Dependence between electrocatalytic activity and the size of platinum crystallites

The dependence of the electrocatalytic activity of platinum deposited on a carbon carrier by anodic oxidation of hydrogen on the size of platinum crystallites has been investigated. The influence of the basic character of the surface compounds existing on the carbon carrier on the size of the crystallites and the rate of their growth has been established.

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, , . , , .

     

Thermogravimetric and kinetic study of a clodronic acid complex formed with sodium

Thermal stability of the clodronic acid complex formed with sodium (Na₂CCl₂(HPO₃)₂ ·4H₂O) was studied using both dynamic and isothermal thermogravimetric analyses as well as mass spectra. The thermal decomposition has two stages: dehydration and loss of two molecules of hydrogen chloride. Using the isothermal TG data the first step was found to be a phase-boundary reaction while the second step obviously cannot be described with just one reaction mechanism. The final residue of the dynamic TG analyses above 810 K was found to be sodium metaphosphate.

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Zusammenfassung Sowohl mittels dynamischer und thermogravimetrischer Untersuchungen als auch and Hand von Massenspektren wurde die thermische Stabilität des mit Natrium gebildeten Säurekomplexes Na₂CCl₂(HPO₃)₂·4H₂O untersucht. Die thermische Zersetzung vollzieht sich in zwei Schritten: Dehydratation und Verlust von zwei Molekülen HCl. Auf Grund der isothermen TG Angaben ist der erste Schritt eine Phasengrenzreaktion, während der zweite Schritt mit einem einzigen Reaktionsmechanismus nicht eindeutig beschrieben werden kann. Das Endprodukt der DTG Analyse oberhalb 810 K erwies sich als Natriummethaphosphat.

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-Na₂CCl₂/HPO_3/2·4H₂O — , - . , , , . , , . 810 .

     

Relation between the catalytic and acidic properties of zeolite catalysts

Influence of the strength and concentration of non protic centers on the catalytic activity of metal-zeolite catalysts in isomerization of n-butane has been studied. A relationship between the specific activity and the center strength is suggested.

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-. , .

     

Monolayer vanadia on titania systems from alkoxide precursors. Part III. Activity in secondary alcohol oxidation

The activity of V⁵⁺ ion monolayer supported on anatase, rutile, and anatase-rutile mixed carrier and of bulk V₂O₅ was examined in isopropyl alcohol and cyclohexanol oxidation. Catalysts exhibited remarkable activity in ketone formation. At higher temperatures benzene was the predominant product of cyclohexanol reaction.

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V⁵⁺, , - V₂O₅, . . .

     

Chloride ion oxidation on various Pt surfaces in the presence of adsorbing organic substance

While chlorine evolution in the low overpotential region takes place preferentially on the weakly adsorbing surface sites, in the presence of cyclohexene the strongly adsorbing region is involved. This change in the reaction zone is the result of the occurrence of a new reaction which dominates the recombination of chlorine atoms.

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, . , .

     

Selectivity of catalytic processes under forced cyclic operation

The influence of oscillations in the feed concentration on the selectivity of a catalytic process has been studied for parallel reactions. The selectivity increase in periodic operations depends on both the type of kinetic functions and the non-steady-state properties of the catalysts.

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. , .

     

Isoprene hydrogenation in the presence of cobalt pohosphine complexes

The influence of the type of phosphine on the yield of methylbutenes in isoprene hydrogenation with complex cobalt catalysts has been studied. The complex H₃Co[P(n-C₄H₉)₃]₃ has been identified by the NMR method in the catalytic system Co(C₅H₇O₂)₂+P(n-C₄H₉)₃+Al(C₂H₅)₃. A mechanism of isoprene hydrogenation is suggested.

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. Co(C₅H₇O₂)₂+P(n-C₄H₉)₃+Al(C₂H₅)₃ H₃Co[P(n-C₄H₉)₃]₃. .

     

Rearrangement ofα -trifluoromethyl-β-dialkylamino-β-fluoroacrylic acid N.N-dialkylamides

Conclusions When heated in the presence of a catalytic amount of BF₃ etherate,-trifluoromethyl--diethylamino--fluoroacrylic acid N, N-dimethylamide is reversibly isomerized to-trifluoromethyl--dimethylamino--fluoroacrylic acid N, N-diethylamide. The methyl esters of-trifluoromethyl--diethylammo--fluoroacrylic acid and-trifluoromethyl--phenoxy--fluoroacrylic acid N,N-dimethylamide are not isomerized under the same conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.1, pp.137–141, January, 1976.     

Vapor-phase oxidation of 2,6-dimethylpyridine on vanadium-molybdenum catalysts

The catalytic activity of vanadium-molybdenum catalysts in oxidation of 2,6-dimethylpyridine is compared with their adsorption properties and phase composition. The increase of molybdenum content results in the decrease of irreversible adsorption and total conversion of 2,6-dimethylpyridine. The reversible adsorption depends on the phase composition and character of crystalline modifications of MoO₃ in the catalysts.

