Reaction Kinetics, Mechanisms and Catalysis最新文献

This study systematically evaluates three methodologies for quantifying the heat required for biomass pyrolysis (HRP), namely differential scanning calorimetry (DSC), power monitoring, and heat balance calculation, employing four typical agricultural residues (camellia shell, tobacco stalk, cassava straw, and eucalyptus) as substrates. DSC analysis, conducted under nitrogen atmosphere with heating rates of 10, 20, and 30 °C/min, yields HRP values in the range of –0.472 to –1.123 MJ/kg. Additionally, experiments were carried out on a screw pyrolyzer equipped with an energy monitor to obtain the HRP. The HRP, as determined by the energy meter, ranges from 0.756 to 0.936 MJ/kg. Conversely, the HRP calculated through the heat balance method varies from 2.026 to 2.672 MJ/kg.

In this work, the Se-π acid-catalyzed oxidative ring-closing reaction of (E)-4-phenylbut-3-enoic acid promoted by either 2-iodosobenzoic acid (IBA) or 3,4,5,6-tetrafluoro-2-iodosobenzoic acid (FIBA) was theoretically studied at PBE0-D3(BJ)/Def2-TZVP/SMD(MeCN)//PBE0-D3(BJ)/Def2-SVP/SMD(MeCN) level of theory. The most likely reaction mechanisms were screened out, catalytic cycles were proposed, and the rate-determining steps and the activation Gibbs energy barriers of all the catalytic cycles were investigated. The acidity of breaking C-H bonds determines the regioselectivity of the β-elimination reaction. The reasons why the structural differences between IBA and FIBA lead to different reaction yields have also been discussed in detail.

This study introduces a multiscale model for ammonia synthesis catalysts that integrates intrinsic kinetics, intraparticle diffusion, and deactivation mechanisms, specifically water vapor self-poisoning and long-term aging. Extending the Temkin-Pyzhev kinetic framework, the model incorporates a size-dependent self-poisoning coefficient (γ(dp)), a time-dependent aging factor (af(t)), and a Thiele modulus-based effectiveness factor (η). Calibrated with experimental data, it accurately predicts nitrogen consumption rates (r_N2) for catalyst particle sizes ranging from 0.6 to 9.0 mm and operational lifetimes of 2 to 5 years, with errors as low as 0.8% for larger particles. Unlike traditional models, this approach quantifies reduction-induced deactivation, which significantly impacts larger particles by markedly reducing activity. Implemented in MATLAB, the model provides a predictive tool for optimizing catalyst design and reactor performance under industrial conditions. By linking microkinetic, transport, and deactivation phenomena, this work enhances the efficiency and longevity of ammonia synthesis processes, both traditional and novel.

In this study, ZnO nanoparticles were synthesized via coprecipitation at three different temperatures (20 °C, 40 °C, and 80 °C), and their structural, morphological, optical, and photocatalytic properties were comprehensively examined. X-ray diffraction confirmed a hexagonal wurtzite structure for all samples, with crystallite sizes decreasing from 41.8 nm (Zn20) to 34.8 nm (Zn80) as synthesis temperature increased. These findings were further supported by FTIR analysis. Scanning electron microscopy revealed uniform pseudo-spherical morphologies, while UV–Visible and photoluminescence (PL) analyses showed a systematic increase in bandgap energy from 3.13 eV to 3.20 eV. Notably, PL measurements indicated significantly reduced emission intensity for Zn80, implying retarded electron–hole pair recombination and thus more efficient charge carrier separation. Photocatalytic experiments demonstrated that Zn80 exhibited the highest performance, achieving 96% degradation of methylene blue under simulated solar irradiation within 60 min. This superior activity is attributed to its optimized defect structure, improved charge carrier dynamics, and increased surface area. Furthermore, scavenging tests confirmed hydroxyl radicals (⋅OH) as the dominant reactive species, and Zn80 maintained remarkable stability and reusability over four consecutive cycles with negligible efficiency loss. This work presents a novel approach focusing on the systematic investigation of coprecipitation synthesis temperature as a single, controllable parameter to tailor the properties of ZnO nanoparticles. Unlike conventional methods that rely on dopants, surfactants, or composite materials, this strategy demonstrates that significant enhancements in photocatalytic activity can be achieved through simple temperature modulation, paving the way for cost-effective and scalable production of high-performance ZnO photocatalysts.

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The α-, β-, γ-MnO₂ and MnO₂-Ag catalysts were synthesized by a simple hydrothermal method and tested for photocatalytic oxidation of formaldehyde. The catalysts were characterized by experimental and theoretical methods to explain the reason for the enhanced catalytic performance. The results indicated that variations in crystal structure significantly influenced catalytic activity. The introduction of Ag into MnO₂ facilitates the formation of new energy levels, which enhances electron–hole separation efficiency. Subsequently, it promotes the generation of superoxide radicals (•O₂⁻) and hydroxyl radicals (•OH), thereby significantly enhancing formaldehyde removal efficiency. Among all the catalysts, γ-MnO₂-Ag exhibited superior catalytic performance, achieving a formaldehyde conversion rate of 90.82% within 120 min. Owing to its efficient photocatalytic oxidation performance and straightforward synthesis method, γ-MnO₂-Ag shows great potential as a promising catalytic support material for HCHO catalysis.

