Том 58, № 6 (2017)

The pattern of the quantitative relationship between the rate constant of the quadratic branching of reaction chains and the rate of nonthermal flame propagation is determined by the example of the chain decomposition of nitrogen trichloride. It is shown that, due to this functional relationship, the values of the rate constants for the NCl₂ + NCl₂ = N₂ + 4Cl reaction determined by the stationary rate of the decay of the flame of the nitrogen chloride and, independently, by the spectroscopic kinetic study of NCl₂ radical consumption are almost the same.

The reactions X• + HCR₂ONO₂ → XH + R₂C=O + •NO₂ are very exothermic due to the cleavage of the weak N−O bond and the formation of the energy-intensive C=O bond. The quantum chemical calculation of the transition state of these reactions for X• = Et• and EtO• used as examples showed that they actually proceed in one elementary act as eliminations with concerted fragmentation. The kinetic parameters were estimated within the framework of the intersecting parabolas model; the parameters allow the calculation of the activation energy and rate constant from the enthalpy of the above reaction. For a series of reactions involving the Et•, EtO•, RO•₂, and •NO₂ radicals, on the one hand, and a number of alkyl nitrates, on the other, their enthalpies, activation energies, and rate constants were calculated. Based on the data obtained, new kinetic schemes of the chain decomposition of alkyl nitrates involving eliminations with fragmentation were proposed.

The photocatalytic transformations of carbon tetrachloride and aliphatic primary alcohols in the presence of iron trichloride and a molar ratio of components FeCl₃: CCl₄: ROH = 1: 300: 2550 were studied. CCl₄ is transformed into chloroform and hexachloroethane after exposure to a mercury lamp (250 W) to the FeCl₃–CCl₄–ROH system at 20°C, whereas the primary ROH alcohols are selectively oxidized into acetals (1,1-dialkoxyalkanes). The maximum conversion of CCl₄ reaches 80%. The kinetics and mechanism of the photocatalytic conversion of the FeCl₃–CCl₄–ROH system are considered.

This paper reports the synthesis of layered zinc/sodium and zinc/potassium octanoates (A₂[Zn(C₈H₁₅O₂)₄], A = Na⁺ or K⁺), two underexplored carboxylates, through reaction of the octanoate of the desired alkali metal with a zinc salt. After drying and chemical characterization, their catalytic activities were tested in the esterification of octanoic acid with isopropanol. Conversion values were high for the reactions conducted under following conditions: temperature 155°C, isopropanol/octanoic acid molar ratio = 8: 1, catalyst/ octanoic acid ratio 7 wt %, and reaction time 2 h. Isolation of the catalysts after esterification showed that the materials were converted into zinc octanoate in situ.

The results of a study on the activity and operational stability of an Au–Pd/MFI/Al₂O₃ catalyst in the reaction of ethanol conversion into a gasoline fraction of hydrocarbons are reported. In the presence of the Au–Pd/MFI/Al₂O₃ catalyst, ethanol was almost completely converted into an alkane–aromatic fraction of C₃–C₁₁ hydrocarbons at 300°C in an atmosphere of Ar; the yield of this fraction was as high as 90% on a feed carbon basis. It was established that, in the presence of the bimetallic Au–Pd catalyst, the yield of the target fraction increased by 10%, as compared with that on a monometallic Au-containing sample. The Au–Pd/MFI/Al₂O₃ catalyst exhibited much higher stability in a long-term experiment in comparison with the previously tested pilot sample of Pd–Zn/MFI/Al₂O₃. After a 40-h operation, the yield of the target fraction of C₃₊ hydrocarbons in the presence of the Au–Pd/MFI/Al₂O₃ catalyst decreased by 15%. The treatment of the catalyst with hydrogen led to the complete restoration of its activity. The structure of the Au–Pd active constituents was studied by transmission electron microscopy X-ray photoelectron spectroscopy. methods of the and microscopy.

Palladium catalysts on various types of supports were studied in the liquid-phase hydrogenation of diphenylacetylene. Samples of Pd/SiO₂–Al₂O₃, Pd/MgAl₂O₄, Pd/Al₂O₃, and Pd/TiO₂ were characterized by the chemisorption of the CO and IR spectroscopy of adsorbed CO. The use of n-hexane as the solvent increases the reaction rate, which can be explained by the better solubility of hydrogen in the liquid phase. It is established that the acid–base properties of the support do not affect the activity and selectivity of the catalysts in the reaction under study. However, they alter the electronic state of palladium. According to the catalytic tests, Pd/TiO₂ has the highest activity (turnover frequency) and selectivity to alkene. The comparison of the obtained catalytic data and the results of IR spectroscopy made it possible to conclude that this is due to the electron density redistribution between the palladium and TiO_x particles, which is caused by the strong metal–support interaction.

This review is dedicated to the effect of water as the main by-product of the Fischer–Tropsch synthesis on the process. The reasons for the negative effect of water are analyzed and the possible versions of the control of its participation in the process are considered. As an optimal solution to the problem, the use of zeolites in the H form as the constituents of cobalt catalysts for the Fischer–Tropsch synthesis is proposed. Bibliography: 148 references.

