International Journal of Chemical Kinetics最新文献

For high-dimensional complex combustion reaction kinetic systems, conventional simplification methods based on elementary reaction approaches (e.g., sensitivity analysis [SA]) struggle to derive compact reduced mechanisms due to the nonlinear characteristics of the kinetic systems, leading to the widespread adoption of graph-based methods in mechanism reduction. To overcome the dual challenges of reducing high-dimensional stiff mechanisms and resolving the inherent limitations of elementary reaction-based simplification methodologies, a novel mechanism reduction framework employing an improved binary genetic algorithm (IBGA) was established. The IBGA operates through binary-encoded particles where each bit corresponds to an elementary reaction: 0 indicates exclusion from the simplified mechanism, while 1 denotes retention. The optimization objective maximizes the number of zero-value bits while preserving critical combustion characteristics. This methodology was implemented for the mechanism reduction of ethylene and dimethyl ether (DME) combustion systems, etc. Results indicate that the IBGA-based approach achieves significant mechanism size reduction while maintaining accuracy. The ethylene mechanism was reduced to 28 reactions, and the DME mechanism to 40 reactions. Furthermore, in order to further validate the performance of the IBGA reduction method, the ethylene mechanism and DME mechanism are also reduced for predicting both ignition delay time and laminar flame speed. The results shown C₂H₄/air reduced mechanism involving 28 species and 56 reactions and DME/air reduced mechanism involving 31 species and 92 reactions are obtained. The obtained simplified mechanisms exhibit enhanced compactness with preserved prediction fidelity for combustion characteristics. A comparative analysis between the IBGA and deep mechanism reduction (DeePMR) methods in reducing high-temperature LLNL butanol isomers’ mechanisms demonstrates that the IBGA significantly shortens the required computational time for reduction while producing more compact mechanisms.

Inexpensive hierarchically hortensia-like α-Ni(OH)₂ catalysts without prereduction were introduced to the 5-hydroxymethylfurfural (HMF) hydrogenation to 2,5-bis(hydroxymethyl)furan (BHMF) via the catalytic transfer hydrogenation (CTH) process. Given the catalytic performance evaluated on the hortensia-like α-Ni(OH)₂, the catalyst of Ni(OH)₂-OLA synthesized using an oleylamine-assisted solvothermal method has prospective in the HMF hydrogenation to BHMF. A remarkable 95.96% of the BHMF selectivity with 96.81% of the HMF conversion was obtained on Ni(OH)₂-OLA at 135°C for 5 h under N₂ atmosphere using the ethanol as the hydrogen donor. Based on the kinetic analysis, the lowest activation energy of 39.6 kJ·mol⁻¹ and the highest preexponential factor of 19.1 s⁻¹ could be found on Ni(OH)₂-OLA, which revealed the superior catalytic performance in the HMF hydrogenation to BHMF over Ni(OH)₂-OLA. Moreover, excellent stability and reusability also could be found on Ni(OH)₂-OLA, which indicated that the hortensia-like α-Ni(OH)₂ catalysts have the potential for industrialization. The findings of this study provide an efficient catalyst system with low-cost and high-performance for the HMF hydrogenation via the CTH process.

A study was conducted to investigate the oxidation of benzyl alcohol and 2-phenyl ethanol using a copper (III) complex catalyst with ruthenium (III) chloride in an alkaline water-based solution. The researchers maintained a constant ionic strength in the solution throughout the experiment. They found that the rate of the reaction was directly proportional to the concentrations of the oxidant, organic substrate, catalyst, and hydroxyl ions. However, when external sources of periodate ions were added, the reaction rate slowed down. Increasing the ionized potential of the solution had a positive effect on the reaction rate. The researchers calculated various thermal properties, such as activation energy, activation free energy, and activation entropy, to better understand the energetics of the reaction. They used infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy to identify the oxidation products. Based on their experimental findings, they proposed a plausible mechanism to explain all the observed phenomena. This research highlights the use of simple, cost-effective, and environmentally friendly methods for copper oxidation in its +3 state. These methods offer new possibilities for advancements in the field of oxidation reactions.

