Theoretical and Experimental Chemistry最新文献

Based on the ¹¹B NMR study of products of the pyrolysis of tetraethylammonium and tetrabutylammonium tetraborohydrides, the formation of higher hydroborates in such processes is shown to be extremely sensitive to the presence of water vapors at a level of 2.6-2.7 kPa. The conditions in which the corresponding ({mathrm{B}}_{3}{mathrm{H}}_{8}^{-}) and ({mathrm{B}}_{12}{mathrm{H}}_{12}^{2-}) salts are formed by the pyrolysis of Et₄NBH₄ and Bu₄NBH₄ have been found. As a result of this study, a method for Bu₄NB₃H₈ and (Bu₄N)₂B₁₂H₁₂ obtaining with high yields has been developed.

A Co₃O₄ was obtained using the sol–gel method, and its morphology and spectral characteristics have been examined. The presence of polyhedral Co₃O₄ particles with a size of 200-500 nm has been established by means of XRD and SEM methods. It is shown that the obtained material exhibits two values of band gap (1.4 and 2.35 eV), which can be attributed to the presence of cobalt ions in different oxidation states (Co²⁺ and Co³⁺). The photocatalytic properties of the material were studied in the process of CO oxidation. The carbon monoxide conversion is found to exceed 60 % after 180 min of irradiation. A possible mechanism of the process is discussed.

An use of catalysts based on carbon nanomaterials in reactions of hydrogenation of organic compounds with molecular hydrogen, sodium borohydrides, hydrazine, etc. is summarized. Reaction mechanisms, promising directions of development of catalytic systems on the base of carbon nanomaterials, and ways of creation and implementation of new heterogeneous catalytic processes are considered. Existing approaches to the design of carbon nanomaterials aimed at increasing a catalytic reaction rate and the possibility of regulating the selectivities for target products are discussed. Analysis of a nature of active sites on a surface of carbon nanomaterials and a role of surface functional groups in the process of a hydrogen surface migration is carried out.

It has been shown that the coordination polymer [Pd(2-Pymo)₂]_n (where 2-Pymo^– is anion of 2-hydroxypyrimidine) catalyzes C–C coupling of boronic acids and aryl halides. The process of C–C coupling begins after the induction period, duration of which depends on the structure of a boronic acid and the solvent composition. The catalytic activity of [Pd(2-Pymo)₂]_n can be associated with the in situ formation of ultra-small palladium nanoparticles formed upon the reduction of Pd²⁺ by a boronic acid, which results in the destruction of such a complex compound on the surface, whereby the nanoparticles formed move into the colloid solution.

The catalyst for hydrogenation of organic compounds has been prepared by low-temperature decomposition of complex Ni(COD)(DQ) (COD = 1.5-cyclooctadiene, DQ = duroquinone) in a solution in presence of activated carbon Norit. The catalyst is characterized by high dispersion of nickel-containing particles. It is shown that hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline in presence of the obtained catalyst occurred with 99 % yield in the case if the catalyst formed in the reaction mixture in situ, or ca. 40 %, if the catalyst had prior contact with air. It has been shown that other substituted quinolines could be hydrogenated in presence of the developed nickel-containing system.

The oxidation of cyclohexene and its methyl derivative with hydrogen peroxide in the presence of a catalytic system based on polyoxomolybdate and cobalt(II) bromide has been studied. It is found that epoxidation and oxidative dihydroxylation of cycloolefins without changing the initial structure are the main reaction routes at a temperature of 50-60°C, a duration of 5-7 h, and a substrate:oxidizer molar ratio of 1:2. The process further proceeds by oxidative decyclization of epoxide and diol into aliphatic oxyaldehydes and oxyacids under more harsh conditions (T = 70-80°C, reaction duration of 20-24 h, molar ratio of cycloolefin:oxidizer 1:4).

Hydrogenolysis of 10% aqueous solution of glucose into propylene glycol on supported Cu-containing oxides has been studied according to target reaction C₆H₁₂O₆ + 4H₂ = 2C₃H₈O₂ + 2H₂O in a flow mode. It is shown that the best propylene glycol productivity (0.9 mmol C₃H₈O₂/(g_cat·h)) achieves on 23Cu-1Cr₂O₃/Al₂O₃ catalyst at 180°C, 4.0 MPa H₂ under a catalyst load of 1.6 mmol C₆H₁₂O₆/(g_cat·h). Is is found that ethylene glycol, hydroxyacetone, erythritol, glycerol, 1,2-butanediol, 1,2,4-butanetriol, and sorbitol are side products of the reaction.

Nanosized TiO₂ was prepared by hydrolysis of titanium tetraisopropoxide in the presence of a new bacterial strain Bacillus paralicheniformis. It was shown that the sample predominantly consisted of rutile nanoparticles with an average size of 15.4 nm. The obtained TiO₂ possessed photocatalytic activity in the process of dye decolorization in effluents of a textile manufacturing industry. It was found that treatment of such solutions by the bacteria Bacillus paralicheniformis followed by irradiation in the presence of TiO₂ increased the process efficiency.

Samples of crystalline carbon nitride doped with oxygen were obtained, which exhibit high photocatalytic activity in the oxidation of benzyl alcohol to benzaldehyde under the action of visible light. The quantum yield of benzaldehyde formation with the participation of the optimal photocatalyst can reach Φ ≈ 49% at λ_irr = 405 nm, which is almost twice as high as when using undoped crystalline carbon nitride. This effect can be associated both with more intense absorption of light in the visible range of the spectrum due to the appearance of the n → π* band of the electronic transition, and with a better separation of photogenerated charges and inhibition of their recombination.

The effect of the formation temperature of the composites based on Ni phosphides and N,P-doped carbon (Ni_xP_y/N,P-C) obtained by pyrolysis of a mixture of H₃PO₄-doped polyaniline and Ni(II) salt on their phase composition and electrocatalytic properties in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) has been established. It is shown that increasing the pyrolysis temperature from 800 to 900 and 1000°C leads to an increasing in the content of the Ni₂P phase in the composites with simultaneously Ni₁₂P₅ decreasing and NiP eliminating. It is found that the highest activity in HER in an acidic electrolyte, as well as in OER, is inherent to Ni_xP_y/N,P-C formed at 900°C (with a close ratio of Ni₂P and Ni₁₂P₅ particles). The best performance in HER in an alkaline electrolyte is revealed by the obtained at 800°C analogue with dominant NiP particles and the highest N,P-doping level of the carbon.