+, O2˙-, radicals are the main factors that determine of the decomposition process in the identified OFL decomposition mechanism of 6Cnts@ZnC, in which Cnts have the role of transporting and collecting electrons, minimizing the recombination between photogenerated electrons and holes. The OFL degradation pathways of 6Cnts@ZnC were also investigated and identified by the HPLC-MS spectrum and suggested the new degradation mechanism to small molecules that have nontoxic of small molecules to environment site by ADMET model. The OFL degradation obtained 96.44% and set equivalent of degradation after completing 300 min.

(Invited, Digital Presentation) Langmuir-Type Formulation for Atomic-Order Surface Reactions of Reactant Gases on Si (100) and Ge (100) Surfaces

Accurate knowledge of atomically controlled processing for group IV semiconductors is very important for the fabrication of Si-based ultrasmall devices in ultralarge-scale integration [1]. In this review, the Langmuir-type formulation is performed for atomic-order surface reactions of reactant gases on group IV semiconductor (100) surface in ultraclean hot-wall low-pressure CVD. Now, assuming that one reactant molecule M is adsorbed at one free surface site with partial decomposition of M, total site density n0 on the surface is given by n 0 = Q s + Q Ms, (1)where Q s is density of free site; Q Ms, the site density where M is adsorbed.Then the surface adsorption velocity of Q Ms is given bydQ Ms/dt = k Ms P M Q s - k -Ms Q Ms = k Ms P M n 0 - (k Ms P M + k -M) Q Ms, (2)where k Ms and k -Ms is adsorption and desorption rate constants of M, respectively; P M, partial pressure of M. The integration of eq. (2) with Q Ms = 0 at t =0 gives Q Ms= [k Ms P M n 0/(k Ms P M + k -Ms)]{1 - exp[ - (k Ms P M + k -Ms)t]}. (3)The self-limited adsorption given by eq. (3) with fitted n 0 and k Ms (k -Ms = 0) fits the experimental data of CH4 on Si(100) at 500-600oC [2], SiH3CH3 on Si and Ge(100) at 450oC [3], B2H6 on hydrogen(H)-free Si (100) at 180oC [4], PH3 on Ge (100) at 300oC [5], SiH4 on H-free Ge (100) at 260oC [6]. It is mentioned that H-free surface is prepared by preheating at the higher temperature than around 400oC on Si (100) and 300oC on Ge (100) in Ar and at the higher temperature the self-limited amount is scarcely influenced even by H2 in the present condition. In the case of NH3 at 400oC on H-terminated Si (100) [7] and SiH4 at 260oC on H-terminated Ge (100) [6], it is proposed that the NH3 or SiH4 molecules are physically adsorbed self-limitedly at H-terminated sites. Then, total site density n H0 is given by n H0 = Q Hs + Q MHs + Q HMR, (4)where Q Hs is the site density of H-terminated site; Q HMs, the site density where M is adsorbed physically at H-terminated site; Q HMR, the site density where physically adsorbed M at H-terminated site decomposes partially. If the relationship between Q Hs and Q HMs is Q HMs=K HM Q Hs with thermal equilibrium constant K HM, the surface decomposition velocity of Q HMR is given bydQ HMR/dt = k HMR Q HMR = k HMR K HM P M(n H0 - Q HMR), (5)where k HMR is partial decomposition rate constant of adsorbed M.The integration of Eq. (5) with Q HMR = 0 at t =0 gives Q HMR=n H0(1 - exp { - [k HMR K HM P M/(1 + K HM P M)]t}). (6)The H-terminated surface is composed of H-free and H-terminated sites. For fraction x of the H-terminated sites, total site density is n 0 (1 - x) + n H0 x and the self-limited amount is given by Q Ms (1 - x) + Q HMR x.The self-limited adsorption/reaction for NH3 at 400oC on H-terminated Si (100) surface and SiH4 at 260oC on H-terminated Ge (100) surface given by eqs. (3) and (6) with x, n 0, n H0, k Ms, K HM and k HMR fits the experimental data. For the SiH4, SiH3CH3 or PH3 where total site density on the surface is equal to substrate surface atomic density n SSA, it is assumed that the site is the pair site such as Si-Si, Si-Ge or Ge-Ge pair. For CH4, B2H6 or NH3 where the total site density is equal to 2n SSA, it is proposed that the site is one bond of Si or Ge. In the PH3 on Si (100) [5], it is assumed that P atoms of maximum 2n SSA are adsorbed with self-limited reaction rate constant of PH3 at the P occupied sites where PH3 molecules have been adsorbed at Si-Si pair sites [8]. These results demonstrate that the atomic level surface reactions of reactant gases in the practical low-pressure CVD are explained based on the modified Langmuir-type model.

