Reaction Kinetics, Mechanisms and Catalysis最新文献

Copper oxide (CuO) thin films were synthesized on glass substrates with different molar concentrations of precursor (0.2, 0.4, 0.6, and 0.8) using a sol–gel process (dip-coating). The effect of the molar concentration on structural, optical, electrical, and photocatalytic performance was studied. X-ray diffraction (XRD) research reveals that all the samples are polycrystalline and reveal a monoclinic crystal structure. The highest level of crystallinity was observed for the 0.8 M solution, with a crystallite size of 66.55 nm. The scanning electron microscope (SEM) was used to investigate the surface morphology of the films. The transmittance values were recorded using UV–Visible spectrophotometry within the 300–1200 nm wavelength range. The energy band gap of the film is found to increase with increasing concentration from 0.2 to 0.4 M, then decrease as the concentration increases. The four-point probe approach was utilized to conduct electrical measurements to evaluate the resistivity of the films. The resistivity reduces as the molar concentration of precursor solutions increases from 0.2 to 0.8 M. The photocatalytic efficiency of CuO thin films was evaluated via the degradation of Congo Red (CR) dye under sunlight irradiation for 4 h. The findings indicated that films prepared with a 0.6 M precursor demonstrated the highest photocatalytic efficiency, attaining more than 97.21% degradation with a reaction rate constant of 0.5042 ± 0.1466 h⁻¹. This improvement is attributed to the optimized equilibrium between crystallinity, surface morphology, and light absorption.

Hereby, we applied a previously developed method of zeolite-catalyzed gas phase synthesis of unsymmetric ethers for a homologous compound to previously synthesized cyclopentyl methyl ether (CPME)—cyclopentyl ethyl ether (CPEE). This synthesis utilized two bio-based alcohols as feed—cyclopentanol (CYPol) in a mixture with ethanol. From a tested group of commercially available zeolites (FER, MOR, BEA, Y, ZSM-5) the best CYPol conversion and selectivity to CPEE was achieved with medium-pore ZSM-5. We further used this zeolite to investigate the effect of reaction temperature and Si/Al ratio, as well as stability and recyclability of the catalyst. At optimized reaction conditions, we achieved selectivity to CPEE of 72% at CYPol conversion of almost 90%. High reaction temperatures, as well as high acid site concentrations in zeolite lead to favoring CYPol dehydration into cyclopentene over etherification. The catalyst exhibited high stability and good recyclability by calcination. We achieved comparable CPEE selectivity at CYPol conversion under mild reaction conditions to the previously documented CPME synthesis, which is a novel green solvent that utilizes a toxic reagent (methanol) for its production.

In this study, a series of Cu–Mn modified ZSM-5 zeolites (Cu_xMn_y/ZSM-5) were synthesized via the solgel method to investigate their catalytic oxidation performance towards toluene. The influence of Cu–Mn modification on the catalytic oxidation of toluene was systematically examined using various characterization techniques, including XRD, FTIR, BET, XRF, XPS, and TEM. The results indicated that Cu_xMn_y/ZSM-5 maintained the complete framework characteristics of ZSM-5 zeolites and possessed a hierarchical pore structure with pore size distribution dominated by micropores and mesopores. The highly dispersed Cu_xMn_y on ZSM-5 significantly enhanced the relative content of surface Cu⁺ and Mn³⁺ species, with the presence of Cu⁺ facilitating the formation of oxygen vacancies. More oxygen vacancies can significantly improve the oxygen migration rate and thus enhance the catalytic oxidation activity. Among them, Cu_0.5Mn_0.5/ZSM-5 exhibited a higher proportion of low-valence Mn, low-valence Cu, and adsorbed oxygen (O_ads), which is beneficial for the low-temperature catalytic oxidation of toluene. The evaluation of the catalytic oxidation performance towards toluene showed that Cu_0.5Mn_0.5/S-0.1 had the best catalytic effect, with the lowest apparent activation energy of 131.19 kJ mol⁻¹ and a T₉₀ of 256 °C. This research provides a new approach for the development of catalysts for the low-temperature catalytic oxidation of toluene.

