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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  [2281 journals]
  • Mechanism of the reductive dehydration of ethanol into C 3+ alkanes over
           the commercial alumina—platinum catalyst AP-64
    • Abstract: Abstract The mechanism of the reductive dehydration of ethanol (RDE) into C3+ alkanes over the commercial alumina—platinum catalyst AP-64 has been investigated. The catalyst pre-reduction time has an effect on the conversion of ethanol and on that of ethylene, a possible intermediate compound in the RDE reaction. Over the catalyst reduced for 12 h, ethanol turns into a C3-C12 alkane fraction and ethylene turns into a C3-C12 olefin fraction, whose yields are 39.0 and 31.4%, respectively. Energetic parameters of ethanol chemisorption and conversion on a Pt6Al4 cluster have been determined by the density functional theory method using the PRIRODA 13 program. Ethanol dehydration into ethylene proceeds via the successive breaking of C-H and C-O bonds, and the rate-determining step of the process depends on the atom (Pt or Al) to which the OH group of the alcohol is coordinated. Hydroxyl group transfer from the Pt atom to the nearest Al atom is energetically favorable here. It is hypothesized that the main role of the metal-containing cluster is donation of chemisorbed ethylene to the nearest acid sites, on which the ethylene oligomerizes into a C3-C10 hydrocarbon fraction.
      PubDate: 2016-01-01
       
  • Regularities in the consumption of the initial reactants in various
           kinetic regimes
    • Abstract: Abstract Using hydrogen oxidation as an example, it is demonstrated that, when gas ignition is prevented by means of inhibition, there is practically no consumption of the initial reactants because reaction chains do not form for lack of time and the rates of intermolecular reactions are insignificant. When the propagating flame and detonation wave are partially suppressed, the inhibitor is consumed only in chain termination reactions involving reactive intermediate species. Oxygen is additionally consumed in its reactions with products of incomplete inhibitor conversion.
      PubDate: 2016-01-01
       
  • Investigation of structural and textural properties of Ge x MoO 3 system,
           promising catalyst for photocatalytic applications
    • Abstract: Abstract The main objective of this work is to control the structural, textural and electrical properties of the system prepared by mixing molybdenum oxide with different amounts of germanium. The system is expected to be suitable as a catalyst for the photodegradation of methyl red (one of the dyes group) and the results of this study can throw some light on the relationship between the properties of this system and the extent of the dye degradation as indicated by the measurements of the photocatalytic activity. The composite materials (Ge x MoO3) were prepared by solid-state reaction between germanium and molybdenum oxide. The mixtures were made in Ge/MoO3 molar ratios of 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0. The reaction was conducted in air at 700°C. The prepared samples were characterized by X-ray powder diffraction, micro-Raman spectroscopy, nitrogen adsorption measurements, diffuse reflectance spectrometry and UV-Vis absorption spectrophotometry. The addition of germanium has affected the photocatalytic activity of MoO3 as evidenced by an increase in the degradation extent of methyl red from about 14% (for pure oxide) to about 97% for Ge x MoO3 (x = 1). An enhancement in the photocatalytic activity was attributed to the change in the band gap and modification of the textural properties associated with the formation of Ge x MoO3 composites.
      PubDate: 2016-01-01
       
  • Mathematical modeling and analysis of the molar concentrations of ethanol,
           acetaldehyde and ethyl acetate inside the catalyst particle
    • Abstract: Abstract Mathematical modeling of the molar concentrations profile of ethanol, acetaldehyde and ethyl acetate inside the catalyst particle is presented. This kinetic mechanism is based on the system of non-linear reaction diffusion equations. Modified Adomian decomposition method is employed to derive the general analytical expressions of molar concentrations of ethanol, acetaldehyde and ethyl acetate for all possible values of the parameters Φ i , γ i and α i (i = 1, 2, 3). Analytical results are compared with the numerical results, a satisfactory agreement is noted. Valid and invalid region of the solution for all concentrations are provided. These analytical results are useful to understand the behavior of the system.
      PubDate: 2016-01-01
       
