Enhancement of H2- and retardation of O2-adsorption during O2?H2 titration cycles on Pt?Al2O3 catalyst surfaces

The title effects can be eliminated if the slow bleeding of H₂ from freshly reduced CuO-towers (often used as O₂-getters in purifying N₂ carrier gas) can be avoided, then H₂–O₂ titrations of Pt surfaces give consistent values from almost the first titration. Water injected at 25 °C also hardly affects the titer values.

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H₂ O₂ , H₂ CuO ( O₂ N₂ — -). H₂–O₂ Pt . , 25° C, .

     

Molecular Encapsulation of Half-Sandwich Complexes of Iron with Cyclodextrins: New Laminar Materials

The treatment of - and -cyclodextrins with the half-sandwich complexes of iron afford the inclusion compounds CpFe(L₂)XCD ( and ) (X = Cl, I; L = CO; L₂ = dppe, dppe = (Ph)₂P(CH₂)₂P(Ph)₂), [CpFe(L₂)L-]PF₆CD ( and ) L- neutral donor ligands and[(Cp(dppe)Fe)₂-µ-CN]PF₆2CD ( and ). The inclusion compounds [Cp(dppe)Fe-NCCH₃]PF₆-CD and [Cp(dppe)Fe-(¹-dppm)]PF₆-CD have a laminar structure. The - and -cyclodextrin encapsulation effect on the electro-oxidation of the binuclear complex was studied using cyclic voltammetry.The electron-transfer reactions associated with the oxidation of the two different N-bonded and C-bonded organometallic fragments are substantially affected by and encapsulation.     

Oxidation of hydrocarbon mixtures over a complex vanadium catalyst

Vapor-phase oxidation of hydrocarbon mixtures over vanadium oxide (promoted by potassium sulfate)-silica catalyst has been studied. It is shown that the inhibition of the rates of formation of individual products depends on the ability of the added hydrocarbons to similar specific interaction with the catalyst.

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. , , .

     

Solid-Phase Extraction with Slurry Injection of the Resin Into ETAAS for Trace Determination of Thallium in Natural Water

Thallium in natural water samples was determined by electrothermal atomic absorption spectrometry after 1000-fold enrichment by mini solid-phase extraction from a 100-mL sample solution. A Tl-pyrrolidine-1-carbodithioate complex formed in a sample solution of pH 1.6 was extracted on fine particles of a cellulose nitrate resin dispersed in the sample solution. The cellulose nitrate resin was then collected on a membrane filter (25mm^ø) by filtration under suction using a glass funnel with an effective filtration area of 0.64cm². As a result, a circular thin layer of the resin phase with a diameter of 9mm was obtained. Then the resin phase was carved out by an acrylate resin puncher with a 10-mm^ø hole to put it into a sample cup containing 100µL of 10mM HNO₃ containing 0.5mM NaCl. The resin phase was suspended in the solution by ultrasonication. 1000-fold enrichment was thus attained within 15min, and the suspension was delivered to electrothermal atomic absorption spectrometry. The linear calibration graph was obtained in the range of 0–4ng of Tl in 100mL of a sample solution. The detection limit obtained by 3 method was 0.19ng. The proposed method was applied to the determination of Tl in natural water samples. The results showed the concentration of Tl in seawater was 12.1±1.8pgmL^–1 for the calibration graph method and 12.6±1.4pgmL^–1 for the standard addition method. A snowmelt sample contained 20.7±1.0pgmL^–1 of Tl.     

Diffusion of hydrocarbons in mordenite and molecular-sieve selectivity of mordenite catalysts

The diffusion of n-octane and n-propylbenzene in mordenite and the molecularsieve selectivity in hydrocracking of octane-propylbenzene binary mixtures over a mordenite catalyst have been studied. The hydrocarbon diffusivities and molecular-sieve selectivity change are accounted for by diffusion through mordenite channel mouths poisoned with an easily adsorbable hydrocarbon.

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- , () -. , , .

     

Redistribution kinetics of isotope molecules due to reversible bimolecular reactions with several atomic channels

Isotope kinetic equations for reversible bimolecular reactions describe the rearrangement of atoms in activated complexes. It has been established from the model reaction CH₄+HCH₃+H₂ that the isotopic homoexchange of methane via two atomic channels is given by one set of equations with different sets of parameters.

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- . CH₄+HCH₃+H₂ , .

     

On the mechanism of chlorobenzene hydrolysis over Cu promoted lanthanum phosphate

The reaction mechanism of chlorobenzene hydrolysis to produce phenol over Cu promoted lanthanum phosphate has been studied taking into account a parallel reaction through which benzene is formed. There is a competition for the adsorption sites between the reactants and the reaction products.

