Adsorption properties of membrane catalysts

A method for adsorption measurements on catalysts with small surface areas has been devised. The adsorption of argon has been examined on membrane catalysts made from Pd–Ni and Pd–Ru alloys before and after catalytic experiments. A sharp change of the adsorption properties and an increase in the surface areas of catalysts after reactions have been observed.

---

. Pd–Ni Pd–Ru . - .

     

A study of the kinetics of the phase transition aragonite → calcite by dilatometric thermal analysis

The first-order phase transition in the system aragonite-calcite (CaCO₃) was studied with natural and synthetic aragonites. The studies were carried out by dilatometry on a derivatograph, under non-isothermal conditions. It was found that the polymorphic transformation of aragonites into calcite is described by the Avrami equationl=1 — exp (-kt ⁿ ), with the exponentn having a value close to 1. The activation energy values found for the aragonites studied were 184– 205 kJ/mol, while the values of the pre-exponential factorz were 1014-10¹² s^–1 in the conversion rangel=0.10–0.66.

---

Zusammenfassung Der Phasenübergang erster Ordnung wurde im System Aragonit-Kalzit (CaCO₃) an natürlichen und synthetischen anorganischen Aragoniten untersucht. Die Untersuchungen wurden durch Dilatometrie in einem Derivatographen unter nicht-isothermen Bedingungen durchgeführt. Es wurde festgestellt, daß die polymorphe Umwandlung der Aragonite zu Kalziten durch die Avrami-Gleichungl=1 – exp (–kt ⁿ ) beschrieben wird, wobei der Exponentn einen Wert in der Nähe von 1 hat. Die für die untersuchten Aragonite gefundenen Werte der Aktivierungsenergie waren 185 ... 207 kJ/Mol, die Werte des präexponentiellen Faktorsz betrugen 10¹⁴ ... 10¹² s^–1 im Konversionsbereichl=0.10...0.66.

---

Résumé On a étudié la transition de phases du premier ordre qui a lieu dans le système aragonite-calcite (CaCO₃) dans des aragonites minérales, naturelles et synthétiques. Les études ont été effectuées par dilatométrie dans un dérivatographe en conditions non-isothermes. On a trouvé que la transformation polymorphe des aragonites en calcite est décrite par l'équation d'Avramil=- exp (-kt ⁿ ), l'exposantn étant proche de 1. Les valeurs des énergies d'activation trouvées pour les aragonites étudiées se sont élevées à 185 ... 207 kJ/mole, les valeurs du facteur pré-exponentielz à 10¹⁴... 10¹² s^–1, dans l'intervalle de conversionl= =0.10 ... 0.66.

---

- (CaCO₃). : . . , l=1-(–kt ⁿ), n - , . 184–205 / , =10¹⁴-10¹² cek^–1 l=0.10–0.66.

     

Recent progress in numerical methods for the determination of thermokinetics

The results of a multinational concerted programme on the determination of thermokinetics are presented. The purpose of the programme was to compare different numerical methods which have been independently proposed for the determination of thermokinetics from experimental calorimetric data. To achieve this end, the same experimental data, obtained from two heat-flow calorimeters, were distributed and successively analyzed by the different methods. Numerical methods based on the state function theory, on Fourier transform analysis, on dynamic optimization and on a simple differentiation of the data were thus critically tested.

---

Zusammenfassung Es wurden die Ergebnisse der gemeinsamen Arbeiten über die Bestimmung der Thermokinetik mit 4 numerischen Methoden (dynamische Optimalisierung, Methode der Zustandfunktionen, harmonische Analyse und umgekehrte Korrektion) vorgestellt. Die experimentellen Daten wurden mit Hilfe von 2 Kalorimetern mit einer konstanten Temperatur des Isoliermantels ermittelt. Die Durchführung der Versuche ermöglichte ein Vergleich der angewandten Methoden.

---

Résumé Les résultats d'un programme de recherches concerté multinational sur la détermination des données thermocinétiques sont présentés. Le but du programme était de comparer différentes méthodes numériques proposées indépendamment pour la détermination des données thermocinétiques à partir des mesures calorimétriques expérimentales. Pour celà, les mêmes données expérimentales fournies par deux calorimètres à flux de chaleur ont été distribué es et analysées successivement par 4 méthodes: utilisation des variables d'état, analyse de la transformée de Fourier, optimalisation dynamique et simple différentiation des données.

---

. , . , , . , , , .

