Reaction Kinetics, Mechanisms and Catalysis最新文献

We present a meshless method of lines for efficiently simulating two-dimensional nonlinear reaction–diffusion systems. Using positive-definite radial kernels, we derive approximate particular solutions via the Laplace operator and superimpose them to approximate unknown fields and their spatial derivatives without mesh generation. The resulting ordinary differential system is integrated with a high-order solver. We theoretically establish and numerically verify the method’s stability and positivity-preserving properties, ensuring dynamical consistency with the underlying PDEs. Benchmark tests on cross-diffusion Brusselator systems confirm accuracy, robustness, and geometric flexibility. Compared with leading mesh-based and meshless schemes, our approach offers a compatible and high-order framework for reaction–diffusion problems on complex domains.

In this work, hollow ZnO spheres (HS–ZnO) were synthesized via a glucose-templated hydrothermal route, and their structural, textural, and photocatalytic properties were systematically optimized. The HS–ZnO exhibited a large surface area (96.35 m²g⁻¹), uniform hollow morphology, and a narrower band gap (3.12 eV) compared with commercial ZnO. These features enhanced light absorption, charge separation, and adsorption capacity. Under optimized conditions (5 g L⁻¹ catalyst, pH 5,120 min UV irradiation, and 5 mg L⁻¹ Ni(II)), HS–ZnO achieved 88.16% Ni(II) removal, more than twice the efficiency of commercial ZnO (41.37%). Kinetic studies confirmed a pseudo-second-order model, while adsorption equilibrium followed the Freundlich isotherm, indicating chemisorption on heterogeneous surfaces. Control experiments revealed that photoreduction was the dominant pathway. HS–ZnO maintained 76.2% efficiency after five cycles, demonstrating excellent stability and reusability. These results establish morphology-controlled HS–ZnO as a cost-effective and robust photocatalyst for Ni(II) removal from aqueous solutions.

Graphical Abstract

The kinetics of the reaction between tungstate ion and hydrogen peroxide in aqueous medium containing phosphate ions, both in the absence and presence of oxidizable organic substrates (alcohols, polyalcohols and carbohydrates), has been followed spectrophotometrically in the ultraviolet range of the electromagnetic spectrum, following at 225 nm the decay of the limiting reactant (tungstate ion). The reaction showed a deceleration much more accused than expected for a pseudo-first order process. Two different experimental rate constants (k₁ and k₂) have been determined from each kinetic run, k₁ being consistently higher than k₂. The dependence of k₁ on the hydrogen peroxide initial concentration suggested that the main oxidizing agent was a diperoxo tungsten(VI) complex. For the oxidation of alcohols/polyalcohols both rate constants increased with the number of OH groups. In the case of carbohydrates, the monosaccharides were more readily oxidized than sucrose (a disaccharide). Copper(II) ion (an efficient superoxide radical scavenger) strongly catalyzed the reduction of W(VI), whereas the surface of the spectrophotometric cell walls did not affect appreciably the reaction rate. Acrylamide showed a slight inhibiting effect on the rate, but it did not suffer any chemical change itself at the end of the reaction. In the absence of organic compounds, the activation energy associated with k₂ (65 ± 4 kJ mol⁻¹) was considerably higher than that of k₁ (29 ± 2 kJ mol⁻¹). Finally, a mechanism coherent with the available experimental information, involving three different oxidation states of tungsten (VI, V and IV) and three inorganic free radicals (hydroperoxyl, superoxide ion and hydroxyl), has been proposed, the strong deceleration of the reaction being explained by the accumulation in the solution of a long-lived intermediate, W(V), that could be partially reoxidized to W(VI).

Graphical abstract

We demonstrate a calcine-and-use, Mn-promoted Co/γ-Al₂O₃ prepared by single-pot citrate–nitrate auto-combustion that performs in Fischer–Tropsch synthesis without the conventional 600 °C H₂ pre-reduction. Compared with a wet-impregnated benchmark (WI), the auto-combustion sample (SC) forms ~ 10 nm Co domains on a 108 m² g⁻¹ matrix (vs ~ 44 nm on 73 m² g⁻¹ for WI), and H₂-TPR confirms > 90% reducibility below 510 °C, whereas a spinel-bound fraction in WI persists up to 650 °C. Under identical FT conditions (240 °C, 10 bar, H₂/CO = 2, GHSV ≈ 3600 h⁻¹), SC converts 40.7% of CO (WI: 24.2%). At steady state (12–50 h TOS; n = 3), selectivities were: SC CH₄ 30.3%, C₅⁺ 45.6% (STYC₅⁺ 1.66 g h⁻¹ g_cat⁻¹); WI CH₄ 19.8%, C₅⁺ 62.3% (1.35). Carbon balances closed to 98 ± 2%. The activity gain is attributed to an ≈ 4 × larger surface cobalt inventory associated with ~ 10 nm domains. Eliminating high-temperature pre-reduction simplifies operation and reduces thermal input, providing a ready-to-use Co/Al₂O₃ route; stability and scale-up are identified as next steps.

