Analysis of the drying stage in the technology of supported catalysts

The distribution of the precipitated active component has been analyzed using the concepts of moisture transfer mechanism for the evaporation of porous materials. Formulas are proposed for the low-dispersity phase, depending on the precipitation parameter. The calculations performed using a statistical porous environment model are in reasonable agreement with the experimental data.

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- . . , , .

     

Kinetics and mechanism of ruthenium(III) and ruthenium(III)-EDTA catalyzed oxidation of cyclohexanol by molecular oxygen

The kinetics of the oxidation of cyclohexanol by molecular O₂ catalyzed by Ru(III) and Ru(III)-EDTA complexes has been investigated by oxygen absorption method in the pH range 1.75–3.00 at 30°C (=0.1M KNO₃) in a 11 ethanol-water medium. In both cases the reaction was found to be first order with respect to substrate and catalyst concentration. The rate was found to decrease with the decrease of pH in case of Ru(III)-EDTA complex. Ethanol is not oxidized under the reaction conditions. A possible mechanism for the catalytic oxidation of cyclohexanol is proposed.

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O₂, Ru(III) Ru(III)-EDTA, pH 1,75–3,00 30°C (=0,1M KNO₃) - (11). . pH Ru(III)-EDTA. . .

     

Investigation of kinetics and mechanism of maleic anhydride interaction with pentachlorinated phosphorus

Kinetics and mechanism of the interaction of maleic anhydride with pentachlorinated phosphorus have been studied. Kinetic parameters of a model making it possible to control this reaction have been calculated.

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, , .

     

Tracer study of complete oxidation complexes in the oxidative dehydrogenation of butylene

A tracer technique using divinyl-¹⁴C was used to determine the butylene and divinyl contents in the surface complexes of complete oxidation during the oxidative dehydrogenation of butylenes over Bi–Mo, Fe–Sb and Fe₂O₃ catalysts. The rate of decomposition of the surface complexes was found to be independent of their relative butylene and divinyl content.

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–C¹⁴ Bi–Mo, Fe–Sb Fe₂O₃ ., .

     

Influence of the silica support of iron-antimony oxides on the oxidation and ammoxidation of propene

The conversion of propene and the yield of acrylonitrile decrease during ammoxidation with increasing content of silica support of iron-antimony oxides. In constrast to that, during oxidation, the conversion of propene and the yield of acrolein increase with increasing portion of silica in the catalysts. These results show that the appearance of acrylonitrile is not preceded by the formation of acrolein.

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- . , . , .

     

VUV-Photolyse von Methanol bei 1236 Å

Zusammenfassung Es wird über die indirekte und die direkte VUV-Photolyse von luftfreiem Methanol in flüssiger Phase bei 1236 Å berichtet. Bei der Bestrahlung von wäßr. 0,01m-Methanol wurden folgende Produkte und Ausbeuten erhalten: (H₂)=1,00, (HCHO)=0,27, (CH₂OH)₂=0,12, (CH₂OH·CHO)=0,04 und (HCOOH)=0,02. Die Photolyse von flüssigem Methanol lieferte die gleichen Produkte, jedoch mit höheren Ausbeuten: (H₂)=1,50, (HCHO)=0,98, (CH₂OH)₂=0,28 und (CH₂OH·CHO)=0,06. Unter Anwendung von Methanol als Radikalfänger konnte auch die Quantenausbeute der Wasserphotolyse bei 1236 Å, (H,OH)=1,025 verifiziert werden. Wahrscheinliche Reaktionsmechanismen werden diskutiert.

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V.U.V.-Photolysis of methanol at 1236 Å

The indirect and the direct v.u.v.-photolysis of air free methanol in liquid phase at 1236 Å is reported. After irradiation of aqueous 0.01M-methanol the following products were obtained: (H₂)=1.00, (HCHO)=0.27, (CH₂OH)₂=0.12, (CH₂OH·CHO)=0.04 and (HCOOH)=0.02. The photolysis of liquid methanol yielded the same compounds, however with higher amount as follows: (H₂)=1.50, (HCHO)=0.98, (CH₂OH)₂=0.28 and (CH₂OH·CHO)=0.06. Using methanol as a scavenger for the H and OH radicals the quantum yield of the water photolysis at 1236 Å could be verified to be (H,OH)=1.025. Probable reaction mechanisms are discussed.

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Mit 3 Abbildungen

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Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

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 .

