Pulse-chromatographic determination of molybdenum surface by oxygen adsorption in Co?Mo catalysts

A pulse-chromatographic method has been developed for the estimation of molybdenum surface by selective adsorption of oxygen at –78°C in cobalt-molybdenum-alumina catalysts. The surface concentrations of molybdenum in a series of catalysts of different compositions were compared with the activities for cyclohexene hydrogenation and for thiophene hydrogenolysis.

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- –78°C -- . - .

     

Free radical additions to the C=O bond of formaldehyde

The reactions between formaldehyde and n-propyl radicals were studied at 333 and 363 K. Addition to the C=O bond was found to be several times faster than abstraction of the formyl hydrogen atom. With a TST estimate of log(A/dm³ mol^–1 s^–1)=7.9±0.5, 28.0±2.1 kJ mol^–1 was obtained for the activation energy of the addition reaction.

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- 333 363 . C=O . 28.0±2.1 ^–1 , lg(A/ ^{–1 –1})=7.9±0.5 .

     

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.

     

Conversion of pentane to isopentane and isopentane to isobutane catalyzed by a solid superacid in the vapor phase /1/

The title reactions were studied with a solid superacid, which was prepared by exposing Zr(OH)₄ to 1 N H₂SO₄, followed by calcination at 650°C in air. Pentane and isopentane were converted into isopentane and isobutane, respectively, the selectivities being 84% under short contact conditions at 80°C.

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, - Zr(OH)₄ 1 N- H₂SO₄ 650°C . , , 84% 80°C.

     

Influence of neodymium content on the catalytic properties of zeolite NDHNaY

The influence of neodymium content on the catalytic properties of a HNaY zeolite was investigated using the cracking of n-heptane as model reaction. Neodymium zeolites were found to be more active for cracking and hydrogen transfer reactions than zeolites containing lanthanum, cerium or praseodymium.

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HnaY . , , , .

     

Calculation of the mass transfer coefficient with a chemical reaction in a gas-liquid system

A solution of the problem of mass transfer in a turbulent boundary layer has been obtained with a first-order chemical reaction occurring in the liquid phase. The dependence of the enhancement factor for absorption and of the mass transfer coefficient on the model parameters can be used for building up a hierarchic model of the gas-liquid reactor.

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Reasons for different activities of various type catalysts in reactions of oxidation of inorganic substances

The dual role of catalysts in the interaction between an inorganic molecule AB and adsorbed oxygen ZO, as an electron donor (in the oxidative addition of AB) and as an electron acceptor (in subsequent ZO reduction), permits to interpret the orders of activities of various optimal catalysts and their dependence on the AB structure.

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AB ZO — ( AB) ( ZO). AB.

     

Calibration of tube type dilatometers

The general method of calibrating tube type dilatometers is discussed in this report. For the most accurate results, calibration standards of known thermal expansion must be used. For less accurate results, the average thermal expansion for the tube material reported in the literature, or supplied by the tube manufacturer can be used. Accuracies of the order of ±1% can be attained by calibrating with a standard and ±4% by using average values for the tube material.Secondary calibration standards are available from the U.S. Bureau of Standards. Copper and platinum standards are recommended by ASTM. For extremely high temperature, tungsten is about the best standard.

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Zusammenfassung Die allgemeine Methode der Eichung von Rohrdilatometern wird erörtert. Um genaue Ergebnisse zu erzielen müssen Eichstandards bekannter thermischer Ausdehnung verwendet werden Für weniger genaue Ergebnisse können Literaturangaben bezüglich der durchschnittlichen thermischen Ausdehnung des Rohrmaterials, oder die von der Herstellerfirma der Rohre angegebenen Korrekturwerte verwendet werden. Genauigkeiten der Grössenordnung von ±1% können bei der Eichung mittels Standards und ±4% unter Verwendung von Durchschnittsdaten des Rohrmaterials erzielt werden.Sekundäre Eichstandards können von dem U. S. Bureau of Standards bezogen werden. Kupfer- und Platinstandards werden von ASTM empfohlen. Für extrem hohe Temperaturen wird Wolfram als bestes Standardmaterial empfohlen.

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Résumé La méthode générale d'étalonnage des dilatomètres à tige est discutée. Les résultats les plus exacts sont obtenus par l'emploi d'étalons dont le coefficient de dilatation est connu. La valeur moyenne de la dilatation communiquée par la littérature ou fournie par le fabricant de tige peut aussi être utilisée mais les résultats sont moins exacts. Une exactitude de l'ordre de ±1% peut être atteinte en réalisant l'étalonnage avec un étalon et de ±4% en prenant les valeurs moyennes du matériau.Des étalons secondaires sont disponibles auprès de l'U. S. National Bureau of Standards. Le cuivre et le platine sont recommandés par l'ASTM. Aux températures très élevées, le tungstène est à peu près le meilleur étalon.

