


Том 59, № 1 (2018)
- Жылы: 2018
- Мақалалар: 12
- URL: https://journal-vniispk.ru/0023-1584/issue/view/9942
Article
Reactivity of Iodine Atoms in Reactions with Unsaturated and Polar Compounds
Аннотация
The experimental data on the reactions of iodine atoms with olefins, alkyl halides, and oxygencontaining compounds (20 reactions) are analyzed under the model of intersecting parabolas (MIPs). The effect of the following factors on the activation energy of these reactions is found: the enthalpy of the reaction, triplet repulsion, and dipole–dipole interaction of the reaction site with the polar groups and π electrons of the neighboring double bonds. The increments characterizing the contribution from each factor to the activation energy are calculated.



Nitromethane Isomerization during Its Thermal Decay
Аннотация
Different aspects of problem of nitromethane (NM) isomerization during its thermal decay in a wide range of temperatures and pressures are analyzed. Based on the experimental and the published data on new theoretical concepts, two different mechanisms of NM decay, direct and isomerizable, are practically combined into a single complex mechanism.



Measurement of the Rate Constant of a Reaction of Chlorine Atoms with CH3Br in a Temperature Range of 298–358 K Using the Resonance Fluorescence of Chlorine Atoms
Аннотация
The rate constant of the reaction of chlorine atoms with CH3Br was measured in a temperature range of 298–358 K using the resonance fluorescence of chlorine atoms. The possible role of this reaction in atmospheric chemistry and fire extinguishing was discussed. It was found that this reaction is homogeneous in contrast to the previously studied reaction of chlorine atoms with CH3I, with occurs at the reactor surface.



Specific Features of a Two-Phase Bimolecular Chemical Reaction in the Case of the Association of Both Reactants
Аннотация
The effect of the association of both reactants on the kinetics of their bimolecular reaction in the liquid phase is studied. The mathematical modeling of chemical reactions that are described by nonlinear differential equations is performed. The steady states, the conditions for the emergences of intermediates, and the nature of their concentration oscillations in the reaction system are described. It is found that the concentration of the intermediates has two types of oscillations (harmonic and relaxation oscillations) characterized by significantly different times. The relationship between the observed rate constant of the process, the rate constants for the elementary stages, and the reactant concentrations is found.



Oxidation of Water to Molecular Oxygen by One-Electron Oxidants on Transition Metal Hydroxides
Аннотация
Surveyed in this review are the most important achievements in the research and development of catalysts based on Mn, Fe, Co, and Cu hydroxides for the oxidation of water to molecular oxygen by chemical oxidizing agents obtained, for the most part, at Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences. An analysis of the results of kinetic studies on water oxidation in the presence of the above-menthioned catalysts together with data obtained by quantum chemistry methods allowed us to make a conclusion on the general nature and process mechanism both in the presence of artificial catalytic systems based on metal hydroxides and the natural enzyme photosystem II of green plants. The most important properties of hydroxo compounds responsible for catalytic activity in the oxidation of water by one-electron oxidants are discussed, and a possible reaction mechanism is considered.



Kinetic Study and Optimization of Catalytic Peroxide Delignification of Aspen Wood
Аннотация
It is established that the main regularities of the peroxide delignification of aspen wood in the temperature range of 70–100°С in the presence of dissolved (H2SO4) and solid (TiO2) catalysts are similar. With an increase of the temperature, the concentration of hydrogen peroxide and acetic acid, and the hydromodule (HM) values, as well as the duration of the process and the content of cellulose in the cellulose products, increase, while the content of the residual lignin decreases. Simultaneously, the total yield of cellulose products decreases independently of the nature of the catalyst. Delignification processes are satisfactory described by the first-order equation. A sufficiently high activation energy (88 kJ/mol in the presence of H2SO4 and 75 kJ/mol in the presence of TiO2) indicates the absence of significant external diffusion constraints in the selected conditions. The optimal conditions of obtaining cellulose products with a low content of residual lignin from aspen wood are found by the calculation methods. It is shown by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) that the structure of cellulose products obtained corresponds to the structure of industrial microcrystalline cellulose. In the optimal conditions, a high-quality cellulose product can be obtained in mild conditions (the temperature is 100°С, atmospheric pressure) by using a safer and technological TiO2 catalyst instead of a sulfuric acid catalyst.



Redox and Catalytic Properties of Copper Molybdates with Various Composition
Аннотация
Using XRD and temperature-programmed reduction (TPR), phase and structural transformations of copper molybdates Cu3Mo2O9 and CuMoO4 were investigated in the course of their treatment with hydrogen, carbon monoxide or soot. The catalytic properties of copper molybdates Cu3Mo2O9 and CuMoO4 were studied in model oxidation reactions of carbon monoxide and soot. Phase and structural transformations of the molybdates, in particular formation of Cu4–xMo3O12 and Cu6Mo5O18 phases, was shown to have a significant impact on the formation of active state of the catalysts in the model reactions considered.



Temperature Hysteresis in the Reaction of Methane Oxidation on a Palladium-Doped Manganese Hexaaluminate Catalyst
Аннотация
A study of the Pd-containing catalyst based on manganese hexaaluminate by X-ray diffraction analysis, transmission electron microscopy, thermo-programmed reduction with hydrogen, and thermoprogrammed oxidation showed the hysteresis manifested itself in a difference between the temperature dependences of its catalytic activity in the oxidation of methane under the conditions of sample heating or cooling is related to the decomposition of PdO to metallic palladium at temperatures higher than 700–800°C and the subsequent formation of PdO nanoparticles, which are localized on the surface of metallic Pd (30–50 nm) in the form of polycrystalline films with a thickness of 2–5 nm, at temperatures lower than 600–700°C. A near-surface oxide film is formed under the conditions of cooling in oxygen-containing atmospheres, including in the presence of methane. The value of the hysteresis depends on the heat treatment temperature of the catalyst, and it reaches a maximum on the catalysts calcined at 900 and 1000°C.



