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 Subjects -> CHEMISTRY (Total: 809 journals)     - ANALYTICAL CHEMISTRY (48 journals)    - CHEMISTRY (563 journals)    - CRYSTALLOGRAPHY (22 journals)    - ELECTROCHEMISTRY (25 journals)    - INORGANIC CHEMISTRY (41 journals)    - ORGANIC CHEMISTRY (45 journals)    - PHYSICAL CHEMISTRY (65 journals) CHEMISTRY (563 journals)            First | 1 2 3 4 5 6 | Last
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Journal of Planar Chromatography - Modern TLC       (Followers: 6) Jurnal Penelitian Sains (JPS) Jurnal Teknologi Informasi       (Followers: 3) Kinetics and Catalysis       (Followers: 3) Korea-Australia Rheology Journal Langmuir       (Followers: 38) Latvian Journal of Chemistry       (Followers: 1) Lebensmittelchemie       (Followers: 1) Lipid Insights       (Followers: 1) Luminescence       (Followers: 1) Macromolecular Materials & Engineering       (Followers: 4) Macromolecular Rapid Communications       (Followers: 4) Macromolecular Research Macromolecular Symposia Macromolecular Theory and Simulations Macromolecules       (Followers: 31) Magnetic Resonance in Chemistry       (Followers: 4) Main Group Chemistry Marine Chemistry       (Followers: 4) Marine Drugs       (Followers: 4) MATEC Web of Conferences Materials Characterization       (Followers: 25)
 Kinetics and Catalysis     [SJR: 0.25]   [H-I: 19]    [5 followers]  Follow        Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1608-3210 - ISSN (Online) 0023-1584    Published by Springer-Verlag  [2210 journals]
• Deactivation of a Zn-Containing zeolite in ethane aromatization
• Abstract: Ethane conversion into aromatic hydrocarbons over a high-silica ZSM-5-type zeolite doped with zinc by impregnation has been investigated. The deactivation of the Zn-containing zeolite at different stages of ethane conversion has been studied by temperature-programmed ammonia desorption, differential thermal analysis, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The nature and distribution of active phases and coke deposits on the catalyst surface have been determined. The Zn/ZSM-5 catalyst shows a relatively high activity and stable performance in ethane aromatization.
PubDate: 2014-11-01

• The use of boric acid (H 3 BO 3 ) and boron oxide (B 2 O 3 ) for
co-precipitation synthesis of cobalt-boron catalysts: Catalytic activity
in hydrogen generation
• Abstract: The use of boric acid (H3BO3) and boron oxide (B2O3) for the synthesis of cobalt-based catalysts by the co-precipitation technique was investigated and catalytic activities in hydrogen generation were evaluated. Different cobalt salts [cobalt (II) chloride (CoCl2 · 6H2O), cobalt sulfate (CoSO4 · 5H2O) and cobalt(II) nitrate (Co(NO3)2 · 7H2O)] were used with H3BO3 and B2O3 to prepare Co based catalysts. Crystalline, surface and chemical characteristics were clarified using X-ray diffraction (XRD); low temperature adsorption of nitrogen (BET), scanning electron microscopy (SEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Three types of powder samples were obtained according to the different boron sources and cobalt salts, and it was found that an efficient Co based catalyst was obtained by co-precipitation of B2O3 and CoCl2 · 6H2O salt. Additionally, the effect of temperature, stabilizer ratio and NaBH4/catalyst ratio on parameters, characterizing the reaction of hydrogen generation was investigated. The zero order, first order and Langmuir-Hinshelwood kinetic models were used to identify the effect of Co based catalysts on the behavior of the catalytic system in hydrogen generation. Kinetic parameters of hydrogen generation for zero-order kinetic model were calculated for the following conditions: the rate of hydrogen generation is 0.93 L H2 g−1 catalyst min−1, the activation energy is 43.55 kJ mol−1 and the constant of Arrhenius equation is 11 min−1.
PubDate: 2014-11-01