     

Investigation of the self-heating phenomenon in the bulk polymerization of acrylonitrile

The temperature of the polymerizing system was measured with a thermistor during the bulk polymerization of acrylonitrile initiated by azoisobutyronitrile. The temperature of self-heating suddenly rises at a conversion of about 2%. This jump of temperature is presumably caused by the formation of a gel structure and, consequently, the outfall of thermal convection within the system.

---

, -- . , - . - , .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

---

, H⁺. . , , , .

     

Structural changes of NaX zeolite during the H2S+O2 reaction

Infrared spectra in the 600, 700, and 1000 cm^–1 regions and X-ray investigations indicate that during H₂S+O₂ reaction in the temperature region of 293–473 K partial dealumination of the NaX zeolite crystal structure occurs. The dealumination increases with reaction temperature.

---

- 600, 700 7000 ^–1 , H₂S+O₂ 293–473 NaX. .

     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

---

Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

---

Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

---

, - , , () . .

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

---

pH=8+9. .

     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

---

Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

---

, , , . . , . , , . , .

     

Generation of model reactions leading to limit cycle behavior

The system of differential equations by Feistel and Ebeling has been generalized. Some new formal kinetic reactions with two internal components, which may exhibit limit cycle behavior have been studied. Based upon the numerical integration of the deterministic models of these reactions the oscillatory character of the systems has been confirmed.

---

. , . .

     

DTA investigation of the solid-liquid equilibrium for methyl derivatives of naphthalene with some nitroaromatics

The two-component solid—liquid phase eqilibria systems of some methyl derivatives of naphthalene with 2,4,6-trinitrophenol and 2,4,6-trinitrotoluene have been examined by DTA. All systems contain molecular complexes with 11 compositions.

---

Zusammenfassung Zweikomponentige Fest-Flüssig-Phasengleichgewichtssysteme von einigen Methylderivaten von Naphthalen mit 2,4,6-Trinitrophenol und 2,4,6-Trinitrotoluol wurden mittels DTA untersucht. Alle Systeme enthalten Molekülkomplexe der Zusammenserzung 11.

---

2,4,6- 2,4,6-. 11.

     

Influence of mechanical activation on decomposition of a chalcopyrite-pyrite mixture in an oxidizing atmosphere

The influence of the addition of pyrite and mechanical activation on an oxidative decomposition of chalcopyrite was studied. The course of the thermoanalytical curves and X-ray identification of the products showed that addition of pyrite affects mainly the endothermic processes taking place in region of low temperatures but does not significantly influence the temperature of CuSO₄ formation and its content in the products of decomposition. Changes in fine and superfine structure of chalcopyrite brought about by mechanical activation at grinding cause the complex of exothermic oxidative reactions to proceed at temperatures as much as 180 deg lower than for a non activated sample. The endothermic effect of these oxidation reactions become more marked and the proportion of CuSO₄ in the products of the oxidative decomposition increases significantly.

---

Zusammenfassung Am oxidativen Zerfall von Chalkopyrit wurde der Einfluss der Zugabe von Pyrit sowie der mechanischen Aktivierung untersucht. Der Verlauf der thermoanalytischen Kurven und Röntgendiffraktionsanalyse der Produkte zeigten, dass die Zugabe von Pyrit hauptsächlich die sich bei niedrigeren Temperaturen abspielenden endothermen Prozesse beeinflusst, nicht aber die Bildungstemperatur von CuSO₄ sowie dessen Gehalt in den Zersetzungsprodukten. Durch mechanisches Aktivieren mittels Feinmahlen hervorgerufene Veränderungen in der Fein- und Superfeinstruktur lassen die Gesamtheit der exothermen oxidativen Reaktionen bei Temperaturen ablaufen, die etwa 180 Grad unterhalb derer für unaktivierte Proben liegen. Die endotherme Färbung dieser Oxidation wird eindeutiger und der Anteil von CuSO₄ in den Produkten des oxidativen Zerfalles nimmt eindeutig zu.

---

. , . , , - , 180° , . - .

     

Kinetic study of the thermal decomposition of heterocyclic thiol complexes under non-isothermal conditions

The thermal decomposition in the solid-phase has been studied by thermogravimetric (TG) and differential thermal analysis (DTA) techniques for a number of heterocyclic thiol complexes. The method of Coats and Redfern was used to study the kinetics of the thermal decomposition process. The enthalpy changes and activation energies for the decomposition have been calculated.

---

Zusammenfassung Die thermische Zersetzung in fester Phase wurde an einigen heterozyklischen Thiolkomplexen mit den Methoden der dynamischen Thermogravimetrie (TG) und der Differentialthermoanalyse (DTA) untersucht. Die Methode von Coats und Redfern wurde zum Studium der Kinetik des thermischen Zersetzungsvorganges eingesetzt. Die Enthalpie-Änderungen und Aktivierungsenergien der Zersetzung wurden berechnet.

