Catalytic properties of silica-molybdenum catalysts in propylene oxidation

The activity of silica-molybdenum catalyts in propylene oxidation is shown to be determined by the partially dehydrated silica-molybdenum heteropolyacid stabilized by the SiO₂ surface.

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, , SiO₂.

     

Combinations of alkyl radicals with alkyl and substituted allyl radicals

In contrast with expectations based upon simple collision theory, reactions of alkyl radicals with substituted allyl radicals yield cross-combination ratios of =2. Reactions of CH ₃ ^\ with some C₅ radicals give >2, in accordance with theory.

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, =2. CH₃ ^\ C₅ >2, .

     

Thermal dissociation of basic aluminium ammonium sulfate in vacuum

A mathematical model of the thermal decomposition of basic aluminium ammonium sulfate has been developed. The construction of the model consisted in simulation of TG and DTG curves, with the use of kinetic parameters identified on the basis of results obtained in measurements of the rate of thermal dissociation of the compound under isothermal and non-isothermal conditions.

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Zusammenfassung Es wurde das mathematische Modell fur thermische Zersetzung des basischen Ammoniumaluminiumsulfats bearbeitet. Die Struktur des Modells bestand in der Nachbildung von thermogravimetrischen Kurven TG, DTG mittels der kinetischen Parameter, die auf Grund der isothermen und der nichtisothermen Ergebnisse der Untersuchungen nach der Dissoziationsgeschwindigkeit von Verbindungen identifiziert wurden.

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Résumé Un modèle mathématique décrivant la décomposition thermique du sulfate basique d'aluminium et d'ammonium est présenté.La méthode consiste à simuler les courbes thermogravimétriques TG et TGD à l'aide des paramètres cinétiques identifiés sur la base des résultats des déterminations isothermes et nonisothermes de la vitesse de la dissociation du composé.

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. , , .

     

Calorimetric studies of alumosilicate catalysts I. Heat and entropy of cumene adsorption on Mg-metakaolinite at small surface coverages

Differential heats of cumene adsorption at 293 K on Mg-metakaolinite at surface coverages =0.005–0.10 have been measured on a Calvet microcalorimeter. The adsorption heat decreases drastically from 71 to 59 kJ/mol with changing the adsorption from 0.02 to 0.06 mol/m². The presence of two energetically different types of adsorption centers is predicted on the Mg-metakaolinite surface.

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293 Mg- =0,005–0,10. 71 59 / 0,02 0,06 /². Mg-.

     

UV-VIS spectroscopic study of interaction and transformation of allyl alcohol on zeolites HZSM-5

Formation of alkenylcarbenium ions has been proved during transformation of allyl alcohol on zeolite HZSM-5.

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HZSM-5.

     

Rate constants for photochemically induced hydrogen abstraction calculated from spin trapping rates

ESR spin trapping method has been applied to calculate the rate constant for -hydrogen abstraction from ethylbenzene by triplet anthraquinone: k₁=1.1×10⁷ M^–1 s^–1 (error of estimation 25%).

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( ) -CH : k₁=1.1×10⁷ M^–1–1 ( 25%)

     

Kinetics of carbonyl triplet reactions in water

The presence of urea during the gelling of AlPO₄–Al₂O₃ catalysts (AlPO₄/Al₂O₃ weight ratio =3) has been studied with respect to its effect on the porous texture and surface acidity of the resulting gels. An increase in pore volume and mean pore radius with no modification in surface acidity is found when the AlPO₄–Al₂O₃ catalyst is modified by the addition of 5 mol% urea in the AlPO₄ solution.

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, AlPO₄/Al₂O₃ ( AlPO₄/Al₂O₃=3) . , AlPO₄/Al₂O₃ 5 .% AlPO₄ - .

     

Kinetics of bromate-cerium(III) reaction

The induction period and the fast, and slow rates of the bromate-cerium(III) reaction were examined. It was found that the duration of the induction period was inversely proportional to both the bromate and acid concentrations, and that the fast reaction rate was proportional to the square of bromate concentration.

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(III). , , .

     

Materials testing by Dynamic mechanical analysis

Applications of the new 980 Dynamic mechanical analyser (DMA) to the study of thermoplastic polymers, thermosetting polymers and metal glasses have been discussed in this paper. This instrument has also been used to study impact modified thermoplastics [2] elastomers [3] and metals. DMA is one of the thermo-analytical thechniques available to the research or quality control chemist for evaluating the mechanical properties of materials. With the introduction of the 980 it is anticipated that the disadvantages due to long operation time and complexity inherent in older instrumentation will no longer hold back progress towards the full realisation of the technique.

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Zusammenfassung Der Einsatz des neuen 980 Dynamic Mechanical Analysers zur Untersuchung thermoplastischer und auf Hitzeeinwirkung fest werdender Polymere, sowie Metallgläser, wird in dieser Veröffentlichung beschrieben. Dieses Instrument wurde auch zur Untersuchung von durch Stoss modifizierten thermoplastischen Stoffen [2], Elastomeren [3] und Metallen verwendet. Die dynamische mechanische Analyse ist eine der für den Forschungsoder Kontrollchemiker bei der Bewertung der mechanischen Eigenschaften der Stoffe nützlichsten zur Verfügung stehenden thermoanalytischen Techniken. Die Einführung des Modells 980 gestattet die Folgerung, daß die bei den früheren Instrumenten als Nachteil verzeichnete lange Arbeitsdauer und Komplexität nunmehr dem Fortschritt in Richtung vollständiger Realisierung dieser Technik nicht mehr im Wege stehen werden.