• Role of the support in the formation of the properties of a Pd/Al 2 O 3
catalyst for the low-temperature oxidation of carbon monoxide
• Abstract: The Pd/Al2O3 catalysts were prepared by the impregnation of aluminum hydroxide, which was synthesized by precipitation in the presence of polyvinyl alcohol, with a solution of palladium nitrate and were heat-treated at different temperatures. The resulting samples were characterized by X-ray diffraction, electron microscopy, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy and were tested in CO oxidation in two modes: in a temperature-programmed reaction and under isothermal conditions at 20°C in the absence and in the presence of water vapor. The activity of the catalysts in the former mode was almost independent of support preparation conditions, but it was different in the latter mode. The catalyst whose support was obtained in the presence of polyvinyl alcohol and treated at 300°C in an atmosphere of nitrogen exhibited the highest activity in CO oxidation at 20°C. In the absence of water vapor from the reaction mixture, the initial conversion of CO reached 40% and then decreased. In the presence of water vapor, a continuous increase in the conversion of CO to 88% was observed, and the activity was stabilized at this level. The smallest size of palladium metal nanoparticles, the nearly monolayer carbon surface coverage, and the presence of OH groups, which are formed upon the dissociation of water present in the reaction mixture, facilitate an increase in activity.
PubDate: 2014-11-01

• Kinetics of D-glucose hydrogenation over a Ru-containing heterogeneous
catalyst
• Abstract: We studied the kinetics of glucose hydrogenation over a catalyst containing Ru nanoparticles in a super-cross-linked polystyrene matrix. Two hydrogenation pathways, whose rates differ by several orders of magnitude (“fast” and “slow” pathways), were found. The first pathway includes the reaction of glucose from its aqueous solution with hydrogen sorbed on the catalyst’s metal, and the second one includes the reaction of sorbed substrate with hydrogen occurring on the catalyst support due to spillover. A mathematical description of the reaction pathways was proposed, and the most probable scheme of the process was suggested. The role of hydrogen spillover in the kinetics of the occurring processes was considered.
PubDate: 2014-11-01

• Ethanol steam reforming over Co/ZnO and Rh/Al 2 O 3 catalysts in a
microchannel catalytic reactor
• Abstract: The activity of Co/ZnO and Rh/Al2O3 catalysts in ethanol steam reforming was studied in a traditional tubular reactor with a fixed catalyst bed and in a microchannel reactor. At temperatures of 600 and 700°C, the Rh/Al2O3 catalyst was much more active and stable than Co/ZnO. A comparison between the reactors of two types showed that the ethanol steam reforming occurred more efficiently in the microchannel reactor because of intense heat and mass exchange. The specific hydrogen production per unit weight of catalyst in the microchannel reactor was almost twice as high as that in the traditional reactor.
PubDate: 2014-11-01

• Mechanochemical synthesis of CuO-CeO 2 catalysts for the preferential
oxidation of CO in the presence of H 2
• Abstract: Mechanochemical activation was used in the synthesis of CuO-CeO2 catalysts for the preferential oxidation of CO in the presence of excess H2. Catalysts similar in properties to supported CuO/CeO2 systems were prepared from mixtures of copper oxide (5 or 10 wt % CuO) and cerium dioxide with the use of mechanochemical activation. It was found that the time of mechanochemical activation influences the catalytic properties: a maximum conversion of CO into CO2 (97%) at 140°C was achieved with a sample of 10 wt % CuO-90 wt % CeO2 after mechanochemical activation in a ball mill for 90 min. Changes in the phase compositions of the catalysts depending on mechanochemical activation time and reaction mixture composition were studied by X-ray diffraction. The interaction of the oxides of copper and cerium in the process of mechanochemical activation with the formation of new Cu-O-Ce surface structures, which, supposedly constitute active sites for CO oxidation, was found using differential scanning calorimetry and differential thermogravimetric analysis.
PubDate: 2014-11-01

• Efficiency of sulfonic cation-exchange resins used in para - tert
-butylphenol production: A comparison based on the kinetics of
transalkylation in the phenol- tert -butylphenols system
• Abstract: The kinetics of transalkylation in the phenol-tert-butylphenols system in the presence of Amberlyst 36 Dry sulfonic cation-exchange resin has been investigated at 353–403 K in the tert-Bu/Ar = 0.10–0.55 mol/mol range. Kinetic characteristics of the o-tert-butylphenol + phenol ai p-tert-butylphenol + phenol (I) and 2,4-di-tert-butylphenol + phenol ai 2p-tert-butylphenol (II) reactions have been determined. The chemical equilibrium in the presence of Amberlyst 36 Dry is reached much sooner than in the presence of KU-23 10/60, a cation-exchange resin used at present. On passing from Amberlyst 36 Dry to KU-23 10/60, the preexponential factor for reaction (I) increases by a factor of 10 and that for reaction (II) increases by a factor of 2000. Thermodynamic characteristics of reaction (I) between 353 and 523 K have been calculated from experimental data and data available from the literature. The thermodynamic characteristics of reaction (II) have been determined experimentally. The enthalpy and entropy of reaction (I) are equal to those of reaction (II). The difference between the equilibrium constants of these reactions is explained. It is recommended that Amberlyst 36 Dry, which proved more efficient than KU-23 10/60, be used in the industrial production of p-tert-butylphenol.
PubDate: 2014-11-01

