Theoretical and Experimental Chemistry最新文献

NiO-Al₂O₃ and Co₃O₄ oxide catalysts modified with palladium and oxides of rare earth metals (Ce and La) and formed on structured cordierite supports have been studied in the process of methane oxidation at different O₂/CH₄ ratios. It is shown that methane oxidation proceeds without the formation of CO even at an O₂/CH₄ ratio of < 2 (in contrast to nickel-containing catalysts) in the presence of cobalt-containing catalysts modified with cerium and lanthanum oxides. The addition of CeO₂ promotes Co₃O₄ dispersion, increases the number of oxygen vacancies, and prevents agglomeration of the active phase of the catalyst at high temperatures. The modification of Co₃O₄-CeO₂/cordierite with palladium (0.1%) enhances its activity due to increased surface oxygen mobility as a result of the interphase interaction of palladium with cobalt oxides and ceria (according to the TPR-H₂ and XPS data).

A critical review of the last decade’s literature on the synthesis, modification, and properties of layered double hydroxides (LDHs) regarding their use as sorbents for the removal of radionuclides from aquatic environments has been conducted. The evaluation of their adsorption capacity against U(VI), ¹³⁷Cs, ⁹⁰Sr, ⁶⁰Co, ^152+154Eu(III), and ²⁴¹Am has been performed on the basis of the analysis of the effect of the LDH preparation method, the nature of the metal ions in the material layers and compounds intercalated into their interlayer space. It is shown that magnetic composites of LDHs chelated forms have significant advantages for a practical use for the removal of both cationic and, especially, anionic forms of uranium(VI) from aquatic environments. Zn,Al-LDHs intercalated with the inorganic compounds, namely hexacyanoferrate(II) anions and copper(II) hexacyanoferrate, are found to be the most effective for the sorption extraction of ¹³⁷Cs and ⁹⁰Sr radionuclides.

Catalytic properties of two series of Keggin-type heteropolycompounds, H_3–2xMn_xPMo₁₂O₄₀ and (NH₄)_3–2xMn_xPMo₁₂O₄₀ (x = 0.25-1.5), have been studied in the process of oxidation of cyclohexanone and/or cyclohexanol to adipic acid, using 30% hydrogen peroxide, in the absence of organic solvent. The main products and by-products have been identified by means of GC-MS analysis. The highest yields of adipic acid are found in the case of H_1.5Mn_0.75PMo₁₂O₄₀ and (NH₄)₂Mn_0.5PMo₁₂O₄₀ compounds.

The photoluminescence of bulk graphitic carbon nitride (g-C₃N₄), crystalline carbon nitride (CGCN) obtained by thermal treatment of g-C₃N₄ in LiCl and KCl melts, and CGCN treated with a lactic acid solution (AT-CGCN) has been studied. It has been established that the luminescent properties largely depend on their morphology and the presence of impurities as well as structural defects. It is shown that there is an antibatic dependence between the luminescence intensity and the photocatalytic activity of the samples in the ethanol oxidation reaction.

The acidity and basicity of MFe₂O₄ (M(II) = Fe, Mg, Mn, Zn) ferrites of the spinel structure have been characterized by temperature-programmed desorption of NH₃ and CO₂. It is shown that both medium-strength basic and acid sites play an important role in the process of acetone obtaining from ethanol over ferrites. The selectivity of ethanol conversion to acetone depends both on the acid–base properties of the surface and on the ability of the surface oxygen of ferrite to participate in the intermediate redox stages of formation and steam reforming of acetone.

To create highly sensitive semiconductor hydrogen sensors, nanosized tin dioxides with particle sizes of 5-6 and 10-11 nm have been obtained by the sol-gel method using various precursors, as well as Pd-doped materials on their base. The maximum sensitivity to the hydrogen microconcentrations has been found for the sensors based on the nanosized ex-oxalate SnO₂ containing 0.24% palladium. High sensitivity of the obtained semiconductor sensors is explained by the significant influence of surface processes on their electrical resistance due to the smallest sizes of the SnO₂ particles.

The formation of supramolecular complexes of 3-methyl-sulfido-propoxycalix[4]arene-methylene-bis-phosphonic acid with seventeen amino acids in aqueous solutions has been studied and their stability coefficients have been determined by the method of high-performance liquid chromatography. The structures of the supramolecular complexes have been proposed by molecular modeling and the influence of structural factors (the stabilization of different conformations of the obtained complexes depending on amino acid nature: possibilities of the realization of hydrogen bonds and electrostatic interactions between different groups of the amino acids and calixarene) on the stability of the supramolecules has been shown.

VO_x/SiO₂ with different V/Si atomic ratios have been synthesized by hydrothermal method from alkoxides of vanadium and silicon compounds. The prepared samples are characterized by high specific surface area (300-700 m²/g), uniform nanodispersed distribution of vanadia in silica matrix, the absence of crystalline phases, and the absence of the band typical for V=O bond in the Raman spectra. High activity and selectivity of the synthesized catalysts in oxidation of methane to formaldehyde, oxy-dehydrogenation of propane and n-butane have been established.

Superacid (H₀ ≥ –14.52) ternary Zr₃₅Si₅₃Al₁₂ and Zr₂₁Si₆₇Sn₁₁ oxides have been studied by X-ray photoelectron spectroscopy. The high-energy shifts of Zr3d levels indicate the electron density shift from zirconium to silicon atoms, which is facilitated by the presence of tetrahedrally coordinated Al³⁺ and Sn⁴⁺ ions in Zr⁴⁺ environment. Models of the superacid L-sites that include coordinatively unsaturated zirconium ions are proposed.

The current state of research on photocatalytic systems for hydrogen production by metal carbides is considered. Approaches for obtaining of known and latest two-dimensional metal carbides (MXenes) and their composites with the participation of photoactive semiconductors or organic dyes are described. Properties of these materials such as photocatalysts, and precursors used in their obtaining or co-catalysts used in hydrogen production systems where metal carbides act as acceptors and carriers of photogenerated charges or catalysts of the hydrogen evolution reaction are analyzed. The most promising areas of further research are outlined.