Influence of the chlorine content of Al2O3 on its catalytic activity and coke formation

The catalytic activities of aluminas with different chlorine contents for cumene cracking, o-xylene isomerization, n-hexane isomerization and cracking and methylcyclopentane cracking were studied. The catalytic activity and the acidity increase continuously when the chlorine content increases. Coke formation is only noticiable with methylcyclopentane, increasing with the chlorine content of the alumina.

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, -, - . . - , - .

     

Ethanolysis of penta- and tetramethyldisiloxane catalyzed by aqueous hydrochloric acid

The rates of cleavage of the Si–H bond of penta- and tetramethyldisiloxane have been studied. The reaction is first order in the silane and in the dilute acid. However, at high acid concentrations, the rate of reaction is governed by the acidity function of the system: this may indicate fast reversible proton transfer from the solvent to the organosilane in the rate-determining step.

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Si–H - . . , : , .

     

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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. .

     

Kinetics and mechanism of the oxidation of L-ascorbic acid by 2,6-dichlorophenol-indophenol in aqueous solution

The kinetics of oxidation of L-ascorbic acid by 2,6-dichlorophenolindophenol in aqueous solution has been studied. The rate of the reaction decreases with increasing pH since the hydrogen ascorbate ion is less reactive than the unionized L-ascorbic acid. The rate constants for the oxidation of the two species have been evaluated and a plausible mechanism of the reaction is suggested.

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L- 2,6-- . pH, , L- . .

     

Isothermal crystallization measurements on copolyesters by differential scanning calorimetry

Miller's method for isothermal crystallization measurement was used to determine the progress of crystallization of copoly(ethylene terephthalate/isophthalate) and copoly(ethylene terephthalate/5-methoxyisophthalate) by DSC. The evaluation of kinetic parameters is too complicated for higher contents of comonomer and higher values of molecular mass of copolyesters. On the other hand, the experimental results interpreted by the simplified equation well characterized the differences in the rates of crystallization of different copolyesters.

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Zusammenfassung Die Millersche Methode der isothermen Kristallisierung wurde eingesetzt um den Fortschritt der Kristallisierung von Kopoly(Äthylen-Terephthalat/Isophthalat) und Kopoly(Äthylen-terephthalat/5-Metoxyisophthalat) mittels DSC zu untersuchen. Die Auswertung der kinetischen Parameter ist für höhere Ko-Monomergehalte und höhere Molekularmassenwerte der Ko-Polyester zu kompliziert. Andererseits konnten die an Hand der vereinfachten Gleichung gedeuteten Versuchsergebnisse zur Charakterisierung der Unterschiede der Kristallisierungsgeschwindigkeiten der verschiedenen Ko-Polyester mit gutem Erfolg eingesetzt werden.

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Résumé On a appliqué la méthode de détermination de la cristallisation isotherme de Miller à la détermination par analyse calorimétrique différentielle de l'avancement de la cristallisation du copoly(éthylène téréphtalate/isophtalate) ainsi que du copoly(éthylène téré phtalate/5-méthoxy-isophtalate). L'évaluation des paramètres cinétiques est trop compliquée pour les teneurs plus élevées en comonomère et pour les valeurs plus élevées de la masse molaire des copolyesters. D'autre part, les résultats d'expériences interprétés par l'équation simplifiée ont bien caractérisé les différences de vitesses de cristallisation des divers copolyesters.

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. : Ni(NCS)₂(py)₄, (=), CuSO₄ · 5₂ NiSO₄ · 7₂, . , , .

     

ESR studies of ethylene interaction with active sites of supported organometallic catalysts for ethylene polymerization

Peculiarities of ethylene interaction with surface alkyl compounds of Ti³⁺ in catalysts for ethylene polymerization prepared via the reaction between tetrabenzyltitanium and silica have been studied by the ESR method.

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Ti³⁺ , -.

     

Mechanism of thermal decomposition of lead thiosulphate

The thermal decomposition of lead thiosulfate (LTS) was studied by various methods: X-ray phase analysis, IR and ESR spectroscopy, etc. A mechanism of thermal decomposition is suggested, including rupture of the S-S bond and the formation of radicals. According to the mechanism, the reaction rate can be enhanced in the presence of the PbS phase. The formation of PbS is the cause of the topochemical character of the reaction. The composition of the thermolysis products of LTS containing a radioactive isotope of sulfur is predicted.