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** . ** . ** , . ** ± 1% +4% — . . ASTM. .

     

Spectroscopic studies of the state of Cu2+ ions in Cu?Zn?Al oxide catalysts

ESR and electronic spectroscopy have reveled that in low-temperature ZnO the copper ions form Cu–O–Cu type cluster structures with highly covalent bonds and strong exchange interaction between the ions. The nearer environment of the Cu²⁺ ions is an octahedron with distortion towards square planar coordination.

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, ZnO Cu–O–Cu . Cu²⁺- , .

     

Stability and catalytic activity of various cobalt (II)-cyanide complexes in water-monoethanolamine solutions

Stability constants of mono-, di-, tri-, tetra- and pentacyanocobaltate in water-monoethanolamine solution have been calculated. Concentration distributions of these complexes depending on the cyanide to cobalt ratio and rate constants for their isotope exchange in mixed water-monoethanolamine solutions have been determined.

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-, -, -, - - . -- .

     

Modelling of self-oscillations in the combustion of n-heptane-isooctane mixtures

A mathematical model has been constructed to describe the self-oscillation regime of the cool-flame combustion of an n-heptane-isooctane mixture. The character of the dependence of the amplitude and oscillation period on the temperature and mixture composition is in a qualitative agreement with the similar experimental data.

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, --. .

     

Kinetic conversion of complex hydrocarbon mixtures in reforming on platinum/alumina catalysts

General forms of the kinetic equations for the conversion of various hydrocarbons in reforming of multicomponent gasoline fractions on platinum/alumina catalysts have been confirmed experimentally by using a gradientless method.

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Formation of alkyl peroxides in oxidation of alkanes by H2O2 catalyzed by transition metal complexes

Some reactions between alkanes and H₂O₂ in the presence of transition metal compounds, e.g. Cr(VI), V(V), Mn(III), Pd(II), Fe(II), yield alkyl hydroperoxides as main products.

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H₂O₂ , , Cr(VI), V(V), Mn(III), Pd(II), Fe(II), .

     

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 . , . , , .

     

Error analysis of surface area determinations by the chromatographic technique

The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.

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Thermal analysis of mercury(I) sulfate and mercury(II) sulfate

The thermal decomposition of mercury(I) and (II) sulfates has been investigated by thermogravimetry. The solid-state decomposition products have been characterized by infrared and Raman spectroscopy, mass spectrometry and an X-ray diffraction method. It is concluded that mercury(I) sulfate decomposes in two steps, initially forming a mixture of metallic mercury and mercury(II) sulfate — the latter subsequently decomposes without forming a stable intermediate. The stoichiometry of disproportionation of mercury(I) sulfate and the thermal stability range of mercury(I) and mercury(II) sulfates have been established.

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Zusammenfassung Die thermische Zersetzung von Quecksilber(I) und (II)-sulfaten wurde durch Thermogravimetrie untersucht. Die Festphasen-Zersetzungsprodukte wurden durch Infrarot- und Ramanspektroskopie, Massenspektrometrie und Röntgendiffraktion charakterisiert. Es wurde gefolgert, dass Quecksilber(I)sulfat in zwei Stufen zersetzt wird, unter anfänglicher Bildung eines Gemisches von metallischem Quecksilber und Quecksilber(II)-sulfat, welches in der Folge ohne Bildung eines stabilen Zwischenproduktes zersetzt wird. Die Stöchiometrie der Disproportionierung des Quecksilber(I)sulfats und der Bereich der Thermostabilität der Quecksilber(I) und Quecksilber(II)sulfate wurden ermittelt.

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Résumé La décomposition thermique des sulfates de mercure(I) et de mercure(II) a été suivie par TG. On a caractérisé les produits de la décomposition en phase solide par spectroscopies infrarouge et Raman, spectrométrie de masse et diffraction des rayons X. On en a conclu que le sulfate de mercure(I) se décompose en deux étapes, formant initialement un mélange de mercure métallique et de sulfate de mercure(II), ce dernier se décomposant ensuite sans formation d'un intermédiaire stable. Les proportions stoechiométriques de la dismutation du sulfate de mercure(I) et de l'intervalle de stabilité thermique des sulfates de mercure(I) et de mercure(II) ont été établis.

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

     

Adsorbed oxygen species formed by reaction with N2O on CaO

A considerable amount of adsorbed oxygen species is formed by the reaction of N₂O on CaO. It is suggested that these adsorbed species were practically held on 5-coordinated sites.

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- N₂O CaO. , 5-- .

     

TPD studies of benzene adsorption over vanadium-molybdenum oxide catalysts

Benzene is shown to be adsorbed on the surface of a V₂O₅-MoO₃ catalyst in two forms. The activation energies of benzene desorption for its first and second forms are 50 and 134 kJ/mol, respectively, in the latter case the adsorption proceeding with dissociation.

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, - . 50 / –134 /, .

     

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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