International Journal of Chemical Kinetics最新文献

Quasi-tetrahedral o-azophenylboronic acid (azoB-ROH), which contains the protic solvent ROH, is a key species in the colorimetric sensing of saccharides by o-azophenylboronic acid (azoB). In this study, we compared the reactivity of azoB-ROH with that of trigonal azoB and tetrahedral o-azophenylboronate (azoB-OH⁻), and clarified the reaction mechanism of azoB-ROH with cis-1,2-cyclopentanediol and D-glucose. Analysis of the kinetics of the reactions of azoB with cis-1,2-cyclopentanediol and D-glucose in DMSO:water = 1:9 and azoB with cis-1,2-cyclopentanediol in tetrahydrofuran containing a small amount of methanol revealed that there was not much difference in the reactivity of azoB-H₂O and azoB-OH⁻, although the reactivity of azoB was higher than that of azoB-MeOH, that is, the reaction mechanism of azoB-H₂O was essentially the same as that of azoB-OH⁻.

The effect of small fractions of acetaldehyde (CH₃CHO) on the ignition delay time of methane (CH₄) was examined at high pressure. Measurements are reported for the ignition delay time obtained in a rapid compression machine (RCM) at a compression pressure (P_c) of ∼60 bar and temperatures after compression (T_c) in the range 750–900 K for fuel-air equivalence ratios ϕ in the range 1–4. The results show that mixtures of 2%–5% CH₃CHO in CH₄ ignite under conditions at which pure methane does not ignite experimentally. The efficiency of acetaldehyde as a promoter seems to be comparable to that of other oxygenated fuels like alcohols and ethers. For comparison with the experimental results, ignition delay times are computed using an updated reaction mechanism and two mechanisms from the literature for CH₃CHO oxidation. For most conditions, the simulations using the current mechanism agree with the measurements to within a factor of two. The ignition profile shows a pre-ignition temperature rise and two-stage ignition similar to that previously observed in low fractions of dimethyl ether in ammonia; both phenomena are captured by the simulations. Analysis of simulations at constant volume indicates that CH₃CHO is oxidized much more rapidly than CH₄, producing reactive species that initiate the oxidation of CH₄ and generates heat that accelerates oxidation toward ignition. The low-temperature chain-branching reactions of CH₃CHO are important in the early oxidation of the fuel mixture. Additional simulations were performed for equivalence ratios of ϕ = 1 and 4, at a compression pressure (P_c) of 100 bar and T_c = 750–1000 K. The simulations indicate that CH₃CHO has a strong ignition-enhancing effect on CH₄, with small fractions reducing the ignition delay time by up to a factor of 100, depending on the temperature, as compared to pure CH₄.

The inherent autocatalytic kinetics of the urea–urease–H⁺ system positions it as a promising candidate for the design of dynamic materials with time-domain programmable functions. Nevertheless, the stability of the enzyme can markedly influence the temporal evolution dynamics of the system and curtail its widespread applicability. This work employs several kinds of enzyme stabilization methods, including chemical cross-linking, physical coating, solvent stabilization, and solvent-physical coating co-modification, to systematically explore the impact of enzyme stabilization on clock reaction dynamics. Extensive experimental tests and analysis indicate that solvent and chemical cross-linking stabilization methods can better preserve clock dynamics with sensitive switching ability. Nevertheless, due to significant pH changes in the reacting system, the reusability of the enzyme is better retained in the physical coating and solvent-physical coating co-modification methods.

The periodic sinc function interpolation offers a compelling solution to address the issue of noise in the analysis of thermogravimetric analysis (TGA) data, thereby enhancing the outcomes of differential techniques such as the Friedman isoconversional method. In this study, we introduce a novel approach that leverages the periodic sinc function interpolation to directly obtain smooth reaction rates from TGA data, eliminating the reliance on numerical differentiation methods. The efficacy of this method has been confirmed through its application to noisy experimental data derived from the thermal decomposition of various polymers, showcasing its robustness. Readers are provided with the corresponding code for Gnu Octave, serving as a free alternative to MATLAB. Additionally, the activation energies calculated from the experimental data using both the Friedman method and periodic sinc function interpolation closely align with those determined by the integral Vyazovkin method, emphasizing the validity and reliability of this new approach.

Creation of complex chemical mechanisms for hydrocarbon pyrolysis and combustion is challenging due to the large number of species and reactions involved. Reactive molecular dynamics (RMD) enables the simulation of thousands of reactions and the discovery of previously unknown components of the reaction network. However, due to the inherent imprecision of reactive force fields, it is necessary to verify RMD-obtained reaction paths using more accurate methods such as Density Functional Theory (DFT). We demonstrate a method for identification and confirmation of reaction pathways from RMD that supplement an established mechanism, using the example of benzene formation from n-heptane and iso-octane pyrolysis. We establish a validation workflow to extract reaction geometries from RMD and optimize transition states using the Nudged-Elastic-Band method on semi-empirical and quantum mechanical levels of theory. Our findings demonstrate that the widely recognized ReaxFF parameterization, CHO2016, can identify known pathways from a established soot formation mechanism while also indicating new ones. We also show that CHO2016 underestimates hydrogen migration barriers by up to $��40��{�\mathrm{kcal}��\mathrm{mol}�}^{�-�1�}�$ as compared to DFT and can lower activation barriers significantly for spin-forbidden reactions. This highlights the necessity for validation or potentially even reparametrization of CHO2016.

