Kinetics and Catalysis最新文献

The Hofmann degradation reaction converts amides into primary amines, which are essential intermediates in various industrial processes. In this study, we investigate the use of bentonite-supported metal nanoparticles (NPs)—specifically ruthenium and copper–as catalysts for the Hofmann degradation of benzamide to phenylamine. The metal nanoparticles were synthesized via a glycol reduction method, allowing precise control over their size and distribution. Bentonite was chosen as the support material due to its high surface area and cation exchange capacity, which enhance the dispersion and stability of the metal nanoparticles. The successful synthesis of Ru and Cu nanoparticles was confirmed through X-ray photoelectron spectroscopy (XPS), with binding energy values of 283 eV for Ru3d_5/2 and 933 eV for Cu2p_3/2, indicating the presence of metallic Ru and Cu. This confirms the effective reduction of metal ions to their elemental forms. We then conducted the Hofmann degradation of benzamide using bentonite alone, bentonite supported with copper nanoparticles (Bent/Cu-NPs), and bentonite supported with ruthenium nanoparticles (Bent/Ru-NPs) prepared via the glycol reduction method. Notably, Bent/Ru-NPs achieved a reaction efficiency of 62% within approximately 1.5 h at a catalyst dosage of 0.005 g. Additionally, Bent/Ru-NPs demonstrated catalytic stability over four consecutive cycles, maintaining significant activity.

Сommercial cerium-zirconium oxide supports (Ce_0.5Zr_0.5O₂, Ce_0.75Zr_0.25O₂ and Ce_0.4Zr_0.5Y_0.05La_0.05O₂) were used to prepare Ru/CeZrO_x catalysts by the sorption-hydrolytic method with ruthenium loading of ~2 wt %. The catalyst specific surface areas ranged within 80–91 m²/g. The XRD data indicate the formation of a substitutional solid solution. According to the HRTEM data, there are no ruthenium particles on the support surface in Ru/Се_0.75Zr_0.25О₂ and Ru/Ce_0.4Zr_0.5Y_0.05La_0.05O₂ samples. Most likely, the ruthenium particles are in a highly dispersed state. At 500°C and WHSV of 300 000 ({text{m}}{{{text{L}}}_{{{text{N}}{{{text{H}}}_{{text{3}}}}}}}) ({text{g}}_{{{text{cat}}}}^{{-1}}) h^–1, the catalysts demonstrated the highest hydrogen productivity of 73.8–85.4 ({text{mmo}}{{{text{l}}}_{{{{{text{H}}}_{{text{2}}}}}}}) ({text{g}}_{{{text{cat}}}}^{{-1}}) min^–1) and NH₃ conversion of 22–25.5% that compares well with the best results reported in the literature and exceeds the catalysts performance we have previously obtained for Ru/Ce_0.75Zr_0.25O₂ catalyst prepared by impregnation. The activity of most active Ru/Ce_0.4Zr_0.5Y_0.05La_0.05 catalyst remained stable throughout the all test period (~46 h).

On the occasion of the anniversary of the birth of Doctor of Chemical Sciences, Professor Oleg Naumovich Temkin, the results of his scientific and teaching activities are discussed. Professor Temkin made a significant contribution to the development of chemical kinetics, catalysis by metal complexes, mathematical chemistry, and the chemistry of acetylenic compounds. The research school in catalysis, which he co-founded and led for many years, continues to operate and develop his ideas.

The rate constant of the reaction of 6-amino-5-hydroxy-2,3-dimethylpyrimidin-4(3H)-one (1) with peroxyl radicals was measured in a model system of radical chain oxidation of 1,4-dioxane. Oxidation of 1,4-dioxane with atmospheric oxygen was carried out at a temperature of 333 K. Oxygen uptake was monitored using a universal differential manometric setup. It was found that 6-amino-5-hydroxy-2,3-dimethylpyrimidin-4(3H)-one slowed down the rate of 1,4-dioxane oxidation. The effective rate constant of the interaction of the peroxyl radical of 1,4-dioxane with 6-amino-5-hydroxy-2,3-dimethylpyrimidin-4(3H)-one was found: fk₇ = (6.2 ± 0.1) × 10⁵ L mol^–1 s^–1. The stoichiometric inhibition coefficient f = 1.3 ± 0.1 was calculated from the slope of the dependence of the induction period length on the concentration of 6-amino-5-hydroxy-2,3-dimethylpyrimidin-4(3H)-one. The experimental data indicated that 6-amino-5-hydroxy-2,3-dimethylpyrimidin-4(3H)-one has antioxidant properties. It was assumed that the hydroxyl group –OH located in the 5-position of the ring was the site attacked by the peroxyl radical.

