Reaction Kinetics, Mechanisms and Catalysis最新文献

This study extracts potassium from quartz-rich muscovite ore via roast-leaching, employing CaCl₂ derived from periwinkle shells as additives. Various analytical and spectral techniques, including XRD, XRF, and SEM, were utilized for characterization throughout the research. The impact of experimental parameters such as CaCl₂ salt quantities, roasting temperature, leaching duration, and particle size on potassium extraction was thoroughly investigated. Under established conditions (ore to salts mass ratio of 1:5, temperature of 850 °C, particle size − 63 + 56 µm), 99.7% of the potassium was dissolved within 30 min. The roast-leaching process exhibited a reaction order of 1.178, and the estimated activation energy of 33.78 kJ/mol suggested a diffusion-controlled reaction through the product layer as the rate-limiting step for potassium extraction. The multiple regression analysis supports the data reported. To selectively recover potassium from the leach liquor, sodium perchlorate was introduced to precipitate potassium as KClO₄, subsequently thermally decomposed to yield high-purity potassium chloride. This innovative approach demonstrates a sustainable and cost-effective method for potassium recovery from its ore.

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The melamine thermal shrinkage method was used to prepare carbon nitride (g-C₃N₄). Fe/g-C₃N₄ was obtained by impregnation, and Na, K, and Zn additives were added as modifiers. The CO hydrogenation performances of the catalysts were studied before and after modification. The effect of additive modification on the textural properties of the Fe/g-C₃N₄ catalyst and product distribution of CO hydrogenation was investigated by combining several characterization techniques such as N₂ physical adsorption and desorption, XRD, SEM, TEM, FT-IR, TG, CO₂-TPD, Raman, XPS, and contact angle (CA) experiments. The textural characteristics and performance of the catalyst were markedly affected by the additive modifications. Na and K modifications weakened the strong interactions between Fe and g-C₃N₄ and improved the activity of the catalyst; additionally, hydrophilicity was enhanced. The Zn modified catalyst Fe/g-C₃N₄-Zn exhibited a weaker water gas shift reaction activity, and a lower CO₂ selectivity was obtained for CO hydrogenation. In the CO hydrogenation reaction, the Na-modified and K-modified catalysts, which exhibit enhanced surface alkalinity, inhibited secondary olefin hydrogenation and displayed high olefin selectivity and lower CH₄ selectivity. Fe/g-C₃N₄-Na exhibited the highest olefin selectivity, with C₂⁼–C₄⁼ up to 47.5%, and an O/P value of 5.1.

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To alleviate the sluggish kinetics exhibited by anodic Pt-based catalysts in the methanol oxidation reaction (MOR), N-doped carbon nanotube (N-CNTs) supports with uniform anchoring sites were synthesized by calcination pyrolysis, which provided abundant anchoring sites for the subsequent deposition of Pt₃Co. For the first time, small-sized and highly dispersed ordered Pt₃Co intermetallic compounds with different sizes were synthesized by adjusting the hydrothermal reaction temperature employed in the low-temperature N-anchoring strategy. The microstructure and physicochemical properties of Pt₃Co/N-CNTs with different Pt₃Co sizes were analyzed by XRD, STEM, and AC-STEM, and their electrochemical performances were evaluated by a three-electrode system. The results demonstrated that the Pt₃Co synthesized at 140 °C exhibited the superior MOR activity and stability. Specifically, its mass and area specific activities were 4905.3 mA mg⁻¹_Pt and 74.2 mA cm⁻¹ surpassing those of commercial Pt/C (1089.5 mA mg⁻¹_Pt and 16.5 mA cm⁻¹). Moreover, after 800 CV cycles, the current density still retained 78.9% of its initial MOR activity, thus demonstrating superior stability compared to commercial Pt/C (52.5%). The enhanced electrochemical performance of Pt₃Co/N-CNTs-140 can be attributed to the smaller particles size (2.15 ± 0.03 nm) of Pt₃Co, which maximizes the exposure of active site, resulting in a larger electrochemically active area and reduced activation energy for MOR. This effect not only enhances the noble metal utilization but also boosts electrocatalytic activity, thereby providing a new idea for designing robust MOR electrocatalysts with exceptional MOR activity and durability.

The purpose of this study is the pyrolysis of the distilled fractions obtained in the coking process as such and hydrotreated with the aim of diversifying the feedstock used in pyrolysis. The application of hydrotreating followed by pyrolysis, determines the reduction of the aromatic and olefinic hydrocarbons content in the feedstock, which leads to the improvement of the distribution of the reaction products and the decrease in the level of coke deposits, compared to the pyrolysis of non-hydrotreated distillate fractions. This study also aims to calculate the kinetic parameters of the pyrolysis process for non-hydrotreated and hydrotreated coking fraction at three equivalent temperatures: T = 680 °C, T = 695 °C, T = 705 °C.

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In this report, we proposed the hydrothermal synthesis of bismuth doped tungsten trioxide (Bi-WO₃) for H₂ evolution under visible light. The X-ray diffraction (XRD) study suggested the good phase purity and crystalline nature of the prepared Bi-WO₃. The scanning electron microscope (SEM) revealed that Bi-WO₃ are consists of plates like surface morphology. The ultraviolet–visible (UV–vis) spectroscopy showed that Bi-WO₃ has band gap of 2.69 eV whereas pristine WO₃ has 2.6 eV. It is confirmed that Bi-doping increases the optical band gap of the Bi-WO₃. The Bi-WO₃ (catalyst dose = 5 mg) showed H₂ production rate of 104.2 µmol/g/h which is higher than that of pristine WO₃ (73.6 µmol/g/h). Furthermore, Bi-WO₃ (catalyst dose = 30 mg) showed improved H₂ production rate of 334.7 µmol/g/h. The Bi-WO₃ (30 mg) + 4 wt% Pt exhibited the highest H₂ production rate of 637.8 µmol/g/h. It is believed that presence of Pt as cocatalyst boosted the H₂ evolution rate. The synthesized photocatalyst also demonstrated good stability which suggested its reusability up to four cycles.

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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