  • Measuring the kinetic isotope effect at natural isotopic abundances for
           discriminating between the homogeneous and heterogeneous catalytic
           mechanisms in the Heck and Suzuki reactions
    • Abstract: Abstract The kinetic isotope effect (KIE) at the natural abundances of bromine and carbon isotopes in the substrates of the Heck and Suzuki reactions have been investigated to determine the true nature of catalyst in these reactions. Data processing has demonstrated that statistically significant differences between KIE values for the Suzuki reaction of nonactivated bromobenzene are observed upon the replacement of the soluble catalyst precursor with the insoluble one. This finding unambiguously indicates that the reaction takes place on heterogeneous palladium species. Similar experiments on the Heck reaction have demonstrated that the KIE values are insensitive to the nature of the catalyst precursor, which is consistent with the true homogeneous mechanism of catalysis.
      PubDate: 2016-01-01
       
  • Synthesis of nanostructured carbon on graphite electrodes with a supported
           Co catalyst for preparing anodes for microbial fuel cells
    • Abstract: Abstract The synthesis of nanostructured carbon (NSC) on graphite electrodes with a supported Co catalyst by C3 and C4 alkane pyrolysis in the presence of hydrogen has been investigated. Co(II) hydroxo compounds have been deposited onto graphite, and a Co/graphite catalyst has been prepared by the homogeneous precipitation of divalent cobalt from cobalt nitrate solutions in the presence of urea and compounds containing OH groups, namely, lower alcohols (ethanol, n-propanol, and n-butanol) and polyols (ethylene glycol, glycerol, and sorbitol). The effect of Co catalyst preparation conditions on the pyrolytic activity of the catalyst and on the morphology of the synthesized NSC has been investigated. An active Co/graphite catalyst forms in the presence of an alcohol containing 1-3 OH groups. A fairly uniform NSC layer on the graphite surface is obtained at Co(II) nitrate concentrations of 0.05–0.1 mol/L, a urea concentration of 1 mol/L, and glycerol concentrations of 5–20 vol %. The electrochemical characteristics of the electrodes prepared and those of a microbial fuel cell (MFC) involving an NSC/graphite anode and an activated-sludge microbial consortium have been determined. The maximum power of the MFC under the conditions examined is 4.8 mW per square meter of the anode’s geometric surface area.
      PubDate: 2016-01-01
       
  • Recombination of 1,1-dimethylpropyl peroxy radicals in polar solvents
    • Abstract: Abstract The kinetics of 1,1-dimethylpropyl peroxy radicals recombination in polar solvents—water, methanol, and their mixtures—was studied by EPR spectroscopy in combination with the stopped-flow method, and the rate constants of this reaction were determined. Peroxyl radicals were generated by mixing solutions of Ce4+ sulfate and 1,1-dimethylpropyl hydroperoxide. The observed EPR signal of the peroxyl radical is a singlet with a g-factor of 2.015 ± 0.001, and a line width of ΔH = (1.36 ± 0.02) × 10−3 T for methanol and ΔH = (9.7 ± 0.2) × 10−4 T for water. The measured rate constants of (CH3)2C(O2 ·)CH2CH3 radical recombination at 298 K are 2k t = (3.9 ± 0.4) × 104 L mol−1 s−1 for water and 2k t = (5.2 ± 0.5) × 103 L mol−1 s−1 for methanol. A linear relationship between ln(2k t ) and the Kirkwood function (ε−1)/(2ε + 1), where e is the dielectric constant of the medium, has been established, indicating an important role of nonspecific solvation in the recombination of tertiary peroxyl radicals.
      PubDate: 2016-01-01
       
