Reaction Kinetics, Mechanisms and Catalysis最新文献

We have investigated the degradation characteristics of ultra-high molecular weight polyethylene in decalin, and determined the rate constant and activation energy of degradation. We found that oxidative degradation of UHMWPE is more easily achieved than thermal degradation, and oxidative degradation occurs mainly in high oxygen atmosphere. Since the degradation is a reaction with changing molecular weight rather than concentration, we considered the reaction rate with respect to molecular weight. In addition, the kinetic equation with respect to molecular weight conversion was considered to determine the reaction rate constant irrespective of the reaction order, as the order of the reaction increases with temperature, and the reaction rate and Arrhenius constant were determined. In addition, as the order of the reaction increases with temperature, the kinetic equation with respect to molecular weight change rate was considered to determine the reaction rate constant irrespective of the reaction order, the reaction rate and Arrhenius factor were determined.

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.

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 systematically investigates the reduction mechanism of CoAl₂O₄ (100) catalyst in H₂-selective catalytic reduction (SCR) of NO_x using density functional theory (DFT) calculations. The results show that H atoms adsorbed on the three-coordinated oxygen atoms (O_3C) of the CoAl₂O₄ (100) surface exhibit the highest stability, thereby forming Lewis acid sites favorable for NO adsorption. On the CoAl₂O₄ (100) O_3C site pre-adsorbed with H, the dissociation barrier of NO is reduced to 0.43 eV, significantly lower than that on the H-free surface (1.54 eV). The analysis of H₂O and N₂ formation pathways reveals low adsorption energies, enabling easy desorption of products from the CoAl₂O₄ (100) surface. The formation and desorption of N₂O, a by-product, have high energy barriers, suggesting an extremely low probability of N₂O generation in SCR and good selectivity of the catalyst. Moreover, the CoAl₂O₄ (100) surface shows excellent water tolerance but poor tolerance to sulfur, providing crucial references for future optimization of CoAl₂O₄ catalysts.

Herein, we demonstrate that pristine Co-based ZIF-9 exhibits exceptional peroxidase-mimicking activity, catalyzing the oxidation of o-phenylenediamine as a model substrate in the presence of H₂O₂. The nanozyme shows a maximum reaction rate (V_max) of 3.66 ± 0.10 × 10^–5 (M/s) which is 10³-fold higher than horseradish peroxidase (HRP). A simple, rapid, and low-cost colorimetric sensor platform for the detection of H₂O₂ was also developed, demonstrating a linear range of 10⁻⁴ − 1.4 × 10^–3 M and a detection limit of 0.94 × 10⁻⁵ M (S/N = 3).

In this study, we explored the photocatalytic degradation of methyl orange (MO) and Rhodamine B (RhB) via 2.0 wt% I–Bi₂S₃, ZnIn₂S₄, and their composite ZnIn₂S₄/2.0 wt% I–Bi₂S₃ under visible light irradiation. While 2.0 wt% I–Bi₂S₃ revealed insignificant photocatalytic activity, ZnIn₂S₄ showed outstanding efficiency, degrading 94.7% of MO in 150 min and 98.9% of RhB in just 35 min. The composite achieved even better performance, 95% MO degradation (150 min) and 99.7% RhB degradation (35 min), demonstrating a synergistic effect between 2.0 wt% I–Bi₂S₃ and ZnIn₂S₄. TEM, SEM, XRD, XPS, UV–Vis DRS, ESR, photoelectrochemistry, and PL tests were performed to characterize the structure, morphology, and separation efficiency of the products. According to kinetic studies, the photocatalytic degradation kinetics of rhodamine B and methyl orange exhibited various patterns. For Rhodamine B (RhB), a nonlinear exponential decay function was applied to obtain the rate constants, yielding k = 0.17186 ± 0.00147 min⁻¹ for ZnIn₂S₄ and k = 0.25567 ± 0.00405 min⁻¹ for the composite with R² = 0.99. This outcome indicates that RhB degradation follows first order kinetics closely. While the degradation of methyl orange fulfills R² ≈ 0.93, which means it is less consistent with the first order model. The computed rate constants were k = 0.01171 ± 0.00157 min⁻¹ for ZnIn₂S₄ and k = 0.01362 ± 0.00184 min⁻¹ for the composite. MO degradation is characterized by pseudo-first order behavior due to the deviation from linearity of a first order reaction. The boost in photocatalytic degradation was related to the reduction in electron–hole recombination that resulted from the creation of a heterostructure and a doping strategy. This study shows the potential of ZnIn₂S₄-based composites as high-performance photocatalysts for environmental remediation, displaying an exceptional solution for effectively eliminating hazardous organic dyes from wastewater.

