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The energy pathways of possible decomposition and isomerization reactions of iso-propyl (i-C3H7) and n-propyl (n-C3H7) radicals are studied by computational methods of quantum chemistry. The B3LYP, M062X, MP2, and CBS-QB3 methods are used to localize stationary points on the potential energy surface of a system containing propyl radicals. A number of intermediate compounds formed during the isomerization and decomposition of propyl radicals are identified and information is obtained on their structure and thermochemical parameters. Based on the results of the research, a diagram of the energy levels of the system under consideration is constructed. [ABSTRACT FROM AUTHOR]

The study of the oxidation of propane-ethylene mixtures by numerical kinetic modeling allowed us to establish that in the range of 400–600°C with an increase in the conversion of propane with an increase in temperature, the selectivity of propylene formation passes through a maximum whose position depends on the concentration of ethylene in the initial mixture. The addition of ethylene to the initial mixture leads to a reduction in propane consumption and an increase in the selectivity of propylene formation. The conditions under which ethylene introduced into the initial mixture is not consumed during the process are determined; thus, formally it can be considered as a catalyst, and the process of propane oxidation as proceeding in a pseudo-catalytic regime. [ABSTRACT FROM AUTHOR]

The possibility of using 3d-metal oxides as catalysts of self-sustaining catalytic flameless combustion of ethanol was examined. Monolithic catalysts CuO and Cr2O3, supported catalysts 25% CuO/SiO2 and 25% CuO/Al2O3, and ultrasonically treated catalyst 25% NiO/SiO2 can operate for a long time without changes in properties, ensuring 100% ethanol conversion. The wide range of the temperatures reached (300–590°C) allows choosing a catalyst meeting the process tasks. [ABSTRACT FROM AUTHOR]

In order to study the potential energy surfaces (PESs) of systems containing ethylene, hydrogen, and oxygen atoms, quantum chemical calculations are carried out using the hybrid B3LYP method of the density functional theory (DFT) and the composite CBS-QB3 method. An enthalpy diagram reflecting the PES of this reaction system is constructed. It is shown that the addition of a hydrogen atom to ethylene with the formation of an ethyl radical occurs through the formation of a van der Waals complex. The diagram of enthalpies of monomolecular reactions of decomposition and isomerization of the ethoxyl radical is presented in detail, and a conclusion is made about the probability of their occurrence. The global PES minimum of the system describing the sequential addition of hydrogen and oxygen atoms to ethylene is the hydroxyethyl radical. Intermediates CHCH2OH and CH2OCH2 are localized on the PES of the C2H4 + O system and possible pathways for their further transformation are analyzed. The data obtained make it possible to estimate the ranking of individual elementary reactions in the processes of combustion and oxidation of hydrocarbons and the probabilities of various directions for the transformation of chemical species in the studied systems. [ABSTRACT FROM AUTHOR]

This paper presents experimental results on the oxidation of propane and propylene in laboratory reactors and the results of their kinetic modeling, based on the mechanisms represented in literature. It was established that in the oxidation and pyrolysis of propane, chain propagation reactions involving alkyl peroxyl radicals play a significant role. The results of modeling show the possibility of quantitatively match the calculations with the experimental results obtained in laboratory-scale reactors taking into account a number of processes that occur with the participation of active intermediate components on the reactor surface. Contrary to expectations, during the conjugated oxidation of propane and propylene under these conditions, these hydrocarbons barely affect each other's conversion. [ABSTRACT FROM AUTHOR]