• Kinetics of allyl chloride epoxidation with hydrogen peroxide catalyzed by
extruded titanium silicalite
• Abstract: A mechanism is suggested for the heterogeneous catalytic epoxidation of allyl chloride with hydrogen peroxide in methanol. The kinetics of allyl chloride oxidation into epichlorohydrin in the presence of extruded titanium silicalite has been investigated. A kinetic model of the process has been derived from experimental data, and the activation energies of the target and side reactions, the rate constants of the reactions, and the adsorption equilibrium constant have been determined. The allyl chloride epoxidation process has been tested using a bench-scale continuous apparatus, and the adequacy of the kinetic model has been estimated.
PubDate: 2014-11-01

• Influences of organic compounds on the visible light induced
photocatalytic reduction of Cr(VI)
• Abstract: The objective of this work is to study how the nature of organic compounds influences on the reduction of Cr(VI). The photocatalytic reduction of Cr(VI) was carried out in the presence of various organic compounds under visible light, a remarkable promotion effect on Cr(VI) reduction was observed in most cases. The results indicate that the electronic and structural characteristics of different organics are important factors for the reduction of Cr(VI). A suitable redox potential was important for the organic compounds to promote the reduction. Organic compounds with the electronic property of conjugative effect indicated promotion effect, while indicated inhibition effect with inductive effect. The chelating agents served not only as the electron donors, but also formed complexes with Cr(VI) and/or its reduction products.
PubDate: 2014-11-01

• Conditions of deposition of TiCl 4 used in preparing the silylated Ti-HMS
and their effect on catalytic epoxidation of propylene
• Abstract: Silylated Ti catalysts based on hexagonal mesoporous silica (Ti-HMS) were prepared by chemical vapor deposition of TiCl4 on HMS silica modified by vapor silylation. The influence of TiCl4 deposition conditions on surface properties and catalytic performance of the catalysts were investigated. Among the methods used to characterize the catalysts were N2-adsorption, Inductively coupled plasma-atomic emission spectrometry (ICP-AES), Ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy. Catalytic activity was evaluated in the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant. Most of Ti ions in HMS mesoporous silica occupy tetrahedral sites and these sites are responsible for the efficient epoxidation activity. The Ti content incorporated in silica decreases with increasing calcination temperature. The experiments indicated 400°C as an appropriate deposition temperature since higher deposition temperatures favor the formation of low active Ti species. A deposition time of 2 h is a sufficient time interval for incorporating Ti into HMS mesoporous silica. A suitable calcination temperature can be estimated as 700°C while higher calcination temperatures promote the formation of low active Ti species. Propylene oxide in high yields (> 95%) can be obtained in the epoxidation of propylene over the catalysts described in the work. The mechanism proposed for the deposition reaction suggests that the incorporation of Ti into HMS is due to silica interaction of Si-OH with TiCl4, chlorination removes Cl-containing Ti species and in this way decreases the Ti content of catalysts at high deposition temperatures.
PubDate: 2014-11-01

• State and properties of ion-exchanged cations in zeolites: 2. IR spectra
and chemical activation of adsorbed methane
• Abstract: Methane adsorption by hydrogen and cationic forms of various zeolites has been investigated by diffuse reflectance IR spectroscopy. In methane adsorption on faujasites, protons, univalent alkali metal cations, and divalent alkaline-earth cations exert similar perturbation and polarization effects on the methane molecule. Adsorbed methane in high-silica zeolites is perturbed by alkaline-earth cations somewhat more strongly than in faujasites and still more strongly by divalent transition metal cations. In the latter case, as in hydrogen adsorption, which was considered in the previous report, the interaction between methane and the zinc form of zeolite ZSM-5 at elevated temperatures causes the heterolytic dissociative adsorption of methane with the formation of methyl fragments and acidic hydroxyl groups bound to zinc ions.
PubDate: 2014-11-01

• Kinetics and mechanism of the interaction between HAuCl 4 and rutin
• Abstract: The kinetics and mechanism of the reaction of HAuCl4 with rutin and the size of the resulting gold nanoparticles have been studied by UV-vis, FTIR, and surface-enhanced Raman spectroscopy (SERS), atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The reaction includes the formation of a rutin complex with HAuCl4 and its decomposition yielding Au atoms. The gold nanoparticles result from Au ions and atoms at the second stage. This stage can be described in terms of a second order kinetic equation. The rate constant and Gibbs energy of the second stage of nanoparticle formation have been determined.
PubDate: 2014-11-01

