International Journal of Chemical Kinetics最新文献

The kinetics of dimethyl 1,4-cyclohexanedicarboxylate (DMCD) hydrogenation, via the half-hydrogenated product methyl 4-(hydroxymethyl) cyclohexanecarboxylate (MHMCC), to 1,4-cyclohexanedimethanol (CHDM) in gas phase was established over CuMnAl catalyst. The intrinsic kinetic experiments were carried out on a fixed-bed reactor under a wide range of reaction conditions with temperature varied from 493 to 523 K, pressure varied from 4 to 6 MPa, and weight hourly space velocity of DMCD varied from 0.948 to 3.792 h⁻¹. Eight rival possible two-site LHHW models were proposed to simulate the experimental results. The model involving dissociative adsorption of esters and surface reaction as the rate-determining step was found to fit the experimental data best. The rather large activation energy values (138.4 and 121.4 kJ·mol⁻¹) of two reactions (DMCD to MHMCC and MHMCC to CHDM) suggest that the reactions are both temperature sensitive. The coefficients of determination (R²) for DMCD conversion and CHDM selectivity were 0.989 and 0.983 respectively. Statistical and thermodynamic test further verified the reliability of the results.

In CTAB micellar medium, the kinetic investigation of Ru(III) promoted oxidation of L-glutamic acid (Glu) by [Fe(CN)₆]³⁻ was carried out by recording the decline in absorbance at 420 nm, which corresponds to [Fe(CN)₆]³⁻. By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH⁻], ionic strength, [CTAB], [Ru³⁺], [Glu], [Fe(CN)₆³⁻], and temperature using the pseudo-first-order condition. The findings demonstrate that [OH⁻], [CTAB], and [Glu] are the key parameters that have a discernible impact on reaction rate. In the studied concentration range of Ru(III), [Fe(CN)₆]³⁻, and at lower [Glu] and [OH⁻], the reaction displays first-order kinetics. The incremental trend in reaction rate with electrolyte concentration demonstrates a positive salt effect. CTAB substantially catalyzes the process, and after reaching a maximum, the rate remains nearly constant at increased [CTAB]. The observed decline in the CMC of CTAB may be caused by the reduced repulsion between the positively charged heads of the surfactant molecules caused by the negatively charged OH⁻, and [Fe(CN)₆]³⁻. The activation parameters also support the outer-sphere electron transfer mechanism as recommended by us.

The hydrolysis reactions of crystal violet (CV) and p-nitrophenyl acetate (PNPA) by sodium hydroxide in cetyltrimethylammonium bromide (CTAB) micellar solution were studied in this work. Combined with the Boltzmann probability of ionic species in an electrostatic potential field, a model with a numerical scheme was developed based on the nonlinear Poisson−Boltzmann equation in the micelle-cell consisting of the reactants and the surfactant. The numerical solution gives the ionic species distribution in the micelle phase and the radius of the micelle-phase. The dielectric constant of the micelle-phase varies in the range of 39.8−54.4. The second-order reaction rate constants in the micelle-phase were determined using the electrostatic and dipolar free energy models. For the basic hydrolysis of CV and PNPA, the overall second-order rate constants are three to five times and 1.4 times greater than the corresponding values in water, respectively. The rate enhancement occurs due to the distribution of the reactive ionic species in the cell region and the enhancement of the Coulombic and dipolar interactions among the ionic and polar reactants.

The reaction HO + SO → H + SO₂ (R_t) and its reverse (R_-t) play an important role in environment and the combustion of sulfur-containing fuels. However, their kinetics is of high uncertainty as its reaction profile is complicated with multiple deep complexes and channels. In this work, the kinetics and mechanisms of R_t and R_-t are studied comprehensively based on a newly developed full-dimensional accurate potential energy surface (PES) with the aid of machine learning. This highly accurate PES is interfaced with the software Gaussian. Then reliable information, including the energy, structures, and vibrational frequencies of the stationary points, as well as the minimum energy path and variational analysis can be efficiently determined. The variational transition state theory (VTST) and Rice−Ramsperger−Kassel−Marcus (RRKM) theory are employed to obtain the rate coefficients of each elementary reaction. The temperature- and pressure-dependent rate coefficients of R_t are derived by the RRKM-based master equation with hindered rotor and free rotor model considered. In addition, the effect of isotope substitution for the hydrogen is investigated on the reaction kinetics. Meanwhile, the quasi-classical trajectory (QCT) calculation is performed on the PES-2020 to obtain the temperature-dependent reaction kinetics.