A value-based method for the numerical identification and analysis of critical (limiting) states in chemical reaction systems is described. The extreme behavior of the reaction system, in which its behavior changes qualitatively with small changes in the initial parameters, is proposed to use when evaluating the critical states of reactions. The problem of the calculus of variations with the target condition is solved using the Pontryagin maximum principle. The value-based approach, which consists in the Hamiltonian systematization of kinetic equations of multistep reactions, is distinguished by the relative simplicity of the calculation procedures and makes it possible to determine the values, i.e., the kinetic significances of the individual chemical steps and chemical components of the reaction. According to the pressure–temperature (P–T) diagrams, three known self-ignition limits are described using the kinetic model of a reacting mixture of hydrogen and oxygen as an example, which includes forty two separate steps and eight chemical components. The existence of the fourth new degenerate limit in the H2/O2 reaction system is predicted. The limiting phenomena are chemically interpreted by identifying the value-based numerical subordination of chemical components and individual steps of the kinetic mechanism of the reaction of hydrogen with oxygen. [ABSTRACT FROM AUTHOR]

Tests on propane pyrolysis in a two-sectioned flow reactor have shown that the introduction of ethylene into the feed mixture leads to an increase in the propylene yield. Under certain conditions, the ethylene content in the mixture at the inlet and outlet of the reactor remains constant. At high temperatures, the process can be accompanied by the formation of tarry products. The absence of oxygen-containing byproducts makes the cocracking of propane and ethylene more attractive than the oxidative pyrolysis of propane. [ABSTRACT FROM AUTHOR]

The catalytic activity of tungsten carbide WC and a mixture of tungsten carbides (WC + W2C) obtained by mechanochemical and plasma-mechanochemical methods in the reaction of dry reforming of methane at a pressure of 650 Torr, the ratio CH4 : CO2 = 1 : 1 in the temperature range of 400–960°C was studied. It was shown that the nanopowder of tungsten carbide, with an average particle size of 40 nm, produced by plasma-mechanochemical method, has a higher catalytic activity in the reaction of dry reforming of methane than the catalyst prepared by mechanochemical method. It was also established that with a decrease in the average particle size from 40 to 18 nm, the activity of the catalyst based on WС, obtained by the plasma-mechanochemical method increases and at 950°C the conversion of methane reaches 55%. [ABSTRACT FROM AUTHOR]

The catalytic activity of nanosized powders of hexagonal α-MoC and α-WC with average particle size of 17 nm obtained by thermal carbidization of MoO and WO oxides in the flow of methane-hydrogen mixture, preliminarily activated by the vibrationally excited molecules of hydrogen was studied. Amorphous powders obtained by this method exhibit high activity associated with structural features. This was a crucial factor for the low-temperature synthesis of nanosized carbides (500 °C for MoC and 600 °C for WC). It was shown that nanosized carbides exhibit high catalytic activity in cyclohexane dehydrogenation yielding benzene, and cyclodehydrogenation of n-heptane yielding toluene. The analysis of the obtained data allow to conclude that the observed drastic difference in activity and selectivity of the carbides with nano- and microsized particles is conditioned by the effect of nanocarbides particle size and defects of structure that have been formed during low-temperature synthesis. The synthesized carbide catalysts are stable in air and keep their catalytic activity over a long period. [ABSTRACT FROM AUTHOR]

It has been shown that in the case of noncatalytic oxidative pyrolysis of propane, the admixture of ethylene in the reactants significantly increases the concentration of propylene in the products. This process can be arranged in such a manner that the ethylene will not be noticeably consumed, i.e., will actually act as a propylene formation catalyst. This arrangement opens up a possibility to design a selective process for producing propylene directly from propane. [ABSTRACT FROM AUTHOR]

The influence of the ratio of the reactants on the characteristics of the cooxidation of ethylene and methane in a two-section flow reactor is examined. It is shown that the radical oxidation of ethylene implicates methane into the oxidation process. The interaction of the thereby formed methyl radicals with ethylene leads to a significant increase in the yield of propylene, an effect that enables to consider the co-oxidation of ethylene and methane as a promising method for producing propylene. A methane-rich flame stabilized on the surface of a flat permeable matrix is proposed as a more efficient source of methyl radicals for converting ethylene into propylene. [ABSTRACT FROM AUTHOR]