Bis (8-hydroxyquinoline) manganese (Mnq₂) material was prepared by the liquid-phase synthesis method. The material was characterized by SEM, FTIR, UV–vis, BET, and PL. The synthesized Mnq₂ was used as a photocatalyst, and methylene blue (MB) was used as the targeted contaminant to study the effect of the addition amount of Mnq₂ on the photocatalytic performance. The findings indicated that the reaction conformed to the Langmuir–Hinshelwood pseudo-first order kinetic model, with the degradation efficiency (D) and the reaction rate constant (k) displaying a consistent variation trend. When the addition amount of Mnq₂ was 40 mg, the degradation effect on the 20 mg/L methylene blue solution was the best. After 210 min of degradation, D = 98.23%, and k = 0.02109 min⁻¹. After three cycles, the degradation rate still remained above 95%. Different addition amounts could achieve a degradation rate of over 95% after 210 min of degradation. This suggests that Mnq₂ holds potential for the remediation of methylene blue-containing wastewater, exhibiting favorable photocatalytic activity and stability in the process.

This study reports a green synthesis of bimetallic gold–palladium nanoparticles (Au–Pd BNPs) using Passiflora edulis fruit peel extract as a sustainable reducing and stabilizing agent. Transmission electron microscopy revealed uniformly dispersed spherical nanoparticles with a core–shell structure, comprising a dense Au core and a thinner Pd shell, and an average diameter of 15.9 ± 2.4 nm. The core–shell architecture was further confirmed by X-ray diffraction (XRD), while Fourier-transform infrared spectroscopy (FTIR) indicated the involvement of hydroxyl and carbonyl-containing phytochemicals in nanoparticle formation. X-ray photoelectron spectroscopy (XPS) verified the presence of elemental Au and Pd in Au–Pd BNPs. The catalytic activity of monometallic (AuNPs, PdNPs) and bimetallic (Au₃Pd₁, Au₁Pd₁, Au₁Pd₃) nanoparticles was assessed in the NaBH₄-assisted reduction of rhodamine B (RhB) and methyl orange (MO). Among all catalysts, Au₁Pd₃ BNPs exhibited superior performance, achieving > 99% reduction of both dyes within 5 min. The reactions followed pseudo-first order kinetics, with apparent rate constants of 14.7 ± 0.6 × 10⁻³ s⁻¹ for RhB and 16.1 ± 0.5 × 10⁻³ s⁻¹ for MO, obtained from the nonlinear exponential fitting. These findings highlight the effectiveness of green-synthesized Au–Pd BNPs as promising catalysts for rapid and efficient dye degradation.

The co-pyrolysis of rice husk (RH) and date palm seeds (DS) was conducted with a focus on their physicochemical properties, thermal decomposition behavior, and thermo-kinetic analysis. During co-pyrolysis, synergistic interactions at various blending ratios were also analyzed. Thermal degradation behavior was investigated using a thermogravimetric analyzer, with kinetic analysis performed via the Friedman method and master plot technique. The blended samples exhibited improved fuel properties. As the DS proportion increased, the TG curves exhibited greater mass loss. A pronounced synergistic effect was observed in the 75%DS + 25%RH blend, where a consistently negative deviation in ΔW indicated stronger interactions between the components. The 75%DS + 25%RH blend exhibited consistent negative deviation in activation energy (ΔE_a) values when α exceeded 0.55, signifying a consistently positive synergy during co-pyrolysis. A significant reduction in average activation energy (E_a) was also observed when the DS proportion was 75%, confirming positive synergy. The average pre-exponential factor (A) values for the blends decreased with increasing DS proportion, indicating a reduction in the frequency of molecular collisions. The pyrolysis of all samples generally followed diffusion and order-based mechanisms. Thermodynamic analysis revealed positive change in enthalpy and gibbs free energy values, confirming that additional energy is required for the co-pyrolysis process.