Vol 58, No 4 (2017)

Experimental data concerning reactions of the bromine atoms with haloalkanes and carbonyl compounds (25 reactions) have been analyzed within the intersecting parabolas model. The following factors have an effect on the activation energy of these reactions: enthalpy of reaction, triplet repulsion, electronegativity of reaction center atoms, dipole–dipole and multidipole interactions of the reaction center with polar groups, and the interaction of π electrons with electrons of the reaction center. The increments characterizing the contribution from each factor to the activation energy of the reaction have been calculated. The increment ΔEμ, which characterizes the dipole–dipole interaction in the transition state, and the dipole moment of the polar group (μ) are correlated by the following empirical equation: ln(ΔE_μ/Σμ) = −0.14 + 0.47(ΔE_μ/Σμ) − 0.024(ΔE_μ/Σμ)².

Basic kinetic parameters of the catalytic oxidation of dodecyl mercaptan in kerosene in the presence of silica-immobilized pyridinium or imidazolium chlorocuprate complexes have been determined. The composition of the copper-containing anions and the oxidation kinetics depend on the nature of the ionic liquid and on the method of its synthesis. The compositions developed in this study are usable in the removal of hydrogen sulfide and light mercaptans from the oil stripping gas.

The short-time polymerization of isoprene under the action of a TiCl₄/MgCl2−i-Bu₃Al heterogeneous catalyst has been investigated. Pulse mixing of the catalyst and monomer in a cylindrical tubular reactor with a certain length followed by ethanol injection has made it possible to carry out polymerization for 0.1−0.7 s. In the first 0.3 s, when there is a considerable rise in the activity of the catalyst, living polymerization of isoprene takes place. In this period, polyisoprene has up to 95% trans-1,4 units. Extending the polymerization time to 0.7 s diminishes the average molar mass of polyisoprene, broadens its molar mass distribution, and decreases the concentration of trans-1,4 units to 83%. The data of this study have been analyzed on the basis of the kinetic continuity of the polymer chain initiation and growth.

The effect of the temperature of thermal pretreatment of the precursors of the Cr–Mg catalyst on its physicochemical properties (specific surface area and elemental composition) and catalytic properties has been experimentally investigated. The dehydration of the precursor takes place up to a temperature of ~500°С, making it possible to tune the catalyst composition by varying the heat-treatment temperature. The samples prepared from precursors with various compositions differ in their specific surface area and catalytic activity. The highest activity is shown by the catalyst prepared by heat treatment of the precursor at 330°С.

Dialkyl disulfides R₂S₂ where R = Me, Et, or Pr, both as individual compounds and as their mixtures, isolated from petroleum products can turn into alkanethiols and dialkyl sulfides under the action of catalysts having strong acid sites and medium-strength basic sites on their surface. In a helium atmosphere, the main conversion products are alkanethiols, while dialkyl sulfides form in low yield at a selectivity of no higher than 20%. A much higher dialkyl sulfide selectivity is attained in the reaction involving methanol. The most efficient catalyst for this reaction is alumina, with which the dialkyl sulfide selectivity is up to 99%.

Magnetic carbon based solid acid has been synthesized via the one-pot hydrothermal carbonization of chitosan, magnetic core and hydroxyethylsulfonic acid at 160°C for 4 h. Chitosan was used as the carbon resource to protect the magnetic core from hydroxyethylsulfonic acid. The magnetic carbon based solid acid owned high BET surface and core shell structure, which provided the easily accessible acid sites on the carbon shell. The novel carbon based solid acid exhibited high activities for the hydrophobic alkylation of 1- dodecene and benzene, which was difficult to activate by traditional carbon based solid acids. The simple magnetic recovery added the advantages of the solid acid. The high activities for hydrophobic reactions, high stability and magnetic recovery were the key properties of the solid acid, which greatly enlarged the application area of the solid acid.

