Supercooling phenomena in the binary systems: Acetamide-electrolytes

This paper presents a final discussion on studies of solutions of electrolytes in molten acetamide. These studies deal with cryoscopic and ultrasonic (by shear waves) techniques and reveal the complexity of the behaviour of these systems due to strong ion-solvent interactions.

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Zusammenfassung Die über Lösungen von Elektrolyten in geschmolzenem Acetamid ausgeführten Untersuchungen werden diskutiert. Diese Untersuchungen erstrecken sich auf kryoskopische und Ultraschall-Methoden und vermitteln ein Bild von der durch starke Ionen-Lösungsmittel-Wechselwirkungen bedingten Komplexität des Verhaltens dieser Systeme.

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Thanks are due to CNR and MPI (Rome) for financial support, and to R. Borgarucci for technical assistance.     

Mechanism of formation of applicable linear boron-nitrogen polymers

This paper contains a literature review on the mechanism of formation of applicable linear boron-nitrogen polymers.

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Zusammenfassung Dieser Artikel enthält eine Literaturübersicht über den Bildungsmechanimus anwendbarer Bor-Stickstoffpolymerer.

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Résumé Cet article contient une revue des publications sur le mécanisme de formation des polymères de bore-azote.

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On the dioximine complexes of transition metals

Twelve new complexes NH₄[Co(DH)₂(SO₃)(amine)]·t H₂O (DH ₂=dimethylglyoxime) have been synthesized and characterized. Their i.r. spectra show the SO₃ to be co-ordinated to the Co atom through the S atom. The thermal decompositions of a series of derivatives of this type have been investigated with a derivatograph. The first process is an endothermic dehydration reaction, occurring in a single stage or in two successive ones. The loss of the crystallization water is followed by another endothermic reaction, without a clear stoichiometry, which is referred to as deamination. At higher temperatures, exothermic pyrolysis processes occur. From the TG curves, kinetic parameters have been derived for the dehydration and deamination reactions.

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Zusammenfassung Zwölf neue Komplexe der allgemeinen Formel NH₄[Co(DH)₂(SO₃)(amin)]·t H₂O (DH=Dimethylglyoxim) wurden synthetisiert und charakterisiert. Die IR-Spektren zeigen, daß SO₃ über das S-Atom koordinativ an das Co-Atom gebunden ist. Die thermische Zersetzung einer Reihe von Derivaten dieses Typs wurde mittels eines Derivatographen untersucht. Der erste Prozeß ist die in einem einzigen oder in zwei aufeinander folgenden Schritten verlaufende endotherme Dehydratisierung. Auf die Abgabe des Kristallwassers folgt eine andere endotherme Reaktion unklarer Stöchiometrie, die als Deaminierung bezeichnet wird. Bei höheren Temperaturen verlaufen exotherme Pyrolyseprozesse. Aus den TG-Kurven wurden kinetische Parameter für die Dehydratisierung und die Deaminierung bestimmt.

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NH₄Co(DH)₂(SO₃)(a)]·tH₂O, DH ₂ — . , . . , . «». . .

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Self-oscillations in the cool-flame combustion of a model n-heptane-isooctane mixture

Self-oscillation found experimentally in the cool-flame combustion of a model n-heptane-i-octane mixture has been studied in dependence on the composition of the reaction mixture. Calculations based on the CSTR model are in qualitative agreement with experimental data.

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Catalytic properties of Ti?Mo oxide catalysts in propylene oxidation

Catalytic properties of Ti–Mo oxide catalysts are shown to be determined to a great extent by the Ti–Mo heteropoly acid anchored to the TiO₂ surface which is formed during the catalyst preparation.

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Adsorption characteristics of a Hungarian natural mordenite and its acid treated derivatives

A mordenite-containing rock from the Tokaj-mountains was investigated. The effect of the treatment with hydrochloric acid solutions of various molarity was established. From gas adsorption measurements, scanning electron microscopic investigations and measurements with a mercury porosimeter conclusions were drawn on the changes caused by acid treatment. Slight changes in the texture were found, but no damage in the crystal structure could be observed.

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Hydrogen profiling in thin films using coincident ERD

By using the coincident measurement, an ERD method has been established and used for hydrogen profiling in thin foils. In the present study, 6 MeV has been used as incident particle, the scattered and the recoiled proton from one collision were coincidentally detected at 150 (proton) and 173.9 (). This method has been used for hydrogen profiling of 5.6 m Mylar and 8.6 m aluminium foils. Because of the coincident measurement, the background is largely reduced, and its minimum detection limit is about 0.5% (atomic), lower than the conventional ERD method. The measured depth resolution in 5.6 m Mylar is 0.6 m. It is possible to use this method for hydrogen profiling in thin foils of several micron thickness.     

