Kinetics and Catalysis最新文献

Supported LaFe_{1 – x}Ni_xO₃/α-Al₂O₃ (x = 0, 0.6, 1) perovskite containing catalysts are prepared by impregnation of a high-temperature block carrier based on α-Al₂O₃ with a suspension of the active component followed by heat treatment at 900°C. The catalysts were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and temperature-programmed reduction with H₂ (H₂-TPR) methods and studied in the reaction of high-temperature decomposition of nitrous oxide. It is shown that all the supported catalysts are two-phase and contain only corundum and perovskite phases. The parameters of the crystal structure and the X-ray size of the corundum phase in the supported catalysts do not differ from the carrier. The observed slight increase in the cell volume for nickel-containing perovskites in supported catalysts may be due to an increase in the vacancy content in them. According to H₂-TPR data, the temperatures of the reduction peaks of the supported catalysts do not differ from the reduction peaks of the unsupported perovskites, which indicates that the active component is not modified by the carrier. In terms of activity, the supported catalysts can be arranged in a row LaNiO₃/α-Al₂O₃ > LaFe_{1 – x}Ni_xO₃/α-Al₂O₃ > LaFeO₃/α-Al₂O₃, which corresponds to the row activity of unsupported perovskites. Catalyst LaNiO₃/α-Al₂O₃ with LaNiO₃ content ~7%, monoliths height 20 mm and contact time 0.06 s demonstrates ~94% N₂O conversion degree at 900°С.

We investigated the kinetics of ethylene polymerization using a metallocene/MAO/ Al(Et)_1.5(OC₂H₅)_1.5 ternary catalytic system at 60–90°C and 600 kPa. Three different unbridged metallocene catalysts were used: (Ind)₂ZrCl₂ (I), (BenzInd)₂ZrCl₂ (II), and (Flu)₂ZrCl₂ (III). We studied the effects of ligand structure, co-catalysis, and the activation energy of the deactivation reaction. Depending on the catalyst concentration, deactivation proceeds as a first-order reaction. In the ternary catalytic system, the half-life is highly dependent on the ligand structure, with the activation energy of deactivation for catalyst I being lower than for catalysts II and III. At 60°C, the half-lives of unbridged metallocenes I and II are slightly lower than that of III. With increasing temperature, the half-lives of II and III decrease similarly, but I deactivates much faster.

The review covers current advances in the catalytic hydrogenation of α-methylstyrene to isopropylbenzene. The focus is on platinum group catalysts (palladium, platinum, rhodium, iridium), their activity, selectivity, kinetics, and thermal stability, as well as reactor designs that improve the efficiency of the process. The prospects for using more accessible metals—nickel, iron, cobalt, manganese, and molybdenum—are highlighted, including the features of multicomponent systems and stability issues. The influence of the environment and new carriers, including plasma-activated graphene materials, on the kinetics and selectivity of hydrogenation is considered. The review serves as a basis for the development of innovative and sustainable technologies in the chemical industry.

Widespread application of any catalyst requires rigorous testing in the reaction of interest. Hydrogen-peroxide-based advanced oxidation processes (AOPs) are attracting growing attention because they oxidize pollutants rapidly, completely, and with minimal formation of by-products. Here we report the performance of a porous M₃O₄–poly(dicyclopentadiene) nanocomposite (Mn₃O₄/p(DCPD)) as a heterogeneous Fenton-like catalyst for the decolorization of methylene blue (MB), a dye that is toxic to humans and aquatic ecosystems. The influence of key operating variables—reaction time, initial dye concentration, H₂O₂ dosage, temperature, and catalyst loading—was examined systematically. Under the optimum conditions (0.25 g/L catalyst, 20 mg/L MB, ambient temperature), the dye was fully degraded within 120 min. The catalyst is easily processed, separated, and reused, making Mn₃O₄/p(DCPD) a promising candidate for sustainable AOP treatment of dye-contaminated water.

The influence of transition state shape selectivity (TSSS) on the catalytic activity of zeolites in the Diels–Alder reaction was investigated using the Monte Carlo method. As a fundamental theory, we consider TSSS on the example of the interaction of transition states (TS) of some Diels–Alder reactions with cavities of LTA and FAU zeolites. Interactions between cyclopentadiene and acrylonitrile, cyclopentadiene and maleic anhydride were considered as Diels–Alder reactions. Na- or Ca-containing LTA and FAU and K-containing LTA are considered as zeolites. The prediction of catalytic activity was carried out by simulation of adsorption by the Monte Carlo method using the Material Studio program. Thus, the nature of the interaction of the transition state of the reactions under consideration with the topology of the selected zeolites was considered.