Catalytic Etching of Platinoid Gauzes during the Oxidation of Ammonia by Air. Reconstruction of Surface of Platinoid Gauzes at 1133 K in Air, in Ammonia, and in an NH3 + O2 Reaction Medium
Аннотация
The structure, morphology, and chemical composition of the surface and near-surface layers of platinoid wires of polycrystalline gauzes, containing Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) after treatment at 1133 K in various media—in air, in ammonia, and after NH3 oxidation in air—are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). A thin film is found on the surface of the initial gauze containing an oxide layer of Rh2O3 with a thickness of ~2 nm, on the surface of which an inhomogeneous graphite-like layer 10–50 nm thick is located. It is shown that the heat treatment of gauzes in air leads to the partial removal of the surface graphite-like film that forms the reticulated structure on the wire surface. The treatment of gauzes in an ammonia atmosphere leads to the complete removal of the graphite-like and oxide layers and to the growth of metal grains of ~10 μm. After the catalytic reaction of NH3 oxidation, a deep structural rearrangement of the surface layer of the wire takes place, as a result of which crystalline metal agglomerates of ~10 μm are formed. It is supposed that the reaction of NH3 molecules with oxygen atoms penetrated on the defects leads to the local increase of temperature, due to which the metal atoms emerge on the surface and form large crystalline agglomerates and pores in the region of the grain boundaries.



Gas-Phase Carbonylation of Dimethoxymethane to Methyl Methoxyacetate on Solid Acids: The Effect of Acidity on the Catalytic Activity
Аннотация
The gas-phase carbonylation reaction of dimethoxymethane (DMM) to methyl methoxyacetate on different solid acids was studied. It was established that this reaction was accompanied by the occurrence of a side reaction of DMM disproportionation into dimethyl ether and methyl formate. It was shown that the activity of solid acids in both of the reactions depends on the strength of Brønsted acid sites according to an equation like the Brønsted–Evans–Polanyi–Semenov correlations.



Effect of the Calcination Temperature and Composition of the MnOx–ZrO2 System on Its Structure and Catalytic Properties in a Reaction of Carbon Monoxide Oxidation
Аннотация
The effect of the calcination temperature and composition of the MnOx–ZrO2 system on its structural characteristics and catalytic properties in the reaction of CO oxidation was studied. According to X-ray diffraction analysis and H2 thermo-programmed reduction data, an increase in the calcination temperature of Mn0.12Zr0.88O2 from 450 to 900°C caused a structural transformation of the system accompanied by the disintegration of solid solution with the release of manganese ions from the structure of ZrO2 and the formation of, initially, highly dispersed MnOx particles and then a crystallized phase of Mn3O4. The dependence of the catalytic activity of MnOx–ZrO2 in the reaction of CO oxidation on the calcination temperature takes an extreme form. A maximum activity was observed after heat treatment at 650–700°C, i.e., at limiting temperatures for the occurrence of a solid solution of manganese ions in the cubic modification of ZrO2. If the manganese content was higher than that in the sample of Mn0.4Zr0.6O2, the phase composition of the system changed: the solid solution phase was supplemented with Mn2O3 and β-Mn3O4 phases. The samples of Mn0.4Zr0.6O2–Mn0.6Zr0.4O2 exhibited a maximum catalytic activity; this was likely due to the presence of the highly dispersed MnOx particles, which were not the solid solution constituents, on their surface in addition to an increase in the dispersity of the solid solution.



Controlling the Catalytic Properties of Copper-Containing Oxide Catalysts
Аннотация
The results of a systematic study of the formation of Cu–Zn, Cu–Zn–Al, Cu–Zn–Cr, Cu–Zn–Si, Cu–Cr, and Cu–Si oxide catalysts with a widely varied ratio between their components are generalized within the chemical approach developed by G.K. Boreskov to establish the quantitative relation between their chemical composition and catalytic activity. Simultaneously, their catalytic properties, such as selectivity and activity, are measured under the same conditions in the methanol synthesis and dehydrogenation and water gas shift reactions, whose common feature is a reductive reaction medium. The activity of Cu–Zn–Al–Cr— Si-oxide catalysts in all the studied reactions is governed by the Cu0 nanoparticles formed on their surface in the process of reductive activation. Nanoparticles of different catalysts have similar sizes (3–8 nm). However, the ratios between the catalytic activities per unit of the copper surface area for catalysts with various structures of their oxide support (spinel, wurtzite, zincsilite, or silica type) are appreciably different in each reaction. The relation between the chemical composition of a catalyst and its catalytic activity in a certain reaction is established by the chemical composition of its precursor representing a hydroxo compound, i.e., the nature of the selected cations and the quantitative ratio between them. The decomposition of hydroxo compounds to oxides (and the further activation of oxides) should be performed at medium temperatures, providing the incomplete elimination of ОН– and CO32- anions, i.e., the formation of anion-modified oxides. The structure of the latter and the type of interaction between Cu0 nanoparticles and an oxide support are governed by the structure of the hydroxo precursor compound.


