Theoretical and Experimental Chemistry最新文献

The effect of alkali metal ions (Na⁺ or K⁺) on the acid–base and catalytic properties of Zn-Mg(Zr)Si oxide systems in the process of obtaining 1,3-butadiene from ethanol was studied. It was found that the modification of Zn-MgSi oxide systems promotes an increase in the 1,3-butadiene selectivity (at temperatures ≥670 K) by reducing the number of formation sites of by-products. In the composition of Zn-ZrSi oxide systems, alkali metal cation additives lead to a decrease in the ethene and diethyl ether selectivity due to a decrease in the content of strong acid sites that are active in the ethanol dehydration reaction.

A method of obtaining a solid polymer electrolyte for lithium-ion batteries based on polyethylene oxide-containing (PEO) supramolecularly organized system segmented polyurethane – segmented oligourethane with LiClO₄(PUU-OUU-LiClO₄) is proposed. The introduction of LiClO₄ into PUU-OUU leads to an extreme increase in the glass transition temperature and ionic conductivity by 1 and 2 orders of magnitude when compared to OUU-LiClO₄ and PUU-LiClO₄ systems (up to 2.0·10^–4 S/cm at 60°C), respectively, which is associated with a change in the lithium-ion transport mechanism.

A method for obtaining hierarchical BEA, MOR, MFI, MTW, and GIS zeolites and nanocomposites by partial recrystallization of perlite and obsidian in the presence of polyquaternary ammonium salts, which act as structure-directing agents, is proposed. The obtained materials are characterized by a developed specific surface, the presence of Lewis (up to 98 μmol/g) and Bronsted (5-105 μmol/g) acid sites and show catalytic activity in the process of 1,1-diethoxyethane production from acetaldehyde and ethanol.

It has been found that pyrolysis of hybrid precursors containing polypyrrole, H₄PVMo₁₁O₄₀, and reduced graphene oxide (rGO) contributes to the production of nanocomposites based on V-doped Mo₂C and N,P-doped rGO, which are promising electrocatalysts for hydrogen evolution reaction (HER). It has been shown that vanadium doping increases the activity of electrocatalysts in HER (both in acidic and alkaline electrolytes) when compared to the analog obtained by unsubstituted H₃PMo₁₂O₄₀. In particular, it is manifested in a significant reduction of hydrogen evolution overpotential, anodic displacement of a process onset potential, and reduction of a Tafel slope dependence.

An original approach to the creation of new nanocomposite anode materials based on PbO₂ and to the processes of composite formation due to the influence of selective adsorption of valve metal oxides and different types of surfactants on both electrochemical and colloid-chemical processes in the near-electrode zone is considered. It is shown that variation of deposition electrolyte composition, current density, and temperature allows one to change the content of additives in composites and to provide control of morphology, texture, phase composition, physicochemical properties, electrocatalytic activity, and selectivity of electrocatalysts based on PbO₂ in target processes.

The nature of mineralizing agent (HF, NH₄F) and the Si/F ratio in the synthesis conditions is found to affect the formation of Zr- and Cu-containing acid sites on the surface of zirconium-containing hierarchical zeolites (Cu/Zr-MTW) modified by copper (2 wt.%). It is shown that in the conversion of 50 and 80 vol.% ethanol the highest yield of 1,3-butadiene is achieved in the presence of Cu/Zr-MTW (NH₄F, Si/F = 4) catalyst, which is characterized by higher total surface acidity according to TPD-NH₃.

It is shown that the KF/γ-Al₂O₃ catalyst obtained by the sol–gel method has a greater activity in the process of transesterification of methanol and rapeseed oil to biodiesel compared to KF/γ-Al₂O₃ prepared by impregnation. The highest yield of biodiesel (96.5%) is achieved with use of KF/γ-Al₂O₃, prepared at molar ratio KF to γ-Al₂O₃ 1.3:1. High conversion of rapeseed oil to biodiesel is explained by the relatively high basicity and specific surface of KF/γ-Al₂O₃.

It is shown that C₄-C₆ hydrocarbons and magnetite with an average particle size of 43 nm are products of low-temperature hydrogenation of iron carbonate, which is formed in the process of CO₂ capturing by iron oxides at 250°C and high hydrogen pressure.

Modern design approaches to electric energy storage devices based on nanostructured electrode materials, in particular, electrochemical double layer capacitors (supercapacitors) and their hybrids with Li-ion batteries, are considered. It is shown that hybridization of both positive and negative electrodes and also an electrolyte increases energy density of an electrochemical system, thus, filling the gap between supercapacitors and batteries in terms of specific energy and power, as well as charge rate and the number of charge-discharge cycles.