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2,6- . 2,6-. MoO₃ .

     

The effects of cyclodextrin inclusion of the ferrocenemonocarboxylate anion on the kinetics of its oxidation by bis(pyridine-2,6-dicarboxylato)cobaltate(III) in aqueous solution

The effects of -, -, dm-(heptakis(2,6-di-O-methyl)--) and -cyclodextrins (CD) on the kinetics of the electron-transfer reaction of the ferrocenemonocarboxylate anion (FCA^–) with bis(pyridine-2,6-dicarboxylato)cobaltate(III) have been investigated in aqueous solution (0.20 M Na₂HPO₄, pH 9.2) at 25.0°C. Substantial decreases in the rate constants for the electron-transfer reactions were observed upon cyclodextrin inclusion of the reductant, due to an increase in the FCA^0/– reduction potential and to the insulation of the reductant from oxidant. The inclusion stability constants for {FCA·CD}^– were evaluated from the¹H NMR and kinetic data, and the order of the stability constants was found to be -CDdm-CD-CD>-CD.     

Chemistry and Structure of Diterpene Derivatives of the Kaurane Series: V. Isosteviol Anhydrides

(4,8,13)-13-Methyl-16-oxo-17-norkaurane-18-carboxylic acid (isosteviol) anhydride is synthesized, which is a first representative of bisditerpene compounds of the kaurane series. The structures of the anhydride and isosteviol chloride were studies by X-ray diffraction and quantum chemistry (AM1).     

Thermal and some other properties of the complexes crystallizing from the system Ni(II)-en-[Ni(CN)4]2−-H2O

Seven complex compounds exhibiting the compositions Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) and-Ni(en)₂Ni(CN)₄ (VII) were prepared from the system Ni-en-[Ni(CN)₄]^2–-H₂O. These compounds were examined by the methods of infrared spectroscopy, X-ray powder diffractometry, UV-VIS reflectance spectroscopy, and also by the measurement of magnetic moments. The thermal stability, the stoichiometry of thermal decomposition and the mutual transformations were investigated with a derivatograph. The reactions proceeding according to the following schemes were observed if the system was heated to appropriate temperature: (I)(II)(III)(V)(IV) and (VI)(VII)(III)(V)(IV) Process (VII)(III) represents isomerization. The reversibility of the process (V)(IV) is due to the high hygroscopicity of the anhydrous complex. The changes in structure in the course of the individual processes are discussed.

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Zusammenfassung Aus einem System Ni-en-[Ni(CN)₄]^2–-H₂O wurden sieben Komplexe der Formeln Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) und-Ni(en)₂Ni(CN)₄ (VII) hergestellt. Diese Verbindungen wurden mittels IR-Spektroskopie, Röntgenpulverdiffraktometrie, UV-Reflexionsspektroskopie und durch Messungen des magnetischen Momentes untersucht. Die Wärmestabilität, die Stöchiometrie des thermischen Zerfalles und die gegenseitigen Umwandlungen wurden mittels eines Derivatographen untersucht. Wird das System auf geeignete Temperaturen erhitzt, kann der Reaktionsverlauf durch folgendes Schema dargestellt werden: (I)(II)(III)(V)(IV) und (VI)(VII)(III)(V)(IV).Der Prozeß (VII)(III) verkörpert eine Isomerisierung. Die Umkehrbarkeit von Prozeß (V)(IV) ist auf die ausgeprägten Hygroskopieeigenschaften des wasserfreien Komplexes zurückzuführen. Es werden die im Ablaufe der einzelnen Prozesse vorgehenden Strukturveränderungen besprochen.

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Ni- -[No(N)]² -₂ Ni(en)₃Ni(CN)₄ · ₂ (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄-2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2,5H₂O (VI) -Ni(en)₂Ni(CN)₄ (VII). , , - , . , . (I)(II)(III)(V)(IV) (VI)(VII)(III)(V)(IV). (VII)(III) . (V)(IV) . .

     

Kinetics of cerium(IV) oxidation of propionic acid in perchloric acid: Role of solvent

The oxidation rate of propionic acid (PROA) by cerium(IV) in aqueous perchloric acid (1.0–6.0 mol/dm³) is proportional to the PROA concentration, the total order of the reaction being two. It was found that the rate is related to the values of Hammett's acidity function (H₀) in agreement with both Zucker-Hammett's hypothesis and Bunnett-Olsen's criterion, the water acting as a proton transfer agent. A mechanism consistent with the findings is proposed.

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() (IV) (1,0–6,0 /³) . (H₀) -, -. . .