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This study focuses on the production of high-value chemicals from pistachio soft skin (PSS). The biooils generated from the pyrolysis of PSS, both with and without calcium oxide and calcium carbonate as catalysts, were examined at pyrolysis temperatures of 573 and 773 K. Various analytical techniques, including thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), gas chromatography (GC), and gas chromatography-mass spectrometry (GC/MS), were employed to investigate the effects of different process parameters on the quality and quantity of the products. The maximum yield of the produced biooil was approximately 27.6%, achieved at 773 K using CaCO₃ as the pyrolysis catalyst. Over 35 chemical components were identified in the biooil through GC/MS analysis. The predominant components of the biooil include 5-methyl-2-pyridinamine (30%), 3-undecylphenol (14%), 3-pentadecylphenol (9%), phenol (9%), 1,2-benzenedicarboxylic acid diisooctyl ester (4%) and hexadec-7-en-16-olide (2.5%). The chemical compositions of the produced biooils at the two different pyrolysis temperatures, with and without catalysts, were relatively similar. However, several new components were identified at higher temperature, and the yields of certain chemicals varied by up to 5% depending on the catalyst used. These results show the significant potential of producing value added chemicals from the biomass of PSS.

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This study investigates the kinetics and reaction mechanisms of the chloride ion (({text{Cl}}^{ - })) removal from sea sand through catalytic ozonation, employing a synthesized manganese oxide-loaded biochar (MnO_xBC) catalyst. The MnO_xBC was prepared via wet impregnation and characterized by XRD, FTIR, XPS, XRF, and SEM. The catalytic performance was systematically evaluated by varying parameters, including catalyst dosage, ozone dosage, water/sand ratio, and reaction temperature. Under optimal conditions (0.15 g/L catalyst dosage, 25 mg/L ozone dosage, 3:1 water/sand ratio, 50 ℃ temperature, and 15 min reaction time), the chloride removal efficiency (CRE) reached 98.17%, a significant enhancement from 85.75% achieved by water washing alone. Scavenger experiments with tert-butyl alcohol (TBA) and 1,4-benzoquinone (p-BQ) confirmed that the degradation pathway is dominated by hydroxyl radicals (*OH) and superoxide radicals (*({text{O}}_{2}^{ - })). XPS analysis revealed a redox cycle between Mn³⁺ and Mn⁴⁺ as the central catalytic mechanism for ozone decomposition into reactive oxygen species (ROS), which subsequently oxidize ({text{Cl}}^{ - }) through a multi-step pathway. Kinetic analysis indicated that the reaction followed a pseudo-first-order model, with the catalytic process significantly increasing the apparent rate constant. This work provides fundamental insights into the catalytic ozonation mechanism and kinetics, revealing MnOₓBC as an effective catalyst for chloride oxidation in solid matrices.

Graphical abstract

The effect of external field on the oxidative degradation of AFB1 by plasma activated water was at the M06-2X/aug-cc-pVTZ//M06-2X/6-31G(d) level. For both ·OH addition and ozonolysis of vinyl bond of the terminal furan ring, bimolecular rate coefficients increase with increasing of external field. An increase in the external field leads to an increase in solvent viscosity and, consequently, a decrease in the diffusion rate coefficients. These two opposing effects ultimately result in a decrease in the apparent rate coefficients for ·OH addition and an increase for ozonolysis under the external field. The activation energy for ·OH addition process decreases from 17.02 to 12.17 in the presence of an external field 0.0004 a.u., while the pre-exponential factor decreases by about 12 times. In the ozonolysis process, the activation energy decreases from 10.37 to 10.31, and the pre-exponential factor increases by about 1.26 times. For the degradation of AFB1 by ·OH and ozone in the presence of an external field of 0.0004 a.u., the temperature dependence of the apparent rate coefficients within the range 298.15–320 K is given by lnk = (–1463.8/T) + 27.063 and lnk = (–1240.8/T) + 14.208. It can be concluded that AFB1 degradation is highly diffusion-controlled, with the external field exerting a negative impact on the process.

