Propylene oxidation over tin-molybdenum oxide catalysts

The influence of preparation of tin-molybdenum catalysts on their phase composition and activity has been elucidated. The mutual dissolution of Sn and Mo oxides leads to a considerable increase in their activities and selectivities in the partial oxidation of propylene to acetone.

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. , .

     

Coadsorption of ethylene and oxygen on an iridium surface

It is established that the hydrocarbon coverage (0<1) formed at T<400 K on the Ir surface is oxidized upon oxygen exposures to CO and H₂O by an adsorption mechanism. Complete oxidation to CO₂ and H₂O is achieved at T350 K after C₂H₄ exposures of the oxygen coverage.

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, (<1), T<400 K Ir, CO H₂O . CO₂ H₂O T350 K C₂H₄ .

     

Coke deposition on naphtha reforming catalysts: I. Influence of the hydrocarbon feed

During hydrocarbons reactions over Pt/Al₂O₃ the catalyst is covered by coke. It is accepted that coke formation occurs on metal and acid sites. During normal heptane and methylcyclopentane reforming it was found that the nature and the rate of coke deposited on the catalyst surface was not same, depending on the structure of the hydrocarbon feed.

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Pt/Al₂O₃ . , . , - .

     

A rapid method of determination of specific surface areas

An apparatus and a method for the rapid determination of specific surface areas are described. The method is based on low temperature adsorption of nitrogen from the air and requires determination of the adsorbed gas at two relative pressures. The accuracy of the method, as compared with the BET technique, is ±9% for the adsorbents studied.

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. . , BET, ±9% .

     

Effect of ligands on the hydrogenation selectivity in the presence of rhenium catalysts

It has been established that the catalytic activity of rhenium oxohalide complexes with phosphorus- or sulfur-containing ligands in hydroganation of C₆–C₁₀ olefins, nitrobenzene and p-nitrotoluene is primarily determined by the original ligand to rhenium ion bond. Chain length of olefins does not affect their hydrogenation rate.

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- C₆–C₁₀, - - . .

     

Estimation of kinetic parameters in oxidative dehydrogenation of n-butenes over SnO2?Sb2O4 catalysts

Kinetic curves measured in the oxidation of n-butenes over a SnSb=31 mixed oxide catalyst were fitted by the kinetic model put forward in a previous paper. The goodness of fitting shows that the kinetic behavior of this complex reaction system can be described by a mechanism involving acidic and redox sites on the catalyst surface.

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- SnSb=31 , . , , - .

     

Monohydrates of strontium and barium hydroxide

The monohydrates of strontium and barium hydroxide have been prepared by decomposition, under vacuum, of the corresponding octahydrates. X-ray powder data for both compounds are reported, together with that for anhydrous strontium hydroxide; the latter is included in order to clarify an apparent anomaly in the literature.

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Zusammenfassung Es wurden die Monohydrate von Strontium und Bariumhydroxid im Vakuum aus den entsprechenden Octahydraten hergestellt. Röntgenographische Daten für beide Verbindungen sowie für wasserfreies Strontiumhydroxid wurden gegeben; für Letzteres, um gewisse Anom alien in der Literatur zu klären.

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Résumé Préparation des hydroxydes de strontium et de baryum monohydratés par décomposition dans le vide des octohydrates correspondants. Etude par rayons X de ces composés ainsi que de l'hydroxyde de strontium anhydre, dans le but, pour ce dernier, d'élucider certaines anomalies de la littérature.

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, . , ; , .

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The authors wish to thank Mr. A. Miller for taking the X-ray powder photographs.     

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 . , , , , , .

     

Ag(I) solid solutions in zirconium dihydrogen phosphate. Thermal behaviour and phase changes

The thermal and redox behaviours of some Ag-low-converted zirconium phosphates have been investigated by thermoanalytical and X-ray methods: the conditions for obtaining Ag solid solutions in phases are reported.

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Zusammenfassung Das thermische und Redoxverhalten einiger Zirkoniumphosphate niedriger Ag-Konversion wurde durch thermoanalytische und Röntgenmethoden studiert; über die Bedingungen zum Erhalten von Ag-Festphasenlösungen in HH-Phasen wird berichtet

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Résumé On a étudié le comportement thermique et oxydo-réducteur de quelques phosphates de zirconium faiblement converti par Ag, en se servant des méthodes d'analyse thermique et des rayons X: on communique les conditions permettant d'obtenir des solutions solides d'Ag dans les phases .

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- Ag- . HH.

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Paper in part presented at the 6th ICTA, in Bayreuth (Germany), July 1980.

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We thank Dr. M. A. Massucci, of our Institute, for helpful discussions and suggestions.     

The use of calorimetric data for estimation of the point defect concentration in solids

Calorimetric methods which allow estimation of the point defect concentration in solids are reviewed. Special attention is paid to the calculation of defect parameters based on the analysis of excessive heat capacity, and to correlations between the thermodynamic parameters of melting and the energetic parameters of point defect formation. The applicability of the thermodynamic approach to the study of intrinsic disorder in solids is demonstrated.

