Reaction Kinetics, Mechanisms and Catalysis最新文献

This study investigates the synthesis of a cost-effective sawdust-derived adsorbent through an acidic and alkaline treatments, providing an alternative material for water purification specially for mercury removal. The Scanning Electron Microscopy revealed a porous structure, the Fourier transform infrared spectroscopy confirmed the existence of wide range of functional groups, and the Thermogravimetric analysis affirmed its thermal stability. Notably, the adsorbent exhibited an exceptional mercury uptake capacity of 528 mg/g according to Langmuir isotherm model, surpassing conventional low-cost alternatives. The kinetics adsorption data were modeled by nine kinetic models, likewise the adsorption isotherms data were modeled by eight isotherm models. The thermodynamic parameters, indicates that the removal process of mercury by activated sawdust is spontaneous and exothermic nature, occurs in less randomness at this interface. This research underscores the adsorbent’s promise for mercury removal, making a significant contribution to sustainable environmental remediation practices. The economic viability, coupled with its impressive performance metrics, positions this sawdust-derived adsorbent as a promising candidate for addressing water contamination challenges.

To understand the detailed reaction kinetics and mechanism of the reaction between Hg and HF, theoretical investigations of their reactions at different temperatures were carried out. The results suggest that the reactions goes through two steps. In the first step, Hg interacts with HF to form a complex HF⋯Hg, and then the F atom of HF approaches to Hg to form the transition state H∙∙∙F∙∙∙Hg, the bonding between F and Hg atoms results in the formation of HgF. Subsequently, the second HF molecule takes part in and it interacts with HgF to form the intermediate HF∙∙∙HgF, and then the transition state H∙∙∙F∙∙∙HgF forms due to the approaching of F atom of HF to Hg atom of HgF, finally the product HgF₂ is produced after the F and Hg atoms are bonded. The temperature significantly influences the reaction process. The weak interaction in the formation of the complex HF∙∙∙Hg as well as the intermediate HF∙∙∙HgF was illustrated by quantum theory of atoms in molecules (QTAIM). The kinetic parameters including the pre-exponential factor A, activation energy E_a and reaction rate k at different temperatures were calculated, and the expressions of reaction rates k for the reactions between HF and Hg to form HgF as well as HgF₂ were derived. The results would provide valuable insights into the chemical reaction of Hg and HF, the mechanism and the kinetics.

This study presents a novel approach for optimizing graphene yield from waste Zn/C battery graphite through response surface methodology (RSM) and a fractional factorial design. By focusing on graphite extracted from spent batteries and employing a statistically designed experiment, this work contributes to sustainable graphene production with good efficiency. We employed a fractional factorial design (2^5–1) to identify the influence of five key factors on graphene yield (Ye): reaction time, initial solution temperature, solution pH, bias voltage, and electrolyte concentration. A quadratic regression model was developed using response surface methodology (RSM) and validated through variance analysis (α ≥ 0.98). Subsequently, optimal conditions were determined through analytical methods, identifying the stationary point of the model and assessing the determinant value of the Hessian matrix. These optimal conditions were characterized by a reaction time (t) of 54.6 min, an initial solution temperature (Ti) of 34.5 °C, and a bias voltage (V) of 15.42 V. Under these conditions, the predicted graphene yield (Ye) was 40% ± 3%.

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This study explores the esterification of levulinic acid with 1-pentanol, employing Dowex® 50WX8 as a catalyst under microwave irradiation. Key parameters such as the pentanol/acid molar ratio, temperature, and catalyst loading were evaluated and utilized for kinetic modeling. The kinetic behavior of the reaction was investigated using a dual-model approach: a pseudo-homogeneous model to account for the microwave effect and catalytic contributions modeled through LHHW and Eley–Rideal mechanisms. The best model was chosen based on statistical results obtained from Markov Chain Monte Carlo (MCMC) analysis, which involved an LHHW model with the surface reaction as the limiting step, resulting in an activation energy of 50.6 kJ mol⁻¹ for the catalytic synthesis of pentyl levulinate. The role of the alcohol in the esterification route was explained, and catalytic stability was confirmed, with the catalyst maintaining activity over multiple cycles. The absence of mass transfer limitations was proved using the Weisz–Prater criterion. A plausible reaction pathway was proposed for the levulinic acid esterification over the 50WX8 catalyst.

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The carboxylic multi-walled carbon nanotube-loaded nickel (Ni/c-MWCNT) catalyst prepared by the excess impregnation method was used for the hydrogenation of oleoresin-based turpentine (OBT) into high energy density fuel. Benefiting from small nickel nanoparticle sizes (about 10 nm) and the carrier’s high surface area, a hydrogenation rate of 99.1% was achieved at 145 °C and 3 MPa, superior to a commercial 5 wt.% Pd/C. Hydrogenated oleoresin-based turpentine (HOBT) satisfied the density, flash point, and freezing point outlined by the American Society of Testing and Materials standard. Hydrogenation improved the oxidative stability, smoke point, and calorific value of OBT while changing its color to water white. The impact of blend ratio on the blended biomass fuel performance was evaluated by measuring the smoke point, density, kinematic viscosity, calorific value, freezing point, and flash point of biofuels blended with HOBT and exo-tetrahydrodicyclopentadiene (JP-10). When HOBT was blended up to 20% (v/v) with JP-10, the performance of blended biomass fuel was comparable to that of JP-10 and even superior at freezing temperatures.

