Kinetics and Catalysis最新文献

The use of natural gas as a motor fuel in distributed energy systems and transport requires a clear understanding of the kinetics of the effect of methane homologs on its ignition. The results of kinetic modeling of the ignition of methane mixtures with air and a small admixture of light hydrocarbons presented in this paper help explain the reasons for such unexpected experimental results as the similar effects of C₂–C₆ methane homologs on ignition, despite their significantly different reactivity. The significantly higher reactivity of methane homologs leads to their rapid thermal decomposition, the main product of which is ethylene, even before methane ignition. Methane ignition is directly affected by ethylene oxidation, which is independent of its source.

Natural gas is routinely odorized with trace sulfur compounds, such as methanethiol (CH₃SH), to enable leak detection. Although methane, the primary component of natural gas, is commonly used as the reference fuel in combustion studies, the oxidation behavior of CH₃SH in premixed methane flames remains poorly characterized, despite its presence in natural gas, biogas, and refinery streams. This study presents a detailed kinetic mechanism for simulating CH₃SH-doped premixed CH₄ flames across a broad equivalence ratio range (Φ = 0.7–1.3). Results reveal a strong stoichiometric dependence: lean flames (Φ = 0.7) promote complete oxidation, yielding high concentrations of SO₂ and SO₃, which pose risks of acid deposition and corrosion. In contrast, rich flames (Φ = 1.3) suppress SO_x formation but significantly enhance the production of reduced sulfur species (H₂S and CS₂) by up to an order of magnitude. Stoichiometric conditions (Φ = 1.0) yield a mixed speciation profile. These findings underscore the critical need for precise equivalence ratio control. We propose staged combustion strategies; employing slightly rich primary zones followed by oxidizing post-treatment as a promising approach for cleaner utilization of odorized natural gas.

Cobalt oxide catalysts with different sulfate loadings (1, 3, and 5 wt %) were synthesized via precipitation and subsequent sulfation, followed by calcination at 500°C. The structural, textural, and acidic properties of the catalysts were systematically investigated using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, N₂ adsorption–desorption, and pyridine-adsorbed FTIR spectroscopy. Results revealed that moderate sulfation (3 wt %) significantly enhanced surface area (118.70 m²/g), mesoporosity, and surface acidity, while excessive sulfate loading (5 wt %) led to pore blockage and reduced accessibility of active sites. Catalytic tests demonstrated that the Co-3S catalyst achieved complete NH₃ conversion (100%) with excellent N₂ selectivity at a remarkably low temperature of 200°C, outperforming both pure Co₃O₄ and samples with lower or higher sulfate ratios. The superior activity was attributed to the synergistic effect of balanced Brønsted–Lewis acidity and optimized textural properties. Furthermore, Co-3S exhibited outstanding stability and reusability over multiple reaction cycles. These findings highlight that a moderate sulfate ratio is crucial for tailoring the surface and catalytic properties of cobalt oxide, offering a cost-effective and efficient alternative for selective ammonia oxidation.

This research aims to develop a PdAg/TiO₂ catalytic film enriched with palladium on the surface of nanoparticles for selective semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) in microcapillary reactor. Here we report an effective and versatile synthesis of colloidal core-PdAg/open shell-Pd NPs (PdAg₄@Pd) by using a facile successive reduction method. Coating the core-PdAg₄ with shell-Pd NPs enables a significant improvement in the activity of PdAg₂/TiO₂ (up to 24 times) for the selective semihydrogenation of a MBY. High-angle annular dark-field scanning transmission electron microscopy analysis reveal the presence of Ag atoms on Pd shell which is responsible for the suppression of MBY full hydrogenation by the Pd NPs. The as-fabricated on inner surface of microcapillary reactor film with PdAg₄@Pd/TiO₂ nanocomposites produces a 2-methyl-3-buten-2-ol (MBE) with selectivity 96 at 97% conversion and maintains good performance during 72 h. The proposed strategy can be used for the synthesis of an efficient single-atom alloy catalyst (SAAs) for selective hydrogenation of an alkynols in the pharmaceutical industry.