TiO₂ photocatalytic materials with different nickel doping contents were successfully prepared by using the sol–gel method. Through a variety of advanced characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), ultraviolet–visible absorption spectroscopy (UV–Vis), and Fourier transform infrared spectroscopy (FTIR), Photoluminescence (PL), BET surface area, the structural and performance of the prepared catalysts were comprehensively characterized. Meanwhile, organic dyes were selected as the target degradable substances, and the photocatalytic efficiency was systematically tested. Using the batch experiment method, the photocatalytic degradation activity of Ni-doped TiO₂ (Ni-TiO₂) on Rhodamine B(Rh-B) dye was deeply investigated. The experimental results showed that when the Ni doping content was 1%, Ni-TiO₂ exhibited the highest degradation rate, reaching 98.22%. To clarify the intrinsic mechanism of this excellent performance, the catalyst was analyzed in depth, and it was found that the doped samples could generate more electron–hole pairs. Compared with pure TiO₂, the average effective mass of photogenerated electrons and holes in Ni-TiO₂ was smaller. The smaller effective mass significantly promoted carrier migration and effectively inhibited the recombination of carriers. In addition, through density functional theory (DFT) calculations, the above experimental results were further verified, providing a theoretical basis for the mechanism of improving photocatalytic performance.

A novel zinc-based metal–organic framework was successfully employed as a catalyst in the Claisen–Schmidt condensation reaction for the synthesis of azo-chalcone. The catalyst demonstrated excellent recyclability and maintained high activity after the reaction without loss of effectiveness. The synthetic protocol allows for simple product isolation, easy workup, and efficient purification, supporting potential scale-up for industrial applications. Quantum chemical calculations provided insights into the electronic and structural properties of the synthesized azo-chalcone. Molecular docking studies revealed strong binding affinity of the chalcone to Escherichia coli DNA gyrase, with a docking score of − 10.794 kcal/mol. Key interactions involved hydrogen bonding and van der Waals forces, particularly with the amino acid Asn46, which is critical in ATP hydrolysis inhibition. The compound also displayed favorable drug-like properties according to Lipinski’s rule and absorption, distribution, metabolism, elimination, and toxicity profiles.

Graphical Abstract

This work utilized mixture of α-Fe₂O₃ and modified Al₂O₃ as a catalyst for the FTS, where Al₂O₃ was modified by Ca, Mg or Zr to influence the formation of active phase of FTS. Based on SEM, XRD, XPS, H₂-TPR and CO-TPD analysis, it has been observed that the promotional effects of Ca/Al₂O₃ resulted in the highest content of θ-Fe₃C phase as an activate carbide phase for olefins generation, and realized the maximum all olefins selectivity of 69%.

A series of catalysts were synthesized using USY zeolite modified with oxalic acid and ammonium fluorosilicate for light cycle oil (LCO) highly selective hydrocracking to benzene, toluene, xylene, and ethylbenzene (BTXE). The Ni-Mo/Y0.2–0.15 catalyst had the maximum LCO hydrogenation to BTXE yield (24.40 wt%) at oxalic acid and ammonium fluorosilicate concentration of 0.2 mol/L and 1.5 mol/L. Among them, the hydrolysis of ammonium fluorosilicate produces HF and Si(OH)₄. Oxalic acid and HF may remove aluminum from molecular sieves, decrease acidity, and increase pore size. Si(OH)₄ accesses the hydroxyl holes created by dealumination, delaying aluminum elimination while maintaining crystallinity and improving yield of BTXE. Nevertheless, excessive concentration of oxalic acid and ammonium fluorosilicate is harmful for the USY structure.

In this study, Au/Cu-Apatite catalysts were prepared by substituting Ca in hydroxyapatite with Cu and loading Au. The structural properties of the catalysts were investigated and their catalytic performance were evaluated in the conversion of 1,2-propanediol to methyl lactate. Results indicate that, compared to the unsubstituted Au/HAP catalyst, the Au/Cu-Apatite catalyst demonstrates higher conversion of 1,2-propanediol and selectivity for methyl lactate. Under optimal conditions, the 2Au/Cu-Apatite-2 catalyst achieved a 1,2-propanediol conversion of 71.6% and a methyl lactate selectivity of 64.6%. This enhanced performance is attributed to the Au–Cu interaction, which modulated the oxidizing activity of Au active sites, thereby accelerating the rate of the catalytic oxidation of 1,2-propanediol, the rate-controlling step, and improving the overall reaction conversion. Furthermore, the Au/Cu-Apatite catalyst significantly enhanced the conversion of the intermediate hydroxyacetone to methyl lactate, resulting in an increased selectivity of methyl lactate in the final product.