The influence of the initial concentration of oxygen and temperature on the oxidative conversion of propane in a two-sectional flow reactor at constant pressure and contact time was studied. It was shown that an increase in the initial concentration of oxygen not only increases the conversion of propane, but also affects the ratio of the reaction products. The yield of ethylene and propylene was found to depend on the initial propane to oxygen ratio and reaction temperature. [ABSTRACT FROM AUTHOR]

The nanopowders of Ni and Co metals and their alloy were prepared by plasma-assisted milling, and the activity of catalysts on their basis was studied in the carbon dioxide reforming of methane (CDRM) at atmospheric pressure. It was found that the catalytic activity of Ni nanopowder rapidly decreased because of the blocking of its surface by coking products. Co powder exhibited lower but stable activity, which gradually decreased as a result of coking only 300 h after the onset of reaction. A Ni-Co alloy (1: 1, by weight) is an active and selective catalyst for CDRM. Its catalytic activity appeared at 400°C; at 870°C, conversion reached 90% and remained unchanged for 500 h. The initial activity was restored by the regeneration of a catalyst based on the Ni-Co alloy with molecular hydrogen for several hours at 400°C. [ABSTRACT FROM AUTHOR]

Determination of the oxygen radical absorption capacity (ORAC) served to discover antiperoxyradical activity of dimethyl selenoxide (DMSeO). The antiperoxyradical capacity of DMSeO is higher than that of the water-soluble analog of α-tocopherol and trolox and close to the value determined for the butylated hydroxy toluene (BHT). The redox parameters of DMSeO were determined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The anodic oxidation peaks of DMSeO on the CV and DPV voltammograms in the potential range from −1200 to 1500 mV relative to Ag/Ag in CHCl confirm antioxidant activity of DMSeO towards oxidants and peroxyl radicals. It was established that NaSeO in the acidic medium at pH = 3 shows the antiradical activity towards the stable radical of 2,2′-diphenyl-1-picryl hydrazyl (DPPH) and acts as a two-electron oxidant by trapping two DPPH radicals. [ABSTRACT FROM AUTHOR]

Solvent effect of dimethyl sulfoxide (DMSO) on the oxidation-reduction properties of ascorbic acid (AA) was studied by the electroanalytical method of differential pulse voltammetry (DPV) in a three-electrode cell at 37 °C. Dimethylsulfoxide was found to considerably decrease the oxidation ability of AA due to the formation of molecular complexes between AA and DMSO through the intermolecular hydrogen bonds and shift the anodic peak potential toward the positive values, with its intensity being decreased. Kinetic spectrophotometric measurements in the UV-vis regions of the reaction of the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) with AA confirmed the stabilizing effect of the Lewis base DMSO on the reactivity of the neutral form of AA and its intermediates with respect to DPPH. The mechanism of oxidation of AA with the radical DPPH· in the presence of DMSO was considered. [ABSTRACT FROM AUTHOR]

The decomposition of 1-chloro-4-ethylbenzene under UV irradiation (λ = 253.7 nm) in the presence of dioxygen and the dioxomolybdenum(VI)dichloro[4,4′-dicarboxylato-2,2′-bipyridine] complex anchored on the TiO surface has been investigated. The catalytic cycle includes the photostimulated transfer of the oxo-oxygen atom from the surface dioxomolybdenum(VI) complex to the substrate followed by the oxidation of reduced Mo(IV) by dioxygen (in the absence of UV irradiation). The major reaction products are chlorobenzene, CO, and HO. Chlorobenzene results from the photocatalytic decomposition of intermediate 4′-chloroacetophenone under the reaction conditions. [ABSTRACT FROM AUTHOR]

