Solid state reaction between dichromates and oxalates

The thermal investigation of the reaction taking place between dichromates and oxalates in the solid state has been done taking two systems of potassium dichromate-potassium oxalate and sodium dichromate-sodium oxalate. The techniques employed include thermogravimetry, differential thermal analysis, infrared spectroscopy and X-ray diffraction studies. The results indicate a stoichiometric reaction of dichromate and oxalate in 11 ratio to give the corresponding chromate as the sole product.

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Zusammenfassung Anhand der Systeme Kaliumdichromat-Kaliumoxalat bzw. Natriumdichromat-Natriumoxalat wurde eine thermische Untersuchung der Festkörperreaktion zwischen Dichromaten und Oxalaten durchgeführt. Dazu wurden thermogravimetrische, dififerentialthermoanalytische, IR-spektroskopische und Röntgendiffraktionsverfahren angewendet. Im Ergebnis zeigte sich eine stöchiometrische Reaktion von Dichromat und Oxalat im Verhältnis 11, die das entsprechende Chromat als einziges Produkt liefert.

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, , — — . , 11 .

     

Thermal analysis of macromolecular “Haloamines”

The TG, DTG and DTA curves of macromolecular macroporous N-halogeno- and N,N-dihalogenosulfonamides are reported and interpreted. To compare their thermal behaviour with that of their unfunctionalized matrices, analogous studies were performed on the porous styrene-divinylbenzene(20%)copolymer and its sulfonamide derivative.

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Zusammenfassung Die TG-, DTG- und DTA-Kurven makromolekularer makroporöser N-Halogen- und N,N-Dihalogensulfonamide werden beschrieben und gedeutet. Zum Vergleich wurde das thermische Verhalten des unsubstituierten porösen Styren-(20%)Divinylbenzen-Copolymeren und seines Sulfonamids in gleicher Weise untersucht.

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, TA N-- N,N- . , .

     

The UV-VIS spectroscopic study of the interaction between WCl6 and esters of carboxylic acids

The reaction of WCl₆ with methyl 10-undecenoate and methyl palmitate has been studied. The rate constant of the first step of the reaction has been established and compared with that of the WCl₆+(CH₃)₄Sn reaction. On the basis of this comparison the influence of the reaction of WCl₆ + ester on the ester metathesis is discussed.

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WCl₆ -10- -. , WCl₆+(CH₃)₄Sn. WCl₆+ .

     

Mechanism of hydrogenation of nitric oxide on platinum catalysts in acidic solution

To explain the mechanism of hydrogenation of NO in 2 M H₂SO₄, the kinetics of the hydrogenation of hydroxylamine to ammonia were studied. The rate constant of this reaction was compared with the ratio of rates at which NH₃OH⁺ and NH ₄ ⁺ were generated by the hydrogenation of NO. Both of these products are formed from NO via parallel reactions of a common intermediate. A mechanism for the hydrogenation of NO and the shift of the catalyst of the potential is proposed.

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NO 2M H₂SO₄ . NH₃OH⁺ NH₄ ⁺ NO. NO . . ., NO .

     

Electrochemical model of alkane oxidation by cytochrome P-450

Catalytic oxidation of alkanes to alcohols and ketones was shown to take place in an electrochemical cell with iron porphyrin deposited on a graphite cathode. The oxidation mechanism was assumed to be similar to that of cytochrome P-450 action.

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, . , P-450.

     

Contribution a l'etude de l'oxyde de cadmium en milieu alcalin

Résumé L'étude de la réaction de NaOH sur CdO ou Cd(OH)₂ a nécessité de reprendre celle des courbes ATG et ATD de NaOH à différents stades de pureté. Ceci a permis, en particulier, de préciser l'existence de l'eutectique ternaire NaOH-Na₂O-Na₂CO₃ dans les mélanges réactionnels traités, d'exclure la possibilité de la présence de peroxyde. Le produit de la réaction, obtenu avant 130°, est plus stable à la chaleur que NaOH. Son spectre IR est compatible avec l'existence d'un hydroxocadmiate de sodium.