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Zusammenfassung Die thermische Zersetzung von Bleithiosulfat PbS₂O₃ wurde durch Röntgenphasenanalyse, IR- und ESR-Spektroskopie und Thermogravimetrie untersucht. Ein Mechanismus der thermischen Zersetzung wird angegeben, der über die Trennung von S-S-Bindungen und die Bildung von Radikalen verläuft. Nach diesem Mechanismus wird die Reaktionsgeschwindigkeit in Gegenwart der PbS-Phase beschleunigt, was den topochemischen Charakter der Reaktion bedingt.Für die Verteilung radioaktiven Schwefels auf die Zersetzungsprodukte unterschiedlich markierten (PbS^*SO₃ bzw. PbSS^*O₃) Bleithiosulfats wird eine Vorhersage gemacht.

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, - . , S—S . , . . , .

     

Thermal analysis in reactive atmospheres

By using reactive atmospheres, the area of application of thermal analysis is expanded considerably to cover many aspects of high temperature research into fuels, extractive metallurgy, materials and catalysts. This article reviews the design of apparatus and its application in kinetic and thermodynamic studies involving atmospheres such as H₂, CO, N₂, NH₃, CO₂, H₂O, SO_2or3, H₂S, S₂, Cl₂, HO, F₂ and HF at low or high pressures and as low pressure plasmas. Apart from gas-solid reactions, the important influence of a controlled product gas atmosphere on decomposition reactions is discussed also. Gas-solid adsorption and solubility studies are not included.

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Zusammenfassung Das Anwendungsgebiet der thermischen Analyse wird durch Arbeiten in reaktiver Atmosphäre beträchtlich erweitert, so dass Hochtemperaturuntersuchungen auf solchen Gebieten wie Brennstoffe, extraktive Metallurgie, Material- und Katalyseforschung möglich werden. Dieser Übersichtsartikel behandelt die Konstruktion der Geräte und ihre Anwendungen bei kinetischen und thermo-dynamischen Untersuchungen in solchen Gasphasen wie H₂, CO, N₂, NH₃, CO₂, SO_{2o der 3}, H₂S, S₂, Cl₂, HCl, F₂ und HF sowie im Niederdruckplasma. Ausser Gas-Festkörperumsetzungen wird auch der Einfluss einer geregelten Produktgas-Atmosphäre auf Zersetzungsreaktionen diskutiert. Auf die Adsorption von Gasen an Festkörpern und Löslichkeitsuntersuchungen wird nicht eingegangen.

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, , , . , , , , , , , - , , , , . — , . - .

     

A thermoanalytical study of treated wools

Previous studies of fibrous keratins have enabled assignments to be proposed for the endothermic processes identified in the relatively complex DTA curve. From this base, the influence of well defined chemical modifications to keratin on their observed DTA curves has been discussed. Wools are specifically treated commercially to improve shrink resistance and machine washability. To achieve these desired characteristics wools are treated, (a) by special oxidative processes, (b) with specific polymers, and (c) by combinations of (a) and (b). The DTA curves of wool samples which have been subjected to each of the three different treatments were reproducibly recorded. The significance of differences between these curves and that for the untreated fibre are discussed. Although characteristic differences in the DTA curves of wools after specific treatments can be distinguished, differential thermal analysis cannot be regarded as a general tool for such treatment characterisation. It is considered that thermogravimetry should offer a greater potential for this purpose.

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Zusammenfassung Vorangegangene Untersuchungen über faserige Keratine ermöglichten Zuordnungsvorschläge für die in der verhältnismässig komplexen DTA-Kurve befindlichen endothermen Vorgänge. Auf dieser Basis wurde der Einfluss gut definierter chemischer Veränderungen in Richtung Keratin auf ihre beobachteten DTA-Kurven erörtert. Die Wollen werden im Handelsmaßstab spezifisch behandelt um ihre Widerstandsfähigkeit gegenüber dem Eingehen zu erhöhen und ihre Waschbarkeit in der Maschine zu fördern. Um diese erwünschten Charakteristika zu erreichen werden die Wollen a) durch spezielle Oxidationsvorgänge, b) mittels spezifischer Polymere und c) mit kombinierten Verfahren von a) und b) behandelt. Die DTA-Kurven von jedem dieser drei verschiedenen Behandlungen unterworfenen Wollproben wurden reproduzierbar aufgezeichnet. Die Signifikanz der Unterschiede dieser Kurven gegenüber denen der unbehandelten Fasern wird erörtert. Obwohl sich charakteristische Unterschiede in den DTA-Kurven der spezifisch behandelten Wollen beobachten lassen, kann die Differentialthermoanalyse nicht als ein allgemein anwendbares Verfahren zur Charakterisierung solcher Behandlungen betrachtet werden. Es wird angenommen, dass die Thermogravimetrie für diesen Zweck grössere Möglichkeiten bietet.

