Kinetics and Catalysis最新文献

Basing on the results of mathematical modeling it has been demonstrated for the first time that two completely different mechanisms of reaction rate oscillations can be observed in the same model of a heterogeneous catalytic reaction. One mechanism corresponds to oscillations that arise in the ethylene oxidation reaction due to oxidation–reduction of the nickel surface, while the other mechanism for rate oscillations in this reaction is associated with the periodic deposition and removal of surface carbon. It has also been shown for the first time that two various limit cycles, corresponding to different mechanisms for the occurrence of reaction rate oscillations, can coexist at the same temperature, reaction mixture composition, and reaction stage constants for ethylene oxidation on nickel.

Layered perovskite-like Sr₂TiO₄ is a promising catalyst for oxidative coupling of methane (OCM)—a potential direct route to produce C₂ (ethane + ethylene) hydrocarbons, especially, ethylene. In this work, Sr_{2 – х}Ln_xTi_{1 – y}Fe_yO₄ (Ln = La, Pr, х = 0, 0.1; y = 0–0.3) layered perovskites with partially substituted positions of Sr (La, Pr) or Ti (Fe), were synthesized by sol–gel method using polymeric precursors and wetness impregnation followed with calcination at 900–1000°C. The samples were characterized by X‑ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), adsorption and temperature-programmed hydrogen reduction (H₂-TPR). It was revealed that Sr₂TiO₄ doping with La leads to formation of nanocomposite material containing Sr₂TiO₄, La‑doped SrTiO₃ and La₂O₃ while Sr₂TiO₄, Sr₃Ti₂O₇ and Pr₆O₁₁ are observed in the case of Pr. Fe–doped samples with x = 0.1–0.2 are the single-phase systems. Testing of the obtained doped materials in oxidative coupling of methane has shown the correlation of their catalytic activity with H₂-TPR data and also with the ratio ({text{O}}_{2}^{{2 - }})/O^2– (the surface adsorbed and surface lattice oxygen, correspondingly) and peculiarities of O^2–. The higher СН₄ conversion and C₂ selectivity for the La-doped catalyst is due to appearance of O^2– reduced at medium temperature. The low activity of Pr and Fe doped samples is conditioned by the presence of a large amount of surface adsorbed oxygen ({text{O}}_{2}^{{2 - }}) facilitating CO_x formation and decreasing C₂ selectivity.

Anderson-type sodium hexamolybdoaluminate(III) is used for the synthesis of quinoxaline derivatives using 1,2-diketone and 1,2-diamine in aqueous medium at room temperature. This catalyst is characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and thermogravimetric analysis (TGA). The Al(III) catalyst is a heterogeneous catalyst that was successfully recovered and recycled four times without major loss of activity. The methodology is environmentally benign and offers excellent product yields. The (Na₃[AlMo₆O₂₄H₆]·8H₂O) is biologically evaluated for its cytotoxic activity against human breast adenocarcinoma cell lines. This catalyst exhibited moderate cytotoxic activity compared to the standard drug 5‑fluorouracil (5-FU), with a cell viability of 62.48% and an IC₅₀ value of 144.573 μg/mL.

The Diels–Alder (DA) reaction between 3-methyl-3-penten-2-one (MP) and myrcene is experimentally examined and theoretically modeled as part of the Iso E Super synthesis process. The results reveal that the DA reaction between MP and myrcene follows a typical electron-demand mechanism, and the para-product (2) is the most stable structure. With the addition of the AlCl₃ catalyst, the reaction energy barrier drops significantly from 132.85 to 61.38 kJ/mol, easing the reaction conditions. The AlCl₃ catalyst exhibits the highest catalytic activity among the catalysts tested, especially in isooctane solvent, of which the conversion of myrcene reaches 88.51% and the total selectivity for the cyclization intermediate of Iso E Super is 92.86%. Additionally, it was observed that increasing the Lewis acidity strength leads to higher conversion and selectivity for the para-product of myrcene. This can be attributed to the enhanced electrophilicity of the second carbon atom in MP upon interaction with the catalyst, which makes it more reactive towards the electron-rich carbon atoms of myrcene.

Alkyl furfuryl ethers are promising additives to motor fuels, which can be produced by reductive etherification of furfural with alkyl alcohol. The Cu/Al₂O₃ catalyst was prepared using a copper ammonia complex as the precursor of active component. The catalytic behavior of the physical mixture of the Cu/Al₂O₃ catalyst and ZSM-5-Al₂O₃ composite was studied in the reductive etherification of furfural in a flow reactor using H₂ as a reducing agent. This process involves the sequential hydrogenation of furfural on the Cu⁰ sites of the Cu/Al₂O₃ catalyst, followed by the etherification of the resulting furfuryl alcohol on the acid sites of zeolite. The highest yield of 2‑(isopropoxymethyl)furan (IMF) of 85% was achieved over the catalytic system (0.25–0.5 mm) including HZSM-5(Si/Al = 40)-Al₂O₃ due to the optimal concentration of strong Brønsted acid sites in the composite. A physical mixture of the Cu/Al₂O₃ catalyst and the 30% ZSM-5(40)-Al₂O₃ composite, in the form of granules (trilobe extrudates of 2–5 × 1.25 mm), showed an IMF yield of 72.5%.

