Active coke formation in oxydehydrogenation of ethylbenzene to styrene

In oxydehydrogenation of ethylbenzene to styrene catalytic active centers are created by coke formed during the reaction. Formation of active coke can be made evident by product analysis in the first minutes of operation and by analysis of the carbonaceous resisdues by temperature programmed oxidation (TPO) and EPR.

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. , , , .

     

Kinetics of EDTA-catalyzed oxidation of Indigo Carmine by vanadium(V)

The reaction is first order both in vanadium(V) and substrate and is markedly inhibited by H⁺ ions. Kinetic evidence for the formation of a 11 complex of vanadium(V) and EDTA is obtained. The stability constant of this complex and its thermodynamic parameters were evaluated. A suitable mechanism is proposed.

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(V), H⁺. 11 (V) . . .

     

X-ray and thermal studies of ferroelectric Dy2(MoO4)3

Dysprosium molybdate, Dy₂(MoO₄)₃, displays a ferroelectric phase transition at 145 °C. The X-ray and thermal (DTA, TG and DSC) properties of this compound have been studied. The X-ray study confirmed the ferroelectric phase in the orthorhombic space group Pba2. Thermal analysis demonstrated the existence of a ferroelectric and another phase transition in this compound.

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Zusammenfassung Dysprosiummolybdat, Dy₂(MoO₄)₃ (Abk.: DMO), ein Vertreter der Seltener-denmolybdatreihe zeigt bei 145 °C einen ferroelektrischen Phasenübergang. Röntgendiffraktion und thermische Eigenschaften (DTA, TG, DSC) der genannten Verbindung wurden untersucht. Auf Grund der Röntgendiffraktionsuntersuchung gehört die ferroelektrische Phase in die orthorhombische Raumgruppe Pba2. Mittels Thermoanalyse konnte bei dieser Verbindung die Existenz ferroelektrischer und anderer Phasenübergänge nachgewiesen werden.

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145 °C. (, ) . , Pba2. .

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The authors wish to thank Prof. A. Paul and Mr. R. Bhatnagar for their kind help in some of the experimental work. One of us (MR) gratefully acknowledges a Fellowship from DST, Government of India.     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. I. Influence of the addition of ZSM-5

The influence of ZSM-5 on the behavior of a Pt–Re/Al₂O₃ catalyst was studied in normal heptane reforming in order to compare activity, selectivity and life of Pt–Re/Al₂O₃ and a mixture of Pt–Re/Al₂O₃ and ZSM-5 catalysts. It is suggested that the presence of ZSM-5 results in less pronounced catalyst deactivation but not in a sufficient increase in aromatic selectivity.

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ZSM-5 Pt–Re/Al₂O₃ - , Pt–Re/Al₂O₃ ZSM-5. , ZSM-5 , , .

     

High activity of MgO catalyst prepared from magnesium oxalate for the hydrogenation of butadiene

High activity of magnesium oxide prepared by thermal decomposition of magnesium oxalate for the hydrogenation of 1,3-butadiene has been examined by XPS and IR, together with the isomerization of 1-butene. XPS spectra of MgO differed from those of two other MgO catalysts. With Ar etching, the binding energies of Mg2p and 01s shift, which is related to the surface basicity. Both basic and acidic sites are responsible for hydrogenation, but isomerization proceeds only on basic sites.

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, 1,3- 1-, . MgO ; Ar 2p 1s Mg, . , , , - .

     

Monolayer vanadia on titania systems from alkoxide precursors. Part I. Physicochemical properties

The physicochemical properties of V⁵⁺ ion monolayers supported on anatase, rutile, and anatase-rutile mixed carrier, using vanadyl triisobutoxide as the precursor have been investigated. The coordination and reducibility of surface vanadyl species were found to depend strongly on carrier material and its calcination temperature. The supported monolayers exhibited completely different reduction behavior than bulk V₂O₅. The rutile supported catalyst was the most resistant for reduction.

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- V⁵⁺, , -, - . . , V₂O₅. , .

     

Formation of oxalates and carbonates in the thermal decompositions of alkali metal formates

The influences of gaseous and solid reactants on the yields of oxalates and carbonates in the thermal decompositions of alkali metal formates have been studied. A mechanism of formation of these products is proposed, which explains the influences of basic and acidic species formed in the medium on the thermal decompositions of the alkali metal formates.