     

Dehydration-dehydrogenation of 1- and 2-butanols on lanthanide oxide catalysts

Catalytic decomposition of 1- and 2-butanols on the rare earth oxides CeO₂, Pr₆O₁₁, and Me₂O₃ (Me=La, Sm, Eu, Dy, Ho and Yb) has been studied. Dehydration-dehydrogenation selectivity of these oxides was analyzed from the point of view of the fractional selectivity (S_F). For the decomposition of 2-butanol and the product distribution on the lanthanide oxides, preferential orientation to Hofmann olefin as well as a cis/trans ratio slightly higher than that of the equilibrium value is observed.

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1- 2- CeO₂, Pr₆O₁₁ Me₂O₃ (Me=La, Sm, Eu, Dy, Ho Yb). - (S_F). 2- , , / .

     

Influence of carbon dioxide on the position of oxygen adsorption equilibrium on silver

Due to interaction with carbon dioxide, when some adsorbed oxygen atoms on silver surfaces are converted into carbonate groups, the binding energy diminishes and the volatility of adsorbed oxygen rises.

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, , .

     

A gradientless airtight glass reactor with a detachable catalyst chamber

A gradientless airtight glass reactor supplied with a detachable chamber for the catalyst has been developed. It is designed for investigations on the kinetics of heterogeneous catalytic processes and the determination of catalytic activities at atmospheric and reduced pressures by the flow-circulation and quasi-static techniques.

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. - . , .

     

Interrelation of addition reactions of hexachlorocyclopentadiene and bromine to N-arylimides of endo-and exo-bicyclo[2,2,1]hept-5-ene-2,3-dicarboxylic acids

A comparative analysis of the relative reactivities of N-arylimides of endo-and exobicyclo[2,2,1]hept-5-ene-2,3-dicarboxylic acids for the addition reactions of hexachlorocyclopentadiene and bromine has been carried out. According to different correlations the transition states of these two processes are shown to be similar.

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N- - - [2,2,1] -5--2,3- . .

     

Degradation of rocket insulator at high temperature

The degradation of a rocket insulator compound based on ethylene propylene diene rubber (EPDM) containing asbestor, cork and iron oxide (Fe₂O₃) as fillers has been studied at high temperature (up to 600°) by using differential thermal analysis (DTA) and thermogravimetry (TG). The changes in physical properties on high-temperature aging are also reported. EPDM gum vulcanizates involving different types of diene, namely ethylidene norbornene (ENB), dicyclopentadiene (DCPD) and 1,4-hexadiene (HD), were used. In each case, the kinetic parameters for degradation have been evaluated. From these data, the lifetime of the rocket insulator compound has been found.

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Zusammenfassung Die Zersetzung einer Raketenisolator-Verbindung auf Äthylen-Propylen-Dien-Gummibasis (EPDM) mit Asbest, Kork und Eisenoxid (Fe₂O₃) als Füllstoffe wurden bei hohen Temperaturen (bis 600°) mittels Differentialthermalanalyse (DTA) und Thermogravimetrie (TG) untersucht. Die bei Hochtemperaturen eintretenden Veränderungen der physikalischen Eigenschaften sind ebenfalls angegeben. Verschiedene Typen von Dienen, nämlich Äthyliden-norbornen (ENB), Dicyclopentadien (DCPD) und 1,4-Hexadien (HD) enthaltenden EPDM-Gummivulkanisate waren Gegenstand der Untersuchung. In allen Fällen wurden die kinetischen Parameter der Zersetzung ermittelt. Aus diesen Daten wurde die Lebensdauer der Raketenisolator-Verbindung bestimmt.

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600° (), , . , . , , 1,4- . . .

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The authors are grateful to the Indian Space Research Organization for funding, and acknowledge the help and suggestions from Mr. T. S. Ram and Mr. Baby John, R.P.P., V.S.S.C., Trivandrum. The authors are also grateful to Prof. S. K. De, Rubber Technology Centre, and Prof. R. Ghosh, Chemistry Department, I.I.T., Kharagpur.

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The authors thank Mr. Asutosh Ghosh, Indian Association for the Cultivation of Science, for experimental assistance.     

[Fe(phen)3]2+ aquation in aqueous polyacrylamide solution

The aquation of tris(1, 10-phenanthroline) iron(II) has been studied in aqueous polyacrylamide solutions. The rate increases up to 2.8 times at low polymer concentrations, and subsequently decreases. These effects are attributed to changes in the local water activity in the region of the complex.

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(1, 10-) (II) . 2,8 , . .

     

Deamination of butylamines on the surface of acidic oxide catalysts

Studies of the deamination of tert-, sec- and n-butylamines on several silicate and phosphate catalysts at 543–704 K have revealed that the reaction proceeds only with the participation of protonic cneters, its rate is independent of the strength of acidic centers and affected only by the amine structure. Butylammonium ion conversion is suggested to be the rate-determining step.

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-, - - 543–703 . , . , . , .