The activity and stability of Me/Cd_0.3Zn_0.7S (Me = Au, Pt, Pd) photocatalysts in the course of hydrogen production from water under the action of visible radiation have been investigated. The mechanism of activation and deactivation of the catalysts have been elucidated for the first time using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. An increase in the hydrogen evolution rate is observed for all of the catalysts at the early stages of testing. The highest hydrogen evolution rate, 5.4 μmol/min, is afforded by the 1%Pt/Cd_0.3Zn_0.7S catalyst. The activity of the Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S catalysts becomes constant 7.5–9 h after the beginning of the photocatalytic test, while in the case of Pd/Cd_0.3Zn_0.7S the hydrogen evolution rate increases over the initial 6 h and then decreases. These specific features of the catalysts likely correlate with the initial state of the metals on the support surface. In particular, supported palladium is in the form of PdO, while gold and platinum are in the metallic state. The Au/Cd_0.3Zn_0.7S and Pt/Cd_0.3Zn_0.7S photocatalysts are activated due to metal encapsulation; the 1%Pd/Cd_0.3Zn_0.7S catalyst, due to the partial reduction of PdO to PdO_x. The 1%Pd/Cd_0.3Zn_0.7S catalyst is deactivated because of the aggregation of nanoparticles of the cadmium sulfide–zinc sulfide solid solution.

Kinetic features for the carbon erosion (CE) of bulk NiCr alloy (NiCrA, nichrome wire 0.1 mm in diameter) were studied at 450–750°C under conditions of the catalytic decomposition of 1,2-dichloroethane vapor in a reductive atmosphere (H₂). It was found that the CE process takes place more efficiently in the temperature range from 550 to 720°C, leading to the disintegration of the bulk alloy with the formation of a fibrous carbon product. The apparent activation energy of the process was estimated to be 16.8 ± 0.9 kJ/mol. The realization of CE is hampered outside the optimal temperature range because of chlorination (T < 500°C) or blocking of the alloy’s surface by carbonaceous deposits (T > 720°C). The kinetics of the process is characterized by the existence of an induction period, whose duration decreases with an increasing temperature (from 40 min at 550°C to 6 min at 710°C). According to scanning and transmission electron microscopy data, the submicron metallic particles (0.2–0.4 μm) catalyzing the growth of carbon fibers with disordered structure result from the disintegration of the NiCr alloy.

The promoter nature effect on the sensitivity of Mo/Al₂O₃, Ni–Mo/Al₂O₃, Co–Mo/Al₂O₃, and Ni‒Co–Mo/Al₂O₃ catalysts to dodecanoic acid in the hydrotreating of a mixture containing dibenzothiophene and naphthalene has been investigated. The experiments have been carried out using a flow-through setup. The catalysts have been prepared using the PMo₁₂ heteropoly acid, Сo(Ni) citrates, and Co₂Mo₁₀ heteropoly acid and have been characterized by high-resolution transmission electron microscopy. The highest hydrodesulfurization activity in the presence of dodecanoic acid is shown by the trimetallic catalyst Ni–Co–Mo/Al₂O₃. The introduction of Ni is favorable for dodecanoic acid conversion via the hydrogenation route, thus increasing the С₁₁: С₁₂ ratio in the conversion products. Effective dodecanoic acid adsorption constants under the hydrotreating conditions have been calculated using the Langmuir–Hinshelwood model.

A comparative study of the catalytic characteristics of monometallic Pd/α-Al₂O₃ and bimetallic Pd–Zn/α-Al₂O₃catalysts in the liquid-phase hydrogenation of structurally different substituted alkynes (terminal and internal, symmetrical and asymmetrical) was carried out. It was established that an increase in the reduction temperature from 200 to 400 and 600°C led to a primary decrease in the activity of Pd–Zn/α-Al₂O₃ due to the formation and agglomeration of Pd1–Zn1 intermetallic nanoparticles. The Pd–Zn/α-Al₂O₃ catalyst containing Pd1–Zn1 nanoparticles exhibited increased selectivity to the target alkene formation, as compared with that of Pd/α-Al₂O₃. Furthermore, the use of the Pd–Zn/α-Al₂O₃ catalyst made it possible to more effectively perform the kinetic process control of hydrogenation because the rate of an undesirable complete hydrogenation stage decreased on this catalyst.