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The investigation of the reaction of sodium hydroxide with CdO or Cd(OH)₂ made necessary some studies on the DTA and TG curves of sodium hydroxide samples of different purities. These studies have evidenced the formation of a ternary eutectic NaOH-Na₂O-Na₂CO₃ in the heat-treated reaction mixtures, and have also shown that no peroxide is present. The product of reaction obtained below 130° had a greater thermal stability than NaOH. On the basis of the infrared spectrum the existence of a sodium hydroxocadmiat can be assumed.

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Zusammenfassung Die Untersuchung der Reaktion von Natriumhydroxyd mit CdO oder Cd(OH)₂ erforderte eine neue Untersuchung der DTA und TG Kurven des NaOH von verschiedenem Reinheitsgrad. Dies bewies das Vorhandensein eines ternären Eutektikums NaOH-Na₂O-Na₂CO₃ in den behandelten Reaktionsgemischen, weiterhin, daß kein Peroxyd gegenwärtig ist. Das vor 130° erhaltene Reaktionsprodukt besitzt höhere thermische Stabilität als NaOH. Aufgrund der infraroten Spektren darf die Existenz eines Natriumhydroxocadmiats angenommen werden.

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NaOH CdO Cd(OH)₂ . NaOH-Na₂O-Na₂CO₃ . , 130°, , NaOH. - .

     

Determination of the kinetic parameters of the multi-stage thermal decomposition of solids under non-isothermal conditions by the non-linear estimation approach

The activation energy of decomposition of aluminium hydroxidevs. weight loss was estimated from thermogravimetric data collected over a wide range of heating rates, without resorting to the model of the reaction mechanism.These activation energy values were subsequently used to distinguish individual dehydration stages and to determine the best models of the reaction kinetics for these stages.Finally, the overall decomposition model was formulated, and its parameters were determined by the non-linear estimation approach.

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Zusammenfassung Die Aktivierungsenergie der Zersetzung von Aluminiumhydroxid wurde in Abhängigkeit vom Gewichtsverlust aus einen weiten Bereich von Aufheizgeschwindigkeiten umfassenden thermogravimetrischen Daten gesammelt, ohne auf das Modell des Reaktionsmechanismus einzugehen.Diese Werte der Aktivierungsenergien wurden daraufhin zur Unterscheidung einzelner Dehydratisierungsstufen und zur Bestimmung der besten Modelle der Reaktionskinetik dieser Stufen eingesetzt.Schließlich wurde ein allgemeines Zersetzungsmodell formuliert und seine Parameter durch nichtlineare Schätzungsnäherung bestimmt.

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Résumé On a estimé l'énergie d'activation de la décomposition de l'oxyde d'aluminium en fonction de la perte de poids à partir de données thermogravimétriques obtenues avec un large intervalle de vitesses de chauffage, sans avoir recours au modèle du mécanisme de la réaction. On a utilisé ensuite ces valeurs de l'énergie d'activation pour distinguer les étapés individuelles de la déshydratation et pour déterminer les meilleurs modèles de cinétique réactionnelle correspondant à celles-ci.Enfin, on a formulé un modèle général de décomposition et déterminé ces paramètres par approximations non linéaires.

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, , . . .

     

Orientation towards alcohols in CO, H2 reactions on some iron catalysts

Adding rare earths like dysprosium or lanthanum to silica-supported iron or iron-copper catalysts enhances the formation of C₁ to C₅ alcohols and the total conversion in CO–H₂ reactions. Copper rises the alcohol orientation and also the reactivity.

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, - SiO₂ C₁ C₅, CO–H₂. , .

     

Dispersity of (Ru+Pd)/SiO2 catalysts and their properties in CO hydrogenation and ethane hydrogenolysis

The decreased activity of bimetallic catalysts obtained by the interaction of Ru₃(CO)₁₂ with Pd/SiO₂ in the synthesis of hydrocarbons from CO and H₂ and in ethane hydrogenolysis compared with Ru/SiO₂ is due to the dilution, of ruthenium by less active palladium atoms.

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, Ru₃(CO)₁₂ Pd/SiO₂, CO Ru/SiO₂ .

     

Catalytic activity of CaO?CaF2 binary systems in the Claus reaction

Activity of CaO–CaF₂ catalysts in the Claus reaction has been studied as a function of catalyst composition and of the time of catalyst operation in the reaction. Opposite effects of low and high fluoride content on the Claus activity have been found. A new type of reducing centers is suggested to be responsible for the increase in the activity observed in the case of fluorine-rich catalysts.