• Acetylene hydrochlorination over mechanically activated K 2 MCl 4 (M = Pt,
Pd) and K 2 PtCl 6 catalysts: The HCl/DCl kinetic isotope effect and
reaction mechanisms
• Abstract: It is demonstrated that HCl molecules participate in two steps of acetylene hydrochlorination with gaseous HCl over mechanically activated K2MCl4 (M = Pt or Pd) and K2PtCl6 catalysts, namely, the hydrochlorination of π-coordinated acetylene (rate-limiting step) and protodemetallation. It is confirmed that the same intermediate—β-chlorovinyl derivative of Pt(II)—is involved in protodemetallation over the Pt-containing catalysts. Possible mechanisms of the two reaction steps are considered.
PubDate: 2014-11-01

• Template synthesis of titanium dioxide coatings and determination of their
photocatalytic activity by aqueous oxidation of humic acid
• Abstract: In this work, aqueous photocatalytic oxidation of humic acid, present in various waters as naturally occurring compound or anthropogenic pollutant, was studied using self-synthesized titanium dioxide coatings. To obtain the latter, template synthesis, widely used for the production of photocatalysts with improved surface properties and activity, was applied with variations in template material, N-cetyl-N,N,N-trimethylammonium bromide content. The catalysts were characterized using XRD, UV-VIS spectroscopy, and SEM. The activity of TiO2 coatings in the degradation of humic acid proved to be superior to that of commercial photocatalyst P25 (Evonik) The dependence of the photocatalysts’ performance on the template content in the synthesis precursors, which was responsible for the various surface features of the coatings, was established and explained.
PubDate: 2014-11-01

• The effect of catalyst preparation on the activity of MoO 3 -SiO 2
catalyst in transesterification of diethyl oxalate
• Abstract: Transesterification of diethyl oxalate (DEO) with phenol over MoO3-SiO2 catalysts prepared by the sol-gel technique (MoO3-SiO2 (SG)) and the impregnation method (MoO3-SiO2 (I)) was conducted to produce diphenyl oxalate (DPO), which can be used as a precursor for manufacturing diphenyl carbonate (DPC). The sample MoO3-SiO2 (SG) containing 12 wt % of MoO3 showed the best performance with 71.0% conversion of DEO and 32.0% selectivity to DPO. Compared to MoO3-SiO2 (I), improvements in the DEO conversion and DPO selectivity with MoO3-SiO2 (SG) were 16.1 and 7%, respectively. Crystal structure and phase composition of MoO3-SiO2 (I) and MoO3-SiO2 (SG) catalysts with varying MoO3 contents were investigated. The sample MoO3-SiO2 (SG) with a similar chemical composition to MoO3-SiO2 (I) has a larger specific surface area, indicating that the active component is well dispersed on the surface of the MoO3-SiO2 (SG) catalysts. Results of XRD and XPS measurements suggest a high degree of dispersion of MoO3-SiO2 (SG) catalysts that can account for an increase in DEO conversion and DPO selectivity. Coordinately unsaturated MoO3 species play a significant role in the catalytic performance of MoO3-SiO2 (SG) catalysts in transesterification of DEO with phenol. In addition, IR measurements of pyridine adsorption and NH3-TPD data indicate that the amount of acid sites on the surface of MoO3-SiO2 (SG) exceeds that found for the surface of MoO3-SiO2 (I). An enhanced concentration of surface MoO3 species in tetrahedral coordination coupled with the presence of weak Lewis acid sites appear to be the main reason why MoO3-SiO2 (SG) catalysts are superior to the MoO3-SiO2 (I) system.
PubDate: 2014-11-01

• Formation of platinum sites on layered double hydroxide type basic
supports: III. Effect of the mechanism of [PtCl 6 ] 2− complex
binding to aluminum-magnesium layered double hydroxides on the properties
of supported platinum in Pt/MgAlO x catalysts
• Abstract: While synthesizing platinum catalysts supported on aluminum-magnesium oxides (Pt/MgAlO x ), we established that, in the binding of the Pt(IV) chloro complex to aluminum-magnesium layered double hydroxides (LDHs), the mechanism of the metal complex-support interaction depends on the nature of the interlayer anion of the LDH. The synthesis may yield chemically identical Pt/MgAlO x samples differing in the particle size and electronic structure of supported platinum. The higher dehydrogenating activity of the catalyst obtained by binding the [PtCl6]2− complex in the interlayer space of LDH via exchange with interlayer OH− anions is possibly due to the larger proportion of metallic platinum (Pt0) in this catalyst. In the catalyst prepared from hydrolyzed platinum complex species using LDH with CO 3 2− interlayer anions, platinum is mainly in an oxidized state similar to Pt2+.
PubDate: 2014-11-01