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Zusammenfassung Kalorimetrische Methoden zur Abschätzung der Konzentration von Punktdefekten in Festkörpern werden zusammengestellt. Aufmerksamkeit verdienen die Berechnung von Defektparametern aus einer Untersuchung der Exzeß-Wärmekapazität und Korrelationen zwischen thermodynamischen Parametern des Schmelzens und energetischen Parametern der Punktdefektbildung. Die Anwendbarkeit eines thermodynamischen Ansatzes zur Untersuchung der Eigenfehlordnung in Festkörpern wird demonstriert.

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. , . .

     

Catalytic activity of CaO?CaF2 binary systems in the Claus reaction

Activity of CaO–CaF₂ catalysts in the Claus reaction has been studied as a function of catalyst composition and of the time of catalyst operation in the reaction. Opposite effects of low and high fluoride content on the Claus activity have been found. A new type of reducing centers is suggested to be responsible for the increase in the activity observed in the case of fluorine-rich catalysts.

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CaO–CaF₂ . , . , , .

     

X-ray diffraction study of palladium catalysts. Influence of the preparation method on the dispersity of metallic phase

Influence of different methods of catalyst preparation on their phase composition and the crystallite dispersity has been demonstrated.

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.

     

Phase coexistence and complicated dynamics in open catalytic systems

The simplest catalytic system with surface phase transitions in CSTR has been studied. It is shown that the possible number of steady states is directly determined by that of phase coexistence regions on the phase diagram of the adsorption layer.

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. , , .

     

Ethylene hydroformylation over a nafion-supported rhodium catalyst

Ethylene hydroformylation over a Nafion-supported rhodium catalyst has been studied under atmospheric pressure in the temperature range of 100–135 °C, using the transient response method.

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, , 100–135°C, .

     

Studies on the catalytic decomposition of nitrous oxide on lanthanum cobaltate

The catalyst LaCo₂O₄ crystallizing in CaFe₂O₄ type structure has been synthesized and its physicochemical characteristics evaluated. The kinetics of decomposition of nitrous oxide, studied in the temperature range 400–460°C at 50 and 200 Torr of the reactant gas, was found to obey an expression corresponding to strong inhibition by product oxygen. A reaction mechanism has been proposed based on the existence of Co²⁺–O^2––Co³⁺ clusters on the surface.

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LaCo₂O₄, CaFe₂O₄, - -. , - 400–460°C 50 200 Qu , -, . Co²⁺–O^2––Co³⁺ .

     

Reactivity of coordinated O2? ion-radicals in the oxidation of organic compounds

By the flow ESR method, the rates of the reaction of the radical complex Ti(IV)(O ₂ ^– ) with some aromatic compounds in aqueous solution have been measured. An elementary step of these reactions seems to be one-electron oxidation with the formation of a substrate cation-radical.

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- Ti(IV)(O ₂ ^– ) . - -.

     

On the role of symmetric hydrogen bonds of increased strength in isotope exchange of dihydrogen with water-alkaline solutions

The chemical effect of a hydrogen bond of increased strength responsible for the existence of H₃O ₂ ^– and determining mainly the E_a of the catalytic isotope exchange (IE) of hydrogen with water-alkaline solutions (WAS) is discussed. Assuming that the H₃O ₂ ^– associates are also effective in the case of water-alkaline melts (WAM), experimental kinetic evidence in favor of the suggested treatment of the IE mechanism is considered.

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, H₃O ₂ ^– E_a () (). H₃O ₂ ^– - () .

     

Thermodesorption of mixtures. Hydrocarbon, hydrogen sulfide and oxygen from the surface of molybdenum sulfide

The presence of hydrogen sulfide and oxygen in mixtures increases the number of sites for dissociative desorption on the surface of MoS₂ as compared with the adsorption of individual hydrocarbons. This phenomenon can be explained by a change in the coordination state of the active sites (molybdenum ions) upon the adsorption of the gases mentioned.

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, MoS₂ . .

     

Thermal activation of Al2O3 supported MoO3 and WO3 metathesis catalysts

Alumina-supported MoO₃ and WO₃ catalysts were activated for the metathesis of propene by thermal treatment in Ar. Temperatures up to 1140 K are required for catalysts with low metal contents. These exhibit the highest specific activities though they are known to be highly resistant to reduction. It is proposed that the active sites are formed from Mo(VI) and W(VI) species under the conditions employed.

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MoO₃ WO₃, Al₂O₃, . 1140 . , , . , , Mo W.

     

Determination thermogravimetrique des energies d'activation I

Résumé Après une revue critique de divers procédés d'obtention thermogravimétrique des énergies d'activation, on sélectionne certains d'entre eux en vue de les appliquer d'une part à la déshydratation thermique de divers borates et acides boriques, d'autre part à l'oxydation du nickel à température élevée. On compare les résultats qu'ils fournissent respectivement.

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After a critical survey of various methods available for the determination of activation energies by thermogravimetry, certain methods are applied to the thermal dehydration of various borates and boric acids and to the oxidation of nickel at high temperature. The results are compared.

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Zusammenfassung Nach einer kritischen Übersicht verschiedener Verfahren zur Bestimmung von Aktivierungsenergien mittels Thermogravimetrie werden einige Ausgewählte auf die thermische Dehydratierung verschiedener Borate und Borsäuren, so wie auf die Oxydation des Nickels bei erhöhter Temperatur angewendet. Die verschiedenen Ergebnisse wurden verglichen.

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