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, , , . .

     

X-ray diffraction studies of reforming platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber indicate that in a stream of hydrogen starting from 550–600 K, platinum is practically completely reduced. In several cases at higher temperatures a platinum hydride is also formed.

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, , 550–600 ; .

     

Kinetics of oxidative sulfonation of butylamine in the presence of CuCl2

Kinetic regularities of butylamine sulfonation to N, N-dibutylsulfamide in the presence of copper(II) chloride have been studied. Reaction mechanism involves the formation of Cu(II) amine complexes, their subsequent interaction with SO₂ and the redox decomposition of an intermediate to final products.

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N-N- (II). Cu(II), SO₂ - .

     

Stability of hyperbolic reactors

For the one-phase tubular reactor, a new mathematical model is suggested, viz. a hyperbolic system of first order partial differential equations instead of the usual second order parabolic ones. This physically better model is investigated from the point of view of stability via the second Lyapunov method.

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. .

     

Hydrocarbon conversion on promoted rhodium/Al2O3 catalysts

In (E+Rh)/Al₂O₃ catalysts (E=Sn, Pb, Mo and W) the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion change drastically. For modified rhodium the decrease in the hydrogenolysis rate of C–C bonds in paraffins leads to an increased yield of the products of non-destructive conversion of n-hexane.

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(E+Rh)/Al₂O₃ (E:Sn, Pb, Mo, W) , , -. C–C -.

     

Synthesis and Catalytic Applications of Dendrimer-Templated Bimetallic Nanoparticles

Dendrimers, well-defined hyper-branched macromolecules with characteristic globular structure, have emerged as an attractive material in the field of catalysis and have been considered as a new type of host for the accommodation of guest molecules by virtue of their three-dimensional structure having interior void space. In line with the prospect of dendrimer as a nanoreactor, various metal nanoparticles have been successfully prepared via encapsulation in or formation of particles surrounded by dendrimer branches. However, it is worth noting that most of the previous studies have been confined to the monometallic nanoparticles, and bimetallic nanoparticles have been scarcely exploited yet. In this article, we present the synthesis and characterization of dendrimer-templated bimetallic nanoparticles and their application to catalysis.     

Determination of hydrogen chemisorbed on supported nickel catalysts by dimethyl zinc

Nickel supported on various metal oxides was titrated with dimethyl zinc tetrahydrofuranate at 130°C. The amount of hydrogen chemisorbed on nickel was evaluated from the amount of methane evolved after subtraction of OH groups of the support. The fraction of hydrogen bonded to nickel varied between 24–83 % of the overall hydrogen measured in dependence of support and correlated with activity of catalysts in the reaction of diethylene glycol with ammonia.

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, , 130°C. , , OH . , , 24 83% .

     

Reaction of vinyl radicals with propylene in the gas phase

The reaction of vinyl radicals with propylene and propyl radicals was investigated in the gas phase. The radicals were produced by mercury sensitized decomposition of molecular hydrogen followed by addition of hydrogen atoms to propylene and acetylene. Vinyl radical adds to propylene effectively while hydrogen atom abstraction does not occur.

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. , , . , , .

     

Interaction of some antibiotics with hydroxypropyl-β-cyclodextrin

The interaction between 19 antibiotics and hydroxypropyl--cyclodextrin (HPCD) was studied by reversed-phase thin-layer chromatography. HPCD formed inclusion complexes with 16 compounds, the complex always being more hydrophilic than the uncomplexed drug. The intensity of interaction significantly increased with increasing specific hydrophobic surface area of the guest molecule proving the preponderant role of hydrophobic interactions in inclusion complex formation. The intensity of the HPCD-drug interaction significantly decreased with increasing concentration of methanol in the environment indicating that methanol can also enter the cyclodextrin cavity and inhibits competitively the inclusion complex formation or the free energy of transfer from water to the HPCD cavity should be less negative at higher concentration of methanol in the aqueous medium.Dedicated to Professor József Szejtli.     

Synthesis of 19-hydroxysteroids I. New synthesis of 19-hydroxytestosterone

For obtaining 19-hydroxytestosterone from dehydroepiandrosterone a new scheme of synthesis has been developed the key stages of which are the reduction of the 17-keto group to a 17-alcohol, the functionalization of the 19-methyl group via the bromohydrin with the formation of a 6,19-epoxide, the selective hydrolysis of the free -acetoxy group, the conversion of the 3-hydroxy-5-bromo derivative into the ⁴-3-ketone, and the reductive cleavage of the 6,19-epoxide ring.Institute of Bioorganic Chemistry, Belorussian Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 672–678, November–December, 1992.     

