Effect of rhenium and chlorine on catalytic activity of L-zeolite Pt-catalysts

Interaction of components of L-zeolite Pt-Re catalyst and their effect on the dehydrocyclization of n-hexane has been examined.

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- L n -.

     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields

The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation to-Fe₂O₃ was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe₃O₄ and FeO at the expense of Fe₂O₃ is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

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Zusammenfassung Der Einfluß eines elektrischen Feldes auf die thermische Dehydratisierung des amorphen hydratisierten Eisen(III)oxids in oxidierenden, inerten und reduzierenden Atmosphären wurde durch Röntgendiffraktometrie untersucht. In oxidierenden und inerten Atmosphären wurde die Umwandlung zu -Fe₂O₃ durch elektrische Felder gefördert, besonders an der negativen Elektrode. Die Form der Kristallite des Produkts war ebenfalls an der negativen Elektrode am größten. Beide Ergebnisse werden durch die Proteinwanderung zur negativen Elektrode erklärt, wo diese Wasser bilden, das für die kristalline Phase als Keimbildner fungiert. In reduzierenden Atmosphären wird die Bildung von Fe₃O₄ und FeO auf Kosten von Fe₂O₃ durch elektrische Felder besonders an der negativen Elektrode erleichtert. Mögliche Reaktionsmechanismen werden erörtert und die Rolle der Protonen bei der Stabilisierung defekt-spineller Zwischenstufen und Produkte besprochen.

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Résumé L'effet d'un champ électrique sur la déshydratation thermique de l'oxyde de fer(III) hydraté amorphe a été étudié par diffractométrie des rayons X, dans des atmosphères oxydante, inerte et réductrice. En atmosphères oxydante et inerte, le champ électrique facilite la transformation en -Fe₂O₃, en particulier à l'électrode négative. La taille des cristaux formés est également plus élevée à l'électrode négative où il se forme de l'eau qui agit comme agent de nucléation de la phase cristalline. En atmosphère réductrice, le champ électrique facilite la formation de Fe₃O₄ et FeO, aux dépens de Fe₂O₃, en particulier à l'électrode négative. On considère les mécanismes de réaction possibles et on discute le rôle des protons sur la stabilisation des produits et des intermédiaires défauts-spinelles.

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- (III) , . -Fe₂O₃ , , . , , . Fe₃O₄ FeO Fe₂O₃ . , .

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The author is indebted to P. J. Melling for assistance with the measurements in H₂/N₂ atmospheres.     

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

     

Effect of electronic interaction between metal and support: How the nature of Ru/Al2O3 is modified

It is a well known fact that when supported on different supports, a transition metal may show different catalytic behavior. In some cases it is claimed that the differences in the acidity of supports are due to this phenomenon. In this work, by adding increasing amounts of MgO to Al₂O₃, the number of acid sites and hence the acidity of Al₂O₃ were monotonically decreased. The behavior of Ru supported on these mixed supports was investigated with IR, and it is concluded that the interaction between metal and acid sites on the surface is the most important factor for the changing properties.

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, , . . Al₂O₃ MgO Al₂O₃. Ru -, , -.

     

Modelling of quantitative DTA equipment I. Electric analog approach

For an electric model, relationships have been established as a function of the DTA baseline shift, the intensity of the signal, the slope of the leading edge, the heating rate, the thermal resistance of the heating disc built into the DTA apparatus, the contact resistance between the disc and the sample holders, and the heat resistance between the two measuring sites. Some of the relationships obtained supported knowledge acquired earlier by other approaches, and some furnished new information. The limits of use of this simple model are indicated.

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Zusammenfassung Unter Anwendung eines elektrischen Modells wurden Zusammenhänge als Funktion der Verschiebung der Basislinie der DTA, der Signalintensität, der Steile der Leitkante, der Aufheizgeschwindigkeit, des Wärmewiderstandes der in das DTA-Gerät eingebauten Heizscheibe, des Kontaktwiderstandes, zwischen Scheibe und Probenbehälter und des Wärmewiderstandes zwischen den beiden Meßstellen ermittelt. Ein Teil der erhaltenen Zusammenhänge bestätigte von anderen Annäherungen her bereits vorliegende Kenntnisse, ein anderer Teil lieferte neue Informationen. Auf die Grenzen und der Nutzen dieses einfachen Modells wurden hingewiesen.