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Zusammenfassung Der einfluß von gasförmigen und festen Reaktanten auf die Ausbeute von oxalaten und Karbonaten bei der thermischen Zersetzung von Alkalimetallformiaten wurde untersucht. Es wurde ein Mechanismus für die Bildung dieser Produkte vorgeschlagen, der den Einfluß der während der thermischen Zersetzung von Alkalimetallformiaten entstehenden Basen und Säuren erklärt.

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, . , , .

     

Characterization of high-technology materials by emanation thermal analysis

The principles of the emanation thermal analysis, based on the measurement of inert gas release from solids, are given. Results of the computer modelling of inert gas release curves during heating of porous and dispersed samples are demonstrated.Examples of the characterization of high-tech ceramic materials and raw materials for their preparation by means of emanation thermal analysis are given, such as the evaluation of reactivity and sinterability of ceramics powders, quality testing of intermediate and final products of advanced technology materials (such as thoria, urania, ferrites, superconducting oxide ceramics, etc.).

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Zusammenfassung Es werden Grundlagen für die Emanationsthermoanalyse /ETA/ auf der Basis der Messung der Inertgasfreisetzung bei Feststoffen gegeben. Ergebnisse von computermodellierten Inertgasfreisetzungskurven bei Erhitzen von porösen und dispersen Proben werden angeführt.Weiterhin werden Beispiele für die mittels ETA durchgeführte Charakterisierung von Spitzentechnologiekeramikmaterialien und den Rohstoffen zu deren Herstellung gegeben: Auswertung von Reaktivität und Sinterbarkeit von Keramikpulver, Qualitätskontrolle der Zwischen- und Endprodukte aus modernen Rohstoffen /wie z. B. Thorerde, Uranerde, Ferrit, supraleitende Oxidkeramiken usw./.

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, , . . - , , - /, , , . /.

     

Quantitative thermal analysis V. Role of the flowing gas phase in the analysis of disperse materials

In the analysis of disperse materials, the thermophysical characteristics (rate, thermal conductivity, thermal capacity) of the gas flowing through the pores of the sample are of great importance in determinations of the heats of phase transformations. We have found that the peak areas corresponding to the phase transformations may either decrease or increase with increasing flow rate of the gas. The largest errors (as high as 15%) caused by gas flow in the pores of the disperse material occur when the thermal conductivities of both the solid material and the gas in which the analysis is performed are low. The experimentally derived relationship between the peak area, the flow rate and thermal conductivity of the gas, and the dispersity and thermal conductivity of the solid phase permits calculation of the possible error, and hence application of measures for its reduction.

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Zusammenfassung Bei der Analyse disperser Materialien sind die thermophysikalischen Kenndaten (Geschwindigkeit, Wärmeleitfähigkeit, Wärmekapazität) des durch die Poren der Probe strömenden Gases für die Bestimmung der Phasenübergangswärmen von großer Wichtigkeit. Wir haben festgestellt, daß die den Phasenübergängen zuzuschreibenden Peakflächen mit steigender Strömungsgeschwindigkeit des Gases entweder kleiner oder größer werden. Die größten durch die Gasströmung in den Poren verursachten Fehler (bis zu 15%) treten dann auf, wenn sowohl die Wärmeleitfähigkeit des Festkörpers als auch die des Gases, in dem die Analyse ausgeführt wird, niedrig sind. Die experimentell abgeleitete Beziehung zwischen der Bergfläche, der Strömungsgeschwindigkeit und Wärmeleitfähigkeit des Gases und der Dispersität und Wärmeleitfähigkeit der festen Phase erlaubt die Berechnung des möglichen Fehlers und damit das Ergreifen von Maßnahmen zu dessen Verringerung.

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( , , ) , .

     

Study of thermochemical conversions of alicyclic polyimides

The thermochemical conversions of certain polyimides obtained by the polycondensation of dianhydrides of alicyclic tetracarboxylic acids and 4,4-diaminodiphenyl oxide were studied by different methods of thermal analysis (thermogravimetry, mass-spectrometric evolved gas analysis, and pyrolytic gas chromatography). The thermal dissociation of dianhydride fragments according to the reverse reaction of retrodiene synthesis is the basic reaction that determines the thermal stabilities of the polymers studied. It is shown that the absence of endoethylene bonding or its substitution by oxygen in the dianhydride fragments leads to increases in the thermal stabilities of alicyclic polyimides.