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In this work, the definition of deactivation kinetic model (DKM) has been given under some assumptions and its features were illustrated through comparison with prior kinetic models such as DM (deactivation model), Langmuir rate equation, pseudo kinetic model and unreacted SCM (shrinking core model). DKM is based on fractional conversion of solid and concentration of fluid phase, which is one of the different kinetic models for the heterogeneous processes. DKM has no thermodynamic equilibrium quantities such as adsorption amount (q_e) unlike the previous pseudo-order models. Therefore, DKM can offer more accurate kinetic parameters than other models. Main equations of DKM can be solved by using Matlab functions such as “ODE” and “lsqnonlin”. This DKM is a semi-empirical and apparent kinetic model for fluid/solid heterogeneous processes and its kinetic equations can be used not only in heterogeneous reactions, but also in adsorption processes.

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In this research, three distinct ternary-nanothermites were subsequently integrated into double base propellant formulated with nitrocellulose (NC) and diethylene glycol dinitrate (DEGDN). These nanothermites consisted of magnesium and aluminum alloy (MgAl) as fuel and metal oxides (CuO, NiO, and TiO₂) acting as oxidizers. Experimental results demonstrated the uniform distribution of the three investigated nanothermites throughout the NC/DEGDN composite. DSC findings indicated a significant increase in the overall heat release of the NC/DEGDN double base propellant upon the addition of the three nanothermites. It is found that the type of oxidizer within the nanothermite composition played a crucial role in the thermo-kinetic proprieties of the NC/DEGDN propellant. Specifically, nanothermites incorporating CuO and TiO₂ acted as catalysts, substantially enhancing the thermolysis of the propellant. In contrast, MgAl–NiO exhibited a stabilizing effect on the thermal decomposition of NC/DEGDN propellant. These findings offer appreciated insights into the tailoring properties of double-base propellant by selectively incorporating specific nanothermites based on their oxidizer content.

Two Mo-Bi based catalysts were prepared with the assistance of PMMA with different sizes, and tested in selective oxidation of tert-butanol to methacrolein. The prepared catalysts, especially C-PM-6 with μm-PMMA, exhibited excellent catalytic performance. Based on the characterization results (BET, MIP, SEM, TEM, XRD, FTIR), the effects of the assistance of PMMA with different sizes were verified. Without modifying the highly active Co₆Fe₄Mo₁₂Bi_1.5O_x phase, the formation of over-oxidation MoO₃ phase was effectively inhibited due to the decomposition of PMMA particles. Importantly, the PMMA assistance could develop hierarchical pore structures, especially mesoporous pores of 6 nm for C-PM-6 catalyst, by preventing primary particles’ agglomeration. Therefore, the mesoporous/macroporous specific surface area obviously increased and thus the abundant active sites were exposed. More importantly, in the newly-formed mesopores pores, there happened Knudsen or molecular diffusion with relatively high mass transfer coefficient, avoiding the overoxidation of target product MAL. From the perspective of reaction engineering, our finding may suggest a new way for developing ultra-high performance commercial selective oxidation catalyst.

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In this study, we synthesized a novel ceramic material Bi_0.5Na_0.5Ti_0.95 (Ni_0.2Fe_0.2Sb_0.6)_0.05O₃ named BNT-NFS via the solid-state route and assessed its efficacy as a photocatalyst for removing methylene blue dye from wastewater. The synthesized samples underwent thorough characterization using thermogravimetric analysis combined differential thermal analysis TGA-TDA, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and UV–Visible measurements. TGA-DTA and XRD analyses confirmed the successful formation of BNT-NFS material at 1150 °C, exhibiting a hexagonal phase structure. FTIR analysis revealed an intense band at 421 cm⁻¹, corresponding to metal-oxide vibrations in the BNT-NFS spectrum. SEM observations unveiled a distinct microstructure of BNT-NFS composed of grains of varying sizes. BET analysis indicated that the prepared BNT-NFS powder possessed a significant specific surface area of 261.36 m²/g. Optical and photocatalytic assessments demonstrated that BNF-NFS perovskite is a semiconductor material with a band gap of 2.73 eV, exhibiting satisfactory photocatalytic activity for methylene blue MB dye removal. Notably, the removal efficiency reached 60% after 210 min of exposure to sunlight irradiation. This result is better than that registered for the pristine BNT.

In this study, the UVA-induced degradation of Basic Red 18 and Reactive Red 180 was examined using a photocatalytic treatment system using magnetic activated carbon derived from the fruit rind of Brachychiton populneus. Numerous factors, including the pH of the solution, the dose of photocatalyst, and the initial concentration of the dye, have been optimized because they affect the photocatalytic activity of magnetic activated carbon.The pH of the solution (6 for basic Red 18 and reactive red 180) and 0.75 g L⁻¹ of magnetic activated carbon with a degradation rate of 100% and 82% for Basic Red 18 and Reactive Red 180, respectively, are the parameters that should be set at their optimal values for an initial dye concentration of 50 mg L⁻¹. Superoxide and electrons are the main active species and play a major role in the photocatalytic degradation of dyes by magnetic activated carbon under UVA light irradiation. The two dyes had five cycles of reuse, according to a study on magnetic activated carbon that was completed under optimal conditions.