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Résumé A l'aide d'un modèle électrique, on a établi des relations décrivant l'influence de la dérive de la ligne de base ATD, de l'intensité du signal, de la pente du bord du pic, de la vitesse de chauffage, de la résistance thermique du disque de chauffage incorporé dans l'appareil ATD, de la résistance de contact entre le disque et les porte-échantillons et enfin, de la résistance thermique entre les deux points de mesure. Une partie des relations obtenues confirme les connaissances déjà acquises par d'autres approches, l'autre partie fournit des renseignements nouveaux. Les limites d'utilisation de ce modèle simple sont indiquées.

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, , , , , , , . , — . .

     

Catalytic activity of tantalum hydride in parahydrogen conversion

The kinetics of parahydrogen conversion were studied on tantalum hydride at a hydrogen pressure of 2 Torr, in the temperature range 20–100 °C. For samples with high hydrogen content (H/Ta>0.7) the Arrhenius plot shows a distinct break at 52 °C near to the order-disorder transition temperature. For the ordered -Ta hydride phase the activation energy and preexponential factor are lower than those for the disordered phase of the Ta-H system.

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- 2 20–100°C. (H/Ta>0,7) 52°C -. - Ta- - Ta-H.

     

Application of emissionless infrared diffuse reflectance spectrometry for following reactions of adsorbed alcohols on an alumina catalyst

IR spectra of adsorbed alcohols on alumina were measured under the reaction conditions at elevated temperatures. The transient response of IR absorption intensity indicates that alkoxides are reactive adsorbed species but carboxylates are not. The rate constants of surface reactions were calculated from the transient response.

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, . , , , —, .

     

Molybdenum hexacarbonyl catalyzed photooxygenation of cyclohexane by air dioxygen in acetonitrile solution

ESR and XPS investigations on Cu/–Al₂O₃ catalysts with various amounts of Cu loading are reported. Experimental data are related to the surface structure and dispersed state of catalysts. The results show that ESR can be used as a means of charaterizing monolayer dispersed state for paramagnetic supported catalysts.

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Cu/–Al₂O₃ . . .

     

Effect of surfactants on the cleavage of the N?O bond in O-(2,4-dinitrophenyl)-cyclohexanone oxime

Kinetics of cleavage of N–O bond in O-(2,4-dinitrophenyl)-cyclohexanone oxime with hydroxide ions both in the presence and absence of surfactants has been studied. The reaction is accelerated by cationic micelles, slightly by non-ionic micelles and there is no effect of anionic micelles. A plot of the rate constant vs. [surfactant] shows a maximum corresponding to the CMC of surfactant.

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NO O-(2,4-) - , - (). , , - . , .

     

Experimental study of particle-to-liquid mass transfer in two-phase fixed and fluidized beds

Primary experimental results for local particle-to-liquid mass transfer in two-phase fixed and fluidized beds and in free flows are reported. A hypothesis on the mechanism of the effect of turbulent pulsations is suggested.

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, . .

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Catalytic properties of nickel phosphates. Isomerization of butenes

The effect of calcination temperature on the catalytic properties of nickel phosphate has been studied using the isomerization of butene-1 as a test reaction. A simple relationship was found between the catalyst activity in isomerization and the hydroxy content of the catalyst surface. Interrelations between the activity of the catalyst and its structure are discussed.

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, -1 . . .

     

Acetylacetonate of indium: Structure and reactivity with 1,3-dienes

The reaction of isoprene and 2,3-dimethyl-1,3-butadiene with indium tris-acetylacetonate, afforded C- and O-al-kylation products together with an oligomeric mass. A mechanism of diene transformation is proposed in which -diene-metal species could be involved.

