


Vol 58, No 4 (2017)
- Year: 2017
- Articles: 19
- URL: https://journal-vniispk.ru/0023-1584/issue/view/9907
Article
Factors determining the reactivity of the bromine atom toward haloalkanes
Abstract
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(ΔEμ/Σμ) = −0.14 + 0.47(ΔEμ/Σμ) − 0.024(ΔEμ/Σμ)2.



Determining role of the chain mechanism of hydrazine oxidation and decomposition in kinetically controlled combustion and explosion
Abstract
It has been inferred from experimental data that the hydrazine oxidation and decomposition reactions occur via a branched-chain and a nonbranched-chain mechanism, respectively. Taking into account the chain nature of these processes helps explain the observed regularities under the critical autoignition conditions, including their “anomalous” character and the combustion-to-explosion transition.



Effect of the composition of the immobilized copper-containing ionic liquid on the dodecyl mercaptan oxidation kinetics
Abstract
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.



Novel palladium catalysts immobilized on functionalized chlorinated polyvinylchloride nanofiber mats
Abstract
Well-defined chlorinated polyvinylchloride (CPVC) nanofiber mats were fabricated by electrospinning, and then chemically modified with 1,3-propanediamine (CPVC–NH) and glutaraldehyde (CPVC–NOH) to immobilize palladium active species. The chemical modification could significantly improve the tensile strengths of the CPVC nanofiber mats. Adsorption of Pd(II) ions showed that the treatment of fiber mats with glutaraldehyde decreases it schelating ability. Transmission electron microscopy and X-ray diffraction analysis indicated that palladium species were dispersed more homogeneously on the CPVC–NH fibers than on the CPVC–NOH fibers. Results of Mizoroki–Heck reaction showed that the catalytic activity of Pd catalyst supported on CPVC–NOH fibers was superior to that of the Pd catalyst supported on CPVC–NH fibers. Thus, chemical modification of supporting materials with suitable chelating groups is an efficient way to control the catalytic performance of supported Pd catalysts.



Short-time isoprene polymerization under the action of a titanium–magnesium catalyst
Abstract
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.



Effect of the nature of the active-component precursor on the properties of Pt/MgAlOx catalysts in propane and n-decane dehydrogenation
Abstract
The Pt/MgAlOx catalysts, in which a mixed aluminum–magnesium oxide obtained by the heat treatment of corresponding layered double hydroxides was used as a support, were studied. The effects of the nature of active-component precursors ([PtCl6]2–, [PtCl4]2–, and [Pt3(CO)6]62-), and the Mg/Al ratio in the support on the anchoring of complexes, the disperse state of platinum, and the properties of the obtained catalysts in the reactions of propane and n-decane dehydrogenation were found.



Pretreatment effect on the properties of the Cr–Mg catalyst for the gas-phase hydrofluorination of perchloroethylene into pentafluoroethane
Abstract
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.



Reaction between carbon dioxide and propylene oxide catalyzed by cobalt and chromium porphyrin complexes: The effect of reaction conditions on the reaction rate
Abstract
The effect of the conditions (time, temperature, pressure, and cocatalyst/catalyst ratio) on the rate and selectivity of the reaction between СО2 and propylene oxide catalyzed by TPPCrCl and TPPCoCl (TPP is 5,10,15,20-tetraphenylporphyrin) has been studied. The time variation of the reaction rate has been analyzed by measuring the СО2 uptake during the reaction. The observed dependences of the reaction rate on the temperature and cocatalyst/catalyst ratio are similar for TPPCrCl and TPPCoCl. In the presence of TPPCoCl, the reaction yields a mixture of poly(propylene carbonate) and a cyclic carbonate, while when TPPCrCl is used, only the cyclic carbonate is synthesized.



Catalytic synthesis of dialkyl sulfides from dialkyl disulfides
Abstract
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%.



Nucleation kinetics of heterogeneous catalyst: Pd/thin layer of MgO (100)
Abstract
The kinetics describing the formation of the system Pd/thin layer of MgO (100) surface was investigated by applying programs developed on the basis of Fortran Software. The simulation is based on studies related to nucleation, crystallite growth, coalescence and diffusion of clusters on the surface of thin films. The density of Pd islands is obtained by simulating the deposition of 1 × 1013 atoms cm–2 s–1 in 150 s. The density of clusters first increases to reach a plateau. Then, it either remains some time at a nearly constant value or decreases slowly after the saturation regime gives way to the coalescence stage. This phenomenon is explained via island migration process at the surface. The coalescence time strongly depends on the deposition temperature, the coalescence occurs when the substrate temperature is high. Also, the surface coverage decreases when the substrate temperature increases. The coalescence is pronounced at a low surface coverage. It involves the migration on the surface, defined as the dynamic coalescence and precedes the process of the formation of immobile islands that predominates at high extents of surface coverage.



One-pot synthesis of a novel magnetic carbon based solid acid for alkylation
Abstract
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.