Gold metal particles were vacuum deposited onto the iron oxide surface and the effect of thermal treatment on the resulting Au/Fe₂O₃ samples at 30–800°C in vacuum and reaction media with different chemical compositions, i.e., 5 mbar of O₂, 5 mbar of CO, and 5 mbar of CO + 5 mbar of O₂, was studied by X-ray photoelectron spectroscopy. During the gold deposition, the increase in the intensity of the Au4f line was shown to be accompanied by its shift toward lower binding energies, which is due to the increase in the particle size of gold. Starting from a certain amount of deposited gold, the binding energy E_b(Au4f_7/2) reaches the value typical of bulk gold metal. During the heating of Au/Fe₂O₃ in vacuum or a reaction medium, fine gold particles agglomerate into coarser ones, which is manifested in the decrease in the relative [Au]/[Fe] atomic ratio. The tendency of gold particles toward agglomeration depends on the composition of the reaction medium: the process proceeds most efficiently in the CO + O₂ mixture and less intensively in CO, and the highest stability was observed upon treatment in O₂. It is assumed that the decrease in the [Au]/[Fe] atomic ratio during the thermal treatment of Au/Fe₂O₃ in CO + O₂, CO, and vacuum could be not only due to agglomeration but also due to the encapsulation of the gold particles by the reduced fragments of the support.

The bimetallic MoWS₂/Al₂O₃ catalyst was synthesized using the Keggin-type mixed heteropolyacid H₄SiMo₃W₉O₄₀. The monometallic catalysts SiMo₁₂/Al₂O₃ and SiW₁₂/Al₂O₃ based on the H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀ acids are prepared as reference samples. The sulfidized catalysts are analyzed by temperature-programmed reduction with hydrogen, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Their catalytic properties are studied in the cohydrotreatment of dibenzothiophene (DBT) and naphthalene on a flow-type setup. The introduction of three molybdenum atoms into the structure of an oxide precursor is shown to increase the degree of sulfidation of the tungsten particles by 20% in comparison with SiW₁₂/Al₂O₃. The DBT turnover frequency in the hydrodesulfurization (HDS) on the sites on the edges of the active phase of the SiMo₃W₉/Al₂O₃ catalyst is shown to be 5.5 times higher than in the presence of SiW₁₂/Al₂O₃. The bimetallic sample demonstrated the highest selectivity in the preliminary DBT hydrogenation route and activity in the prehydrogenation of naphthalene. The high level of activity of the SiMo₃W₉/Al₂O₃ catalyst was due to the formation of a mixed Mo_xW_(1–x)S₂ active phase with a MoW oxide precursor, whose structure contained both metals bonded at the molecular level.

The problem of the mathematical modeling of the catalyst deactivation process inside a spherical grain with a parallel first-order deactivation mechanism has been solved in the work [9] by the finite difference method. This paper presents a simpler method for the solution of this problem. It is shown that the set of nonlinear partial differential equations for planar, cylindrical, and spherical grains can be reduced to a boundary problem for two ordinary differential equations with respect to the spatial variable, where time is a parameter. The obtained equations are solved by the shooting method using Mathcad functions. For illustration, the profiles of relative catalyst activity and dimensionless reagent concentration are calculated for a spherical grain at a Thiele parameter of 5 and different time moments, together with the dependence of the degree of internal grain surface utilization on dimensionless time. Some asymptotic dependences are proposed for these parameters over a long time period.

A series of composites containing hexagonal tungsten trioxide (h-WO₃) and reduced graphene oxide (rGO) sheets are synthesized via a modified one-step hydrothermal route without assisted additive. The composites are characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy. The new procedure made it possible to increase the reduction degree of GO. Based on the evidence presented hexagonal WO₃ grows on the surface of graphene through chemical interactions with the surface. The visible-light photocatalytic degradation of methylene blue shows that the h-WO₃/rGO composites exhibit superior photocatalytic performance of 96% with a maximum degradation rate achieved under visible-light irradiation for 6 h. The speculations concerning the mechanism of photocatalytic reactions are discussed. The improved photocatalytic activity can be accounted for by the increased adsorption toward chemical species, the enhanced light absorption and an efficient separation of photogenerated electron-hole pairs and transfer of charge carriers.

Ni@CeO₂ core–shell catalysts were synthesized via a facile surfactant-assisted hydrothermal method and their catalytic performance in the dry reforming of methane (DRM) reaction was evaluated. A variety of techniques including XRD, N₂ adsorption–desorption, SEM, TEM, TPO, TGA were employed to characterize the prepared or spent catalysts. The encapsulation by the CeO₂ shell, on one side, can restrict the sintering and growth of Ni nanoparticles under harsh reaction conditions. On the other side, compared to the conventional shell material of SiO₂, CeO₂ can provide more lattice oxygens and vacancies, which is helpful to suppress coke deposition. Consequently, the Ni@CeO₂ core–shell catalysts exhibited better catalytic activity and stability in the DRM reaction with respect to the referenced Ni@SiO₂ core–shell catalysts and Ni/CeO₂ supported catalysts.