Veränderung des thermischen Verhaltens von Kaolinit durch mechanische Aktivierung

Zusammenfassung Es ist bekannt, daß die Eigenschaften von Kaolinit nicht nur durch eine Kalzinierung oberhalb 600 °C, sondern auch durch intensive mechanische Beanspruchung stark verändert werden können. Die durch eine Intensivmahlung erzeugte Reaktivitätssteigerung kann durch eine Verbesserung der Säurelösbarkeit des Al₂O₃-Anteiles, das veränderte thermische Verhalten und strukturelle Veränderungen gekennzeichnet werden. In der vorliegenden Arbeit geht es um einen Beitrag zur methodischen Aufklärung der strukturellen und thermischen Veränderungen von Kaolinit, insbesondere durch Einsatz thermoanalytischer und IR-spektroskopischer Methoden. Als intensives Zerkleinerungsaggregat wurde eine Scheibenschwingmühle eingesetzt.

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It is already known that the properties of kaolinite can be changed substantially not only by calcination above 600° but also by intensive mechanical stress.A reactivity increase induced by intensive grinding can be characterized by an increase of acid solubility of the Al₂O₃ content, by changed thermal behaviour and by structural changes. The paper presented contributes to the methodic explanation of structural and thermal changes of kaolinite, especially by the use of thermoanalytical and IR spectroscopic methods. The intensive grinding was performed in a vibration-disc mill.

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Résumé Il est déjà connu que les propriétés de la kaolinite peuvent être profondément modifiées non seulement par calcination au-dessus de 600 °C, mais aussi par contrainte mécanique intense.Une augmentation de la réactivité induite par broyage intense peut être caractérisée par une augmentation de la teneur en Al₂O₃ déterminée par solubilité en milieu acide, par le changement du comportement thermique et par des modifications structurales. Le présent article contribue à l'explication méthodique des changements structuraux et thermiques de la kaolinite, spécialement à l'aide des méthodes d'analyse thermique et de spectroscopie infrarouge. Le broyage intense a été effectué dans un broyeur à disques vibrants.

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, 600°, . l₂₃ , . . .

     

Temperature-programmed reduction and temperature-programmed oxidation of nickel and copper-nickel catalysts with addition of palladium supported on alumina

Reducibility and reoxdation of nickel and copper-nickel catalysts with addition of palladium supported on alumina have been investigated by the TPR and TPO methods. Palladium has been found to be an effective promoter of reduction of catalysts under study.

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- , , . , .

     

Effect of catalyst pretreatment on activity and selectivity of hydrogen-Y zeolite for o-xylene isomerization

A study of the influence of calcining for ammonium-exchanged Y-zeolite was made. Activity and isomerization selectivity increased with catalysts pretreated in the order He2 -Y, . He2<22. , O₂ . , .

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CSIRO, Division of Materials Science, Catalysis and Surface Science Laboratory, University of Melbourne, Parkville, Victoria, 3052, Australia     

On the nature of active centers in catalysts for propylene oxidation to acetone

Acid-base properties of binary tin-oxide catalysts for the oxidation of propylene to acetone have been studied. It has been revealed that active catalysts should have both Brönsted acid- and base centers.

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- . , .

     

Der Einfluss der Temperaturführung auf die Kinetische Auswertung Nichtisothermer Reaktionen

Zusammenfassung Das Problem der rationellen Lösung des Zeitintegrals stand bei der kinetischen Auswertung nichtisothermer Prozesse häufig zur Diskussion. Nun werden für lineare und nichtlineare Aufheizung gemäß dT/dt=Q·T_b mitb von 4 bis –2 Auswerteverfahren vorgestellt, die in jedem Fall eine vollständige Korrektur derjenigen kinetischen Parameter gestatteten, die durch linearisierte Auswertung erhalten worden sind. Diese Methode der vollständigen Exponentialintegrale zeigt, daß eine klare Abstufung nach dem Typ der Aufheizung besteht. Die notwendigen Korrekturen fürb=1, 2 und 3 sind kleiner als fürb=0 d.h. für lineare Aufheizung. Die vier Korrekturtabellen sind für Verfahren der kinetischen Analyse anwendbar, denen ein Aktivierungsansatz nach Arrhenius bzw. Eyring zugrunde liegt. Die Realisierung nichtlinearer Aufheizprogramme wird empfohlen.