Al_{1 – x}Mg_xCr₂O₄ nanochromites, where x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10, were synthesized by citrate gel auto combustion technique. The X-ray diffraction study confirms the synthesized nanochromites belong to the spinel structure with the FD₃M space group, and the average crystallite size was 20 to 24 nm, which was calculated from the Debye–Scherrer formula. The distribution of these sizes would be seen in the SEM pictures, providing light on the uniformity. About 550 and 625 cm^–1 wavenumber domain FTIR bands are present in the FTIR spectrum, which correlate to the metal-oxygen bonds stretching vibrations of the octahedral (Mg–O bond linkage) and tetrahedral (Cr–O or Al–O bond linkage) sites. Using Tauc plots, the bandgap energy of the material was calculated, i.e., in between 2.21–3.26 eV. Fluorescence (FL) emission in the 400 nm region was seen in the PL spectra. Two organic industrial pollutants, such as Methylene Blue (MB) and Acid Red 18 (AR18), were utilized to examine the photocatalytic activity under visible light. Anticancer activity of Al_{1 – x}Mg_xCr₂O₄ nanochromites tested with HeLa CCL2 cells. Antibacterial activity is carried out by two gram-positive and two gram-negative bacterial agents, namely Staphylococcus aureus (ATCC6538), Bacillus subtilis (ATCC11774), Escherichia coli (ATCC8739), and Klebsiella pneumoniae (ATCC10031). Antifungal activity is investigated by two fungal pathogens (candida albicans (ATCC10231) and Aspergillus niger (ATCC1015)) by a pour plate method.

Using the activated chemiluminescence method, it was found that in the presence of monosaccharide additives, the antiradical activity of phenolic carboxylic and hydroxycinnamic acids in the reaction with 2-amidinoisopropane-2-peroxyls in an aqueous medium at pH 2 increases significantly. The found synergistic effect is most pronounced (over 90%) at a phenolic acid : monosaccharide ratio in solution of 7 : 3 (with a total mixture concentration of 8 × 10^–5 mol/L) for binary mixtures of sinapic, gentisic, and ferulic acids with galactose, mannose and glucose. The mechanism of the synergistic action of the compositions in the reaction with peroxyl radicals consists in the formation of an intermolecular hydrogen-bonded complex of the acid with the reduced and oxidized forms of the monosaccharide. The transition states and activation parameters of the synergistic reactions were calculated using the DFT method. It has been established that participation in the reaction with peroxy radicals of ferulic acid in the composition of complexes with galactose and the corresponding galactonic acid contributes to a decrease in the enthalpy of activation of the reaction by 14–21 kJ/mol (compared to the reaction without the addition of monosaccharide) and the manifestation of experimentally established synergistic effects.

The reactivity of pyrazolone derivatives towards secondary peroxyl radicals was studied in a model system of radical chain oxidation of 1,4-dioxane. The objects of study were 3-methyl-1-phenyl-2-pyrazolin-5-one (1), 5-amino-1,2-dihydro-1-phenyl-3H-pyrazol-3-ol (2) and 3-amino-1-phenyl-2-pyrazolin-5-one (3). The reaction kinetics were monitored by measuring the rate of oxygen uptake at 333 K. 1,4-Dioxane acted as a solvent and a source of peroxyl radicals. Compounds 1, 2, 3 were found to interact with peroxyl radicals with a rate constant (fk₇ × 10^–4, L mol^–1 s^–1) of 6.1 ± 0.3, 17.8 ± 1.7, and 3.7 ± 0.4, respectively. The stoichiometric inhibition coefficient f was found to be ~2.

The Pd–S-containing samples prepared using elemental sulfur were tested in the hydrogenation of representatives of various classes of unsaturated compounds (acetylenic hydrocarbons, alcohols, and alkylanthraquinones). It was shown that the hydrogenation of acetylenic derivatives catalyzed by Pd–nS/NaZSM-5 catalysts was characterized by a sigmoidal profile of kinetic curves with an induction period, which increased as the [S] : [Pd] ratio raised from 0.25 to 1.0. Using phenylacetylene hydrogenation as a model reaction, various origins of the S-shaped kinetic dependence and competing hypotheses were discriminated. A method for enhancing the activity of Pd–S-containing samples in the hydrogenation of unsaturated compounds under mild conditions was proposed.