Mathematical simulation of the formation of liquid products from catalytic cracking gases over a zeolite-containing catalyst modified with Group VI and VIII metals
Abstract
The kinetics of the formation of liquid products from catalytic cracking gases over a zeolite-containing catalyst in a flow reactor in the temperature range from 260 to 420°C at GHSV = 30–264 h–1 and an on-stream time of 5–25 s has been investigated. A kinetic model for the process proceeding according to a likely scheme is proposed. The rate constants and activation energies of certain reactions involved in the process have been determined. A mathematical model of the process taking into account the mass and heat balances, as well as hydrodynamic conditions, has been developed. The concentration and temperature fields and the pressure over the catalyst bed height have been calculated. The target product yield on has been plotted as a function of the on-stream time.



Photocatalytic hydrogen production using Me/Cd0.3Zn0.7S (Me = Au, Pt, Pd) catalysts: Transformation of the metallic catalyst under the action of the reaction medium
Abstract
The activity and stability of Me/Cd0.3Zn0.7S (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/Cd0.3Zn0.7S catalyst. The activity of the Au/Cd0.3Zn0.7S and Pt/Cd0.3Zn0.7S catalysts becomes constant 7.5–9 h after the beginning of the photocatalytic test, while in the case of Pd/Cd0.3Zn0.7S 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/Cd0.3Zn0.7S and Pt/Cd0.3Zn0.7S photocatalysts are activated due to metal encapsulation; the 1%Pd/Cd0.3Zn0.7S catalyst, due to the partial reduction of PdO to PdOx. The 1%Pd/Cd0.3Zn0.7S catalyst is deactivated because of the aggregation of nanoparticles of the cadmium sulfide–zinc sulfide solid solution.



Oxidation of 4-methoxy-1-naphthol on promoted platinum catalysts
Abstract
Oxidative coupling of naphthols is a useful method for the formation of new carbon-carbon bonds in organic synthesis. In the presence of hydrogen peroxide, platinum supported on activated carbon catalyses this reaction. The outcome is influenced by the solvent, the reaction temperature and the physical structure of the catalyst. The catalyst structure is determined by the synthesis method and the modifier used (Bi or Sb). Within 40 min 4-methoxy-1-naphthol can be converted to 4,4'-dimethoxy-2,2'-binaphthalenyl-1,1'-diol with a yield of up to 94%, or to 4,4'-dimethoxy-2,2'-binaphthalenylidene-1,1'-dione with a yield of 92%. High amounts of quinoid byproducts (≤22%) are observed in nitromethane as the solvent.



Kinetic features of the carbon erosion of a bulk NiCr alloy during the catalytic decomposition of 1,2-dichloroethane
Abstract
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.



Active sites of the functionalized coals and carbons for oxygen reduction reaction in a fuel cell
Abstract
The active sites of the coals and carbons functionalized with added nitrogen, oxygen and iron were studied for the oxygen reduction reaction (ORR) in a fuel cell. The catalysts were characterized based on the XPS, Raman, TEM, XRD and N2 adsorption measurements. The ORR activity was promoted by the addition of iron and aluminum as the inorganic components of the ash to the ash-free brown coal. The ORR activity of the ash-components added to the ash-free brown coal was correlated to the ID/IG ratio (deficient carbon degree) and the pyridinic nitrogen based on the Raman and XPS analyses, respectively. The active sites of the brown coal were formed at the pyridinic nitrogen on parts of the defective carbons associated with iron on the alumina. On the other hand, for the nitrogen-doped carbons without iron, the ORR activity was related to the pyrrolic-NH, pyridinic nitrogen species and the defective carbon degree. Based on these results, the active sites of the iron-added and nitrogen-doped coals and carbons were the iron sites coordinated with the pyridinic nitrogen, while the active sites of the iron-free and nitrogen-doped carbons without iron were the pyrrolic-NH and pyridinic-NH+ sites of parts of the defective carbons. The difference between the active sites of the nitrogen-doped coals and carbons in the presence of iron and those in the absence of iron was discussed. These results suggested that the pyridinic N as a base site transformed into pyridinic-NH+ as an acid site by attack of the proton from the anode.



Promoter nature effect on the sensitivity of Ni–Mo/Al2O3, Co–Mo/Al2O3, and Ni–Co–Mo/Al2O3 catalysts to dodecanoic acid in the co-hydrotreating of dibenzothiophene and naphthalene
Abstract
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.



Formation of supported intermetallic nanoparticles in the Pd–Zn/α-Al2O3 catalyst
Abstract
The structure of the Pd–Zn/α-Al2O3 catalyst, which was prepared by a joint impregnation method, was studied. According to XRD analysis data, supported intermetallic Pd–Zn particles were formed in a temperature range of 200–600°C. At 600°C, the crystal lattice of substitutional solid solution based on Pd (FCC) was finally rearranged into the tetragonal lattice of Pd–Zn. A shift of the Pd3d5/2 line in the XPS spectrum indicated the formation of the Pd–Zn intermetallic compound.



Intermetallic Pd1–Zn1 nanoparticles in the selective liquid-phase hydrogenation of substituted alkynes
Abstract
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.