Propylene polymerization titanium–magnesium catalysts in the presence of ethers are synthesized. It is shown that aliphatic ethers and 1.1-diethers are participated in the formation of magnesium chloride although they are not contained in catalysts. Aromatic ethers (except methyl phenyl ether) are ineffective in the MgCl₂ formation. Subsequent adding of the phthalate (DBP/Mg = 0.05 mol) lead to the synthesis of the phtalate titanium–magnesium catalyst which in the case of aliphatic ethers and 1.1-diethers have catalytic properties higher than the titanium–magnesium catalyst for comparison (DBP/Mg = 0.05 mol) and close ones (for some ethers) to the standard titanium–magnesium catalysts (DBP/Mg = 0.2 mol). Comparative analysis of the composition of phthalate titanium–magnesium catalysts prepared using ethers or ketones and X-ray data indicate a close size of MgCl₂ crystallites in both cases. The composition of titanium–magnesium catalysts synthesized in the presence of ethers is consistent with the distribution of dimeric TiCl₄ complexes alternating with chlorine vacancies (…□TiTi□TiTi…) on the lateral cuts 104.

Platinum catalysts with the additives of vanadium and tin were synthesized and studied in the reaction of methylcyclohexane dehydrogenation to toluene. Experimental data were obtained for the process of methylcyclohexane dehydrogenation, which are consistent with the synergistic effect of vanadium addition to a platinum–alumina catalyst in hydrogenation and dehydrogenation reactions, as predicted by quantum-chemical calculations.

The X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy were used to study the features of anchoring of the [Ir₂(COD)₂Cl₂] complex on the surface of modified silica gel L–SiO₂ (where L is NC₅H₅–CH₂–CH₂–, N(CH₃)₂–CH₂–CH₂–CH₂–, NH₂–C₃H₆–) depending on the nature of the linker and the conditions of preparation of the systems. The catalytic activity was tested in reactions of gas-phase selective hydrogenation of propylene with parahydrogen (p-H₂). According to the XPS data, a single-site iridium catalyst is prepared in all cases. Analysis of the XPS spectra indicates the possibility of anchoring the complex through one of the iridium atoms while preserving the dimer. It was shown that at different durations of interaction of the iridium complex solution with modified NH₂–C₃H₆–silica gel approximately the same amount of the complex is anchored, but the nature of the complex coordination changes. For the sample obtained by long-term interaction of the complex solution with the modified support (24 h), a high increase in the NMR signal was observed at 60°C, while in the case of the sample prepared by short-term interaction (1 h), the signal increased with a rise in temperature to 80°C.

A nickel-based catalyst supported on alumina–zirconia–ceria oxides was investigated to evaluate its performance in the dry reforming of glycerol. The reaction was carried out at 700°C and atmospheric pressure, with a glycerol/CO₂ molar ratio of 1. The catalyst demonstrated stable performance for 7 hours onstream, achieving glycerol and CO₂ conversions of 60% and 47%, respectively, with corresponding H₂ and CO yields of 48% and 58%. Thermogravimetric analysis (TGA) confirmed carbon deposition; however, this did not lead to significant catalyst deactivation. These results highlight the potential of the synthesized catalyst for glycerol conversion for the production of syngas and hydrogen from renewable feedstock.

The catalytic peroxidase-like properties of silver nanoparticles (Ag NPs) immobilized into a polymethacrylate matrix (PMM) were studied. The Ag NPs were prepared by thermal reduction of silver cations preimmobilized in a PMM. The morphology of the nanocomposite was studied using scanning electron microscopy (SEM), and the average size of the synthesized individual spherical nanoparticles was 18 ± 5 nm. It was demonstrated that silver nanoparticles immobilized in a polymethacrylate matrix (PMM–Ag⁰) exhibited pronounced peroxidase-like activity in the oxidation reaction of a chromogenic substrate, indigo carmine, under the action of H₂O₂. The Michaelis–Menten model was used to estimate the kinetic parameters of the reaction. The Michaelis constants (K_m) of 0.1 and 1.0 mM for indigo carmine and H₂O₂, respectively, indicated a strong affinity of the substrates to silver nanoparticles in PMM.

The article is devoted to the experimental and theoretical study of regular and complex oscillations during ethylene oxidation on the nickel foil. The simplest mathematical model was based on the 14-stage mechanism of reaction including the stages of oxidation and reduction of the Ni catalyst. A precursor-mediated adsorption of CO and C₂H₄ was shown to be the crucial condition for the origin of the oscillatory behavior under reducing conditions. It was demonstrated that for real values of the parameters, the mathematical model can simulate both regular and irregular oscillations, as well as the “mixed-mode” oscillations observed in the experiment. For the first time oscillations with different properties and distinct mechanisms of their occurrence were detected in the same model. It was demonstrated that oscillations occurred as a result of a strong dependence of the reaction rate on the concentration of active sites due to a variation in the concentration of the surface oxide or the surface carbon.