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The problems of rational solution of the time integral in kinetical evaluation of nonisothermal processes have often been discussed. Evaluation procedures are now presented for linear and nonlinear heating according to dT/dt=Q·T^b, withb between 4, and –2. In every case a complete correction of the kinetical parameters is possible if they are obtained by linearized plotting. This method of complete exponential integrals shows a clear graduation with the type of heating function. The corrections necessary forb=1, 2 and 3 are less than those forb=0, i.e. linear heating. Four tables of correction values are applicable to all procedures of kinetical analysis which are based on activation parameters from the Arrhenius or Eyring equations. Nonlinear heating programmes are recommended.

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Résumé On a souvent discuté les problèmes soulevés par la solution rationnelle de l'intégrale du temps dans l'évaluation cinétique des processus non-isothermes. On présente ici des méthodes d'évaluation dans le cas de chauffages linéaire et non-linéaire, selon dT/dt=Q·T^b avecb entre 4 et –2. Une correction complète des paramètres cinétiques est possible dans tous les cas, si ceux-ci ont été obtenus par des fonctions linéarisées. Cette méthode d'intégration complète des exponentielles montre une graduation nette selon le type de la fonction du chauffage. La correction nécessaire pourb=1, 2 et 3 est inférieure à celle pourb=0, c'est-à-dire pour le chauffage linéaire. Quatre tables de correction basées sur les paramètres d'activation des équations d'Arrhenius et respectivement d'Eyring peuvent être appliquées à tous les procédés de l'analyse cinétique. On recommande de réaliser des programmes de chauffage non-linéaires.

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. , dT/t=Q. ^b 4 -2. , . . , b=1, 2 3, b= . . . , , , . .

     

Thermal decomposition of azoisopropane

The gas phase pyrolysis of azoisopropane has been investigated in a static system in the temperature range 494–546 K. On the basis of gas chromatographic analysis a mechanism is proposed to account for the experimental results.The rate constant of azoisopropane decomposition can be given by the expression {ie383-1}

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494–546^o . - . , : {ie383-2}

     

ESR spectra of O2? on SnO2. effect of adsorbed CO on the conditions of stabilization of O2?

The physical adsorption of CO molecules on SnO₂ is shown to be accompanied by a reversible change in the ESR parameters of CO ₂ ^– anion radicals. The effect of CO is different for SnO₂ samples with different life histories.

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, CO SnO₂ - O ₂ ^– , CO SnO₂ .

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

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CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

Thermal equilibrium between vanadyloctaethylporphyrin and hydrogenated porphyrin during the hydrodemetallation process

Hydrogenation of the vanadyloctaethylporphyrin VO(OEP), is a reversible reaction which may occur without a catalyst. The thermodynamic data have been deduced from experiments performed in a batch reactor. Both H^o and S^o are positive; this can be explained by the aromatic character of chlorin, the reaction product. From a kinetic point of view, the rate order relative to H₂ is equal to one.

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VO(OEP), , . . H^o S^o , , . , .

     

Design and application of a liquid-flow adsorption micro calorimeter based on the Calvet-type DAK 1-1 microcalorimeter (USSR)

The construction and the properties of a liquid-flow adsorption microcalorimeter are described. The calorimeter is based on the commercially available Calvet-type DAK 1-1 microcalorimeter (USSR), which has been equipped with a flow system consisting of a pump, several sets of heat exchangers and an adsorption cell. The minimum detectable heat effect is 1W up to a flow rate of 30 cm³/h.Results on the application of the calorimeter to adsorption and desorption processes of nonionic (Triton X-100) and anionic (styrene phosphonic acid) surfactant solutions in water at an-Al₂O₃ surface are presented and discussed.