     

Kinetics of the thermal dehydration of variscite and specific surface area of the solid decomposition products

The surface properties of active solids resulting from decomposition of AlPO₄ · 2 H₂O by thermal treatment in vacuum and in air are studied in connection with the parameter governing the kinetics of the dehydration process. The values obtained for the activation energies of decomposition under isothermal conditions agree acceptably well with those computed from TG curves by the Freeman and Carroll method. Kinetic results, which are analysed in terms of the Mampel theory, strongly suggest that the activation energy of the nucleation process determines the rate of surface formation, and justify the observed fact that the specific surface areas of samples treated in vacuum are higher than those of samples treated in air.

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Zusammenfassung Die Oberflächenbeschaffenheiten der aktiven Festkörper, welche bei der thermischen Behandlung im Vakuum oder in Luft als Zersetzungsprodukte von AlPO₄ · 2 H₂O entstehen, werden im Zusammenhang mit dem die Kinetik des Dehydratisierungsvorganges steuernden Parameter studiert. Die bei isothermen Bedingungen für die Aktivierungsenergien der Zersetzung erhaltenen Werte sind in befriedigender übereinstimmung mit denjenigen, welche mittels der Methode von Freeman und Carroll aus den TG-Kurven errechnet wurden. Die gemäß der Mampel-Theorie analysierten kinetischen Ergebnisse lassen darauf schließen, daß die Aktivierungsenergie der Nukleationsvorgänge die Geschwindigkeit der Oberflächen-Entstehung bedingt und rechtfertigen die Beobachtung, nach welcher die spezifische Oberfläche vakuumbehandelter Proben größer ist als die der luftbehandelten.

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Résumé On étudie les propriétés de surface des solides actifs provenant de la décomposition de AlPO₄ · 2 H₂O par traitement sous vide et dans l'air et on les rapporte aux paramètres gouvernant la cinétique du processus de déshydratation. Les valeurs obtenues en conditions isothermes pour les énergies d'activation de la décomposition sont en accord acceptable avec celles calculées à partir des courbes TG par la méthode de Freeman et Carroll. Les résultats cinétiques qui sont analysés dans le sens de la théorie de Mampel font conclure que c'est l'énergie d'activation du processus de nucléation qui détermine la vitesse de la formation de la surface; ils justifient le fait observé que la surface spécifique des échantillons traités sous vide est plus grande que celle des échantillons traités dans l'air.

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, Al ₄ · 2₂ , , . , , , . , , , , , , , , .

     

On the reduction of NiO forms in magnesia supported catalysts

Reducibility of Ni/MgO catalysts has been studied by the temperature-programmed reduction (TPR) technique in the temperature range of 373–1273 K. The profile of reduction reveals the presence of various forms of NiO. The effects of nickel loading and treatment temperature on catalyst reducibility have been evaluated. The formation of NiO–MgO solid solution controls the whole reduction of Ni/MgO system.

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Ni/MgO 373–1273 . NiO. . Ni/MgO NiO–MgO.

     

Investigations of solid phase transitions of low molecular organic compounds by differential scanning calorimetry

For the purpose of finding temperature standards for DTA at the temperature below 150°, some solid transitions of low molecular organic compounds were measured by differential scanning calorimetry. Among fourteen materials, we have concluded to select transitions for hexachloroethane (71°) and hexamethylbenzene (110°) as candidates for such standards.

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Zusammenfassung Zur Temperaturnormung unter 150° die DTA Methode wurden verschiedene organische Verbindungen von niedrigem Molekulargewicht und geeigneten Umwandlungen in fester Phase durch Differential Scanning Kalorimetrie geprüft. Von 14 verschiedenen Substanzen wurden Hexachloräthan (71°) und Hexamethylbenzol (110°) zum gesuchten Zweck geeignet gefunden.

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Résumé Pour le but de trouver des étalons de température au-dessous de 150°C pour l'ATD, on a examiné les transitions en phase solide de différents composés organiques de bas poids moléculaire à l'aide d'un analyseur enthalpique différentiel. Sur les 14 échantillons étudiés, on propose l'hexachloroéthane (71°) et l'hexaméthylbenzène (110°) comme étalons.

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150° . , 14 (71°) (110°), .

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The authors wish to thank Dr. H. G. McAdie of the Ontario Research Foundation, Canada, for his kind suggestions on this work.     

Steric substituent effect on the resin catalyzed hydrolysis of alkyl acetate esters

The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, E_s. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, S^x, values increase in the order: n-octyl-

, , 70%- . , , E_S. . , . , S^*, : --<-<, .