Influence of chemical composition of carbon catalysts on their adsorptive properties in catalytic oxidation of o-xylene

It has been established that o-xylene chemisorption on coals requires the presence of nucleophylic surface sites. Selectivity in o-xylene oxidation over carbon catalysts depends not only on their structure, but also on their surface functional groups.

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Characterization of coke by hydrogen and carbon analysis

Coke deposited on heterogeneous catalysts can be characterized by temperature programmed oxidation. The comparison between the amount of CO₂ produced and the amount of O₂ consumed gives the ratio H/C. For Pt/Al₂O₃ catalysts it has been shown that coke deposited on the metal is less dehydrogenated than coke deposited on the support.

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- . CO₂ O₂ H/C. , Pt/Al₂O₃ , .

     

Note on the kinetics of dehydrogenation of cyclohexane

Kinetic data available for Pt and Ni suggest doubts about the acceptance of the method applied by V.I. Anikeev et al. [1] as basis for Kinetic Laws for cyclohexane dehydrogenation on Pd/C catalysts.

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Pt Ni , . . . [1] Pd/C.

     

Kinetic analysis of the liquid-phase depolymerization of trioxane from programmed-temperature data

An experimental method for the determination of kinetic data for liquid-phase reactions under linear rise of temperature is explained for the depolymerization of trioxane. Integral kinetic analysis of the data is performed in order to determine the kinetic model and the kinetic parameters. Experiments have been carried out at different heating rates between 0.5 and 2 deg/min, leading to similar kinetic parameters. The obtained results are in agreement with the kinetic model and parameters obtained from isothermal kinetic analysis. The programmedtemperature method seems to be a useful tool for a quick determination of kinetic models, avoiding experimental work.

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Zusammenfassung Eine experimentelle Methode zur Bestimmung der kinetischen Daten von Reaktionen in flüssiger Phase bei linearer Temperaturerhöhung wird am Beispiel der Depolymerisation von Trioxan erklärt. Eine integrale kinetische Analyse der Daten wird ausgeführt, um das kinetische Modell und die kinetischen Parameter zu ermitteln. Bei unterschiedlicher Aufheizgeschwindigkeit zwischen 0,5 und 2 K/min ausgeführte Experimente ergaben ähnliche kinetische Parameter. Die erhaltenen Ergebnisse stimmen mit dem kinetischen Modell und den kinetischen Parametern, die durch isotherme kinetische Analyse erhalten wurden, überein. Die Temperaturprogrammierung scheint eine brauchbare, experimentelle Arbeit einsparende Methode zur schnellen Bestimmung des kinetischen Modells zu sein.

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. . , (0,5–2° .), . , . , .

     

Interaction of propylene with a V2O5/Al2O3 catalyst

IR-spectroscopic studies indicate that on the oxidized surface of V₂O₅/Al₂O₃ catalysts propylene interacts mainly with Brönsted acid centers to form an alcoholate type complex transforming into acetone. On the reduced surface propylene is stabilized as a -complex of V³⁺ and V⁴⁺ ions.

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- , V₂O₅/Al₂O₃ , . - V³⁺ V⁴⁺.

     

Vapor phase Beckmann rearrangement of cyclohexanone oxime over fluorinated alumina catalysts

The Beckmann rearrangement of cyclohexanone oxime to caprolactam has been studied in the vapor phase over fluorinated alumina catalysts containing 1 to 61 wt. % F. Addition of fluorine enchances the catalytic activity of Al₂O₃. Selectivity to caprolactam shows a maximum in the fluorine range 11–31%. It is likely that an optimum distribution of Lewis and Brönsted acidic sites on the catalyst surface is responsible for the high selectivity observed at intermediate fluorine contents. Addition of water to the gas phase causes a decrease in selectivity.

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, 1 61 . % . Al₂O₃. 11–31%. , , . .

     

Application of continuous and selective water detector for quantitative measurements

A standard method was developed for investigation of the adsorbed water in ionexchange resins. The previously-dried anion-exchange resins in Cl, SO₄ and HSO₄ form were investigated by simultaneous TG, DTG and DTA measurements (derivatograph), and the evolved gases were passed through the continuous and selective water detector system developed earlier.It was found that in the case of SO₄ and HSO₄-form resins two types of water binding (loosely and strongly-bound water) could be distinguished. The second step, the stronglybound water step, could not be observed in the DTG curves, because the release of the bound water and the decomposition of the fixed ionic group take place simultaneously. As the two types of water peaks strongly overlap, their quantitative evaluation was carried out by graphical analysis.