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Zusammenfassung Konstruktion und Eigenschaften eines Flüssigkeits-Strömungs-Adsorptions-Mikrokalorimeters werden beschrieben. Das Kalorimeter wurde weiterentwickelt aus dem Calvet-Mikrokalorimeter DAK 1-1 (USSR), das mit einem Strömungssystem aus einer Pumpe, verschiedenen Wärmeaustauschern und einer Adsorptionszelle ausgestattet wurde. Der kleinste nachweisbare Wärmeeffekt liegt bei 1W bis zu einer Durchflussgeschwindigkeit von 30 cm³ h^–1. Mit dem Kalorimeter erhaltene Messergebnisse zur Adsorption und Desorption wässeriger Lösungen von nichtionischen (Triton X-100) und anionischen (Styrenphosphonsäuren) Tensiden an-Al₂O₃ werden dargestellt und diskutiert.

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, 1-1 (), , , . 1 30 ³/. ( X–100) (- ) -l₂₃.

     

A new preparation technique of catalysts characterized by small metal crystallites

The present study reports a new and original technique for obtaining nickel catalysts characterized by small metal crystallites. The catalysts were prepared on -Al₂O₃. The total surface of the carrier was 37.5 m²/g. The preservation of the appropriate procedure and conditions of preparation allow a large expansion of active nickel surface (mean crystallite size 2.0–3.0 nm) in spite of the quite hard conditions of reduction (773 K and 3 h).

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, . -Al₂O₃. 37,5 ²/. ( 2,0–3,0 ) (3 773 ).

     

Effect of medium composition on the monooxygenase activity of immobilized hemin in aniline oxidation

The effect of the composition of the reaction medium on the rate of aniline oxidation to p-aminophenol by hydrogen peroxide on hemin immobilized on -propylimidazole-modified silica has been studied. Organic solvent additives (alcohols, esters and nitriles) are shown to increase the reaction rate. The observed effect is attributed to the decrease of the medium dielectric constant.

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

     

Structural and thermal studies on sisal fibre

Mechanical characteristics of sisal fibre, such as UTS and Young's modulus, have been determined. The thermal degradation of sisal fibre has been observed by running its DSC and TG/DTG.

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Zusammenfassung Die mechanischen Kennwerte (UTS, Young's Modul) von Sisalfasern wurden bestimmt. Der thermische Abbau von Sisalfasern wurde mittels DSC und TG/DTG untersucht.

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, . / .

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The authors wish to thank Dr. R. K. Tiwari, Dr. S. V. Prasad and Dr. M. Patel for their useful suggestions.     

Bromine hydrolysis control and two consecutive oscillatory domains in closed, cerium-catalyzed glyoxylic acid Belousov-Zhabotinsky systems

In closed, cerium-catalyzed glyoxylic acid Belousov-Zhabotinsky systems we found a new dynamic behavior, viz. the observation of two oscillatory regimes separated by a nonoscillatory region. Mechanisms for this intermediate nonoscillatory domain are discussed.

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- , , , . .

     

Temperature-programmed hydrogen desorption from water on bimetallic catalysts Ir?Fe/Al2O3

Desorption of hydrogen liberated in the process of water decomposition on bimetallic catalysts (3% Ir–Fe/Al₂O₃) at linear temperature growth was observed. In the case of iridium the amounts of desorbing hydrogen are relatively small, whereas for iron they are many times greater.

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, 3% Ir–Fe/Al₂O₃ . , , .

     

Mechanism of Michael addition of ethyl acetoacetate to chalcone catalyzed by activated Ba(OH)2

Preliminary studies of the mechanism of Michael addition of ethyl acetoacetate to chalcone are presented. Different products may be obtained with good yields (80%) and selectivities (100%), under different reaction conditions. A mechanism based on the geometric characteristics of the active site of activated barium hydroxide (C-200) is proposed.

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. (80%) (100%). (C-200).

     

Reaction mechanism and principles of choosing catalysts for selective oxidation at C?H bonds

Reaction mechanism for selective oxidation of organic compounds at C–H bonds is discussed. The criteria of selecting catalysts for these reactions have been formulated; 1) fast heterolytic activation of C–H bonds; 2) relatively slow primary activation of oxygen; 3) fast diffusion of oxygen vacancies; 4) fast electron transfer from the adsorbed substrate to catalyst.

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C–H . : 1) C–H ; 2) ; 3) ; 4) .