The thermal decomposition of cerium(III) nitrate hexahydrate into cerium oxide was studied under argon and air atmospheres via simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). XRD and SEM analyses revealed that the synthesized cerium oxide had an average crystallite size of 20 nm, although agglomeration resulted in secondary particles up to 1 μm in size. The decomposition was monitored under nonisothermal conditions, and the thermal analysis data were evaluated from a kinetics point of view by isoconversional and model-fitting methods. The isoconversional expanded Friedman demonstrated a clear dependence of the activation energy (Eₐ) on the degree of conversion (α), which supports a complex mechanism. Both atmospheres yielded CeO₂ formation, but through rather different mechanisms. Namely, the Ar atmosphere forms CeO₂ through multiple stages, keeping a high concentration of Ce(III) ions, and preventing the oxidation process from Ce(III) to Ce(IV) ions. Decomposition in the air was more energetically favorable compared to the argon atmosphere. The activation energy values were obtained as follows: 156 and 232 kJ mol⁻¹ (expanded Friedman), 190 and 285 kJ mol⁻¹ (Discrete model), and 166 and 280 kJ mol⁻¹ (N-th order) for air and Ar atmosphere. Based on these results, a reaction mechanism was proposed for the thermal decomposition of cerium(III) nitrate hexahydrate in both atmospheres.

In this study, the optimization process was carried out by varying the parameters of temperature, reaction time, and catalyst ratio in the hydrodeoxygenation (HDO) reaction. The optimization design was designed by the response surface methodology (RSM) using the Box Behnken design (BBD). NH₃-TPD analysis of the catalyst showed that the acidity of CuO/HZSM-5 was 0.7548 mmol/g, and the STEM image showed a fairly even distribution of metals in the zeolite. Based on the optimization method with BBD showed the significance of the model and quadratic term of temperature (A²), reaction time (B²), and catalyst mass (C²). GC–MS analysis indicated reduced acid and methoxyphenol groups alongside increased ester, phenol, and hydrocarbon compounds. The upgraded product exhibited higher carbon concentration and lower oxygen concentration, achieving a deoxygenation rate of approximately ~ 64%. Additionally, kinematic viscosity decreased compared to raw bio-oil, while the HHV improved from 10.27 to 16.23 MJ/kg. This upgrading process presents valuable avenues for future research.

In this work, we explored the role of Lewis acid catalysts such as Scandium triflate (Sc(OTf)₃) and Copper triflate (Cu(OTf)₂) in accelerating [4+2] cycloaddition reactions of 3-alkyl-2-vinylindoles and β,γ-unsaturated α-ketoesters using DFT calculations with the B3LYP functional and SDD and 6-311G(d,p) basis sets. This includes studies that are focused on understanding how catalytic parameters like reaction pathways, regioselectivity, or efficiency contribute to these transformations. Using molecular electron density theory (MEDT) and computational studies to analyze these catalytic effects, the catalysts were found to enhance the electrophilicity of β,γ-unsaturated α-ketoesters to a great degree, favoring a polar pathway and regioselectivity. Among the wide range of catalysts being screened, Sc(OTf)₃ was confirmed as the best one with the catalytic ability of activating bond cleavage and stabilizing intermediates, especially favoring the fastest exo pathway leading to the main product P-1. Furthermore, molecular docking and absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis suggested that synthesized indole-harboring pyrans have promising potency against HIV-1 and SARS-CoV-2. Notably, P4 and P3 showed relatively high binding affinities against HIV-1 whereas P1 showed a trespass degree of binding toward SARS-CoV-2 proteins that is more than existing benchmark drugs in certain aspects. These compounds have been reported to possess favorable ADME profiles, high gastrointestinal absorption, and blood–brain barrier permeability that highlighted their potential to be leads for antiviral drug development.