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Zusammenfassung Thermochemische Umwandlungen einiger Polyimide, die durch Polykondensation der Dianhydride alicyclischer Tetracarbonsäuren mit 4,4-Diaminodiphenyloxid dargestellt waren, wurden durch verschiedene thermoanalytische Methoden (TG, massenspektrometrische EGA und Pyrolyse-Gaschromatographie) untersucht. Die thermische Spaltung der Dianhydrid-Komponente nach einer Retro-Diensynthese ist die Hauptreaktion, die die thermische Stabilität der Polymeren bestimmt. Bei Abwesenheit der endo-Ethylen-Bindung in der Dianhydrid-Komponente oder Substitution durch eine Etherbindung wird die thermische Stabilität von Polyimiden mit alicyclischen Baugruppen erhöht.

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, - , 4,4- . , , . , - , .

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The authors would like to thank Yu. A. Sazanov and L. A. Shibaev (IVS AN SSSR, Leningrad) for help in the mass-spectrometric thermal analysis of the polymers.     

Evaluation of the activation energies of elementary propagation steps in the catalytic polymerization of olefins

The possible relation between the activation energies of adsorption and insertion reactions and the heat of olefin adsorption for the two-step mechanism of propagation have been evaluated on the basis of calculated preexponential factors for the propagation rate constants and the experimental activation energies of propagation.

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, .

     

Crystallization kinetics of LDPE/Ny6 blends

The crystallization behaviour of low density polyethylene/nylon 6 blends has been investigated as a function of the composition.The melting points of the polymers are almost uninfluenced by the presence of the other homopolymers except for blends with a nylon content of 75–90%.Blends with 10% nylon content do not exhibit the crystallization peak during the cooling step probably because of the low concentration and high viscosity of the low density polyethylene matrix.The crystallinity degree of the polyethylene is independent of the composition, while some variations are shown by the polyamide.Finally the rate of nucleation is strongly affected by the composition, in particular for the nylon phase.

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Zusammenfassung Die Abhängigkeit des Kristallisationsverhaltens von 6 Polyethylen/Nylon-Gemischen geringer Dichte von der Zusammensetzung wurde untersucht. Der Schmelzpunkt eines jeden Polymers ist nahezu unbeeinflußt von der Anwesenheit des anderen Homopolymers ausgenommen die Gemische mit einem Nylongehalt von 75–90%. Die Gemische mit einem Gehalt von 10% Nylon zeigen während des Abkühlungsschrittes keinen Kristallisationspeak, was wahrscheinlich auf die niedrige Konzentration und auf die hohe Viskosität der Polyethylenmatrix mit geringer Dichte zurückzuführen ist. Der Kristallinitätsgrad des Polyethylens ist unabhängig von der Zusammensetzung, während ein Einfluß des Polyamids festzustellen ist. Die Keimbildungsgeschwindigkeit ist stark von der Zusammenstzung abhängig, was besonders für die Nylonphase gilt.

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— 6 . , 75–90% , . 10% , , , . , . , , .

     

Promoting effect of alkali oxides on Bi?Mn catalysts activity in oxidative coupling of methane

The addition of small amounts of alkali metal oxides into Bi–Mn oxide catalysts enhances both their activity and selectivity in oxidative coupling of methane. A linear dependence between the concentration of basic sites on catalyst surface and the rate of catalytic reaction have been established.

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Bi–Mn . .

     

Calorimetric studies of adsorptive properties of metallic carbides and nitrides of transition elements. Adsorption of H2, CO and O2 on titanium nitrides

Adsorption heats of hydrogen, oxygen and carbon monoxide on titanium nitrides have been measured calorimetrically in the temperature range from 473 to 673 K. With increasing Me/N ratio, the adsorption heat of oxygen grows.

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, 473–673 . Me/N.

     

Precipitation of aluminium hydroxide in the presence of surfactant and its effect on the surface acidity

Surface acidity of aluminas prepared by precipitation from sodium aluminate solutions and nitric acid with and without surfactant were determined by IR spectroscopy. It was found that the amounts of aprotic acidic sites increase with increasing pH of precipitation and with increasing concentration of surfactant used in the course of precipitation and washing of the precipitate.

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, -. , -, .

     

IR spectroscopic studies of CO interaction with surface zirconium hydrides

IR spectroscopic studies of CO interaction with surface zirconium hydrides have revealed that it proceeds through a step of CO adsorption on these hydrides at 163–273 K with the subsequent insertion of CO across the Zr-H bonds at T>293 K and the formation of surface formyl compounds.

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CO . , CO 163–273 CO Zr-H 293 .

     

Ethylene oxidation by lithium nitrate in the presence of palladium acetate in acetic acid

Data are reported on variations of the gas phase volume and product accumulation in ethylene oxidation by lithium nitrate in acetic acid solutions, catalyzed by palladium acetate. An assumption is made on the routes of nitrate ion reduction.

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, , . -.