  • Liquid phase selective hydrogenation of phenol to cyclohexanone over Ru/Al
           2 O 3 nanocatalyst under mild conditions
    • Abstract: Abstract Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique using RuCl3 · nH2O as a precursor. Ru nanoparticles were supported on Al2O3 to synthesize Ru nanocatalyst. The nanocatalyst was characterized by various techniques like XRD, SEM, TEM and BET analysis. The catalyst was used for hydrogenation of phenol under mild condition. The activity of the catalyst was checked by varying different parameters such as reaction temperature, time, H2 partial pressure, metal loading and catalyst amount. The catalyst was recovered from product and reused up to four times without significant loss in its catalytic activity. After a reaction time of 1 h, Ru/Al2O3 nanocatalyst showed high reactivity (82% conversion) and selectivity to cyclohexanone (67%) at 80°C and 20 bar hydrogen pressure.
      PubDate: 2016-01-01
       
  • Catalytic reactions of dimethyl disulfide with thiophene and benzene
    • Abstract: Abstract The gas-phase reaction of dimethyl disulfide with thiophene proceeds under the action of acid catalysts under atmospheric pressure at 160–350°C and a residence time of τ = 0.6–21 s to form thioalkylation and alkylation products. Dimethyl disulfide reacts with benzene to form only alkylation products. Catalysts containing both strong protic and Lewis acid sites, as well as basic sites of moderate strength, are the most active ones.
      PubDate: 2016-01-01
       
  • Are amines basic or nucleophilic catalysts for oxirane ring opening by
           proton-donating nucleophiles?
    • Abstract: Abstract The behavior of amines as catalysts for oxirane acidolysis and phenolysis has been studied using kinetic methods. The apparent catalytic and noncatalytic reaction rate constants have been estimated. It has been demonstrated that the noncatalytic pathway has almost no effect on the apparent reaction rate constant. In order to determine the character of the behavior of amines (bases/nucleophiles) in this reaction, their reactivity has been analyzed within the conceptions of basic and nucleophilic mechanisms of catalysis. Based on the quantitative amine structure—catalytic activity correlation, it has been shown by comparing the values of correlation coefficients (r) of equations describing mechanisms for various reaction systems that, in the reactions of oxiranes with proton donors (carboxylic acids and phenols), the catalytic activity of tertiary amines/pyridines is determined by their nucleophilicity rather than basicity.
      PubDate: 2016-01-01
       
  • The role of phosphine and 1,2-diimine complexes of nickel in the oxidation
           states 0, +1, and +2 in the catalyzed di-, oligo-, and polymerization of
           ethylene
    • Abstract: Abstract The turnover frequency and number have been determined for eighteen catalytic systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene complexes of nickel in the formal oxidation states 0, +1, and +2 in the oligoand polymerization of lower alkenes. The main catalytic characteristics are almost independent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are presented for nickel(I) 1,4-diazo-1,3-butadiene complexes and radical anions resulting from the reactions of the cocatalyst with nickel α-diimine complexes. Reactions describing the formation, functioning, decomposition, and regeneration of the catalytically active nickel hydride complexes are proposed.
      PubDate: 2016-01-01
       
  • Mathematical modeling of self-oscillations in ethane oxidation over nickel
    • Abstract: Abstract The methodology of constructing a phenomenological model for complex heterogeneous catalytic reactions is described in detail. The proposed approach is applicable to development of mathematical models describing the onset of self-oscillations in hydrocarbon oxidation on the transition metal surface. The approach is based on construction of a microkinetic scheme taking into account the formation of main reaction products and intermediates, on estimation of the heat of reaction, activation energy, and preexponential factor for elementary steps and includes development and a subsequent analysis of the corresponding mathematical model. Catalytic reactions are considered in the ideal adsorption layer approximation without taking into account the relationship between coverages and spatial coordinates. Accordingly, the mathematical model is an independent system of ordinary differential equations. This methodology is used to develop a point (lumped) model for ethane oxidation over nickel, which is based on a 36-step microkinetic scheme taking into account the oxidation and reduction of nickel and the formation of total (CO2 and H2O) or partial (CO and H2) ethane oxidation products, as well as the dehydrogenation of ethane into ethylene. The proposed model predicts the onset of self-oscillations in this reaction at atmospheric pressure in the temperature range from 850 to 1400 K. The kinetic oscillations are caused by the cyclic oxidation and reduction of nickel. The self-oscillations of the reaction rate are accompanied by oscillations of the catalyst temperature. The results of modeling are compared with experimental data.
      PubDate: 2016-01-01
       
