Kinetics of thermal dehydration of Ba(ClO3)2 · H2O

The kinetics of thermal dehydration of microcrystalline powders and single-crystals of barium chlorate monohydrate were studied by differential scanning calorimetry. The computer elaboration of thermal data showed that a single kinetic law could not account for the whole decomposition; moreover, different laws had to be used for powders than for single-crystals, whose reaction appeared diffusion-limited towards the end of the dehydration. Optical microscopy was extensively used as an independent source of information to clarify some of the thermal results and to gain a deeper insigth into the possible reaction mechanism.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung mikrokristalliner, Pulver und einzelner Kristalle von Bariumchlorat Monohydrat wurde mittels Differential-Abtastkalorimetrie untersucht. Die Computerverarbeitung der thermischen Angaben zeigte, dass für die vollständige Zersetzung nicht ein einziges kinetisches Gesetz gültig ist, sondern, dass für Pulver, bzw. für einzelne Kristalle, deren Reaktion gegen Ende der Dehydratisierung als diffusionsbegrenzt erscheint, verschiedene Gesetze eingesetzt werden müssen. Als unabhängige Informationsquelle wurde die optische Miskroskopie weitläufig eingesetzt um einige thermische Ergebnisse zu klären und eine tiefere Einsicht in den möglichen Reaktionsmechanismus zu gewinnen.

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Résumé La cinétique de la déshydratation thermique du chlorate de baryum monohydraté en poudres microcristallines et en monocristaux, a été étudiée par analyse calorimétrique différentielle (DSC). L'évaluation des données thermiques par ordinateur a montré qu'une seule loi cinétique n'était pas applicable à l'ensemble de la décomposition; de plus, dans le cas des poudres, on doit appliquer des lois différentes de celles des monocristaux dont la réaction paraît être limitée, vers la fin de la déshydratation, par la diffusion. La microscopie optique a été largement utilisée comme source indépendante d'information afin de clarifier certains résultats thermiques et d'acquérir une connaissance plus profonde du mécanisme probable de la réaction.

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The authors are indebted to Prof. Enzo Ferroni for helpful advice and to C.N.R. for financial support.     

Epoxidation of propylene with tert-butyl hydroperoxide in the presence of heterogeneous polymeric catalysts

A series of heterogeneous polymeric molybdenum containing catalysts on the basis of weak acid cation exchanger Amberlite IRC-84 in an organic and water medium was prepared. The catalysts activity and selectivity in the epoxidation of propylene with tert-butyl hydroperoxide are compared. Data about the chemical structure of catalytically active molybdenum containing centres of the modified cation exchanger were obtained.

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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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Shape selectivity and maximum molecular size in methanol to hydrocarbons transformation

The maximum product size obtained during methanol to hydrocarbons transformation on medium and large pore zeolites and amorphous silica-aluminas is not governed by shape selectivity but it is a consequence of operational conditions and other process characteristics such as the occurrence of cracking reactions.

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Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

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Specificity of hydrogen adsorption on chromia-supported platinum group metal catalysts

Hydrogen adsorption on chromia supported Pd, Rh and Pt was studied under various pretreatment conditions. The reduction temperature influences strongly the hydrogen uptake for all these metals. Platinum supported on chromia shows an unusually high hydrogen adsorption stoichiometry.

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Pd, Rh Pt, Cr₂O₃, . , . Cr₂O₃ .

     

51V NMR studies of systems V2O5-KHSO4 and V2O5?K2SO4

Systems V₂O₅–KHSO₄ and V₂O₅–K₂SO₄ have been studied by the⁵¹V NMR method. The first system demonstrates the same states of vanadium as the previously studied V₂O₅–K₂S₂O₇, in this system a compound with an equimolar ratio of components has been found. In V₂O₅–K₂SO₄ the state of vanadium differs from the above systems and the formation of a compound with V/K=4 is observed.

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⁵¹V KHSO₄–V₂O₅ K₂SO₄–V₂O₅. , K₂S₂O₇–V₂O₅, . K₂SO₄–V₂O₅ V/K4.

     

Dehydroxylation and catalytic activity of dealuminated Y zeolites

Dehydroxylation and catalytic conversion of m-xylene over dealuminated zeolites were studied.

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Vapor phase oxidation of methylpyridines on zeolite catalysts

It has been established that zeolites containing Pd and Cu ions catalyze the vapor phase oxidation of methylpyridines. In oxidation of 2-methylpyridine on PdCuNa-mordenite at 375 °C the yield of 2-pyridinecarbaldehyde is 40 % of its theoretical values.

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, , Pd Cu, . 2- PdCuNa- 2- 375°C 40% .

     

Thermal investigation of the phase composition of poly(ethylene terephthalate). Analysis of different methods of determination of the degree of crystallinity of partially crystalline substances

The literature data on the degree of crystallinity of non-deformed poly(ethylene terephthalate) measured at various temperatures have been subjected to comparative analysis. There is no correlation between the results obtained by the different methods. The reason for this is shown to be the imperfections in the methods of determining the degree of crystallinity, which do not provide the true composition of the crystalline phase. Consideration has been paid to the validity of the main principles involved in the thermal method of determining the degree of crystallinity, so as to eliminate the imperfections in the existing methods and to provide the correct value of the mass of the crystalline phase. The phase composition of PET has been analyzed by the thermal method at different temperatures and conditions of crystallization. A marked difference from the literature data is observed in the range of low temperatures.

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Zusammenfassung Eine vergleichende Analyse der Literaturangaben bezüglich des bei verschiedenen Temperaturen gemessenen Kristallisationsgrades von nicht-deformiertem Poly(äthylen-terephthalat) wurde durchgeführt. Zwischen den mit verschiedenen Methoden erhaltenen Ergebnissen besteht keine Korrelation. Es wurde gezeigt, daß der Grund hierfür in der Unvollkommenheit der Methoden zur Bestimmung des Kristallisationsgrades liegt, da diese nicht die wahre Zusammensetzung der Kristallinen Phase angeben. Die Gültigkeit der wichtigsten Prinzipien, welche die thermische Bestimmung des Kristallisationsgrades unter Ausschaltung der Unvollkommenheit der bestehenden Methoden gewährleisten und den richtigen Wert der Masse der kristallinen Phase angeben, wurden in Erwägung gezogen. Die Analyse der Phasenzusammensetzung von PET wurde durch die thermische Methode bei verschiedenen Temperaturen und Kristallisationsbedingungen durchgeführt. Ein deutlicher Unterschied zu den Literaturangaben kann im Bereich der niedrigen Temperaturen beobachtet werden.

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