Reaction Kinetics, Mechanisms and Catalysis最新文献

Density function theory (DFT) calculations are employed to investigate double transition metal atoms anchored on the defective boron nitride for N₂ reduction in this work. By comparing the stability, N₂ adsorption energy, selectivity and activity of NRR, Mn₂@d-BN with N defect, and TM₂@d-BN (TM = Fe, V, Co and Mn) with B defect are selected as candidates. Moreover, the result shows that Mn dimer anchored on BN with B defect exhibit excellent catalytic performance for nitrogen reduction via alternating mechanism, with the potential of − 0.44 V. With regard to this work, we provide a screening scheme to explore highly efficient double-atom metals catalysts for the electrocatalytic nitrogen reduction reaction.

In the present investigation, biomass-based carbon microsheets were synthesized using melamine and corn cob powder as carbon precursors. Three adsorbents were prepared: Carbon microsheets 500 (CMS-500), biomass-based carbon microsheets (BCMS-500), and BCMS-F-500, which were characterized using different analytical techniques. Synthesized adsorbents were optimized for simultaneous adsorption of Ni(II) and Cr(VI) from an aqueous solution. Adsorption was optimized by varying the values of operating parameters, including reaction pH, adsorbent and adsorbate concentration, temperature, and contact time. Maximum adsorption of Cr(VI) was achieved at pH 2 and of Ni(II) was achieved at pH 6 using a 0.5 g/L adsorbent dose and 20 mg/L for each metal concentration. The adsorption of metal ions increased with increasing temperature. The Langmuir adsorption isotherm model best fitted the adsorption of Cr(VI) with both adsorbent and Ni(II) by CMS-500. While the Freundlich adsorption isotherm models were best suited for the adsorption of Ni(II) by BCMS-500, To understand the adsorbent properties, the adsorbent was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), and an X-ray diffractometer (XRD). CMS-500 and BCMS-500 were found to be highly effective adsorbents that can be applied for the effective management of Cr(VI) and Ni(II)-contaminated wastewater.

In this work, the reaction kinetics between oxygen and ammonium sulfite obtained from the wet desulfurization process was investigated in a bubble reactor with cobalt sulfate as a catalyst under the condition of sulfite concentration of 0.38–1.18 mol/L, temperature of 15–40 °C, and cobalt concentration of 0.6 × 10⁻³–1.5 × 10⁻³ mol/L. The reaction order with respect to sulfite is zero and oxygen is 1.5, and cobalt is 0.5. The apparent energy of activation is 20.45 kJ/mol. The mechanism of sulfite oxidation was discussed. The experimental results are valuable for the process optimization of ammonium sulfite oxidation and industrial design in the wet ammonia desulfurization system.

This work presents a comprehensive study on the dielectric properties of shellac-based composites with varying filler concentrations of (SiC) and iron (Fe) particles, complemented by scanning electron microscopy (SEM) analysis. Shellac, a natural biopolymer known for its excellent film-forming abilities, biodegradability, and insulating properties, was chosen as the matrix material. The dielectric properties, including permittivity and dielectric loss, are measured by LCR Meter across a frequency range from 100 Hz to 8 MHz to evaluate the effects of filler concentration. This study reveals that the incorporation of SiC and Fe particles significantly enhances the dielectric constant and exhibits complex frequency-dependent behavior in dielectric loss. SEM analysis provided insights into the microstructural changes induced by the fillers, correlating with the observed dielectric properties. The results indicate that the dielectric performance of shellac composites can be effectively tailored through the precise control of SiC and Fe particle concentrations, attributed to interfacial polarization and Maxwell-Wagner-sillars effects. This work underscores the potential of shellac composites as sustainable, high performance dielectric materials for advanced electronic applications, contributing to the development of eco-friendly electronic devices.

The present study investigates the thermal behavior, devolatilization index, heat variations, kinetic and thermodynamic characteristic parameters, volatile components and possible chemical reactions of double-base propellant pyrolysis. Thermogravimetric analysis (TGA), in-situ Fourier transform infrared spectroscopy (FTIR) and online TGA-FTIR mass spectrometry are employed. The findings indicate that alterations in temperature and heating rate significantly affect the pyrolysis process, exhibiting a triphasic behavior, where the initial stage may be considered as a single-step reaction, primarily involving the pyrolysis of nitroglycerin. The pyrolysis of nitrocellulose predominantly occurs in the third stage. With the increase of heating rate, the reaction rate of the first stage decreases, whereas that of the second stage increases, resulting in a temperature hysteresis phenomenon. The maximum instantaneous heat flow and the total heat flow both increases, while the full width at half maximum decreases, thereby enhancing the combustion performance and reaction intensity of double-base propellant, while reducing the thermal stability. 450–550 K is the main exothermic temperature range. The average activation energies for the first and second stages of double-base propellant pyrolysis, determined using three effective kinetic methods, are 107.14 kJ/mol and 379.14 kJ/mol. The model g(α) = (1− (1− α)^(1/3))² can accurately characterize the first pyrolysis stage from a kinetic perspective. The average values of ∆H, ∆G and ∆S are 231.83 kJ mol⁻¹, 231.83 kJ mol⁻¹ and − 35.06 J K⁻¹. The pyrolysis of double-base propellant is an unstable and non-spontaneous endothermic reaction with decreasing stability as the reaction progresses. The major components of volatiles produced and the potential chemical reactions involved are identified.