In this work, perfluoroheptene 2- and 3-C₇F₁₄ stereoisomer specific gas-phase OH reaction rate coefficients, k, were measured at 296 K in ∼600 Torr (He bath gas) using a relative rate (RR) method. Gas-chromatography (GC) with electron capture detection (ECD) was used for the separation and detection of the stereoisomers. Rate coefficients for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, and (Z)-3-C₇F₁₄ were measured to be (in units of 10⁻¹³ cm³ molecule⁻¹ s⁻¹) (3.60 ± 0.51), (2.22 ± 0.21), (3.43 ± 0.47), and (1.48 ± 0.19), respectively, where the uncertainties include estimated systematic errors. Rate coefficients for the (E)- stereoisomers were found to be systematically greater than the (Z)- stereoisomers by a factor of 1.6 and 2.3 for 2-C₇F₁₄ and 3-C₇F_14, respectively. Atmospheric lifetimes with respect to OH radical reaction for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, (Z)-3-C₇F₁₄ were estimated to be ∼33, ∼56, ∼36, and ∼86 days, respectively, for an average OH radical concentration of 1 × 10⁶ molecule cm⁻³. Quantitative infrared absorption spectra were measured as part of this work. Complimentary theoretically calculated infrared absorption spectra using density functional theory (DFT) are included in this work. The theoretical spectra were used to evaluate stereoisomer climate metrics. Radiative efficiencies (adjusted) and global warming potentials (GWPs, 100-year time-horizon), were estimated to be 0.12, 0.19, 0.12, and 0.23 W m⁻² ppb⁻¹ and 1.9, 5.1, 2.1, 9.3 for (E)-2-C₇F₁₄, (Z)-2-C₇F₁₄, (E)-3-C₇F₁₄, (Z)-3-C₇F_14, respectively. Atmospheric degradation mechanisms are discussed.

Application of formation flights to civil aviation is gaining interest, primarily due to the fuel burn reduction achieved by flying through another aircraft's wake. However, it is emerging that there are additional, less-recognized climate benefits via reduction in ozone and contrail warming through this concept. The NO_x threshold level is defined as when the loss rate for OH by reaction with NO₂ is equal to the loss rates for OH with CO and CH₄, beyond which level, ozone formation will decrease. In this study, The NO_x threshold level was calculated at different altitudes and found that at cruise altitude (∼10 km), the amount of NO₂ required for parity in OH loss with loss due to reaction with CO and CH₄ is around 2 ppb. The spatial and temporal NO_x threshold levels were estimated by STOCHEM-Common Representative Intermediate (CRI) global chemical transport model and In-service Aircraft for Global Observing System (IAGOS) measurement data and found that northern midlatitudes of the atmosphere are the most favorable region existing with the smallest NO_x thresholds (0.5 ppb) needed before reduction in ozone formation is likely to occur at cruise altitude of aircraft. Incorporating the major air traffic corridors into the coarse spatial resolution of the chemical transport model overestimated the NO_x compensation point, that is, increased photochemical ozone production. Thus, a simple one-dimensional (1D) aircraft plume dispersion model was developed with higher spatial and temporal resolution for considering aircraft plumes and its chemistry more accurately. The model run shows that the impact of formation flying aircraft emissions on spatially averaged ozone could be halved if the aircraft could maintain separations inside 4 km relative to well separated flights of 10 km or more.