  • Kinetika i Kataliz : 55 years in the bibliometric dimension
    • Abstract: Abstract A bibliometric and thematic analysis of publications in Kinetics and Catalysis in 1960–2014 has been carried out using the CAPlus, WoS, Scopus, and RSCI databases.
      PubDate: 2016-01-01
       
  • Effect of the particle size of the TiCl 4 -Al i -Bu 3 catalyst on the
           contribution from mono- and bimetallic active sites to the polymerization
           of isoprene
    • Abstract: Abstract The interaction between the coordinatively unsaturated surface of ß-TiCl3 particles and a liquid phase in the TiCl4-Ali-Bu3 catalyst is responsible for the final particle size and the regularities of isoprene polymerization. The correlations of the catalyst activity and the molecular characteristics of polyisoprene with catalyst particle size in the course of catalyst formation and reactivation are indicative of the occurrence of two groups of active sites. “Surface” active sites correspond to the monometallic Cossee model, and they are characterized by low activity and low 1,4-cis specificity in the polymerization of isoprene. “Colloid” active sites have a bimetallic structure and produce polyisoprene at a high rate; the concentration of 1,4-cis units in the resulting polyisoprene is as high as 97%. The contribution from the colloid active sites to the polymerization of isoprene increases with the particle size of ß-TiCl3.
      PubDate: 2016-01-01
       
  • Active component of supported vanadium catalysts in the selective
           oxidation of methanol
    • Abstract: Abstract The structure of catalysts based on vanadium oxide supported on different oxides (SiO2, γ-Al2O3, ZrO2, and TiO2) was investigated. Their catalytic properties in the selective oxidation of methanol in a temperature range of 100–250°C were studied. It was shown that the nature of the support determines the structure of the oxide forms of vanadium. The supporting of vanadium on SiO2 and γ-Al2O3 leads to the preferred formation of crystalline V2O5; the surface monomeric and polymeric forms of VO x are additionally formed on ZrO2 and TiO2. It was established that the crystalline V2O5 oxide is least active in the selective oxidation of methanol; the polymeric forms are more active than monomeric ones. The mechanism of the selective oxidation of methanol to dimethoxymethane and methyl formate on the vanadium oxide catalysts is considered.
      PubDate: 2016-01-01
       
  • XPS study of gold oxidation with nitrogen dioxide in model Au/C samples
    • Abstract: Abstract The interaction of NO2 with model samples obtained by the gold sputter deposition onto the surface of highly oriented pyrolytic graphite (HOPG) has been studied by X-ray photoelectron spectroscopy (XPS). It has been shown that 3D metal particles characterized by an Au4f 7/2 binding energy (BE) of 84.0 eV form on the initial smooth graphite surface. During the sputter deposition onto the surface of HOPG preliminarily activated by means of ion etching, gold atoms chemically bound to the carbon atoms form in the area of surface defects. Such atoms are characterized by a positive shift of BE(Au4f 7/2). It has been established that the 3D particles are resistant to the action of NO2 under the pressure XXXXXXXX mbar at room temperature. On the contrary, atomic gold oxidizes under these conditions into Au(III) complexes bound to the graphite surface. It is assumed that gold atoms on the support surface play the role of active sites of gold catalysts in oxidation reactions.
      PubDate: 2015-11-01
       