Oxalyl chloride, $�{\text{(ClCO)}}_2$, is widely used as a photolytic source of Cl atoms in reaction kinetics studies. $�{\text{(ClCO)}}_2$ photolysis is typically assumed to produce Cl atoms with an overall yield of 2 via three-body dissociation, $��{\text{(ClCO)}}_2�+�h�\nu �\to �\text{Cl}�+�\text{CO}�+�{\text{ClCO}}^{\ast }�$, followed by fast subsequent ClCO unimolecular decomposition of either the energetically excited $�{\mathrm{ClCO}}^{\ast }$ fragment, $��{\text{ClCO}}^{\ast }�\to �\text{Cl}�+�\text{CO}�$, or the thermalized ClCO radical, $��\text{ClCO}�+�M�\to �\text{Cl}�+�\text{CO}�+�M�$. However, a study

The experimental data over CuO/ZnO/ZrO₂ catalyst for a wide range of operating conditions were used to develop the kinetics of the reaction CO₂ hydrogenation to methanol. Three kinetic models such as the power law model, the Graaf kinetic model, and the Park kinetic model were tested against the experimental data. Both the mechanistic models have been developed based on the Langmuir-Hinshelwood-Hougen-Watson approach and are specific only to the methanol synthesis from CO/CO₂ hydrogenation. In an attempt to reduce the number of parameters in the two models, the abridged forms of these models were also tried. Overall, 25 kinetic rate equations were tested and the best-fit kinetic rate expression with optimized parameters was worked out. Both the integral and differential methods of kinetic analysis were employed and their efficacy in finding the best-fit expression was compared. The MATLAB built-in function fminsearch was employed to perform the regression of the data. The Graaf model in its parent form, but with the new optimized values of the parameters, was found to be the best-fit rate model. The Graaf kinetics, with re-estimated parameters, could be helpful in designing and simulating a methanol synthesis reactor operating on CO₂ and H₂ feed and utilizing a CuO/ZnO/ZrO₂ catalyst.

Reduction of large combustion mechanisms is usually conducted based on the detection and elimination of redundant species and reactions. Reaction elimination methods are mostly based on sensitivity analysis, which can provide insight into the kinetic system, while species elimination methods are more efficient. In this work, the species-targeted local sensitivity analysis (STLSA) method is proposed to evaluate the importance of species and eliminate non-crucial species and their related reactions to simplify kinetic models. This paper comprehensively evaluates the effectiveness of STLSA across various combustion scenarios, including high and low-temperature ignition and laminar flame speed, using diverse mechanisms like USC Mech II, JetSurf 1.0, POLIMI_TOT_1412, NUIGMech1.1 and so on. Comparisons with graph-based methods, such as DRG and DRGEP, highlight STLSA's superior efficiency and accuracy. Moreover, STLSA is compared to species-targeted global sensitivity analysis (STGSA), demonstrating significant computation cost savings and comparable model reduction capabilities. The study concludes that STLSA is a robust and versatile tool for mechanism reduction, offering substantial improvements in computational efficiency while maintaining high accuracy in predicting key combustion properties.

As part of a series of studies of hydrogen-atom transfer or tautomerization reactions of imidic acid–amide species, $���H�─�O�═�C�─�N�─��\rightleftharpoons ��O�═�C�─�N�─�H��$, we report the rate constants for a set of 24 five-membered cyclic compounds at low, 50–300 K, and high, 500–1500 K, temperatures. These rate constants are for both the high temperature direct reaction and for that mediated by an additional water molecule which facilitates the hydrogen transfer reaction at low temperatures. In the latter case we show that the rate of reaction from a pre-reaction complex can be rapid at temperatures down to 50 K on a 1 ms timescale and is dominated by quantum mechanical effects as evaluated by small-curvature and quantised-reaction-states tunnelling. In addition, we present thermochemical data such as enthalpies of formation, entropies, isobaric heat capacities and enthalpy functions for these largely unknown species which span a range of compounds from pyrolidinone to oxo-tetrazoles.

The kinetics of total organic carbon (TOC) destruction during supercritical water gasification (SCWG) of glucose were studied at 400–500°C and 25 MPa in a 600 mL batch reactor. Both TOC and water concentrations are critical for the conversion of TOC in supercritical water, especially at longer residence times. Initially, it was assumed that the TOC destruction reaction followed first-order kinetics ignoring the water concentration. However, experimental results showed that the feed-to-water ratio had a significant effect on TOC decomposition. Considering the water concentration in the reaction, the reaction orders of TOC (2.35) and water (1.45) were calculated using nonlinear regression analysis (the Runge-Kutta method). The estimated pre-exponential factor (k’) and activation energy (E) were calculated to be 8.1 ± 2/min and 90.37 ± 9.38 kJ/mol respectively.