Metal oxide catalysts, which can compete with commercial platinum and chromium catalysts for nonoxidative propane dehydrogenation (PDH), are of significant practical and scientific interest. In this study, the catalytic activity of bulk zinc oxide promoted with La, Y, V, Fe, Co, Ni, W, Mo, Cu, Ce, Mn, In and Sn was screened in PDH, and this allowed selection of Fe, Co, and Mo as the most promising additives. Subsequent screening of the catalytic performance of a titania-supported zinc oxide promoted by the selected elements indicated that Mo increased the short-term catalytic activity the most, while Fe and Co provided higher catalyst stability. The catalysts were characterized by low-temperature nitrogen adsorption, X-ray diffraction analysis and transmission electron microscopy. PDH reaction, catalyzed by Mo–Zn/TiO₂ at 600°C and tested in fixed-bed flow-type reactor at a gas hourly space velocity (GHSV) of 7500 mL h⁻¹ ({text{g}}_{{{text{cat}}}}^{{ - 1}}) (propane/N₂ = 1/10), afforded up to 29% propane conversion with 95% propylene selectivity.

Aluminum–magnesium layered double hydroxide (LDH) was obtained for the first time using the product of reaction between water and aluminum preliminarily activated by Ga–In eutectic alloy. This by-product of the reaction for hydrogen production was used as a reagent in the proposed hydrothermal synthesis of MgAl-LDH and allowed obtaining a material with a structure and properties similar to LDH synthesized by the conventional co-precipitation method. Supported palladium catalysts prepared using synthesized LDHs were highly selective in the aqueous-phase hydrogenation of furfural to furfuryl alcohol, probably due to modification of palladium with gallium introduced from the eutectic alloy at the stage of aluminum activation.

A method is proposed for estimating the rate constants of growth reactions, chain transfer, and the concentration of active centers in ion-coordination polymerization using the right end of the molecular weight distribution (MWD). Experimental MWD data from samples obtained at the start of polymerization demonstrate that the concentration of active polymerization centers and the rates of growth and chain transfer reactions can be estimated through computational experiments with Monte Carlo simulation of the polymerization process. The formation of MWD was simulated for polymerization schemes with instantaneous and slow initiation.

A novel hypercrosslinked porous polymer-based solid acid with an embedded pyridinium moiety in the polymeric framework was synthesized via the quaternization of 4,4'-bipyridine (BPy) and 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP), followed by polycondensation and sulfonation. This approach represents a key advancement by integrating the pyridinium moiety directly into the rigid polymer skeleton, thereby effectively preventing pore blockage typically encountered with physically immobilized bulky ionic liquids (ILs). The polymer possesses a rigid biphenyl framework, which provides sufficient sulfonation sites for high acidity. The hypercrosslinked structure ensures high stability and a surface area of 1162 m²/g for the solid acid. The ionic liquid moiety in the polymer provides special active sites, and the free coordinating anions make these sites highly accessible to reactants. The novel hypercrosslinked porous polymer-based solid acid with a pyridinium moiety exhibited high catalytic activity in biodiesel synthesis via the esterification of oleic acid (98.7% conversion) and the integrated esterification-transesterification of waste oil (99.1% total yield), respectively. The novel solid acid could be recycled nine times with minimal activity loss (from 99.1 to 97.2%). The pyridinium moiety, high surface area, high acidity (3.4 mmol/g), and rigid aromatic framework were the key factors contributing to the high activity, making the novel solid acid a promising candidate for industrial applications.

High-temperature oxidation of NH₃ with air to NO oxide on catalytic platinum alloy gauzes is used in the industrial production of nitric acid. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) with the probe electron energy of 5 and 20 keV were used to characterize chemical composition of the etching structure on Pt(poly) after NH₃ oxidation with air at a pressure of 3.6 bar and 1133 К. Pt, Fe, Si, Al, Mg, O, N and C were detected in the etching structures, which contain oxide particles, crystal platinum pyramids and etch pits (grooves). Pt and О were detected in high concentrations (22.2–69.0 at %), while other elements—in low ones (0.2–8.4 at %). Oxide particles ca. 100 nm in size with the composition MgFe₂O₄ and a spinel structure are formed from Mg, Fe impurities during NH₃ oxidation. Nucleation and growth of platinum pyramids, etch pits and deep etch grooves proceed during the capture of Pt and PtO₂ from gas phase by MgFe₂O₄ particles, migration of Pt atoms through the oxide particles to the metal-oxide boundary, and their attachment to the Pt crystal lattice. The formation of etching structure can proceed by the vapor-liquid-solid (VLS) mechanism.