Kinetics and Catalysis最新文献

It was supposed that, in the reaction of oxyethylation of alcohols, the kinetically independent unit is not a monomeric alcohol molecule, but a linear chain alcohol associate consisting of an average of n alcohol molecules, and that the reaction rate is of the first order not in the total concentration of all alcohol species, but in the concentration of these associates. The kinetic aspects of this phenomenon were considered. It was assumed that reactions of the first order in the concentration of an associated component, which are widespread in liquid-phase chemical kinetics, occur as a result of the release of the reaction product from the associate.

The characteristics of Mn catalysts supported on different carriers (SiO₂ and BEA zeolite) in the processes of ozone decomposition and ozone-catalytic oxidation (OZCO) of volatile organic compounds (VOCs) were studied using n-butane as an example. The parent SiO₂ was inactive in the test reactions, and the characteristics of Mn/SiO₂ were determined by the catalytic properties of the supported MnO_x oxide. In contrast to SiO₂, BEA zeolite demonstrated significant catalytic activity, although at a temperature 50°C higher than that for Mn/BEA. The data obtained allowed us to conclude that the catalytic characteristics of Mn/BEA at 30–100°C were also determined by the Mn component of the catalyst. At higher temperatures, the catalytic properties of BEA significantly affected the course of the OZCO process. The zeolite carrier improved hydrocarbon conversion at 100–200°C and decreased the amount of ozone required for the OZCO process over Mn/BEA.

A series of Ni–Nb₂O₅/SiO₂ catalysts with varying Ni loadings (5–25 wt %) were prepared. The catalytic activity of the materials was evaluated by nitration of toluene. Ni–Nb₂O₅/SiO₂ catalyst showed good catalytic activity, selectivity, and reusability for the nitration of toluene. Under the optimal conditions, conversion of toluene by 88% to mononitrotoluene was achieved with 100% selectivity. Experiments were designed by the Minitab software, and the effect of reaction conditions was investigated. The optimal reaction condition was also achieved for the high amount of total products and the lowest amount of meta-isomer using this software. The reusability of catalyst also was studied in this work at the same operating conditions, and the catalyst was stable for four runs without losing catalytic activity.

The activity of transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) oxides supported on γ-Al₂O₃ in the reaction of ozone decomposition was studied. The catalytic characteristics of the samples with high (NiO/Al₂O₃), low (Cr₂O₃/Al₂O₃), and intermediate (MnO_x/Al₂O₃) activity in ozone decomposition were studied in the process of ozone catalytic oxidation (OZCO) of n-butane. The results obtained allowed us to conclude that the optimal activity of a transition metal oxide in the decomposition of O₃ is of key importance in the OZCO process. At a low rate of ozone decomposition, hydrocarbon oxidation is limited by the rate of formation of atomic oxygen species; at an excessively high rate of decomposition, hydrocarbon conversion decreases due to an competitive process of atomic oxygen recombination. The best catalytic performance in the oxidation of n-C₄H₁₀ was observed for a catalyst based on Mn oxide, which has an optimal activity in the decomposition of O₃.

A series of mono- and bimetallic copper–cerium catalysts based on ZSM-5 zeolite with different aluminum content (SiO₂/Al₂O₃ = 30 and 55) was synthesized by incipient wetness impregnation. The copper content was 0–4.3 wt %, and cerium loading varied in a range from 0 to 6 wt %. The resulting composites were studied by low-temperature nitrogen adsorption–desorption, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, UV–Vis diffuse reflectance spectroscopy, and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of adsorbed CO and tested in the catalytic reaction of CO oxidation with oxygen. A pronounced synergistic effect of catalytic action of copper and cerium associated with the redox interaction between the metals was observed in the systems under study. The catalytic activity of the composites monotonically increased with the fraction of cerium in the bimetallic systems (as the Сu : Ce ratio was changed from 6 to 1). In the presence of the most active catalysts, the temperature at which CO conversion reached 50% was about 100°C. A decrease in the aluminum content of the zeolite contributed to higher catalytic activity. It was found that Cu⁺ ions bound to the surface of CeO₂ particles played a key role in catalysis.

Methods for carrying out coupling reactions in the chemistry of alkynes to form C–C bonds (oxidative dehydrocondensation reactions, Cadiot–Chodkiewicz reaction, and Sonogashira reaction) are analyzed and generalized. Protocols of synthesis of products of these reactions are also presented, including homogeneous and heterogeneous catalytic systems. In all cases, emphasis is placed on the kinetics and mechanisms of reactions with the discussion of the results of kinetic and spectrometric studies of the mechanisms of coupling reactions involving Cu(I, II, III), Au(I, III), Pd(0, I, II), and Fe (0, I, II, III) complexes. Particular attention is paid to the heterogeneous catalysis of oxidation reactions of alkynes with the participation of nanoparticles and nanoclusters of Pd, Au, Ag, and other metals. The nature of the intermediates containing these metals and the relationships between various oxidative and nonoxidative transformations of alkynes are discussed.

