Russian Journal of Physical Chemistry A最新文献

The first measurements are made of the isobaric heat capacity of single-phase pyrochlore ytterbium titanate synthesized and studied via XRD, SEM, and EDX in the 2–1869 K range of temperatures. A magnetic transformation at <20 K and a lack of structural transformations throughout the region of Yb₂Ti₂O₇ are confirmed. Thermodynamic functions (entropy, the increment of enthalpy, and the Gibbs free energy of the formation of Yb₂Ti₂O₇ from elements and binary oxides at 298.15 K) are calculated, and the contribution to the heat capacity of the Schottky anomaly is evaluated.

A new method for processing the results of the temperature-programmed desorption (TPD) of ammonia from heterogeneous catalyst surfaces and an approach for automatic deconvolution of TPD kinetic curves were proposed. This method uses the Polanyi–Wigner kinetic model with formal kinetics approaches for simple reactions, which imposes restrictions on the observed first, second, or third orders. The parameters of the TPD curves were selected based on the inverse simulation using the Runge–Kutta method and fitting them to experimental points using dynamic model parameter changes. As an example, several heterogeneous catalysts were presented in this work. TPD-NH₃ of titanium silicalite-1 and silicalite-1 was obtained using one third-order desorption kinetic equation. TPD-NH₃ of three γ-alumina samples was obtained using two desorption peaks with similar kinetic parameters.

Transpiration method is used to determine the vapor pressures of diesters of malic acid and linear alcohols (C1–C5) over the 303–369 K range of temperatures. The enthalpies of vaporization of the esters at 298.2 K are calculated from the resulting data. Correlations between the enthalpies of vaporization, the Kovats indices, and the number of carbon atoms are derived. The contributions from hydroxyl groups and intermolecular hydrogen bonding ({{Delta }_{{{text{vap}}}}}H^circ (298.15~;{text{K}})) to the overall enthalpy are determined. A modified version of the established QSPR procedure is developed for calculating the enthalpies of vaporization of hydroxy acid esters.

The colloid-chemical properties of water-soluble and poorly soluble poly(ethylene oxide) and poly(propylene oxide) block copolymers (pluronics), as well as the rheological properties of interfacial adsorption layers (IALs) formed by them and the polymer generated during polymerization initiation on the particle surface, were studied. The temperature, surfactant concentration, and polymer effects on the effective elastic modulus, determined during the lateral deformation of IALs, were evaluated. The strongest interfacial layers are formed by the poorly water-soluble pluronic, which contains a hydrophilic polyoxyethylene block surrounded by two hydrophobic polyoxypropylene blocks. The high strength of the interfacial adsorption layer on the particle surface affords polymer suspensions with high (up to 33%) polymer contents and narrow particle size distributions.

The present study reports on the synthesis of an ionic liquid-based nanocomposite and its characterization via structural, thermal and electrical analysis. The compound (M-EtOHmim) was prepared using green chemistry, where the organic cations exchange was achieved through the intercalation of 1‑(hydroxyethyl)-3-methylimidazolium chloride. The results showed that the molecules were successfully immobilized in the matrix yielding a good thermal stability up to 260°C. The DFT computation optimization was carried out to identify the adsorption mechanism. On the other hand, the electrical conductivity analysis revealed that charge transport is strongly related to structural defects and thermal energy. Accordingly, the corresponding electrical parameters were determined. It is evident that the modifications of montmorillonite with ionic liquid significantly changes the physicochemical properties of M-EtOHmim nanocomposite, which can be used in various fields.