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Résumé L'application du nouvel analyseur mécanique 980 à l'étude des polymères thermoplastiques, des polymères thermodurcissables et des verres métalliques est discutée. L'instrument a également été utilisé pour l'étude des thermoplastiques traités par percussion [2], des élastotnères [3] et des métaux. L'analyse mécanique dynamique est l'une des techniques d'analyse thermique les plus utiles pour évaluer les propriétés mécaniques des matériaux, aussi bien en recherche que pour les opérations de contrôle de qualité. Avec l'introduction du modèle 980, il est prévisible que les inconvénients des instruments précédents, dus à la durée et à la complexité des opérations, n'entraveront pas le développement de cette technique.

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980 , . , , . , . 980 , , , , .

     

Effect of hydrothermal treatment on catalytic properties of superhigh-silica zeolites

The effect of hydrothermal treatment of decationized superhigh-silica zeolite on the mechanism of n-hexane conversion has been studied. It has been established that thermosteam modification sharply decreases the cracking activity and increases the selectivity to aromatization reactions. Zeolite acidity markedly decreases, but its crystal structure does not become amorphous.

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-. . .

     

Effect of homogeneous initiator on heterogeneous-homogeneous oxidation of methane

A kinetic method of freezing out free radicals combined with recording ESR spectra was used to study the HCl effect on the partial oxidation of methane over SiO₂. This effect is ascribed to the surface modification of catalyst.

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HCl SiO₂. .

     

Effect of deuteration on the thermal dehydration of lithium sulfate monohydrate

Effects of deuteration on the thermal stability, enthalpy change and kinetic parameters for the thermal dehydration of Li₂SO₄·H₂O were examined by means of TG and DSC. The enthalpy change for the monohydrate was smaller by 1.63±0.75 kJ/mol than that for the monodeuterate. The rate constant for the monohydrate was a little larger than that for the monodeuterate. However, the thermal stability, activation energy and frequency factor were practically unaffected by deuteration of the hydrate. It is suggested that the activation entropy as well as the activation energy should be considered in explaining the kinetic deuterium isotope effect in the thermal dehydration of Li₂SO₄·H₂O.

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Zusammenfassung Die Wirkung der Deuterisierung auf die Thermostabilität, die Enthalpie-Änderungen und kinetischen Parameter der thermischen Dehydratisierung von Li₂SO₄·H₂O wurden durch TG und DSC untersucht. Die Enthalpie-Änderung für das Monohydrat wurde um 1.63±0.75 kJ/mol niedriger gefunden als für das Monodeuterat. Die Geschwindigkeitskonstante für das Monohydrat war etwas größer als für das Monodeuterat. Die Thermostabilität, die Aktivierungsenergie und der Frequenzfaktor wurden jedoch von der Deuterisierung des Hydrats praktisch nicht beeinflußt. Es wird vorgeschlagen, daß bei der Erklärung des kinetischen Deuterium-Isotop-Effekts bei der thermischen Dehydratisierung von Li₂SO₄·H₂O sowohl die Aktivierungsentropie als auch die Aktivierungsenergie berücksichtigt werden müssen.

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, Li₂SO₄·H₂O. 1.63+0.75 /. , . , , . , Li₂SO₄·H₂O.

     

Kinetics and mechanism of phenylacetylene hydrogenation under hydrogen pressure

Kinetic and potentiometric curves of phenylacetylene hydrogenation on a 5% Pt/C catalyst in ethanol under hydrogen pressure have been studied. On the basis of chromatographic data a possible scheme of the process is suggested.

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. 5% Pt/C . .

     

A method for the treatment of experimental data. Kinetic system comprising two irreversible first order consecutive reactions

A method is proposed for the treatment of data from a kinetic system comprising two irreversible first order consecutive reactions (ABC). It is based on the solving of contrary propositions for an ordinary differential equation.

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(ABC). .

     

Investigation of propylene oxidation on multicomponent a Bi-and Mo-based oxide catalyst

It has been established that porpylene oxidation to acrolein on a multicomponent oxide catalyst containing Mo, Bi, Fe, Ni, Co, K, P and SiO₂ follows an alternating oxidation-reduction mechanism and involves the participation of lattice oxygen with the bond energy of about 280 kJ/mol.

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, Mo, Bi, Fe, Ni, Co, K, P SiO₂ 280 /.

     

Thermogravimetric study of diatomites

The thermal curves of diatomites (kieselguhrs) in air display different profiles, depending on the type and quantity of impurities (carbonates, clays, etc.) present. TG and DTG runs can be used for a quick diagnosis of quality, but also give a nearly quantitative picture of the silica content of these minerals.

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Zusammenfassung In Abhängigkeit von Art und Menge der Verunreinigungen (Karbonate, Tonerde usw.) weisen die thermischen Kurven von Diatomiten (Kieselguhr) in Luft unterschiedlichen Verlauf auf. Einfache TG- und DTG-Untersuchungen können als Schnelldiagnose zur Bestimmung der Qualität benutzt werden und geben ausserdem noch ein nahezu quantitatives Bild über den Silikatgehalt dieser Mineralien.

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( ) , (, . .). , .

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The authors acknowledge the financial support of this work by the Comisión Asesora de Investigatión Cientifica y Técnica, Spain, through Project No. PR84-0151.     

Effect of acid treatment on the properties of an activated carbon

The enhancement of the activity of a carbon treated with HF is due to the drastic diminution of its inorganic impurities, which produces an increase of the surface area of the carbon, a stronger Pt-C interaction and a higher Pt dispersity.

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, HF, , , Pt-C Pt.