Raman characterization of amorphous carbon films

Amorphous carbon films, deposited with the LASER-ARC technique, have been characterized using Raman scattering experiments at an excitation wavelength of 633 nm provided by a He-Ne laser. To distinguish between the homogeneous amorphous film and incorporated particles area resolved measurements have been carried out due to the laser spot diameter of 1 m. Typical diamondlike (DLC) films, grown near room temperature, show a broad Raman band between 1000 cm^–1 and 1800 cm^–1 fitted very well by two gaussian distributions. Films deposited at higher substrate temperatures reveal more graphitic features in the spectra. The spectra of particles consists of a graphite-like portion originated from the graphitic structure of the particle and a diamond-like portion caused by the covering DLC film. The degree of disorder and diamond-likeness in the film structure is quantified by the peak position, the full width at half maximum (FWHM) and intensity relation of the fitted D- and G-peaks.     

A Comparative Study of Homemade C18 and Commercial C18 Sorbents for Preconcentration of Lead by Minicolumn Solid Phase Extraction

A comparative study of commercial C₁₈ chemically immobilized on silica and homemade C₁₈, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate (DDTP) in a flow injection preconcentration system is reported. The homemade C₁₈ sorbent was obtained by sorption of poly(methyloctadecylsiloxane) (PMODS) on the silica support followed by immobilization using thermal treatment. The method follows the concept of green chemistry, since there are no toxic residues after synthesis. The complexed Pb was formed in 1.0molL^–1 HCl medium and retained on the minicolumn filled with the sorbents. The elution was carried out using ethanol, and the richest 210µL fraction was collected and analyzed by flame atomic absorption spectrometry. Chemical and flow variables were optimized for each sorbent. The results demonstrated that the performance of the proposed homemade C₁₈ sorbent for preconcentration of Pb complexed with DDTP is very similar to commercial C₁₈ chemically bonded on silica. By processing 25mL, the enrichment factors were 129 and 125 for commercial C₁₈ and homemade C₁₈, respectively. The limit of detection for commercial and homemade C₁₈ was 0.2µgL^–1 and 0.6µgL^–1, respectively. The relative standard deviation (RSD) was lower than 1.2% for both sorbents for a Pb concentration of 100µgL^–1. The method was also applied successfully to the analysis of water samples, and the accuracy was tested by recovery measurements on spiked samples and biological reference material.     

Study of the oxygen distribution in YBa2Cu3O7−x ceramics by (n, α) radiography technique

A technique to determine the oxygen distribution in high T_c superconducting YBa₂Cu₃O_7–x ceramics has been developed which is based on the (n, ) radiography method. The technique enables the non-destructive study of superconducting ceramics as well as monocrystal samples with spatial resolution not worse than 1 m at a relative standard deviation of 1.5%. This technique is used to study the influence of radiation-stimulated diffussion of oxygen on the formation of the superconducting phase in an yttrium ceramic. The oxygen distribution in the samples with a narrow transition (T1 K) and with a transition widened (T10 K) by thermal and thermo-radiative treatment is compared in the experiment. The oxygen distribution radiographs of irradiated and unirradiated samples provide strong evidence for the influence of irradiation on the ordering of superconducting ceramics structure.     

Synthesis of dinuclear group 6 metal carbonyl complexes bridged by 4,4′-bipyrazole ligands

A series of dinuclear group 6 metal carbonyl complexes containing 4,4-bipyrazole ligands [(CO)₅M (-dpz)M(CO)₅)] have been synthesized by the photochemical reaction of 4,4-bipyrazoles with M(CO)₆ [M = Cr, Mo or W; dpz = 4,4-bis-3,5-dimethylpyrazole; 4,4-methylenebis(3,5-dimethylpyrazole)], and characterized by elemental analyses, i.r. and ¹H-n.m.r. spectra. Their electrochemical behavior, investigated by cyclic voltammetry, indicates that all complexes exhibit one quasi-reversible redox peak owing to the presence of two equivalent M(CO)₅ fragments. The crystal structure of (CO)₅W(-dpz)W(CO)₅ [dpz = 4,4-methylenebis(3,5-dimethylpyrazole)] determined by X-ray diffraction, indicates that two W(CO)₅ units are linked by the bridging bidentate ligand, and are located in a mutually cis-position. The molecules form a two-dimensional double-layer sheet by intermolecular hydrogen bonding interactions between the N—H groups and the oxygen atoms of metal carbonyls in the solid state.