Kinetics and Catalysis最新文献

The formation sequence of trimethylpentane (TMP) isomers in the liquid-phase interaction of butyl triflates and butenes with isobutane was studied. In the composition of alkylation products, the fractions of TMP isomers increased in the order 2,2,4-TMP > 2,3,4-TMP > 2,3,3-TMP ( gg ) 2,2,3-TMP upon homogeneous interaction in isobutane or in the order 2,3,4-TMP > 2,3,3-TMP > 2,2,4-TMP ( gg ) 2,2,3-TMP in the isobutane–triflic acid two-phase system. The isomeric composition approached the composition of a usual commercial product with increasing reaction time mainly owing to the isomerization of 2,3,4-TMP and 2,3,3-TMP isomers into a 2,2,4-TMP isomer. The possible mechanisms of formation of primary reaction products were discussed. These products are 2,2,4-TMP and 2,2,3-TMP in the case of butenes and 2,3,4-TMP and 2,3,3-TMP in the case of butyl triflates.

The expansion of the oleochemical industry results in excess glycerol production to the extent it is regarded as a waste. This drives the exploration of value-added products like acrylic acid to address the surplus and associated environmental issues. However, current processes mainly focus on the gaseous phase, requiring high temperatures and complex setups. Although some research delves into liquid-phase glycerol oxydehydration, information remains limited. In this study, SBA-15 supported heteropoly phosphotungstic acid (HPW) catalysts (PW/SBA-15) with varied acid loadings (10–40 wt %) were synthesized for a single-step liquid-phase glycerol oxydehydration. The impact of calcination temperatures (400–700°C) on catalyst properties and activity was explored. Extensive characterization techniques were employed to assess surface, morphological, and structural properties. Optimal conditions were identified: 3 h reaction time, 240°C reaction temperature, and 10 wt % catalyst loading, achieving 98.7% glycerol conversion and 22.5% acrylic acid yield. Glycerol oxydehydration followed a pseudo second-order kinetic model with an activation energy of 134.4 kJ/mol. The 30PW/SBA-15 catalyst exhibited a defined structure, effectively catalyzing glycerol-to-acrylic acid oxydehydration due to strong acid sites and appropriate redox sites.

Using the Pechini method, LaFe_{1 – x}Ni_xO₃ (x = 0, 0.6, 1) perovskite-containing catalysts supported on a monolith corundum support were prepared and studied in the reaction of high-temperature decomposition of nitrous oxide. It is shown that the supported catalysts can be arranged in the following order by activity: LaFeO₃/α-Al₂O₃ > LaFe_0.4Ni_0.6O₃/α-Al₂O₃ > LaNiO₃/α-Al₂O₃, which differs from the activity order of perovskites without a support. The change in the activity order is due to the interaction of the impregnating solution with the support, as a result of which an admixture of the nickel aluminate phase, inactive in this reaction, can be formed in nickel-containing catalysts. The LaFeO₃/α-Al₂O₃ catalyst with an active component content of ~5%, even with a fragment height of 20 mm (and a contact time of 0.06 s), provides a high (~84%) conversion of nitrous oxide, due to the possible presence of an impurity of the dispersed phase of active Fe₂O₃ as well.

Combustion of fossil fuels releases harmful pollutants, particularly sulfur-containing compounds such as alkyl mercaptans, sulfides, disulfides, and thiophenes present in diesel fuel. These pollutants pose significant environmental, health, and economic challenges. Hydrodesulfurization (HDS) using heterogeneous catalysts is a widely employed refinery technique to remove sulfur from diesel. In this study, a novel RN/γ-Al₂O₃@CNTs catalyst was synthesized by incorporating 15% Raney nickel (RN), resulting in a high surface area of approximately 129 m²/g. The catalyst’s HDS performance was evaluated using diesel fuel containing 0.98% sulfur. For comparison, a RN/γ-Al₂O₃ catalyst was also prepared. The RN/γ-Al₂O₃@CNTs catalyst achieved a superior sulfur removal efficiency of 92% in batch HDS tests, significantly outperforming the 80% efficiency of RN/γ-Al₂O₃. These results highlight the potential of RN/γ-Al₂O₃@CNTs as an effective heterogeneous catalyst for improved diesel desulfurization, contributing to reduced environmental pollution.