• Catalytic oxidation of glyoxal to glyoxalic acid over Au-Pd alloy
nanoparticles on hydrotalcite
• Abstract: Synthesis of glyoxalic acid by selective oxidation of glyoxal at ambient temperatures with O2 as an oxidant is an important problem. We found that gold nanoparticles supported on hydrotalcite (Au/HT) exhibit an appreciable catalytic activity for this reaction in the liquid phase. Moreover, Au-Pd/HT, prepared by the deposition-precipitation method is superior in the catalytic behavior to monometallic Au/HT and Pd/HT catalysts. Introduction of palladium enhances ability of the catalysts to oxidize carbonyl to carboxyl, weakens the power to rupture C-C bond and in this way improves the catalytic performance. Furthermore, the Au: Pd ratio also influences the properties of the alloy catalysts. The 1.5Au-1.5Pd/HT catalysts show the highest activity for the selective oxidation at ambient temperature producing glyoxalic acid in 13.4% yield at pH 7.7. Moreover, due to basic properties of hydrotalcite, glyoxalic acid could be synthesized over 1.5Au-1.5Pd/HT in 8.0% yield without adding a base. It is hoped that results of this study can fuel further research in designing new catalysts with alloy nanoparticles supported by hydrotalcite that can be used for the selective oxidation of other useful compounds.
PubDate: 2014-09-01

• Kinetics and possible mechanism of hydrogen chloride oxidation over
supported copper-containing salt catalysts: II. Kinetics of HCl oxidation
in the deacon and methane oxychlorination reactions over the CuCl       class="a-plus-plus">2-KCl-LaCl       class="a-plus-plus">3 catalyst
• Abstract: The kinetics of HCl oxidation at 350–425°C over the supported CuCl2-KCl-LaCl3 catalyst has been investigated using a gradientless technique. The HCl oxidation kinetics in the Deacon and methane oxychlorination reactions has been studied in order to substantially extend the $$Cl_2 \left( {P_{Cl_2 } } \right)$$ partial pressure variation range. When the reaction rate is independent of P HCl, HCl oxidation on the copper-potassium catalysts is described by the same rate equation, irrespective of whether the catalyst contains lanthanum or not. The introduction of lanthanum chloride increases the HCl oxidation rate by one order of magnitude. The rate equation obtained has significant advantages over the equation corresponding to the Kenney-Slama equation. The kinetic features of HCl oxidation over the lanthanum-containing catalyst, whether the process depends on P HCl or not, can be explained in terms of the superposition of the Kenney-Slama dissociative mechanism and the catalytic mechanism suggested here. The role of lanthanum chloride in both HCl oxidation pathways is considered.
PubDate: 2014-09-01

• Microwave synthesis of LaBO       class="a-plus-plus">3 (B = Co, Fe) perovskites
using graphite and citric acid additions
• Abstract: We studied the effects of graphite and citric acid additions on the formation of LaFeO3 and LaCoO3 perovskites upon microwave treatment of crystalline hydrates or nitrate solutions, respectively. The addition of graphite was shown to increase the yield of LaCoO3 perovskite and to result in the formation of crystalline LaFeO3 perovskite even at the microwave treatment stage. Subsequent thermal treatment at 800°C yields single-phase lanthanum ferrite with a high specific surface area (11 m2/g). Due to the addition of citric acid to nitrate solutions, a highly viscous gel forms, which allows preparation of single-phase perovskites with a high specific surface area (up to 34 m2/g) after microwave treatment and calcination. The samples obtained using the admixtures are characterized by a high catalytic activity in methane oxidation. No single-phase oxides form without introduction of these admixtures.
PubDate: 2014-09-01

• Kinetic model of thiourea dioxide decomposition in aqueous ammonia
• Abstract: The kinetics of the decomposition of thiourea dioxide in aqueous ammonia solution at various temperatures and ammonia concentrations has been investigated. The parameters of the individual steps of the process have been derived from experimental data by solving an inverse kinetic problem. The adequacy of the proposed kinetic model to the experimental data has been verified on the basis of the F-test and calculated correlation coefficients for the rate constants of the individual steps of the process.
PubDate: 2014-09-01

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