The effectiveness and mechanism of the antioxidant action of a number of biologically active polysubstituted tetrahydroquinolines in a model reaction of liquid-phase oxidation of 1,4-dioxane have been studied. The research into the properties of these substances in the field of pharmacology is becoming increasingly important due to their ability to act as inhibitors of radical chain oxidation of organic compounds. The fact is that the manifestation of the antioxidant properties of biologically active compounds leads to an increase in the therapeutic effect of potential drugs. In this case, the drug, simultaneously with the function of treating the target disease, additionally slows down the rate of the undesirable process of lipid peroxidation of cell membranes. The oxidation reaction has been observed at 348 K using a manometric technique, measuring the change in the concentration of absorbed oxygen in the gas phase under different initial conditions of the studied antioxidants over time. In the presence of tetrahydroquinoline (THQ) additives, the kinetic curves of oxygen absorption exhibit an induction period (τ) when the rate of oxygen absorption is immeasurably low. The dependence of τ and the rate of inhibited oxidation on the concentration of THQ has been studied and the reaction mechanism formulated, including the stage of regeneration of the inhibitor at the stage of chain termination. Using the method of mathematical modeling, the adequacy of the mechanism to the obtained experimental data has been substantiated, the rate constants of the key stages and parameters of the efficiency of inhibitor f regeneration have been found. When comparing the results of this article with previously published data, it has been found that the mechanism and antioxidant efficiency of tetrahydroquinolines depend on their structure and the nature of the active site of inhibition.

This paper presents a reaction kinetics model for analyzing the coal tar hydrodeoxygenation process from the perspectives of deoxygenation, hydrogenation, and cracking. The model is established based on the data from 24 sets of coal tar hydrotreatment experiments performed at different temperatures, pressures, and liquid hourly space velocity (LHSV) in a fixed-bed reactor. In the established model, the reaction kinetics equations, mass transport equations, and property calculation equations are coupled and solved simultaneously. This model can predict the distribution of H₂ partial pressure, H₂O partial pressure, and the concentrations of oxygen-containing compounds, aromatics, and cycloalkanes along the reactor axis, under different conditions (temperature, pressure, and space velocity). The validation experiments show that the model's prediction error for hydrodeoxygenation reaction product concentration is no more than 1.1%, for hydrogenation reaction product concentration is within 6.5%, and for cracking reaction product concentration is within 8.5%.

In this study, photocatalytic degradation of acetaminophen (ACE) in aqueous solutions under simulated solar light was studied using TiO₂ P25 immobilized on a glass plate by heat attachment method. The major factors affecting the removal of ACE, namely the amount and layers of TiO₂ P25 immobilized, flow rate (Qv) and initial ACE concentration, were analyzed. The structural features of the TiO₂ P25 immobilized were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). TiO₂ was successfully immobilized on the glass plate with the structure of anatase and rutile characteristic of the pattern unmodified TiO₂ P25. SEM micrographs of surface coats of TiO₂ P25 immobilized on glass plates revealed microfractures, which are probably due to the different thermal expansions among the different layers of TiO₂ P25 induced by the subsequent thermal treatment. The adsorption in the dark of ACE on the immobilized P25 and direct photolysis of ACE were studied, being negligible in both cases. The optimal operating conditions were 5 mg L⁻¹ of ACE, 0.28 g of TiO₂ P25 immobilized and a Qv equal to 14 mL s⁻¹. Under these optimal conditions, 100% removal of ACE was achieved after 3 h of reaction. Moreover, a pseudo-first order kinetic model represented well the experimental data. The immobilized TiO₂ P25 was regenerated six times, with no noticeable loss of photoactivity, confirming the high stability achieved by the immobilization procedure, which makes this procedure promising for real applications.

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This study aims to valorize agricultural waste of Leucaena leucocephala pods (LP) as a low-cost precursor for synthesizing high-performance activated carbon (LP-AC) for the removal of methylene blue dye (MB). Phosphoric acid H₃PO₄ was employed as a chemical activator of the LP biomass with a mass ratio of phosphoric acid to the precursor (3/1) before being calcined at 500 °C for 55 min. Box Benken design was investigated to optimize the experimental parameters of initial concentration, adsorbent dose, and pH. Variable optimization indicated that the highest removal efficiency of MB dye, estimated as 99.99%, was noticed at the initial concentration of 300.87 mg L⁻¹, adsorbent dose of 0.049 g, and solution pH of 10.07. Isotherm study revealed that Temkin model shows the best agreement with the experimental data with a correlation coefficient of (R² = 0.990). The adsorption capacity of MB dye was determined as 584.32 mg g⁻¹. The kinetic study suggested that the pseudo-second-order model is the best-correlated model for data fitting with (R² > 0.997). The thermodynamic analysis indicated an enthalpy change (ΔH) of − 18.50 kJ/mol, confirming that the adsorption of MB dye onto LP-AC material is an exothermic process. SEM characterization of the surface showed that the LP-AC exhibits a heterogeneous structure. The BET analysis revealed a remarkable surface area of 1367.30 m² g⁻¹ for the produced carbon, including a blend of mesoporous and microporous structures. Furthermore, complementary analyses including EDS, TGA, and FTIR confirmed the presence of crucial properties, underscoring its potential effectiveness as an adsorbent for removing MB dye.