A robust and sustainable catalytic system was developed by immobilizing a Brønsted acidic ionic liquid (BAIL) on sulfonated polyethylene glycol₄₀₀ (PEG₄₀₀-SO₃H) decorated Fe₃O₄ nanoparticles for the efficient synthesis of tetrazolopyrimidine derivatives. The fabrication of the organic–inorganic hybrid catalyst commenced with the formation of an organic zwitterion via the reaction of N-methylimidazole with 1,4-butanesultone leading 1-methyl, 3-butyl sulfonate imidazolium salt. Subsequently, Fe₃O₄ nanoparticle were decorated by PEG₄₀₀-SO₃H to give Fe₃O₄@PEG₄₀₀-SO₃H core–shell nanoparticles. Finally, through a reflux-assisted grafting process in ethanol, organic zwitterion was anchored on Fe₃O₄@PEG₄₀₀-SO₃H support. The resulting hybrid material was meticulously characterized using advanced analytical techniques, including FTIR, ¹H NMR, XRD, SEM, TEM, TGA, BET and EDX confirming its structural integrity. The catalytic efficacy of the prepared hybrid material was demonstrated in a one-pot multicomponent reaction involving aromatic aldehydes, active methylene compounds, and 5-aminotetrazole. Under optimized conditions, the catalyst exhibited exceptional performance, delivering high yields (87–92%) within remarkably short reaction times (15–35 min) at a minimal loading of 5 mol%. Furthermore, the catalyst’s magnetic properties facilitated facile recovery, while its remarkable reusability was evidenced by sustained activity over four consecutive cycles with negligible loss in yield. Moreover, the introduced anchored BAIL combines the advantages of both heterogeneous and homogeneous catalysis while overcoming the limitations associated with free BAIL.

Graphical abstract

We have investigated the effect of different impurities (CO, CO₂, CS₂, CH₃OH, H₂O, C₄H₄S) on the silicon-bridged diphosphine(PNSiP)/CrCl₃(C₄H₈O)₃/modified methylaluminoxane ethylene tri-/tetramerization system. The results showed that the addition of trace impurities has a certain inhibitory effect on catalytic activity. The influence of impurities on the catalytic activity of the catalyst system was as follows: CO > CO₂ > CS₂ > CH₃OH > H₂O > C₄H₄S. CO showed the most significant inhibitory effect in reducing activity from 1.75 × 10⁶ g/(mol Cr h) to 0.74 × 10⁶ g/(mol Cr h) at an addition of 0.2 ppm. Through the analysis of nuclear magnetic resonance (NMR) and ultraviolet–visible spectrophotometry (UV–vis), we found that carbon monoxide mainly inactivates the catalytic system by coordinating with chromium active sites, while methanol and water reduce the catalytic activity by destroying the structure of modified methylaluminoxane. Furthermore, we also proposed a possible reaction path between carbon monoxide and the chromium active center.

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This study aims to synthesize and characterize copper-alumina (Cu–Al) and cobalt-alumina (Co–Al) oxides materials for the catalytic degradation of the textile dye Methyl Orange (MO) in an aqueous solution. The materials were prepared via the co-precipitation method and characterized using several physicochemical techniques. The effects of key parameters including the oxidant peroxymonosulfate (PMS), catalyst dosage, and dye concentration were investigated to optimize the degradation process. Experimental results revealed that both Cu–Al and Co–Al catalysts exhibited excellent catalytic activity, achieving rapid degradation of Methyl Orange, within 2 min. Radical scavenging experiments indicated that the superoxide radical (O₂^·−) was the primary reactive species involved in the degradation process, contributing up to 93% of the overall removal. High degradation rates were observed for the Cu–Al and Co–Al catalysts, reaching 92% and 93%. This remarkable efficiency was also found during the degradation of the Quinolline Yellow (E104) dye, reflecting the robustness of the catalytic system. Although lower performances were recorded for the dye Metanil Yellow (MY), the results remain promising, with degradation rates of 49% for Cu–Al and 53% for Co–Al.