Theoretical and Experimental Chemistry最新文献

The catalytic activity of rhodium-containing nanocomposites with carbon nanodots and Si, Al and Zr oxides in high-temperature water shift reaction has been established. The role of support lies in regulation of the surface concentration of the active component (Rh) and its localization. The use of the support with a low specific surface promote the localization of the active component on the external surface that leads to the decrease of the distance between supported Rh particles, which is important for the surface migration of intermediate products of the reaction.

It is shown that the initial reaction pathways of the processes of steam reforming of ethanol (SRE) or ethanol to propylene (ETP) conversion can be the same and include dehydrogenation and condensation reactions with the formation of acetaldehyde and acetone. The equilibrium yields of propylene and hydrogen in the ETP process, in contrast to SRE, depend little on both temperature and ethanol concentration. An equation for the determination of hydrogen yield as the function of selectivity of carbon-containing compounds has been proposed, based on which the hydrogen concentration in products of the SRE and ETP processes can be calculated.

Hierarchical CsAlTi-BEA zeolites, due to the presence of a high concentration of Lewis acid sites formed by tetrahedrally coordinated Ti⁴⁺ ions in the zeolite structure and the neutralization of Brønsted acid sites by Cs⁺ cations, exhibit high catalytic activity in the tandem reaction of cyclic carbonate formation from styrene in the presence of tert-butyl hydroperoxide under CO₂ pressure. The conversion of styrene into epoxide and further into carbonate increases with the content of titanium in the samples, while the selectivity for the cyclic carbonate increases with the content of cesium.

The ways of targeted design of effective nanocomposite catalysts based on metal oxide systems and zeolites, in particular BEA type, for the processes of dry/super-dry conversion of methane/biogas for the obtaining of hydrogen and syngas with adjustable H₂/CO ratio as well as oxidative dehydrogenation of C₃-C₄ alkanes with the participation of CO₂ producing valuable olefins and dienes are considered. Isolated metal cations/small clusters exhibit higher activity, selectivity, and stability when compared to bulk structures in alkane dehydrogenation reactions since their activation involves the participation of coordinatively unsaturated metal cations on anionic vacancies. This can serve as a scientific basis for the targeted development of highly active and stable catalysts for such processes.

Dynamic light scattering (DLS), electron paramagnetic resonance (EPR), and gas chromatography-mass spectrometry (GC-MS) methods were used to study interaction products of catalytic system components consisting of organoaluminum compounds (OAC), WCl6, and ethyl alcohol. Organic radicals (g = 2,0037, ∆H = 1,7mT) and W⁵⁺ complexes (g_z = 1,746, g_y = 1,820, g_x = 1,842, g₁ = 1,9957, g₂ = 1,9540, g₃ = 1,9465 at 77 K, and g₀ = 1.9583 at 300 K) with an additional hyperfine structure from two chlorine nuclei ^35,37 Cl have been identified by the EPR method. The formation of such compounds is accompanied by ethane and ethylene release. It is shown that a Cl₆/Et₃Al (Et₂AlCl)/EtOH-based catalytic system of olefin metathesis is a colloidal solution at the initial stages of the interaction of components. The further action of OAC leads to the formation of a molecular solution.

A series of Mn²⁺ -doped hybrid perovskites MAPb_1-xMn_xHal₃ (MA = CH₃NH₃, Hal = Cl and Br in different ratios, x = 0.33, 0.5, 0.67, 0.8) was obtained for the first time by mechanochemical synthesis. It is shown that materials obtained retain the perovskite structure even at the highest content of manganese ions (x = 0.8), and their structural and optical characteristics are mainly determined by the Cl/Br ratio. It is established that dispersions in toluene and nanocomposite films in polystyrene exhibit the intense photoluminescence (PL) due to the formation of pseudo-2D nanoparticles as a result of the ultrasonic disintegration of powders in an organic solvent. It is shown that the PL spectra of dispersions and nanocomposite films based on MAPb_1–xMn_xCl₃ are characterized by the appearance of an additional emission band from Mn²⁺ ions in the red region of the spectrum, due to which it is possible to increase the PL quantum yield from 0.2% (for the undoped sample) to 6.3% (films) and 10.2% (dispersions).

The dependence of the electrochemical characteristics of layered cathode materials LiNi_xMn_yCo_zO₂ (0.4 ≤ x ≤ 0.6; y = 0.2, 0.3; z = 0.2, 0.4) on the method of applying a protective layer of nanoparticles of lithium-conductive material Li_1.3Al_0.3Ti_1.7(PO₄)₃ with NASICON structure onto their surface has been investigated. It is shown that the surface modification reduces the capacity fading during prolonged charge/discharge cycling (up to 15%) and improves the suitability for fast charge/discharge processes.

Comparative analysis of the sorption ability of the obtained carbonate forms of layered double hydroxides with different Ni(II)/Fe(III) ratio and their magnetic nanocomposites toward ({{text{UO}}}_{2}^{2+}) ions in aqueous solutions is performed. The synergistic effect of magnetic composite sorbents based on layered double hydroxides and magnetite on the removal uranyl ions in a wide pH range (3.5-9.5) is shown. Due to the high efficiency in combination with magnetic solid-phase separation, the obtained adsorption materials are promising for the purification of uranium-containing natural and wastewaters.

The current state of research on photocatalytic reforming of organic substances of natural origin using graphite-like carbon nitride, namely its various morphological forms, products of modification by chemical agents, doped with metals and non-metals, nanocomposites with metals and other semiconductors, etc., is considered. Reactions that lead to molecular hydrogen evolution from aqueous solutions of electron-donating organic compounds (lignocellulose, saccharides, alcohols, aldehydes, and acids), processes of simultaneous production of H₂ and oxidation of biomass components with the formation of valuable organic substances, as well as reactions of a reduction of several aldehydes of natural origin are analyzed. Possible ways of further research in this photocatalysis branch are outlined.

It is established that crystalline graphite-like carbon nitride (CGCN) exhibits high photocatalytic activity in the process of chemoselective reduction of furfural to furfuryl alcohol in the presence of co-catalysts under the action of visible light by electron-donating substrates, such as methanol/water and ethanol/water, in an acidic medium. When palladium chloride additives are introduced into the reaction mixture, the rate of the process is higher than with the participation of the Pd/SiO₂ co-catalyst. This phenomenon may be due to the in situ formation of the CGCN/Pd⁰ composite photocatalyst in the presence of PdCl₂, where the photogenerated charges are better separated than in the CGCN-Pd/SiO₂ system. The effective quantum yield of furfural reduction is 56% at λ_irr = 405 nm) under optimal conditions.