The open-source statistical mechanics software described here, Arkane–Automated Reaction Kinetics and Network Exploration–facilitates computations of thermodynamic properties of chemical species, high-pressure limit reaction rate coefficients, and pressure-dependent rate coefficient over multi-well molecular potential energy surfaces (PES) including the effects of collisional energy transfer on phenomenological kinetics. Arkane can use estimates to fill in information for molecules or reactions where quantum chemistry information is missing. The software solves the internal energy master equation for complex unimolecular reaction systems. Inputs to the software include converged electronic structure computations performed by the user using a variety of supported software packages (Gaussian, Molpro, Orca, TeraChem, Q-Chem, Psi4). The software outputs high-pressure limit rate coefficients and pressure-dependent phenomenological rate coefficients, as well as computed thermodynamic properties (enthalpy, entropy, and constant pressure heat capacity) with added energy corrections. Some of the key features of Arkane include treatment of 1D, 2D or ND hindered internal rotation modes, treatment of free internal rotation modes, quantum tunneling effect consideration, transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate coefficient computations, master equation solution with four implemented methods, inverse-Laplace transform of high-pressure limit rate coefficients into the energy domain, energy corrections based on bond-additivity or isodesmic reactions, automated and efficient PES exploration, and PES sensitivity analysis. The present work describes the design of Arkane, how it should be used, and refers to the theory that it employs. Arkane is distributed via the RMG-Py software suite (https://github.com/ReactionMechanismGenerator/RMG-Py).

Two highly Cr (VI) resistant fungal strains, CSF-1 and CSF-2, were isolated and identified as Cladosporium sp. and Penicillium sp., respectively, using 18S rRNA gene sequencing. At optimized growth conditions, the dead biomass of Cladosporium sp. and Penicillium sp. has removed more than 99% of the supplemented Cr(VI). The kinetic study outcomes evidenced that the present fungal Cr(VI) biosorption is best fitting with the pseudo-first-order model with higher R² values (i.e., 0.70–0.95) than that of the pseudo-second-order kinetic model (R² = 0.02–0.73). After analyzing the R² values, it was observed that the Langmuir and Freundlich isotherm models best fit the Cr(VI) biosorption employing fungal biomass.

The five-membered cyclic esters, or γ-lactones, are promising candidates as biofuel additives and green solvent components. A comprehensive study of thermochemical and kinetic properties of γ-butyrolactone (GBL), γ-valerolactone (GVL), γ-caprolactone (GCL), and γ-heptalactone (GHL) has been conducted. The entropy, , specific heat, , enthalpy function, , and the enthalphy of formation at 298.15 K, , as well as the adiabatic ionization potential and single bond dissociation energies are reported. Bimolecular rate constants for the abstraction of H-atom by H^• and CH$�{}_3^{•}$ are presented on a per abstractable hydrogen basis; abstraction at the tertiary carbon site is consistently favored, while abstraction by CH$�{}_3^{•}$ lags behind H^•. Addition reactions of H^• and CH$�{}_3^{•}$ have high barriers and favor addition to the C-center.

Bamboo is abundantly available in India, particularly in the North East regions which can provide a significant energy opportunity in this region. The physicochemical and thermal properties of bamboo species originate from different places are distinct. This study investigates the pyrolysis of 20 different bamboo species from North East regions of India in a thermogravimetric analyser (TGA) at four different heating rates of 10, 20, 30, and 40 K/min. Enormous kinetic and thermodynamic data are presented for 20 varieties of bamboo species. Model-free kinetic methods are used to calculate the kinetic parameters and their values are compared. The average activation energy of all bamboo species is estimated in the range 145.59–219.15 kJ/mol from the Starink method, the method recommended by International Confederation of Thermal Analysis and Calorimetry (ICTAC). Generalized master plot method is used for the determination of reaction mechanism which reveals that most of the bamboo species follow the second-order reaction model (F2) during their thermal degradation. The thermodynamic parameters reveal that the pyrolysis process of all bamboo species is endothermic and it reaches near to the thermodynamic equilibrium.