The activation of H₂ molecules by Pt₄ and Pt₃V clusters was studied by the nudged elastic band (NEB) DFT/PBE0/def2tzvp quantum chemical method with construction of minimum energy paths (MEPs). In the case of Pt₄ and Pt₃V clusters, barrier-free dissociative adsorption of H₂ molecules occurs at the platinum centers, while molecular adsorption of hydrogen occurs on the vanadium atom in Pt₃V with a slight weakening of the H−H bond, but without its breaking. The specific features of coordination of H₂ molecules are explained at the level of the MO method. Migration of the H atom from one cluster metal center to another in the model clusters (as probably in the case of hydrogen spillover) occurs at low activation barriers in the direction of the displacement vector corresponding to the normal vibrations of the system in the transition state. A significant role of Pt−H−Pt and V−H−Pt bridging groups in hydrogen migration has been revealed: they facilitate the transition of H atoms from one metal center of the cluster to another.

Nickel-based Ni–Ce_{1 – x}Zr_xO₂ catalysts were prepared by the Pechini method. The catalyst performance in the CO₂ methanation reaction was studied. The catalysts exhibit high catalytic activity comparable to that of the commercial NIAP-07-05 catalyst of methanation. The catalysts were characterized by X‑ray diffraction methods with experiments using synchrotron radiation, and also by high-resolution electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The method for the preparation makes it possible to obtain fine nickel-containing particles formed during the decomposition of the Ni–Ce–Zr–O substitution solid solution obtained during the synthesis. Because of the decorating effect, however, the surface of nickel-containing particles is poorly accessible to reagents. For this reason, the Ni–Ce_{1 – x}Zr_xO₂ catalysts obtained by the Pechini method are less active than supported Ni/Ce_{1 – x}Zr_xO₂ catalysts.

Synthesis gas is the cornerstone of many chemical processes for manufacturing a broad range of petrochemical products. In this work, a mathematical model was developed for investigation of the CO₂ reforming of methane in a catalytic packed bed reactor. To simulate the reformer, a pseudo homogenous two-dimensional mathematical model was developed and the resulting nonlinear second order partial differential equations were solved using the finite difference method. It was assumed that equilibrium reverse water-gas shift reaction always takes place in the reactor to adjust H₂/CO ratio (≤1). The effect of operating conditions, including bulk density, porosity, inlet gas and wall temperature, reactor diameter, total molar flow of gas and inlet CH₄/CO₂ ratio on the reactor performance were investigated. Finally, the study investigated the effect of H₂/CO ratio on the outlet synthesis gas product at the range of 0.7–1. The validity of the model was investigated and the deviation between the model results and the experimental data was acceptable.

Biocatalysis in both the homogeneous and heterogeneous versions is an independent interdisciplinary direction in scientific and practical research of single-stage conversions of feed reagents (substrates) to valuable marketable products involving, in most cases, a single enzyme as a catalyst. Single-enzyme biocatalytic processes exhibiting all specific features of enzymatic catalysis are a fairly competitive alternative to conventional chemical production. This review provides information on the results achieved by domestic research teams/laboratories that have been involved in extensive and efficient studies in the field of biocatalysis over the past decades and have practical developments protected by RF patents, which, under favorable circumstances, can be offered to commercial enterprises/companies for testing and use on a laboratory and/or pilot-scale with the prospects of industrial scale-up. In the review, special attention is given to targeted systematic studies of lipolytic enzymes (lipases), which have a unique ability to catalyze reactions in a medium of organic solvents, primarily esterification and transesterification reactions, which lead to the formation of valuable products of organic synthesis, such as esters. Lipases are active components of heterogeneous biocatalysts (BCs) synthesized by fixing (immobilizing) these enzymes on the surface of solid adsorbing supports. The review briefly describes the results of studies of domestic research teams and gives complete lists of their reports providing information on the methods of immobilization of target enzymes, the catalytic properties of the developed BCs (enzyme activity, substrate specificity, operational stability) and describing the conditions for biocatalytic processes involving heterogeneous BCs, such as the synthesis of acrylamide and various esters. Taking into account the average activity (А), which is similar to the activity measured at the half-inactivation time (t_1/2), and the operational stability of BCs characterized by the t_1/2 value, a fairly rough assessment of the productivity of BCs is conducted by calculating the amount of valuable product produced (in tons) per kilogram of BC.