Russian Journal of Physical Chemistry A最新文献

The structural, electronic and optical properties of halide perovskite Cs₃Bi₂I₉ with a hexagonal perovskite-type structure under pressure were investigated using first-principles calculations. The calculated structural parameters and elastic constants at zero pressure show a good agreement with the experimental and other theoretical values. Furthermore, the calculated pressure dependence of lattice parameters a(b) and c were studied, and both of them decrease with increasing pressure in the pressure ranging from 0 to 20 GPa. These calculated results indicate that the linear compressibility along c axis is significantly higher than a and b axes, which shows that the intermolecular bonding along the c axis is softer and hence easily compressible than other crystallographic axes. The electronic structure shows the top of the valence band and bottom of the conduction band minima are dominated by Bi s and p states, respectively. According to our calculation, the band gap decreases with increasing pressure. Moreover, in optical properties such as dielectric function, absorption coefficient, reflectivity, refractive index and the extinction coefficient are calculated under pressure.

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.

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.

We report on simulations of BaFe₁₁TiO₁₉’s magnetocaloric effect (MCE) at temperatures between about 4 and 250 K. The MCE in BaFe₁₁TiO₁₉ unexpectedly displays two forms. Among 33 and 204 K, BaFe₁₁TiO₁₉ shows an inverse MCE due to noncollinear ordering. But when the FM goes from 4 to 33 K or over 204 K, a direct MCE is employed. BaFe₁₁TiO₁₉’s advantages may be useful in the hunt for magnetocaloric compounds that exhibit two or more successive magnetic phase changes. BaFe₁₁TiO₁₉ is therefore a very promising magnet for cryogenic refrigeration, with potential uses in the liquefaction and storage of various gases.

Low-permeability and tight condensate gas reservoirs are critically important in gas field development due to their substantial reserves and high economic value. However, retrograde condensation significantly affects oil and gas productivity during development. Understanding the impacts of interfacial phenomena in porous media is crucial for enhancing recovery rates of gas and condensate oil. This study integrates the capillary effect and adsorption into a phase equilibrium model, based on the Peng–Robinson equation of state (PR-EOS), to account for interfacial phenomena. The results indicate that the interfacial phenomena significantly impact the phase behavior of condensate gas. Interfacial effects increased the dew point pressure (P_d) by 0.47 MPa and the maximum condensate oil saturation (S_omax) by 3.95%. Capillary pressure primarily affects fluid phase behavior and mobility, while adsorption influences fluid composition and interfacial tension. When the capillary radius (r) is less than 100 nm, P_d increases rapidly with decreasing r. At a pore radius of 30 nm, P_d and S_omax increased by 1.06 MPa and 5.23%, respectively. Higher heavy component content in the fluids enhances capillary pressure and desorption, leading to increased P_d and S_omax. Ignoring adsorption and capillary effects can adversely affect reservoir development. The established numerical model considering complex adsorption characteristics and capillary pressure is crucial for understanding phase behavior in high-temperature, high-pressure porous media and optimizing development strategies for condensate gas reservoirs.