     

Analyse thermique differentielle et cinetique de reaction

Résumé Dans cette seconde partie, en désignant par la vitesse de chauffe supposée constante et(t) un paramètre dépendant du tempst, caractérisant le degré d'évolution de la transformation considérée, on établit les équations des courbes de température différentielleT== f [, (t)] dans le cas des transformations de phase (fusion, solidification) des transformations allotropiques et dans le cas des réactions de dismutation sans variation de masse. On montre également comment les relations obtenues sont modifiées lorsque l'on considère les réactions avec ou sans variation de masse, inverses de celles déjà étudiées. Enfin, on établit théoriquement les propriétés de la dérivée d/dt T, propriétés dont une est mise à profit dans certaines études de cinétique hétérogène faites à partir des courbes d'analyse thermique différentielle.

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Equations are given for describing the differential temperature curves of phase transformation (fusion and solidification) and allotropic transformations, as well as of dismutation reactions proceeding without any change in weight. It is shown how the obtained relationships are modified according to whether the reaction proceeds with or without weight change. Finally, the properties of the derivative d/dt gDT are established theoretically that can be used to advantage in the investigation of heterogeneous kinetics on the basis of DTA curves.

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Zusammenfassung Die Gleichung der differentialthermoanalytischen KurveT == f[, (t)] für den Fall von Phasenumwandlungen (Schmelzen, Erstarren), von allotropen Umsetzungen und von ohne Gewichtsänderung verlaufenden Umwandlungsreaktionen wurden theoretisch abgeleitet, wobei die konstante Aufheizungsgeschwindigkeit,(t) ein zeitabhängiger, den Verlaufsgrad der Reaktion kennzeichnender Parameter ist. Es wurde gezeigt, wie sich die erhaltenen Beziehungen ändern, wenn die Reaktionen mit oder ohne Gewichtsänderung in entgegengesetzter Richtung verlaufen. Gewisse Eigenschaften der Derivierten d/dtT wurden theoretisch untersucht. Eine von ihnen läßt sich bei der Untersuchung der Kinetik von heterogenen Reaktionen durch die Differentialthermoanalyse verwenden.

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II , (, ) , T=f[,(t)], ,(t) — , , . , . d/dt T; .

     

A study of the surface heterogeneity and catalytic activity of catalysts by means of reaction thermodesorption

Reaction thermodesorption is studied. A generalized wiew is offered regarding the routes along which the transformations take place under the conditions of temperature-programmed desorption.

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. , .

     

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 oxidation of D-altrose by aqua-cerium(IV) in perchloric acid medium

Kinetics of the oxidation of D-altrose by Ce(IV) perchlorate has been studied in perchloric acid medium. At equivalent concentrations the overall order of the reaction is two, being unity in each reactant. The reaction is characterized by a primary positive kinetic salt effect. Perchloric acid has been found to enhance the rate, while the addition of the reaction products retards the rate. No evidence for initial complexation has been obtained. Thermodynamic parameters have been determined and a mechanism consistent with the observed results is proposed.

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D- Ce(IV) . , . . , . . , .

     

Kinetic analysis of thermogravimetric data. XXVI

Ten metal and ammonium salts of the acid H₂[ReCl₆] were obtained by double decomposition reactions, and their pyrolyses in air atmosphere were studied by means of DSC measurements. The kinetic parameters of these reactions were derived and are discussed.

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Zusammenfassung 10 Metall- und Ammoniumsalze der Säure H₂[ReCl₆] wurden durch Doppelzersetzungsreaktionen erhalten. Die Pyrolyse dieser Salze in Luft wurde mittels DSC untersucht. Die kinetischen Parameter dieser Reaktionen wurden ermittelt und diskutiert.

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H₂[ReCl₆]. . .

     

Acid-base and catalytic properties of binary oxides in the oxidative dehydrodimerization of toluene

Acidity and basicity of binary oxide catalysts measured by the CO₂ and NH₃ thermodesorption method are compared with their catalytic activity in oxidative conversion of toluene. The rate of toluene dehydrodimerization is shown to increase with the catalyst basicity.

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CO₂ NH₃ . , .

     

Computation in kinetics, II. Simultaneous regression estimation of rate constants and initial concentrations

The general regression program KILET was used for simultaneous estimation of rate constants and initial concentrations. The method can be used either to improve the quality of fit calculating the possible analytical errors of some initial concentrations of a kinetic experiment or for analytical purposes, i.e. for the determination of analytes, while any side reactions can be taken into account.

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KILET - . - - , - , , .