Methane, a potent greenhouse gas, poses a significant risk when released into the environment. In this work, a Pd/SiO₂@CeO₂ catalyst was developed and evaluated for its methane oxidation performance under oxygen-rich environments. The 2.5 wt % Pd/SiO₂@CeO₂ achieved 10, 50, and 90% CH₄ conversion at 225°C (T₁₀), 257°C (T₅₀), and 275°C (T₉₀). The 2.5 wt % Pd/CeO₂ was used as the reference catalyst that attained CH₄ conversion of 50 and 90% at comparatively higher temperatures of 300 and 350°C under identical reaction conditions. Decreasing the Pd loading in Pd/SiO₂@CeO₂ to 1 wt % increased the T₁₀, T₅₀, and T₉₀ to 257, 300, and 350°C, respectively. Furthermore, in a steady-state experiment of 10 h at 350°C, 2.5 wt % Pd/SiO₂@CeO₂ exhibited excellent durability, sustaining a ≥95% CH₄ conversion without noticeable deactivation. In addition, variation in O₂ (0.5–8%) and CH₄ (0.11–0.5%) concentrations, and gas hourly space velocity (GHSV) between 48 000–58 000 mL g^–1 h^–1 did not affect the methane oxidation performance of 2.5 wt % Pd/SiO₂@CeO₂ at 350°C. Moreover, the 2.5 wt % Pd/SiO₂@CeO₂ catalyst was thermally aged at 700°C for 3 h and still exhibited 90% methane conversion at 350°C. In contrast, the methane conversions of thermally aged 2.5 wt % Pd/CeO₂ catalyst decreased significantly to 46%. Field emission scanning electron microscopy (FESEM) results showed that the developed Pd/SiO₂@CeO₂ catalyst possessed the core-shell structure with Pd and CeO₂ coated on uniform SiO₂ nanospheres (~500 nm). The methane oxidation performance of the developed Pd/SiO₂@CeO₂, when benchmarked against reported similar Pd-based catalysts, displays superior activity under comparable reaction conditions. Overall, the findings highlight the strong potential of Pd/SiO₂@CeO₂ for mitigating methane emissions.

The paper presents the results of a kinetic study of the thermal decomposition of calcium carbonate under conditions of continuous heating to a temperature of 1273 K at a constant rate of 1.25, 2.5, 5, 10, and 20 K/min. The integral method and the Coats–Redfern method were used to describe the reaction mechanism and determine the macrokinetic parameters. Experimental dependences of the logarithm of the preexponential factor on the activation energy were obtained. The dependences of the activation energy and preexponential factor on the heating rate are shown. The effect of the heating rate of calcium carbonate on the activation energy can be explained by the relationship between the heating rate and the concentration of CO₂. Equations are proposed for calculating the reaction rate constant using the integral data processing method and the Coats–Redfern method. It has been demonstrated that the integral method and the Coats–Redfern method allow one to calculate the macrokinetic parameters of the thermal decomposition of calcite with comparable accuracy and taking into account the heating rate in these calculations makes it possible to obtain calculated values of the degree of conversion, the standard deviation of which from the experimental data is <4.1%.

This paper considers the photocatalytic activity of silicon nitride–based composites in the degradation of the pharmaceutical pollutant ketoprofen (KTF). The composites were obtained by nitriding ferrosilicon with various Eu₂O₃ additives (0–7 wt %) in a combustion mode with a preliminary stage of mechanical activation. The samples were studied using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption–desorption, X-ray photoelectron spectroscopy, and diffuse reflectance electron spectroscopy. The photocatalytic activity of the samples was evaluated during the oxidative destruction of KTF under UV irradiation, in particular, with the addition of hydrogen peroxide to carry out the Fenton reaction. It was found that the rate constant of the heterogeneous photocatalytic reaction reached a maximum value (k = 0.041 min^–1) for the composite synthesized with the addition of 7 wt % Eu₂O₃. Under conditions of combined heterogeneous photocatalysis and the Fenton process, the modified samples obtained with 3–7 wt % Eu₂O₃ additives showed the highest efficiency; the degree of KTF degradation reached 52–55% in 10 min.

A formal kinetic study of 2-ethyl-9,10-anthraquinone hydrogenation was carried out over 3% Pd/НZSM-5 and 3% Pd–1.0Р/НZSM-5 catalysts. The qualitative and quantitative composition of the surface layer of the 3% Pd–1.0Р/НZSM-5 sample was determined by X-ray photoelectron spectroscopy. Based on the analysis of metal dispersion, specific activity in 2-ethyl-9,10-anthraquinone hydrogenation, and the concentration of surface Pd(0) atoms in the Pd–P catalysts, the main reasons for the modifying effect of phosphorus were elucidated.

Heterogeneous imidazolium chloroferrate-based catalysts (C1, C2 and C3) were synthesized by three different routes: С1 in three stages, by covalent binding of cation to the silica gel surface and subsequent formation of grafted chloroferrate; C2 in two stages by preliminary synthesis of imidazolium chloroferrate and its adsorption on silica gel; C3 in one stage in which the synthesis of ILs proceeds simultaneously with its adsorption on the support surface. The catalysts were characterized by various physical and chemical techniques and tested in thiophene, dibenzothiophene and pyridine oxidation with H₂O₂. Catalyst C1 was more active than C2 and stable in several successive cycles of the in thiophene reaction. The “one pot” synthesized C3 catalysts was the most active in this model process and showed a TOF value of 25 h⁻¹.