The cycloaddition reaction between cyclopenta-1,3-diene and a mixture of 3-oxo-1-phenylbut-1-en-1-ylium and 4,4,4-trifluoro-3-oxo-1-phenylbut-1-en-1-ylium was investigated using Molecular Electron Density Theory (MEDT), both in the absence and presence of a BF₃ catalyst. This theoretical approach enabled an in-depth examination of the reaction mechanisms, free energy profiles, and stereoselectivity. The reactions favored the formation of specific stereoisomers depending on the catalytic conditions: Product P-2 predominates in the absence of BF₃, while the presence of BF₃ shifts the selectivity toward product P-1. Complementary Electron Localization Function (ELF) and Bonding Evolution Theory (BET) analyses confirmed that both reactions proceed through a non-concerted and asynchronous mechanism, with the formation of the C2–C10 bond preceding that of C3–C12. The presence of the BF₃ catalyst was found to promote a more efficient electron density reorganization, as reflected by earlier and faster development of key bonding interactions. Molecular docking analysis revealed that the incorporation of a CF₃ group significantly enhances the binding affinity of the ligands (P-1 and P-2) to viral proteins, underscoring their potential as antiviral drug candidates. Furthermore, ADMET analysis revealed full compliance with Lipinski’s Rule of Five, favorable molecular weights, excellent predicted gastrointestinal absorption, absence of mutagenic or cardiotoxic effects, and reasonable synthetic accessibility, collectively supporting their suitability as promising oral drug candidates. An adsorption study on silica gel also demonstrated stronger interaction with P-2 due to the CF₃ group, enabling efficient chromatographic separation from P-1.

Spectrophotometric kinetic methods of the determination of absorption capacity in relation to oxygen-centered radicals and to 2,2′-diphenyl picrylhydrazyl stable radical was used to detect antiperoxyradical ability of folates: folic acid (FA) and its structural derivatives: 7,8-dihydrofolate (DHF), 5,6,7,8-tetrahydrofolate (THF), and 5-formyltetrahydrofolate (5-FTHF). It is established that reduced forms of folic acid—DHF and THF, possess significantly higher antiradical ability in comparison with FA and 5-FTHF. Square wave voltammetry method was used to determine redox characteristics of folates. The reaction sites of folates responsible for their antiradical activities were identified, and the most favorable one was discovered.

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In this paper, paraffin was adopted as the matrix, and fly ash was the supporting material. The composite phase change materials loaded with fly ash in different proportions were prepared utilizing the direct impregnation method. The chemical composition of the composite phase change materials of paraffin–fly ash was characterized by XRD and FTIR. The thermal properties were determined by leakage rate testing and thermogravimetric analysis. The kinetic models and parameters of thermal decomposition of the composite phase change materials were obtained through the Coats–Redfern method and the Melak method. The characterization results demonstrated that the thermal stability of composite phase change materials initially improved and subsequently decreased with fly ash addition. The composite containing 5% fly ash exhibited optimal thermal stability enhancement, while maintaining favorable physical compatibility and chemical stability. Kinetic analysis revealed that the activation energy and pre-exponential factor for paraffin decomposition were determined as 121.92–245.11 kJ mol⁻¹ and 2127.78–12,802.39. The activation energy and pre-exponential factor for paraffin–fly ash composite phase change material exhibited ranges of 146.19–170.54 kJ mol⁻¹ and 1547.36–2253.11. The decomposition reaction of the composite phase-change material with the optimal performance (95% paraffin+5% fly ash) can be described by the R1 model under a heating rate of 5 °C min⁻¹. At heating rates of 10 °C min⁻¹ and 15 °C min⁻¹, the decomposition process of this material is more appropriately described by the R3 model. The corresponding reaction kinetic models have been established.

Green-synthesized iron oxide nanoparticles (IONPs) were prepared with the assistance of Camellia sinensis extract and supported at varying loadings on TiO₂ anatase phase doped with 10 mol% CeO₂. These composite materials were investigated as catalysts for the photodegradation of the azo dye methyl orange under UV irradiation. Characterization revealed the formation of amorphous FeO_x nanoparticles, functionalized by polyphenolic compounds from the extract. A progressive decrease in the band gap energy was observed with increasing iron content, ranging from 2.98 to 1.19 eV. Photocatalytic degradation followed a pseudo-first order kinetic model, with up to 95% dye removal achieved after 120 min of UV exposure. The catalyst with 1.9 wt% Fe exhibited optimal performance, demonstrating significantly enhanced photocatalytic activity due to improved light absorption and charge separation.

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