Theoretical and Experimental Chemistry最新文献

Oxygen anion radicals ({O}_{2}^{-cdot }) coordinated with one Mo(VI) have been identified in MoO_x/SiO₂ samples enriched with ⁹⁵Mo isotope. It is shown that unpaired electron is mainly localized on the oxygen ion (g_z = 2.017, g_y = 2.004, g_x = 1.999; A_x(⁹⁵Mo) = 6.1, A_y(⁹⁵Mo) = 6.0, A_z(⁹⁵Mo)=9.1 G; ∆H_x = ∆H_y = 2,2 G and ∆H_z = 2,6 G). Using a special freezing technique, peroxide radicals (CH₃OO^·), which are the products of the reaction of the methyl radical with molecular oxygen in the gas phase, have been identified. The oxidation pathways of methane to methanol with participation of the oxygen ion radicals coordinated directly by Mo(VI) are discussed.

The results of study on the influence of rare earth elements (Y, La, Ce) on physicochemical characteristics and catalytic properties of Mg-Al oxide system in the vapor phase condensation process of ethanol with the obtaining of 1-butanol are presented. The Mg-Al-Y-oxide catalyst is established to have the highest selectivity for the target product 1-butanol, as well as the stability of operation over time. The positive effect of yttrium consists in the formation of additional acidic and basic sites on the catalyst surface.

Kinetics of oxidation of primary alcohols by ethylenediammonium dichromate in dimethyl sulfoxide has been investigated. It is established that all studied alcohols are oxidized according to the same mechanism, which invlolves catalysis by hydrogen ions with the formation of electron-deficient cyclic transition state, and the reaction order for C₂H₄(NH₄)₂Cr₂O₇ is 1. The presence of primary of kinetic isotope effect indicates the C–H cleavage (not the C–C cleavage) in alcohols in the reaction process.

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.