Hydrocarbon hydrogenolysis on nickel-tin catalysts

Hydrogenolysis of ethane, n-hexane and cyclohexane has been studied on nickel-kieselguhr catalysts modified by organic and inorganic compounds of tin. Tin additives decrease nickel reactivity with respect to C–C dissociation, which is ascribed to the formation of surface intermetallides on the catalyst.

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, - - , . . C–C .

     

Effect of medium composition on the monooxygenase activity of immobilized hemin in aniline oxidation

The effect of the composition of the reaction medium on the rate of aniline oxidation to p-aminophenol by hydrogen peroxide on hemin immobilized on -propylimidazole-modified silica has been studied. Organic solvent additives (alcohols, esters and nitriles) are shown to increase the reaction rate. The observed effect is attributed to the decrease of the medium dielectric constant.

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- , , --. , (, , ) . .

     

Interaction between peroxyl radicals of polyatomic esters and aromatic nitrons

Reactivity and rate constants in reactions between peroxyl radicals of ethylene glycol diacetate and aromatic nitrons have been investigated.

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.

     

Catalytic desulfurization of ethanethiol over zinc-forms of NaX zeolites

Zinc exchanged zeolite X was found to catalyze effectively the dehydrosulfurization of ethanethiol. The catalytic activity correlated linearly with the degree of ion exchange and increased with the reaction temperature. The role of zinc cations in the reaction examined is discussed and suggestions concerning the reaction mechanism are put forward.

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X, Zn, . . .

     

Oxidative coupling of alkylbenzenes to diaryls catalyzed by the palladium(II)-heteropolyacid system

Oxidative coupling of alkylbenzenes (benzene, toluene, o-xylene, durene) is shown to proceed in the presence of palladium salts and heteropolyacids under the action of oxygen with a high yield of diaryls. The addition of mercury salts and variation of the solvent affect the reaction rate and isomer composition of the products.

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, (, , -, ) . .

     

m-Xylene conversion over dealuminated Y zeolites studied by the pulse method

m-Xylene conversion was studied over dealuminated Y type zeolites in hydrogen forms, SiO₂ to Al₂O₃ ratios were varied from 4.86 to 12.95.

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- . SiO₂/Al₂O₃ 4,86 12,95.

     

Measurement of adsorption heats of nitrogen on metal nitrides

Adsorption heats q and activation energies of the nitrogen exchange on several metal nitrides have been compared. For the systems capable of changing readily their composition upon varying conditions, the isotope exchange is suggested to be the most reliable method of the determination of q.

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. , , , .

     

Analysis of thermal desorption spectra of oxygen desorbed from rhodium

Thermal desorption spectra of oxygen desorbed from rhodium have been analyzed in terms of models accounting for the effect of lateral interactions between adsorbed particles and of their diffusion into the bulk of metal on the desorption kinetics of O₂. Complex configuration of these spectra is ascribed to the processes of formation/decomposition of surface Rh oxides and the diffusion of particles into the near-surface layers of metal and back to the surface.

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- , O₂ . - O₂ Rh - .

     

Oxidation of propylene to acrylic acid on a Fe?Mo?Bi oxide system

Data obtained in a flow reactor show that iron(III) molybdate doped by bismuth can oxidize propylene to acrylic acid directly in one step. Part of the catalyst works in a partially reduced form and in the preparation of the catalyst the surface acidity must be controlled.

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, , (III), , . .

     

Dilution effect on catalytic pyrolysis of hydrocarbons

It is shown that unlike thermal pyrolysis, the rate of catalytic pyrolysis is greatly affected by dilution of hydrocarbons with inert gases. The nature of this effect has been analyzed.

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, . .

     

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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. .

     

Preparation and properties of supported vanadium-phosphorus catalysts studied by chemical analysis and ESR

The preparation of vanadium-phosphorus catalysts is described, showing the considerable influence of phosphorus on the concentration of V⁴⁺ ions. The oxidation properties were studied by chemical analysis and electron spin resonance. Moreover, ESR spectra show a strong influence of moisture on the structure of the catalysts.

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- , V⁺⁴. , . , , .