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Résumé Des études antérieures sur les kératines fibreuses ont permis de proposer des interprétations sur les effects endothermiques identifiés sur la courbe ATD relativement complexe. Sur cette base, l'influence de modifications chimiques bien définies de la kératine sur les courbes ATD observées est discutée. Les laines, à l'échelle commerciale, sont traitées spécifiquement pour augmenter leur résistance au rétrécissement ainsi que pour améliorer leur faculté de lavage en machine. Afin d'atteindre ces caractéristiques, elles sont traitées soit par des procédés oxydants spéciaux, soit par des polymères spécifiques soit par les deux. Les courbes ATD d'échantillons de laines traitées par chacune de ces méthodes ont été enregistrées de façon reproductible. Les différences observées entre les courbes obtenues avec les fibres traitées et non traitées sont discutées. Malgré des différences caractéristiques, l'analyse thermique différentielle ne peut pas être considérée comme une méthode universelle pour caractériser de tels traitements. La thermogravimétrie pourrait être potentiellement plus adaptée.

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, DTA. , DTA. , , . : ) , ) ) ) ). DTA , . . DTA , . , .

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Paper presented at the 1^st ESTA, Salford U.K.

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We wish to thank Precision Processes (Textiles) Ltd., and the International Wool Secretariat for samples and information. Their co-operation is gratefully acknowledged. One of us (WMF) wishes to record her thanks to the I.W.S. for their support of a research studentship.     

Rh and Pt catalysts activated by UHV treatments

The H₂–D₂ exchange activity of Rh powder was enhanced by high-temperature UHV treatment accompanied with an enrichment of the high-index faces of Rh. The thermal decomposition of H₂PtCl₆·6H₂O under UHV condition resulted in an extremely active Pt powder catalyst.

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H₂–D₂ Rh , - Rh - . H₂PtCl₆·6H₂O Pt .

     

DSC and vapour pressure investigation of some β-diketonates

DSC and vapour pressure measurements are presented on some Be, Al and Cr complexes with 2,4-pentanedione tetramethyl-3,5-heptanedione, 1,1,1-trifluoro-2,4-pentanedione and hexafluoro-2,4-pentanedione. Thermodynamic functions are given for the sublimation, vaporization and melting processes of the substances.

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Zusammenfassung Die Ergebnisse von DSC- und Dampfdruckmessungen einiger Komplexe von Beryllium, Aluminium und Chrom mit 2,4-Pentandion (HAA), Tetramethyl-3,5-heptandion (HTHD), 1,1,1-Trifluoro-2,4-pentandion (HATA) und Hexafluoro-2,4-pentandion (HHFA) werden beschrieben. Die berechneten thermodynamischen Funktionen für Sublimation, Verdampfung und Schmelzen der Komplexverbindungen sind tabelliert.

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, 2,4- , 1,1,1-- -2,4- -3,5- . , .

     

Kinetics of CO hydrogenation on group VIII metals

Kinetics of CO hydrogenation on supported Group VIII metals has been studied. Kinetic equations for CO methanation and Fischer-Tropsch synthesis suggested previously are consistent with the experimental data obtained.

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CO VIII . CO -, , .

     

Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

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 . .

     

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 . , . , - .

     

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 , . , , - .

     

Asymmetric hydrogenation of tryptophan precursors catalyzed by rhodium-DIOP complexes

Z-2-benzamido(acetamido)-3-(3-indolyl)-2-propenoic acids were hydrogenated with neutral and cationic rhodium(I) complexes containing the chiral diphosphine (–) or (+)–2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane [(–) or (+)–DIOP].

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Z-2- ()-3-(3-)-2- () (I), (–) (+)-2,3--2,3--1,4- ()-.

     

On the initial treatment of kinetic data

The kinetic methods usually employed to determine reaction orders involve some sort of mathematical approximation and provide values approximate and very often discrepant. Three methods are reported to determine accurate reaction orders without introducing approximations.

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, , , , . .

     

Catalytic properties of nitrides in ammonia synthesis

Ammonia synthesis on nitrides CeN, UN_1.70 and iron catalyst CA-1 has been examined at pressures of up to 100 bar. Reaction kinetics is described by the Temkin-Pyzhev equation. Activation energy for all samples is similar and equals about 200 kJ/mol. Specific catalytic activity of nitrides is lower than that of the iron catalyst by a factor of 3–4 for uranium and 10 for cerium.

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100 CeN, UN_{1, 70} CA-1. -. 200 /. : 3–4 10 .