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  Subjects -> CHEMISTRY (Total: 846 journals)
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CHEMISTRY (597 journals)

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Journal Cover Kinetics and Catalysis
  [SJR: 0.367]   [H-I: 21]   [3 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1608-3210 - ISSN (Online) 0023-1584
   Published by Springer-Verlag Homepage  [2335 journals]
  • On the initial stage of the free-radical polymerizations of styrene and
           methyl methacrylate in the presence of fullerene C 60
    • Abstract: Abstract It has been demonstrated experimentally and theoretically that the essentially different inhibiting effects of fullerene C60 on the initial stage of the polymerizations of styrene and methyl methacrylate (including complete hampering of styrene polymerization throughout a long induction period) are of common kinetic nature. The difference arises from the competition between C60 and the monomer not for initiating radicals but for radicals originating from the monomer; that is, the difference stems from the competition between the chain propagation reactions and the termination reactions on fullerene molecules. As a consequence, the further development of the process is determined by the relative reactivities of the radicals toward C60 and towards their parent monomers.
      PubDate: 2016-05-01
       
  • Dynamics of topochemical reactions in supported iron Fischer–Tropsch
           synthesis catalysts during their reduction in flowing CO and CO + H 2
    • Abstract: Abstract The reduction of Fe2O3/SiO2 catalysts in flowing CO and CO + H2 in the temperature-programmed and isothermal modes has been investigated by in situ magnetization measurements. The process takes place in two steps, successively yielding magnetite and Hägg carbide. The carbide concentration in the case of reduction with CO is higher than in the case of reduction with the CO + H2. This is assumed to be due to the formation of Fe2SiO4 in the reduction of the catalysts with CO + H2.
      PubDate: 2016-05-01
       
  • Conjugate reactions: New potentials of an old idea
    • Abstract: Abstract Main concepts of the Shilov–Ostwald theory of conjugate chemical reactions are analyzed from the standpoint of complex reaction kinetics, theory of reaction routes, and thermodynamics of irreversible processes. Classification of conjugate reactions and an algorithm of catalytic system design for conducting these processes are proposed.
      PubDate: 2016-05-01
       
  • Preparation method effect on the properties of Ziegler-type hydrogenation
           catalysts based on bis(acetylacetonato)cobalt
    • Abstract: Abstract The turnover frequency and turnover number of Ziegler-type systems based on Co(acac)2 · nH2O (n = 0, 0.5, and 2) and AlEt3 or AlEt2(OEt) are reported in relation to the Al: Co molar ratio and to the concentrations of the initial components. Proton donor compounds have an effect on the catalytic characteristics of the systems. ESR data are presented for the interaction of Co(acac)2 with organometallic compounds (AlEt3, AlEt2(OEt), Li(n-Bu), and (C6H5CH2)MgCl) in the presence of various arenes. Seven preparation methods and a formation scheme are suggested for catalytic species that are active in styrene hydrogenation and are based on Co(acac)2 combined with AlEt3 or AlEt2(OEt) and.
      PubDate: 2016-05-01
       
  • Kinetics of n -propylmercaptan oxidation by cobalt(III)
           octahydroxyphthalocyanine in an alkali medium
    • Abstract: Abstract The specific features of the association of cobalt octahydroxyphthalocyanine in aqueous alkaline solutions have been investigated by electron spectroscopy. The kinetic parameters of the oxidation of n-propylmercaptan by the phthalocyanine complex of cobalt in the absence of oxygen have been determined. The association leads to a decrease in the activity of the complex and to changes in activation parameters.
      PubDate: 2016-05-01
       