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CaO–CaF₂ . , . , , .

     

Kinetic analysis of thermal dehydration and hydrolysis of MgCl2·6H2O by DTA and TG

The thermal decomposition of MgCl₂·6H₂O (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, IR, X-ray diffraction and chemical analysis of Mg and Cl. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgCl₂·H₂O and dehydrochloridization of magnesium hydroxy chlorides. Melting of the phases MgCl₂·6H₂O, MgCl₂·4H₂O and MgCl₂ was also identified in the thermal curves. Thermal weight loss continued up to 800 °C in flowing air or nitrogen, but only up to 700 °C in static air. MgO was the end-product of thermal treatment in both cases.The kinetic parameters of the reaction, the activation energyE, pre-exponential factorA and apparent order of reactionb, were computed by several methods. The activation energy and the apparent reaction order of dehydration were found to increase with decreasing hydration number of the Mg. The dehydrochloridization process had the highest activation energy.

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Zusammenfassung Die thermische Zersetzung von MgCl₂·6H₂O (nicht und teilweise getrocknet) und die Kinetik dieses Prozesses wurden mittels DTA, TG, DTG, IR, Röntgendiffraktometrie und chemischer Analyse von Mg und Cl untersucht. Die im Verlaufe der thermischen Analyse vor sich gehenden Reaktionen sind Dehydratisierung (in Schritten), thermische Hydrolyse von MgCl₂·H₂O und Chlorwasserstoffaustritt aus Magnesiumhydroxychloriden. Das Schmelzen der Phasen MgCl₂·6H₂O, MgCl₂·4H₂O und MgCl₂ ist in den thermischen Kurven ebenfalls zu erkennen. Im Luft- und Stickstoffstrom erfolgt ein Gewichtsverlust bis 800 °C, in statischer Luftatmosphäre dagegen nur bis 700 °C. MgO war in beiden Fällen Endprodukt der thermischen Behandlung. Die kinetischen Parameter der Reaktion (AktivierungsenergieE, präexponentieller FaktorA, scheinbare Reaktionsordnungb) wurden nach verschiedenen Methoden berechnet. Aktivierungsenergie und scheinbare Reaktionsordnung der Dehydratisierung nehmen mit abnehmendem Hydratationsgrad des Mg zu. Die Chlorwasserstoffabspaltung erfordert die höchste Aktivierungsenergie.

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, , , , ( ) . : ( ), . , . 800 °C, - 700 °C. B . , . , . .

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The authors express their appreciation to Dr. Jacob Nathan and Mr. Yoetz Deutch from th Geological Survey, Jerusalem, for the use of the thermal analysis instrument and for useful discussion, and to Mrs. Sarah Erlich from the same institute, for the chemical analysis. The financial support by Everyman's University, Tel-Aviv, and by the Hebrew University of Jerusalem is acknowledged.     

Role of the precursor state in the rate of hydrogen adsorption on thin iron films

Sticking probability for hydrogen adsorption on thin iron films deposited under ultra-high vacuum condtions was studied in dependence on the method of film preparation and the temperature of adsorption. It was observed that Kisliuk's model for a dissociative adsorption fits well the experimental data at low temperature. At high temperature Kisliuk's relation describes the adsorption as well as the Langmuir equation.

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, , . , , , .

     

Nonisothermal kinetics of zinc oxide nonstoichiometrization

The results obtained by studying zinc oxide non-stoichiometrization are presented. The kinetic parameters values under nonisothermal conditions were calculated too. Both the nonstoichiometric zinc oxide composition and the kinetic parameter values are depending on the generating substances.

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Zusammenfassung Die Ergebnisse der Untersuchungen der Nichtstöchiometrisierung von Zinkoxid werden vorgeführt.Die Werte der kinetischen Parameter unter nicht-isothermen Bedingungen wurden eben falls berechnet.Sowohl die nichtstöchiometrische Zusammensetzung des Zinkoxids als auch die Werte der kinetischen Parameter hängen von der das Phänomen auslösenden Substanz ab.