Effects of Nanoparticle Size on the Thermal Decomposition Mechanisms of 3,5-Diamino-6-hydroxy-2-oxide-4-nitropyrimidone through ReaxFF Large-Scale Molecular Dynamics Simulations.

ReaxFF-lg molecular dynamics method was employed to simulate the decomposition processes of IHEM-1 nanoparticles at high temperatures. The findings indicate that the initial decomposition paths of the nanoparticles with different sizes at varying temperatures are similar, where the bimolecular polymerization reaction occurred first. Particle size has little effect on the initial decomposition pathway, whereas there are differences in the numbers of the species during the decomposition and their evolution trends. The formation of the hydroxyl radicals is the dominant decomposition mechanism with the highest reaction frequency. The degradation rate of the IHEM-1 molecules gradually increases with the increasing temperature. The IHEM-1 nanoparticles with smaller sizes exhibit greater decomposition rate constants. The activation energies for the decomposition are lower than the reported experimental values of bulk explosives, which suggests a higher sensitivity.

Effect of La3+ on thermal, structural and morphological properties of Zn–Co ferrite spinel-based pigments

The paper discusses the structural, morphological, and chromatic characteristics of La3+ substituted Fe3+ in Zn–Co–La ferrite embedded in a SiO2 matrix, synthesized through a sol-gel method. The thermal behavior of reactants during the synthesis process revealed the formation of metallic oxalate up to 200 °C and their decomposition into metal oxides that further react and form ferrites. The rate constants of oxalate decomposition into ferrites calculated using the isotherms at 160, 200, 240, and 280 °C decrease with increasing temperature and depend on the Fe3+ substitution with La3+ in Zn–Co–La ferrite. The XRD patterns showed a nano-crystalline, single-phase structure formation. The lattice constant increased from 8.431 Å to 8.466 Å, and the crystallite size registered a growth from 35 to 64 nm with the increase in La3+ cations concentration. FT-IR spectra revealed the existence of the M − O stretching bands from Zn–Co–La ferrite and the formation of SiO2 matrix. Transmission electron microscopy revealed spherically-shaped ferrite particles,with particle sizeraging from,38 to 67 nm. The particle size increases with increasing the La content. The lightness of pigments is low and increases by embedding in opaque ceramic glazes. Synthesized NCs were tested for their potential application as pigments in the ceramic industry through their incorporation into glazes. This evaluation included assessing their color using CIELAB coordinates.

Activate hydrogen peroxide for facile and efficient removal of aflatoxin B1 by magnetic Pd-chitosan/rice husk-hercynite biocomposite and its impact on the quality of edible oil