This study numerically investigated the effectiveness of direct hydrogen addition versus ammonia cracking in reducing unburned ammonia and carbonyl pollutant emissions during ammonia/methanol combustion. Simulation using a modified Chemkin II/Premic code examined equivalence ratios from 0.7 to 1.2 and hydrogen incorporation levels up to 60%. Direct hydrogen addition increased unburned NH₃ emissions by 196% under lean conditions (Φ = 0.7) but only 42% under rich conditions (Φ = 1.2), while ammonia cracking reduced NH₃ emissions by up to 17 000-fold. Formaldehyde decreased by 45.9% (Φ = 1) with hydrogen addition, outperforming ammonia cracking (28% reduction), due to H-radical-driven consumption. Acetaldehyde emissions follow a U-shaped trend increasing under lean conditions, but decreasing in fuel-rich environments, with direct hydrogen addition achieving a 19% reduction at Φ = 1.2. These findings highlight a trade-off between hydrogen strategies, with ammonia cracking better suited for minimizing unburned ammonia and direct hydrogen addition more effective at reducing carbonyl compounds. Optimizing hydrogen enrichment in ammonia/methanol combustion is crucial for balancing emission control and combustion efficiency in future sustainable fuel applications.

In this study three samples of cobalt oxide were prepared via coprecipitation at pH 9.5 using cobalt nitrate as a precursor. They were dried at 120°C before calcining at 400, 500, and 600°C. The crystalline phases were determined using X-ray diffraction (XRD), revealing the presence of the Co₃O₄ phase in all prepared samples in varying proportions. Fourier Transform Infrared Spectroscopy (FTIR) spectra showed distinct bands corresponding to the vibrational motion of the Co–O bond, confirming the formation of cobalt oxide (Co₃O₄). Scanning electron microscope (SEM) analysis of the Co 500 sample revealed particles in the range of 40–350 nm (average ~100 nm) with relatively low agglomeration, while energy-dispersive X-ray spectroscopy (EDX) confirmed a composition consistent with stoichiometric Co₃O₄ (85.7 wt % Co and 13.6 wt % O). Pyridine-adsorbed FTIR spectra indicated that the sample calcined at 500°C possessed the most balanced ratio of Lewis and Brønsted acid sites, which correlated with its highest catalytic activity. The textural properties of all samples were analyzed using nitrogen adsorption data at 77 K, and the adsorption isotherms were found to be type IV, with hysteresis loops indicating capillary condensation in mesopores. The specific surface area reached a maximum of 4.837 m²/g for the sample calcined at 500°C. This sample also exhibited the highest total acidity (0.035 mmol/g) and strong acidic sites (the initial electrode potential value E_i = 73.2 mV), which enhanced catalytic performance. Pore radius calculations further revealed that the samples contained mesopores. The catalytic efficiency of the prepared samples in the ammonia oxidation reaction was evaluated at 450°C. The sample calcined at 500°C demonstrated the highest catalytic activity. The sample calcined at 500°C achieved 100% NH₃ conversion at 475°C and maintained full activity over 10 consecutive cycles, demonstrating high stability and reusability.

An active Pd/MgAlO_x catalytic system providing selective formation of benzyl alcohol in an industrially important reaction of benzaldehyde hydrogenation was synthesized and studied using X-ray diffraction, scanning and HAADF-STEM electron microscopy, nitrogen and CO₂ adsorption, TPR and CO pulse chemisorption methods. Additional advantages of these catalysts include the possibility of regeneration and reuse. For the first time, palladium catalysts based on layered double hydroxides (LDHs), synthesized by the mechanochemical method, have been obtained. It has been shown, that the solid-phase mechanochemical method is effective and more environmentally friendly, and the catalysts, synthesized by this method, are not inferior to samples, synthesized by the traditional coprecipitation method, in their textural characteristics, basicity, activity and selectivity.

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.