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Zusammenfassung Eine Standardmethode wurde zur Untersuchung des absorbierten Wassers in Ionenaustauscherharzen entwickelt. Die vorhergehend getrockneten Anionenaustauscherharze in Cl, SO₄ und HSO₄-Form wurden durch die Methode der simultanenTG, DTG und DTA-Messungen untersucht und die entwickelten Gase das durch früher entwickelte kontinuierliche und selektive Wasserdetektorsystem geleitet.Es wurde gefunden, daß in dem Falle der Harze der SO₄ und HSO₄-Form zwei Typen von Wasser (lose und stark gebundenes Wasser) unterschieden werden können. Die zweite Stufe, die sogenannte «Stark-gebundenes-Wasser»-Stufe konnte an den DTG-Kurven nicht beobachtet werden, da die Freisetzung des gebundenen Wassers und die Zersetzung der fixierten ionischen Gruppe simultan erfolgt. Da die zwei Typen der Wasser-Peaks stark überlappen, wurde ihre quantitative Auswertung under Anwendung einer graphischen Analysenmethode durchgeführt. Die auf äquivalentes Harz bezogenen Angaben in H₂O-Mol waren wie folgt: für Harz in der Cl-Form, 1.464, für die Harze in SO₄ und HSO₄-Form waren die Werte von lose und stark gebundenem Wasser 1.753 und 0.357, bzw. 2.094 und 0.451.

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Résumé On a mis au point une méthode type pour étudier l'eau adsorbée sur les résines échangeuses d'ions. On a étudié par TG, TGD et ATD simultanées les résines échangeuses d'anions sous la forme Cl, SO₄ et HSO₄ préalablement séchées et on a fait passer les gaz dégagés dans le système détecteur d'eau continu et sélectif mis au point précédemment.Dans le cas des résines sous la forme SO₄ et HSO₄, on a trouvé que deux types d'eau (faiblement et fortement liée) pouvai ent être distingués. La deuxième étape, dénommée étape de l'eau fortement liée, ne peut être observée sur les courbes TGD, car le dégagement de l'eau liée et la décomposition du groupe ionique fixé ont lieu simultanément. Comme les deux types de pics dus à l'eau se recouvrent fortement, on a effectué leur évaluation quantitative à l'aide d'une méthode d'analyse graphique. Les données trouvées, exprimées en moles d'H₂O sur résine équivalente, sont les suivantes: pour la résine sous forme Cl 1.464, pour les résines sous formes SO₄ et HSO₄ les types d'eaux faiblement et fortement liées donnent respectivement 1.753, 0.357 et 2.094, 0.451.

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, . Cl, SO₄ HSO₄ , , , , . , SO₄ HSO₄ - , : . , , , . , . , , : Cl-- 1,464, SO₄ HSO₄-- , ,- 1.753; 0.357 2.094; 0.451.

     

Effect of basic additives on properties of V?Sb?Bi oxide catalysts for ammoxidation of xylenes

The introduction of K₂O and Bao additives into supported V–Sb–Bi oxide catalysts enhances their activity in ammoxidation of xylenes. Bond energy and inhomogeneity character of surface oxygen, oxidation states and relative contents of metal cations remain practically unchanged, whereas the concentration of basic sites significantly increases.

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V–Sb–Bi . , , .

     

Role of acid centers of Sn/Mo oxide catalyst in propylene conversion to acetone

Infrared spectroscopic studies of the nature of catalyst centers indicate the presence of Brönsted and Lewis acid centers on the surface. Propylene conversion to acetone proceeds via proton transfer from the surface to propylene with the formation of a (CH₃)₂–C(H)–O–Me type compound, and its subsequent dehydration.

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- , . (CH₃)₂–C(H)–OMe .

     

Hydrogen pressure dependence of the reaction of neopentane with hydrogen over Pd/SiO2 and Pt/SiO2 catalysts

H₂ pressure influences in different ways the reaction rates of neopentane conversion over Pd/SiO₂ and Pt/SiO₂ catalysts. It seems that on Pt/SiO₂ both isomerization and hydrogenolysis involve a common surface intermediate (probably an adalkyl), whereas on Pd/SiO₂ the hydrogenolysis goes via more dehydrogenated species than those involved in isomerization.

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H₂ Pt/SiO₂ Pd/SiO₂. , Pt/SiO₂ (, ), Pd/SiO₂ , .

     

Reduction of higher polymethylbenzenes by the rapid cation exchange of H-mordenite in the conversion of methanol to hydrocarbons

The product distribution in methanol conversion on mordenite is changed by potassium ion exchange depending on the method of ion exchange. The rapid exchange method was the most effective to suppress the formation of higher polymethylbenzenes.

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A Note on Distance Matrices Yielding Elementary Landscapes for the TSP

Symmetric and antisymmetric distance matrices in the single agent traveling salesman problem (TSP) are not the only distance matrices to generate elementary landscapes for swap and 2-opt neighborhoods.