---

Résumé Etude de la décomposition thermique en phase solide de plusieurs complexes thiols hétérocycliques par thermogravimétrie (TG) et par analyse thermique différentielle (ATD). La méthode de Coats et Redfern a été appliquée pour déterminer la cinétique du processus de la décomposition thermique. Les variations d'enthalpie et les énergies d'activation de la décomposition ont été calculées.

---

(TG) (DTA) . . .

---

---

We are grateful to Prof. K. C. Joshi, Head of the Chemistry Department and Dr. A. K. Rai of Rajasthan University, Jaipur for permitting the generous use of the thermorecording balance at the University and to Dr. E. R. Saxena, Assistant Director, Mineral Products and Inorganic Chemicals Division and Mr. P. Narayanachar of Regional Research Laboratory, Hyderabad for their valuable assistance in taking DTA trace. Thanks are also due to Prof. V. V. S. Murti, Head of the Chemistry Department, University of Delhi for his interest in the work. The author (K. A. V.) thanks the University Grants Commission, New Delhi for the award of the fellowship under which these investigations have been carried out.     

Homogeneous kinetics with programmed temperature variations,I

A new method is proposed for the derivation of kinetic parameters of reactions in homogeneous systems, by carrying out kinetic measurements under conditions of programmed temperature variations, instead of performing them under isothermal conditions at different temperatures. The basic relations are given for simple, paralle and complex reactions, without specifying the analytical shape of the temperature programme function.

---

Zusammenfassung Es wurde eine neue Methode zur Ableitung kinetischer Parameter von in homogenen Systemen verlaufenden Reaktionen vorgeschlagen. Die kinetische Messung wurde unter programmierten Temperaturänderungen ausgeführt, anstatt unter isothermischen Bedingungen bei verschiedenen Temperaturen. Die grundlegenden Beziehungen wurden für einfache, parallele oder komplexerweise verlaufende Reaktionen beschrieben, ohne auf die Form der Funktion des Temperaturprogrammes Rücksicht zu nehmen.

---

Résumé On propose une nouvelle méthode de calcul des paramètres cinétiques des réactions en milieu homogène. Les mesures cinétiques sont effectuées en programmant les variations de température au lieu d'opérer en thermostat à différentes températures. On donne les relations fondamentales pour les réactions simples, parallèles et complexes, sans prendre en considération la forme analytique de la fonction du programme de la température.

---

, , , . , .

     

Determination of diffusion coefficients of radicals by photochemical space intermittence method. Temperature effect on the diffusivity of CCl

Diffusion coefficients of CCl ₃ ^. radicals at T=298–343 K have been measured using the photochemical space intermittence method. The estimated activation energy of CCl ₃ ^. diffusion in CCl₃Br solutions amounts to 24 kJ/mol.

---

298–343 . CCl ₃ ^. 24 /.

     

The static microreactor technique a new, simple method for determination of kinetic parameters of gas-phase heterogeneous catalytic reactions

The dehydrogenation of methanol on a silver catalyst was studied in a static microreactor at 376–457°C, with initial methanol partial pressures of 60–90 Torr. The apparent activation energy agrees well with literature data. The experimental data suggest that the static microreactor is a suitable means for the rapid acquisition of preliminary kinetic data.

---

376–457°C, 60–90 . . , .

     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic(III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic(V) to arsenic(III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800°C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2g/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3) of 0.01g/L using a 0.5mL sample. The reagent blank was 0.001±0.0003 absorbance units and the standard deviation of 10 measurements of the 2 g/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

Thermo-dielectric analysis

By means of thermo-dielectric analysis, some natural and synthetic zeolites were studied (clinoptilolite, mordenite,X, Y andA). The results indicate the existence of two effects, one related to water evolution, reflected in a decrease of dielectric constant; the second peak is related to ionic conduction at high temperature. Both peaks characterize zeolites, in thermo-dielectric analysis.

---

Zusammenfassung Einige natürlich und synthetische Zeolithe (Klinoptilolit, Mordenit,X, Y undA) wurden mittels thermodielektrischer Analyse untersucht. Zwei Effekte wurden beobachtet. Der eine ist mit der Abgabe des Wassers verbunden und spiegelt sich in der Abnahme der dielektrischen Konstante wider, der zweite ist durch ionische Leitfähigkeit bei hohen Temperaturen bedingt. Zeolithe können durch beide Effekte charakterisiert werden.

---

- (, ,X, Y ). , . . .