  • Palladiumimmobilized on chitosan nanofibers cross-linked by glutaraldehyde
           as an efficient catalyst for the Mizoroki–Heck reaction
    • Abstract: Abstract Nonwoven chitosan (CS) nanofiber mats were successfully prepared by the electrospinning of the mixture of CS and poly(ethylene oxide) (PEO) in acetic acid aqueous solution. The CS/PEO fiber mats were treated with glutaraldehyde aqueous solution to stabilize fibers in solution. The concentration of glutaraldehyde is important for incorporating swelling properties in the cross-linked CS/PEO fiber mats. The cross-linked CS/PEO fibers (CCS/PEO fibers) were then used as supports for palladium catalysts in the Mizoroki–Heck reaction. The results of the study demonstrated that the catalytic activities of Pd catalyst supported on CCS/PEO fiber (Pd-CCS/PEO fiber) were highly dependent on the concentration of glutaraldehyde in the cross-linking process. Density functional theory (DFT) calculations indicated that the Schiff bond formed between CS and glutaraldehyde could reduce the energy needed to form a chelate complex between the CCS/PEO fibers and palladium active species. This in turn could decrease the activation energy of the Mizoroki–Heck reactions which occur in the presence of the Pd-CCS/PEO fiber catalysts. The optimized Pd-CCS/PEO fiber catalyst was very efficient and stable in the Mizoroki–Heck reaction of aromatic iodides with olefins.
      PubDate: 2016-05-01
       
  • Ziegler-type nickel-based hydrogenation catalysts: The effect of the water
           content of the nickel precursor on the size and nature of the resulting
           particles
    • Abstract: Abstract The size and nature of the nanoparticles forming in systems based on Ni(acac)2 · nH2O (n = 0, 0.5, 3.0) and AlEt3 have been determined by high-resolution electron microscopy and X-ray microanalysis. The nickel cluster size depends on the water content of the precursor. The average particle diameter increases from 1.2 nm (Ni(acac)2 · 0.5H2O precursor) to 2.4 nm (Ni(acac)2 · 3H2O precursor). A homogeneous solution forms in the Ni(acac)2–5AlEt3 system, as was demonstrated by examining the system under an electron microscope whose resolving power allows particles larger than 0.7 nm to be detected.
      PubDate: 2016-05-01
       
  • Kinetics of urethane formation from isophorone diisocyanate: The alcohol
           nature effect
    • Abstract: Abstract The kinetics of the noncatalytic reactions of isophorone diisocyanate with n-propanol, isopropanol, 1,3-diazidopropan-2-ol, propargyl alcohol, and phenol in toluene in the temperature range from 20 to 90°C at the stoichiometric ratio of reactive groups has been investigated by IR spectroscopy. The apparent rate constants for the reactions of the aliphatic and cycloaliphatic isocyanate groups of isophorone diisocyanate with all of the alcohols have been measured. The activation parameters of the reactions of isophorone diisocyanate with n-propanol, isopropanol, and 1,3-diazidopropan-2-ol have been determined. The data obtained are considered in terms of the alcohol structure and molecular organization of solutions.
      PubDate: 2016-05-01
       
  • Polymer-modified supported palladium catalysts for the hydrogenation of
           acetylene compounds
    • Abstract: Abstract Palladium catalysts supported on zinc oxide modified with polyethylene glycol or pectin were synthesized and investigated in the hydrogenation of acetylene compounds. It was established that the polymercontaining catalysts reduce acetylene hyrbons to olefins with high activity, selectivity, and stability. The composition and structure of the obtained composites were studied by elemental analysis, transmission electron microscopy, and XPS spectroscopy. It was found that the nanosized particles of palladium uniformly immobilized on the surface of zinc oxide were formed in the course of the synthesis of a supported polymer/oxide complex.
      PubDate: 2016-05-01
       