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2,3--1,3- – - . , --.

     

Thermal research of montmorillonite synthetized from the oxides SiO2-Al2O3-MgO-CaO

The thermal behaviour of synthetic montmorillonite of relatively simple chemical composition has been studied and interpreted. Montmorillonite was prepared by hydrothermal synthesis at 300° and 8.8 MPa during 165 hours. With the methods of DTA, DTG, TG, X-ray diffraction analysis, infrared spectroscopy and electron microscopy it was proved that the synthetic montmorillonite is a monomineral sample and no differences from natural montmorillonite were observed.

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Zusammenfassung Das thermische Verhalten synthetischer Montmorillonite verhältnismässig einfacher chemischer Zusammensetzung wurde untersucht und gedeutet. Montmorillonit wurde durch hydrothermische Synthese bei 300°C und 8.8 MPa in 165 Stunden hergestellt. Durch die Methoden der DTA, DTG, TG, Röntgendiffraktionsanalyse, Infrarotspektroskopie und Elektronenmikroskopie wurde erwiesen, daß synthetische Montmorillonit eine monominerale Probe ist und keine Abweichungen von natürlichem Montmorillonit beobachtet werden konnten.

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. 165 300° 8.8 . , , , , , .

     

A differential scanning calorimetric study on phase transformations of HgI2

A quantitative study of the different factors that influence the- transformation of mercuric iodide was carried out with differential scanning calorimetry. The transformation temperature and the peak width during the heating of the material were followed. An attempt was made to explain the experimental results.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde der Einfluss verschiedener Faktoren auf die- Umwandlung von Quecksilberjodid quantitativ untersucht. Dabei wurde die Umwandlungstemperatur und die Signalbreite beim Erhitzen der Substanz beobachtet. Es wurde ein Versuch unternommen, die experimentellen Ergebnisse zu erklären.

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, - . . .

     

n-Hexane hydrogenolysis on bimetallic platinum-palladium catalysts

Alumina supported platinum, palladium and bimetallic platinum-palladium catalysts have been investigated in the hydrogenolysis of n-hexane. Results show that, compared with platinum, the activity of bimetallic catalysts is several times lower while the selectivity to hydrogenolytic products increases from 72 to 100%.

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, , , -. , , , 72 100%.

     

Magnetic susceptibility measurement with a Dupont's thermogravimetric analyser

The adaptation of a Du Pont Thermogravimetric Analyser for the measurement of magnetic susceptibility as a function of temperature in the range – 80 °C to 300 °C is described.

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Zusammenfassung Die Adaptation des Du Pont's Thermogravimetric Analyzer zur Messung der magnetischen Suszeptibilität in Abhängigkeit von der Temperatur im Bereich von – 80° bis 300 °C wird mitgeteilt.

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–80°–300 °.

     

Br?nsted sites in H-forms of faujasites obtained from ammonium and guanidine forms

The infrared spectra of H-forms of Y zeolite made from the guanidine and ammonium forms were compared. The Brönsted acid sites have been characterized by adsorption of pyridine. Good correlation between the concentration of Brönsted acid sites and the catalytic activity of the samples has been found. It was concluded that guanidine cations limited localization of OH groups on the surface of the supercages.

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, . , . . , OH .

     

Hydrogen effects on the catalytic activity and selectivity of the zeolites H?NaY and PtH?NaY

The decomposition of methylcyclohexane on H–NaY and PtH–NaY zeolites has been studied. It has been found that the presence or abscence of H₂ affects not only the activity of these catalysts but also their selectivity to dehydrogenation and isomerization products.

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H–NaY PtH–NaY. , H₂ , .

     

Catalytic properties of sodium-containing silica gel in n-heptane decomposition

n-Heptane decomposition reactions on silica catalysts containing various amounts of sodium ions were studied. Ethylene, methane and propylene as well as unbrached -olefins were the main reaction products. The comparison of the experimental and theoretical results suggests a free-radical reaction mechanism.

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- , . , , -. - .