     

Kinetic studies of methanethiol disproportionation

Kinetic regularities in catalytic disproportionation of methanethiol to dimethyl sulfide and hydrogen sulfide have been studied in a flow circulation reactor. A kinetic equation is suggested to describe the reaction on inhomogeneous surfaces.

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- - . , .

     

Synthesis of dimethyl sulfide in the presence of zeolites

In the presence of zeolites, dimethyl sulfide is produced either through CH₃OH interaction with H₂S or via CH₃SH decomposition. In accordance with their activities, in both reactions, zeolites arrange in the same sequence: HZSMHNaY>NaXNaY. Realization of the reaction CH₃OH+H₂S is more difficult compared to methanethiol decomposition.

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CH₃OH H₂S CH₃SH. : HZSMHNaY>NaXNaY. CH₃OH+H₂S , .

     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

Glass transition and crystallization effects demonstrated by thermal analysis of liquid-quenched ternary glasses Te80Ge20−xA x V (AV=Sb,Bi)

In DSC studies of liquid-quenched ternary chalcogenide glasses Te₈₀Ge_20–xA _x ^V (A^V=Sb, Bi), the characteristic temperatures (glass transition and crystallization temperatures) were determined. Changes in the thermal stabilities of these glasses, depending on the element A (Sb, Bi) from group V of the periodic table and on its content in the alloy were evaluated. Moreover, the effect of changes in the glass composition on the glass formation ability expressed by the parameter K_g1 was determined.

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Zusammenfassung In DSC-Untersuchungen abgeschreckter ternärer Chalkogenidgläser des Typs Te₈₀Ge_20–xA _x ^v (A^x=Sb, Bi) wurden die charakteristischen Temperaturen (die GlasÜbergangs- und Kristallisationstemperaturen) bestimmt. Die Änderungen der Thermostabilität dieser Gläser wurden in Abhängigkeit von dem Element A (=Sb, Bi) aus der V Gruppe der Periodensystems und von seinem Gehalt in der Legierung ausgewertet. Ausserdem wurde der Einfluß der Änderungen in der Glaszusammensetzung auf die Glasbildungsfähigkeit, ausgedrückt durch den Parameter K_g1, bestimmt.

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Résumé On a déterminé par analyse calorimétrique différentielle (DSC) les températures caractéristiques (températures de transition vitreuse et de cristallisation), des verres ternaires à chalcogénures formés par trempe à partir du liquide, du type Te₈₀Ge_20–xA _x ^v (A^v=Sb, Bi). On a évalué la variation de la stabilité thermique de ces verres en fonction de l'élément A (=Sb, Bi) du Vème groupe du tableau périodique et de sa teneur dans l'alliage. De plus, on a déterminé l'effet des variations de la composition du verre sur la capacité de formation du verre qui s'exprime par le paramètreK _g1.

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Te₈₀Ge_20–xA _x ^v (A^v=Sb, Bi), , . A(=Sb,Bi) . , K _gl, .

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Research supported by the U. S. National Science Foundation under Grant No. GF 421 76     

Kinetics of oxidation of glycine by aqueous chlorine

The kinetics of oxidation of glycine with aqueous chlorine has been investigated. The reaction is first order with respect to both molecular chlorine and glycine and inverse first order with respect to H⁺. The effect of various factors on the initial rate has also been studied. The kinetic parameters have been calculated and a possible mechanism is proposed.

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. , H⁺. , . .

     

Donor-acceptor concept of covalent interaction of substrate with catalysts

In terms of a unitary approach, the ability of complexes, clusters and metals of transition and nontransition elements for covalent interaction with reagents has been analyzed. the requirements for the catalysts to be efficient in the covalent activation of substrates have been formulated.

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, . .

     

Influence of the pH of the preparation medium on surface properties of magnesium fluoride

The acidity and activity of MgF₂ in cyclohexene reactions wre studied as a function of the pH of MgF₂ preparation. Only samples prepared at pH 1.5 are acidic and catalytically active. It is proposed that the acidity of the MgF₂ surface is connected with the presence of sulfuric acid.

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pH MgF₂. pH 1,5 . , MgF₂ .