  • Kinetics and mechanism of ozone addition to olefins and dienes
    • Abstract: Abstract The mechanism of the initial stage of the ozonolysis of a series of olefins and trans-1,3-butadoiene has been investigated by the B3LYP density functional theory (DFT) method, B2PLYP double hybrid method based on DFT and the MP2 approximation, and CCSD coupled cluster method. Two possible butadiene and olefin ozonolysis mechanisms are considered: concerted 1,3-cycloaddition, which yields a primary ozonide (Criegee mechanism) and stepwise ozone addition via a biradical transition state (DeMore mechanism). The geometries of the initial and transition states and the energies of the elementary steps of the reaction have been determined. The geometric structures of the stationary states determining the rate constant of the reaction have been completely optimized using the above methods and the aug-cc-pVDZ basis set. The rate constants for both reaction pathways have been calculated. For butadiene, the contribution from nonconcerted addition can reaches 25%. According to the MRMP2 method, the overall rate constant (which includes both reaction pathways) is 1778 L mol–1 s–1; according to B2PLYP, 1640 L mol–1 s–1; according to CCSD, 1424 L mol–1 s–1 (aug-cc-pVDZ basis set). These results are in good agreement with experimental data (k = 3 × 103 L mol–1 s–1 and with earlier calculations. The data calculated for olefins are also in agreement with experimental data.
      PubDate: 2016-05-01
       
  • The effect of reaction conditions on MoB activation in 1-octene
           epoxidation with tert -butyl hydroperoxide
    • Abstract: Abstract The change in the surface composition of a MoB catalyst in the epoxidation of 1-octene with tert-butyl hydroperoxide and the effects of the reactant concentrations and reaction products (tert-butanol and 1,2-epoxyoctane) on this process have been studied.
      PubDate: 2016-05-01
       
  • Measuring the rate constant of the reaction between chlorine atoms and CHF
           2 Br by Cl atom resonance fluorescence
    • Abstract: Abstract The rate constant of the reaction between Cl atoms and CHF2Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (k het ≤ 5 s–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10–12 e (–15.56 ± 1.58)/RT cm3 molecule–1 s–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.
      PubDate: 2016-05-01
       
  • Role of the base and endogenous anions in “ligand-free”
           catalytic systems for the Suzuki–Miyaura reaction
    • Abstract: Abstract UV spectroscopic studies combined with kinetic measurements for the Suzuki–Miyaura reaction catalyzed by “ligand-free” catalytic systems have demonstrated that the base is involved in the formation of the palladium complexes ensuring the occurrence of the transmetalation stage. It follows from UV monitoring data for the catalytic reaction involving aryl iodides that a considerable part of palladium during the process is in the form of Pd2+ acid complexes with endogenous anions and does not participate in the main catalytic cycle.
      PubDate: 2016-05-01
       
  • Graphene/BiOI composites synthesized via the oil bath method and their
           application for efficient photocatalytic degradation of methyl orange
           under visible light irradiation
    • Abstract: Abstract An efficient and simple oil bath method for rapid synthesis of graphene/BiOI as visible light active photocatalyst was described. The resultant graphene/BiOI composites were characterized by different techniques, including scanning electron microscopy, X-ray diffraction, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared graphene/BiOI composites for methyl orange degradation was also investigated under visible light irradiation. The results show that BiOI and graphene taken with a mass ratio of 100: 1 exhibited the highest photocatalytic efficiency, which is two times that of pure BiOI. Part of this effect results from higher specific surface area that provides an increased number of active sites. A relatively narrow band gap (2.08 eV) formed in the heterostructure can also contribute to this effect. A suggestion of the photocatalytic mechanism was also offered.
      PubDate: 2016-05-01
       
  • Synthesis of nanostructured carbon on Ni catalysts supported on mesoporous
           silica, preparation of carbon-containing adsorbents, and preparation and
           study of lipase-active biocatalysts
    • Abstract: Abstract This work continues a series of our studies on the synthesis of nanostructured carbon (NSC) by the pyrolysis of H2 + C3–C4 alkane mixtures on nickel and cobalt metal catalysts supported on chemically diverse inorganic materials (aluminosilicates, alumina, carbon) having different textural characteristics (mesoporous and macroporous supports) and shapes (granules, foamed materials, and honeycomb monoliths). Here, we consider Ni catalysts supported on granular mesoporous silica (SiO2). It has been elucidated how the yield of synthesized carbon depends on the Ni/SiO2 catalyst preparation method (homogeneous precipitation or impregnation) and on the composition of the impregnating solution, including the molar ratio of its components—nickel nitrate and urea. The morphology of catalytic NSC and Ni distribution in the silica granule have been investigated using a scanning electron microscope with an EDX analyzer. Carbon-containing composite supports (NSC/SiO2) have been employed as adsorbents for immobilizing microbial lipase. The enzymatic activity and stability of the resulting biocatalysts have been estimated in transesterification reactions of vegetable (sunflower and linseed) oils involving methyl or ethyl acetate, esterification, and synthesis of capric acid–isoamyl alcohol esters in nonaqueous media.
      PubDate: 2016-05-01
       