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Résumé On présente les résultats d'une étude sur la formation d'oxyde de zinc non-stchiométrique. Les valeurs des paramètres cinétiques en conditions non-isothermes sont égale ment calculées. La composition de l'oxyde de zinc non-stchiométrique ainsi que les valeurs des paramètres cinétiques dépendent du composé de départ.

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, , . .

     

Effect of acio properties of the alumina surface on the formation of chlorides during its interaction with CCl4

IR spectroscopy was employed to study acid properties of a series of alumina samples different in the phase composition and in the porous structure. The comparison of the surface acidity with the data on the quantitative formation of Cl^– during the interaction of CCl₄ with alumina indicates that the extent of chlorination of the samples tends to increase with increasing the surface acidity.

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- , . Cl^– CCl₄ , .

     

Catalytic hydrogenation of nitrobenzene on solid sulfides and soluble rhenium thiocomplexes

Studies of the reduction of nitrobenzene in the catalytic hydrogenation on soluble rhenium thiocomplexes and solid ReS₂ and Re₂S₇ indicate that on homogeneous and heterogeneous rhenium sulfides it follows the same mechanism. Thiocomplexes are considered as possible analogs of the active sites in ReS₂ and Re₂S₇ sulfide catalysts.

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ReS₂ Re₂S₇. , . ReS₂ Re₂S₇.

     

Some considerations regarding the kinetics of solid-state reactions

The present state of non-isothermal kinetics for solid-state reactions is discussed on the basis of the literature. Experimental data are given on the effects of sample size, heating rate, particle size and atmosphere on the thermogravimetric (TG) curve, as well as the values of the kinetic parameters calculated from them. One solution of the formal kinetics is introduced.

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Zusammenfassung Der gegenwärtige Stand der nicht isothermen Kinetik von Reaktionen in festem Zustand wird an Hand der Literatur erörtert. Außerdem werden einige Versuchsergebnisse bezüglich der Wirkung der Einwaage, der Aufheizgeschwindigkeit, der Teilchengröße und der Atmosphäre auf die thermogravimetrische (TG) Kurve, sowie der Wert der aus ihr errechneten kinetischen Parameter angeführt. Eine formalkinetische Lösung wird eingeführt

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Résumé On discute, à partir des données de la littérature, l'état actuel de la cinétique nonisotherme des réactions en phase solide. On donne ensuite quelques résultats d'expérience montrant l'influence de la prise d'essai, de la vitesse de chauffage, de la granulométrie et de l'atmosphère sur la courbe thermogravimétrique et sur les paramètres cinétiques calculés. On introduit une solution de cinétique formelle.

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. , , () , . .

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The author wishes to express her thanks to P. Tke for preparing the computer program of the calculations suggested by Zsakó, Coats-Redfern, Coats-Redfern-Dharwadkar, and for running the program, and to Prof. E. Pungor for helping this work with his valuable advice.     

Parametric analysis of eigenvalues of matrices corresponding to linear one-route catalytic reaction mechanism

The parametric analysis of accepted eigenvalues of matrices observed in chemical kinetics and corresponding to the linear n-stage one-route mechanisms with irreversible stages has been conducted. Relaxation times with varying one of the rate constants are given. The possibility of nonmonotonic change of relaxation times with growing rate constants is shown.

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, n- . . .

     

Methanol-based synthesis of hydrocarbons on bifunctional Y-type zeolites

The directions of methanol conversion on Pt, Pd, Zn, Ni metals and Y zeolites and on bifunctional metal-Y-zeolite catalysts have been studied. The increase of the hydrogenation activity of bifunctional catalysts enhances the rate of methanol conversion and decreases the selectivity of hydrocarbon formation.

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- Y, - Y.

     

Evaluation of quantum yields in the presence of an absorbing additive

A method is proposed for the evaluation of quantum yields of photochemical reactions studied in the presence of absorbing additives using cylindrical sample tubes.

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.

     

Alkylation of phenol with alcohols on an aluminium orthophosphate-alumina system as catalyst

The results obtained in the alkylation of phenol in gas phase with different alcohols on an aluminium orthophosphate-alumina system of Kearby type are presented. We conclude that an O-alkylation coexists with a C-alkylation and that the alkylating ability of the alcohols decreases for higher and more branched hydrocarbon chains. Influences of temperature and space time are also discussed.

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, , / . , - - . .