Due to the high heat and chemical stability of aflatoxin B1 (AFB1) with significant impacts on humans/animals and thus it needs to develop a practical and efficient approach for its removal. Herein, we fabricated a magnetic Pd-chitosan/glutaraldehyde/rice husk/hercynite (Pd@CRH-x) composite for efficient detoxification of AFB1. The Pd@CRH-x was obtained by a simple wet-impregnation procedure of CRH complexes followed by pyrolysis. The results confirmed that the unique structure of Pd@CRH-400 effectively improves dispersity, and mass transfer subsequently enhancing removal efficiency in batch conditions. Results indicate 94.30 % of AFB1 was efficiently degraded by 0.1 mg mL−1 Pd@CRH-400 with 4.0 mM H2O2 at wide pH ranges (3.0–10) at 60 min with a decomposition rate constant of 0.0467 min−1. Besides, by comparing the quality factors of edible oil (i.e., acid value, peroxide value, iodine value, moisture, volatile matters, anisidine value, and fatty acid composition), it was confirmed that there was no obvious influence on the physicochemical indicators of edible oil after removal/storage process. Subsequently, the systematic kinetic study and AFB1 degradation mechanism were presented. This study provides a new strategy for the efficient construction of controllable and dispersed Pd-based catalysts using CRH-x as a spatial support for alleviating the risk of toxic pollutants.

On the decomposition mechanism of propanal: rate constants evaluation and kinetic simulations

The reactivity of aldehydes has been the subject of considerable interest in chemical kinetics, with propanal often chosen as the representative species. Despite its relevance, the reactivity of propanal is currently estimated from analogy and fitting of experimental data measured in limited temperature and pressure ranges, while the few literature theoretical studies have focused more on the exploration the potential energy surface (PES) than on the estimation of rate constants. The purpose of this work is to reinvestigate the propanal decomposition kinetics using the ab initio transition state theory based master equation approach with the intent of: (1) Determining accurate rate constants of key reaction channels; (2) Updating and validating an existing kinetic model by simulating available experimental data on propanal pyrolysis. It is found that propanal decomposition at the initial stages of pyrolysis occurs through four unimolecular barrierless reactions to form CHO + C2H5, CH2CHO + CH3, CH3CHCHO + H, and CH3CH2CO + H, and a termolecular pathway leading to the formation of C2H4 + CO + H2. High pressure rate constants were determined for each barrierless reaction channel using Variable Reaction Coordinate Transition State Theory and used to estimate phenomenological temperature and pressure dependent channel specific rate constants integrating the 1 dimensional master equation over the whole PES. The decomposition rate constants so determined are in agreement with the few available experimental data and significantly faster than previous literature estimates. The estimated kinetic parameters were finally implemented into the CRECK kinetic mechanism, leading to an improved agreement with shock tube pyrolysis data from the literature.

Probing the kinetic sensitization effect of NO2 on ethylene oxidation

Exhaust gas recirculation (EGR) has been widely equipped in modern engines for pollutant emission abatement. NOx present in EGR can greatly influence fuel combustion properties in engine operation. Ethylene (C2H4) is well-known a critical intermediate formed via β-scission reactions of alkyl radicals in the pyrolysis and oxidation of hydrocarbons, thus investigating the mutual effects of C2H4 and NOx is beneficial to engine design as well as hierarchically developed strategy of the chemical kinetic model. This study investigated the auto-ignition behavior of C2H4/air mixtures containing different levels of NO2 (0 ppm, 200 ppm, 500 ppm, 3000 ppm) in a high-pressure shock tube at pressures of 1 atm and 24 atm, temperatures of 820–1300 K and different equivalence ratios of 0.5, 1.0 and 2.0. The results showed that the addition of NO2 significantly promoted auto-ignition at high pressure, while only limited effects at low pressure. A detailed kinetic mechanism was proposed based on a hierarchically developed strategy, and it successfully reproduced the experimental data over the entire test conditions. Flux and sensitivity analyses were implemented to explore the sensitization effect of NO2 addition on the ignition kinetics of C2H4. The analysis revealed that NO2 mainly affects the reaction pathway of ĊH2CHO radical, leading to the formation of HONO. The additional generation of ȮH radicals through HONO = NO + ȮH and NO + HȮ2 = NO2 + ȮH accelerate the auto-ignition of C2H4. At low pressure, the decrease in the rate constant of HONO decomposition weakens the role of NO2.