  • Enhanced catalytic performance of Co–Sn composite oxide in styrene
           epoxidation with air
    • Abstract: Abstract A simple calcination process was used to obtain Co–Sn composite oxides, the structure of which was confirmed by the XRD analysis. For comparison, the pure cobalt oxide was also prepared under the same calcination condition. According to TEM measurements, the composite oxide prepared in the presence of Sn had lower particle size than pure cobalt oxide. Accordingly, the presence of Sn increased the specific surface area as evidenced by the BET analysis data. The as-prepared Co–Sn composite oxides were applied as heterogeneous catalysts in the epoxidation of styrene with air and exhibited catalytic activity with 77.9 mol % of styrene converted and 87.1% selectivity for epoxide. These results exceed those obtained for pure cobalt oxide. However, the addition of ions of other metals such as Fe, Ni, Cu, Zn and Mn to the catalyst had a detrimental effect on the styrene epoxidation. The mechanistic considerations are also presented and suggestion is given that the DMF solvent plays a key role in the catalytic epoxidation. Results of the study indicate that Co–Sn composite oxides are efficient heterogeneous catalysts for the epoxidation of styrene with air in DMF.
      PubDate: 2015-11-01
       
  • Development of a macro-micro kinetic model for CO hydrogenation over
           Co–Ni catalyst
    • Abstract: Abstract A novel approach in kinetic study of CO hydrogenation reaction over Co–Ni/Al2O3 catalyst was described. The experimental data were collected using a fixed bed micro reactor under next conditions: pressure 2–12 bar, temperature 230–280°C, molar ratio H2: CO = 1–3, space velocity 2000–2700 h–1. A new Langmiur–Hinshelwood (LH) kinetic model on the basis of formyl mechanism was developed. The apparent activation energy of LH kinetic model, bond energy of carbon, oxygen, hydrogen and some surface intermediate on catalyst surface, activation energies of some surface reactions and catalyst surface coverage were estimated from a new combined LHHW/UPI–QEP methodology. It was postulated that under reaction conditions used, CH2 formation through H-assisted CO dissociation is probably dominant mechanism of hydro-genation over Co–Ni catalyst.
      PubDate: 2015-11-01
       
  • Pd(AcO) 2 supported by 1,3,5-triazine functionalized nanoporous polymers:
           Efficient and recyclable heterogeneous catalysts for Suzuki–Miyaura
           reaction
    • Abstract: Abstract 1,3,5-Triazine functionalized nanoporous polymer (PDVB-triazine-xs, where x stands for the molar ratio of DVB and triazine) was synthesized from copolymerization of 1,3,5-triacryloylhexahydro1,3,5-triazine with divinylbenzene (DVB) cross-linker under solvothermal conditions. The resultant PDVB-triazine-xs act as efficient supports for Pd(OAc)2, which gives the Pd/PDVB-triazine-xs catalyst. Characterizations by N2 isotherms, TEM images, and solid NMR 13C spectrum show that Pd/PDVB-triazine-xs has large surface areas, abundant nanopores, and successful copolymerization of DVB with triazine functional monomer, which showed a high cross linking degree. XRD and elemental maps show Pd was successfully loaded into PDVB-triazine-xs supports, which showed very good dispersion in the samples. Pd/PDVB-triazine-xs showed excellent catalytic activity and good recyclability in Suzuki–Miyaura cross coupling reaction. The preparation of Pd/PDVB-triazine-xs will develop functional nanoporous polymer based catalysts or catalyst supports in the Suzuki–Miyaura reaction.
      PubDate: 2015-11-01
       
  • Effect of iron oxide additives on the physicochemical and catalytic
           properties of the supported Pt/TiO 2 catalysts in the oxidation of carbon
           monoxide
    • Abstract: Abstract The effect of iron oxide additives on the formation of the microstructure, the electronic state, and the catalytic properties of supported Pt/TiO2 catalysts in the reaction of CO oxidation was studied. It was established that the microstructure of the catalyst changed upon the introduction of iron additives and activity in the oxidation of CO increased. The increase in the catalytic activity was explained by a decrease in the particle size of supported platinum and by an increased contribution from the Ptδ+ state. The optimum chemical composition of the catalyst, which ensured the highest catalyst activity in the reaction of CO oxidation, was determined.
      PubDate: 2015-11-01
       
 
 
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