Corrosion of low-carbon steel in a flow of H₂SO₄ solutions containing Fe₂(SO₄)₃ was studied, including media with additions of corrosion inhibitors—catamine AB (a mixture of quaternary ammonium salts) and IFKhAN-92 (3-substituted derivative of 1,2,4-triazole). In these media, partial reactions of anodic ionization of iron and cathodic reduction of H⁺ and Fe(III) cations occur on steel. The former two reactions are kinetically controlled, while the latter is diffusion-controlled. The accelerating effect of Fe₂(SO₄)₃ on steel corrosion in an H₂SO₄ solution is primarily due to the reduction of Fe(III). In contrast, in the inhibited acid, the accelerating effect of Fe(III) cations affects all partial reactions of steel. Data on corrosion of low-carbon steel in the flow of the given media, obtained from the mass loss of the metal samples, are in satisfactory agreement with the results of the study of partial electrode reactions. Steel corrosion in a flow of H₂SO₄ solutions, including in the presence of inhibitors, is accelerated by Fe₂(SO₄)₃. In these solutions, steel corrosion is determined by the convective factor, which is characteristic of diffusion-controlled processes. The IFKhAN-92 inhibitor, unlike catamine AB, significantly slows down steel corrosion in the flow of H₂SO₄ solution containing Fe₂(SO₄)₃. The reason for the higher inhibitory effects shown by IFKhAN-92 for steel in these solutions compared to catamine AB is the more significant slowdown of the partial electrode reactions of the metal.

Cobalt–tetra-4-carboxyphthalocyanine complexes are synthesized. Direct calorimetry is used to determine heat effects of the dissolution of crystalline cobalt tetra-4-carboxymetallophthalocyanine in KOH aqueous solutions of various concentrations (0.002–0.02 mol/L) at 298.15 K. The standard enthalpies of formation of the compound are calculated using additive groups, based on group systematics with a Benson-type classification of fragments that considers the effect of the primary environment of atoms. Standard enthalpies of formation are calculated for products of the dissociation of tetra-4-carboxyphthalocyanine–cobalt complexes in an aqueous solution.

The present work examined the micellar effect of sodium dodecyl sulfate (SDS) on the kinetics of L-sorbose by imidazolium fluorochromate (IFC) oxidant in a 50% (v/v) aqueous acetic acid (AcOH) medium with a consistent ionic strength under the conditions [L-sorbose] ( gg ) [IFC] at 303 K. Perchloric acid was used as the reaction mixture’s primary source of hydrogen ions. The reaction depicted a unit-order dependence on [IFC], [L-sorbose], and [HClO₄]. The effect of sodium perchlorate salt and acrylonitrile were also studied. The oxidation rates decreased with an increase in the dielectric value (D) of the reaction medium, and the outcomes were in accordance with the Amis ((log {{k}_{1}}) and 1/D) and Kirkwood plots ((log {{k}_{1}}) and (D – 1)/(2D + 1)). The reaction showed significant catalysis even before reaching the critical micelle concentration (CMC). However, the observed rate constants stabilized at higher SDS concentrations exceeding the CMC. Piszkiewicz’s cooperativity model was employed to describe the surfactant catalysis. The binding constant (K_D), rate constants, cooperativity index (n), and various thermodynamic parameters in the presence of SDS were evaluated. The products were identified as the lactone of C₅-aldonic acid and formaldehyde. Based on the observed findings, a theoretical mechanistic pathway was suggested.

The isobaric vapor-liquid equilibrium data for the four systems consisting of 1-octene + 2-methyl-thiophene, cyclohexene + 2-methylthiophene, 2,3-dimethyl-1-butene + 2-methylthiophene, and 2,3-dimethyl-2-butene + 2-methylthiophene were determined by using a modified Rose-Williams equilibrium still at 90.00 kPa. All the vapor-liquid equilibrium data measurements passed the thermodynamic consistent test by employing the Herington method. The azeotropic behavior was observed in the 1-octene + 2-methyl-thiophene system. Additionally, the experimental data were correlated by the Wilson model, and they were also compared with the original UNIFAC and UNIFAC Dortmund predictive models. All the results indicated that the measured data were in good agreement with the calculated values obtained from the Wilson. Meanwhile, the UNIFAC Dortmund model can provide better prediction result than the original UNIFAC model.

The quality of hydrogen released from naphthenic substrates (bicyclohexyl and the ortho-, meta-, and para-isomers of perhydroterphenyl) as a result of catalytic dehydrogenation over the 3% Pt/C (sibunit) catalyst has been studied as a key criterion of the high degree of regeneration and recyclization of hydrogen storage systems. It is shown that chemically pure hydrogen without methane and carbon oxide impurities can be obtained by dehydrogenation of liquid organic hydrogen carriers (LOHCs) if the initial aromatic hydrocarbons and naphthenic substrates obtained from them were previously thoroughly thermally treated before the hydrogenation and dehydrogenation reactions, respectively, in an inert gas.