  • Free-radical abstraction reactions with concerted fragmentation and NO
           formation
    • Abstract: The enthalpy and activation energy of reactions involving attack by MeO 2 • and MeO 2 • on CH2 groups of 2-butyl nitrite and 2-nitrosobutane have been calculated by quantum chemical methods. The abstraction of a hydrogen atom is accompanied, in the former case, by concerted N–O bond breaking and, in the latter case, by concerted C–N bond breaking, resulting in NO• formation. On the basis of the results obtained, an algorithm has been developed within the intersecting parabolas model for calculating the enthalpies, activation energies, and rate constants of these types of reactions involving alkyl, alkoxyl, aminyl, peroxyl, phenoxyl, thiyl, and hydroxyl radicals.
      PubDate: 2016-05-01
       
  • Effect of the oxidation state of manganese in the manganese oxides used in
           the synthesis of Mn-substituted cordierite on the properties of the
           product
    • Abstract: Abstract Catalysts based on Mn-substituted cordierite 2MnO · 2Al2O3 · 5SiO2 have been synthesized using different manganese oxides (MnO, Mn2O3, and MnO2) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn2O3 or MnO2 are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn3+ cations. The highest NO x yield (about 76% at 800–850°C) is observed for the MnO2-based catalyst, whose surface contains the largest amount of manganese oxides.
      PubDate: 2016-03-01
       
  • Thermal stability of surface nitrogen–oxygen complexes and phase
           transitions in ZrO 2
    • Abstract: Abstract The IR spectra of surface compounds observed in the course of the temperature-programmed desorption (TPD) of NO x and the TPD spectra are compared. The high-temperature peaks of desorption are related to the decomposition of surface nitrites and nitrates. The low-temperature peaks of NO x desorption with maximums below 140°C are caused by the decomposition of surface nitrosyls. On the heating of surface nitrosyls, the following two reaction paths are possible: desorption at low temperatures and conversion into nitrates. The shape of the TPD spectra of NO depends on the phase composition of test samples. The transition of a tetragonal phase into a monoclinic one occurred upon the surface dehydroxylation of polycrystalline particles with the formation of particles with a tetragonal nucleus and a monoclinic crust. This transition is reversible. The cooling of a sample in a moist atmosphere leads to the transition of the monoclinic crust to the tetragonal phase.
      PubDate: 2016-03-01
       
  • Activation of nickel–chromium hydrogenation catalysts with hydrogen
    • Abstract: Abstract The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of nickel oxide with a hydrogen-containing gas takes place at 250–330°C. The apparent activation energy of this reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide structure shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent activation energy of the reduction of nickel cations to ∼108 kJ/mol. The introduction of 67 at % chromium into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activation energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can be used in optimizing the composition of Ni-containing hydrogenation catalysts and their activation and operation conditions.
      PubDate: 2016-03-01
       
  • Palladium hydrogenation catalyst based on a porous carbon material
           obtained upon the dehydrochlorination of a chloro polymer
    • Abstract: Abstract The applicability of a porous carbon material obtained as a result of the “chemical” dehydrochlorination of chlorinated polyvinyl chloride as a support for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalyst was evaluated in the liquid-phase reactions of nitrobenzene hydrogenation and chlorobenzene hydrodechlorination. Although the specific activity of the catalyst was lower by a factor of 3–4 than that of the samples based on Sibunit and carbon nanotubes, the complete conversion of the initial compounds with the selective formation of end products under mild conditions was achieved at a relatively low palladium content (1.5%).
      PubDate: 2016-03-01
       
 
 
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