Nitrocellulose-containing sediment as renewable resource for hydrogen and high-pure carbon production

Nitrocellulose accumulated in sludge accumulators does not undergo any changes and remains explosive for decades but it can be used as initial recourse for H2 and nanocarbon production through biogas. Anaerobic biotransformation of waste with a nitrocellulose content of about 75% with native microflora, consortia of mesophilic or thermophilic microorganisms from industrial bioreactors under various volume loading of microorganisms and temperature conditions has been studied. Stimulation by an additional source of biogenic elements and the development of native microflora made it possible to reduce the concentration of nitrocellulose by 44% at 35 °C in 100 days. With a biocatalyst volume loading of 30% at 35 °C with mesophilic biocatalyst 39% of nitrocellulose (with 50% initial volume loading) was conversed to biogas, at 55 °C with thermophilic biocatalyst-99%. The rate constant of decomposition of nitrocellulose using a thermophilic biocatalyst was 0.0248 day−1, while the half–life of nitrocellulose was 28 days.

A three-dimensional in-situ self-electrolysis system based on Ni3(HITP)2/graphene-based composite aerogel particle electrodes for efficient deep removal of phenol from coking wastewater

Herein, a Ni3(HITP)2/graphene-based composite aerogel (Ni3(HITP)2/GA) particle electrode is developed for the oxidation removal of phenol with three-dimensional electrode technology. The as-constructed three-dimensional electrode system possesses high in-situ self-electrolysis capacity and achieves highly efficient degradation of phenol, completely removed within 15 min with a decomposition rate constant of 0.3283 min−1. Ni3(HITP)2 in Ni3(HITP)2/GA and the tetradentate Ni–N2O2 coordination bond generated at the composite interface produce H2O2 highly selectively via the 2e- ORR pathway. The graphene layer converts H2O2 into •OH by using the 1e- of Ni3(HITP)2 excitation and the microelectrode action of the particle electrode. Furthermore, the simultaneous generation of •OH and O2•- in the system greatly reduces the dependence on acidic environment and broadens the scope of utilization. The present work provides a new strategy for the efficient construction of particle electrodes in 3D electrode systems, which allows their potential application in the purification of coking wastewater.

In situ ligand-modulated activation of inert Ce(III/IV) into ozonation catalyst for efficient water treatment

As a classic strategy to maximize catalytic activity, modulation of the electronic structure of central metal using organic ligands encounters great challenge in radical reactions exemplified by advanced oxidation processes (AOPs) due to operando destruction of employed ligands. Herein, we provide a paradigm achieving in situ ligand-modulated activation of the originally inert Ce(III/IV) for catalytic ozonation as a representative AOP widely applied in full-scale water treatment. Among the small-molecule carboxylates typically produced from pollutant degradation during ozonation, we find oxalate (OA) is a potent ligand to activate Ce(III/IV), inducing 11.5- and 5.8-fold elevation in rate constants of O3 decomposition and atrazine degradation, respectively. The Ce(III)-OA complex is proved the catalytic active species to boost pollutant degradation, while the catalytic ozonation unusually involves both •OH-dependent and •OH-independent pathways with comparable contributions. Both experiment and density functional theory calculation results show the pronounced electron donating effect of OA as evidenced by the substantial decreases in the charge residing on Ce, the ionization potential, and the Ce(III/IV) electrode potential, affords the activation of the Ce center for efficient ozonation. A comprehensive kinetic model involving 67 reactions is established to verify and elaborate the catalytic mechanism. Moreover, with in situ OA production, trace Ce3+ enables autocatalytic mineralization and codegradation of typical contaminants, which are not observed in case of Fe2+ or Cu2+. In addition, Ce3+ outperforms numerous state-of-the-art ozonation catalysts in terms of mass activity. This study sheds light on sustainable activation of the metal center harnessing operando ligands produced from the catalyzed reaction.