Chemical mechanisms of antioxidant and electron donating function of the hypothalamic proline-rich polypeptides have been clarified on the molecular level. The antioxidant-chelating property of Galarmin and Gx-NH2 was established by their capability to inhibit copper(II) dichloride catalyzed H2O2 decomposition, thus preventing formation of HO• and HOO• radicals. The antiradical activity of Galarmin and Gx-NH2 was determined by their ability to react with 2,2-diphenyl-1-picrylhydrazyl radical applying differential pulse voltammetry and UV–Vis spectrophotometry methods. Galarmin manifest antiradical activity towards 2,2-diphenyl-1-picrylhydrazyl radical, depending on the existence of phenolic OH group in tyrosine residue at the end of the molecule. The presence of antiradical activity and reduction properties of Galarmin are confirmed by the existence of an oxidation specific peak in voltammograms made by differential pulse voltammetry at E∘ = 0.795 V vs. Ag/Ag+ aq. [ABSTRACT FROM AUTHOR]

Chemical mechanisms of antioxidant and electron donating function of the hypothalamic proline-rich polypeptides have been clarified on the molecular level. The antioxidant-chelating property of Galarmin and Gx-NH2 was established by their capability to inhibit copper(II) dichloride catalyzed H2O2 decomposition, thus preventing formation of HO• and HOO• radicals. The antiradical activity of Galarmin and Gx-NH2 was determined by their ability to react with 2,2-diphenyl-1-picrylhydrazyl radical applying differential pulse voltammetry and UV–Vis spectrophotometry methods. Galarmin manifest antiradical activity towards 2,2-diphenyl-1-picrylhydrazyl radical, depending on the existence of phenolic OH group in tyrosine residue at the end of the molecule. The presence of antiradical activity and reduction properties of Galarmin are confirmed by the existence of an oxidation specific peak in voltammograms made by differential pulse voltammetry at E∘ = 0.795 V vs. Ag/Ag+ aq. [ABSTRACT FROM AUTHOR]

The kinetic significance of elementary steps in the liquid-phase reaction of ethylbenzene oxidation inhibited by ionol (2,6-di-tert-butyl-4-methylphenol) was determined with the use of the “value” method. The nature of the effectiveness of ionol from the class of ortho-substituted phenols was considered. It consists in a ponderable role of the reaction of chain carriers (peroxy radicals) with the inhibitor with a decrease in the contribution of the reverse reaction. In this case, the relatively weak participation of the antioxidant at the step of degenerate chain branching and the high reaction rate constant of the interaction of phenoxy radicals with each other are of considerable importance. The value ranking of steps allowed us to diminish them; this simplified the reaction mechanism under various initial conditions. A satisfactory agreement between base reaction mechanisms, which describe experimental results and the behavior of the inhibited reaction under new reaction conditions, is considered as a reliability criterion for the prediction made. [ABSTRACT FROM AUTHOR]

A conceivable method (“value” method) for analyzing the reaction kinetics models of inhibited liquid-phase oxidation of organic compounds was considered. A procedure for the numerical calculations of the molecular structure parameters of an inhibitor and an inhibitor concentration that results in a maximum inhibition of the reaction was presented. In the kinetic model of a chain reaction of liquid-phase ethylbenzene oxidation in the presence of a para-methylphenol inhibitor, the dynamics of contributions from individual steps was calculated. This allowed us to simplify the reaction mechanism. The inhibition of the oxidation reaction due to reactions with the participation of a phenoxyl radical was found to occur under conditions of the quasi-equilibrium $\$RO\_2^\backslash cdot\; +\; \{\backslash em\; p\}-HOC\_6H\_4\text{'}R\; \backslash rightleftharpoons\; RO\_2H\; +\; \{\backslash em\; p\}-^\backslash cdot\; OC\_6H\_4\text{'}R$ The molecular structures and initial concentrations of para-substituted phenols, which are most effective for the given reaction conditions, were determined. [ABSTRACT FROM AUTHOR]

The low-temperature periodical activation of the catalysts based on the metal complexes of nitrogen-containing carbon is observed in the course of isopropylbenzene oxidation. The concentration of the surface hydroperoxide groups responsible for the chain process affects both catalyst deactivation and reactivation. Possible reactions responsible for the deactivation and periodical activation of the catalyst are considered. [ABSTRACT FROM AUTHOR]