The decomposition of azoxy derivatives of dinitropyrazole and furazan, the first example in which an azoxy group is coupled to a pyrazole ring nitrogen, has been studied in detail using DSC, TGA, isothermal TGA, and manometry methods. The studies showed that the degradation of azoxy compounds starts with the cleavage of the bond between the N(O) atom of the azoxy group and the furazan cycle. It was found that under conditions of decomposition product removal, this stage can occur without heat release or with heat release without a pronounced peak. The insignificant heat effect of the initial decomposition stage of azoxy compounds makes it difficult to determine the true kinetic parameters using the standard DSC method, as the observed heat effect is actually due to the decomposition of intermediates. At the same time, decomposition under closed conditions can increase the decomposition rate constants by a factor of 10 or more. A possible mechanism for the decomposition of azoxy compounds has been proposed based on the kinetic data obtained and the analysis of the decomposition products.

This work describes the oxidation of cyclohexane to cyclohexanone and cyclohexanol using a CuO–ZnO catalyst. It was found that the CuO–ZnO catalyst is more active for the oxidation of cyclohexane using H₂O₂ as an oxidizing agent, and further catalyst was characterized by using XRD, FTIR, and XPS analysis. Various reaction parameters, such as the effect of solvent, reaction time, different oxidizing agents, reaction temperature, H₂O₂ to cyclohexane mole ratio, catalyst loading, and stirring speed, have been studied to analyze the catalytic activity. The optimized catalytic activity obtained an 88.2 % conversion of cyclohexane, 86 % selectivity of cyclohexanone, and 14 % cyclohexanol selectivity. The oxidation of cyclohexane and the determination of the activation energy for the reaction was explored using different kinetic models such as the Eley–Rideal and Langmuir–Hinshelwood–Hougen–Watson models. Langmuir–Hinshelwood–Hougen–Watson competitive associative adsorption mechanism with surface reaction as the rate-limiting step is the best-fitted model.

Herein, an efficient adsorbent was prepared at high temperature using sawdust of Melia azedarach plant. The prepared adsorbent was characterized by instrumental techniques like EDX, XRD, SEM, FTIR, TGA, and surface area analyzer. The fabricated activated carbon (AC) was used as an adsorbent for the removal of Pb²⁺ Ni²⁺, and Cu²⁺ from aqueous solution utilizing batch adsorption approaches. At pH 6, the highest elimination of Pb²⁺ and Cu²⁺ was achieved, whereas for Ni²⁺ the optimum pH was 5. The recorded time interval for reaching equilibrium was 60 min in the case of Pb²⁺ and Ni²⁺ metal, whereas 80 min in the case of Cu²⁺ ion. The adsorbent was found to be more effective at high doses, with an optimum dose of 0.05 g. The isotherm models, including Langmuir, Freundlich, Temkin, Jovanovich, and Harkins-Jura models, were utilized to decide the best fit model for explaining the isotherm adsorption data. Out of the tested models, the Langmuir model was more effective with high R² values of 0.997, 0.991, and 0.984, respectively, for Pb²⁺, Ni²⁺, and Cu²⁺ ions. The pseudo-second order model best fitted the kinetics data with high R² values of 0.980, 0.991, and 0.987 correspondingly, for the mentioned ions. The estimated ∆H° values were −22.699, −31.147, and −33.199 J·mol⁻¹ respectively for Pb²⁺, Ni²⁺ and Cu²⁺, indicated the process to be an exothermic one. The favorable nature of the studied adsorption was obvious from the recorded negative values of Gibbs free energy. The fabricated AC could thus be considered as an efficient and cheap alternative to commercially available activated carbon; however, further confirmation and validation of the present findings by other researchers is mandatory.

The truncated Šesták–Berggren (TSB) model has been demonstrated to reliably predict the conversion function of standard reaction models. However, when applying the TSB model to thermal analysis of condensed phase reactions using the integral method, an integration emerges that lacks an analytical solution. This integral can be expressed using special functions like the incomplete beta function and the Gaussian hypergeometric function. The integral method offers the capacity to utilize raw kinetic data directly, thereby obviating the potential for errors arising from the calculation of instantaneous reaction rates with noisy experimental data. In this study using a special function, we have developed a new integral method for combined kinetic analysis of simple reactions under nonisothermal conditions, enabling the estimation of kinetic parameters, including the activation energy, pre-exponential factor, and TSB-form of conversion function through a trial-and-error procedure with linear regression. The validity of the new approach was tested by applying it to the kinetic data of a simulated reaction and the thermal decomposition of poly(methyl methacrylate), yielding results closely matching those obtained using differential method. Furthermore, we provided GNU Octave/MATLAB codes for users to calculate TSB model coefficients for standard reaction models in both differential and integral forms, as well as to estimate kinetic parameters of reactions using their own kinetic data.