Zur thermoanalytischen charakterisierung von amorphen synthetischen,organisch nachbehandelten Kieselsäureprodukten

Zusammenfassung Für eine anwendungstechnische Beurteilung von amorphen synthetischen Kieselsäuren sind neben der Dispersität und Morphologie insbesondere auch strukturelle Eigenschaften bedeutsam. Die vorliegende Veröffentlichung zeigt, daß auf der Basis von thermoanalytischen Untersuchungen eine Unterscheidung unterschiedlicher Kieselsäuretypen möglich ist. Aus den TG- und DTA-Ergebnissen sind dabei Aussagen über die Art und Menge des adsorptiv bzw. chemisch gebundenen Wassers, sowie die oxydative Zersetzung des organischen Beschichtungsmittels abzuleiten.

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Besides dispersity and morphology, structural characteristics are of importance for the estimation of amorphous synthetic silicic acids with regard to their application. The present publication shows that it is possible to identify the different silicic acid types on the basis of thermoanalytical studies. The TG and DTA results provide information on the type and quantity of adsorbed or chemically bound water, and on the oxidative decomposition of the organic coating agent.

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, . . , .

     

Estimation of proton donor ability of surface hydroxy groups in terms of proton affinity

A method to estimate the proton donor ability of hydroxy groups in terms of proton affinity (PA) is suggested. The PA of hydroxy groups of aerosil and of decationated zeolite type Y have been determined.

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(PA). PA .

     

A method for the temperature calibration of pushrod dilatometers

A method for the temperature calibration of pushrod dilatometers and thermomechanical analysis systems using the melting points of metal standards has been established. With this technique, the measured melting temperatures of high-purity metal standards are determined from the sharp change in the length curve which accompanies melting. This procedure was used for the absolute temperature calibration of a pushrod dilatometer capable of operation up to 2000 °C. The results of this calibration show that the technique can be used with a high degree of accuracy and confidence.

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Zusammenfassung Mit Hilfe von Schmelzpunkten metallischer Standards wurde eine Methode zur Temperatureichung von Schubstangendilatometern und TMA-Systemen entwickelt. Die verwendete Technik basiert darauf, daß beim Erreichen der Schmelztemperatur des hochreinen, scheibenförmigen Metallstandards, der zusammen mit einem neutralen Probekörper verwendet wird, eine deutliche, spontan einsetzende Längenänderung in der Dilatometerkurve erkennbar wird. Dieses Verfahren wurde zur absoluten Temperatureichung eines Schubstangen-Dilatometers, das bis 2000 °C arbeitet, angewandt. Die Ergebnisse dieser Kalibrierung zeigen, daß diese Technik mit einem hohen Grad an Genauigkeit und Zuverlässigkeit eingesetzt werden kann.

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, -. - . , 2000 °. , .

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On sabbatical leave from the University of Rhode Island, Kingston, RI 02881, U.S.A.

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The authors wish to express their thanks to Mr. E. Braun, Netzsch Gerätebau, for his work with the dilatometer and the preparation of the test samples.     

Kinetic model for anisol synthesis by methanol alkylation of phenol on a zeolite catalyst

A kinetic model for the reaction of phenol alkylation by methanol on a zeolite catalyst tested is suggested. Estimate of the kinetic parameters confirms the proposed reaction mechanism.

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. .

     

Catalysis of thiophene hydrogenolysis by bimetallic sulfide catalysts of different compositions

The activity of sulfide catalysts M_I/SiO₂, M_I/WS₂, (M_I,W)/SiO₂ and (Ni,M_II)/SiO₂ (M_I is a first row transition metal, and M_II=Nb, Mo, W or Re) in the thiophene hydrogenolysis reaction has been studied. Activities of mono- and bimetallic catalysts are found to change in the same manner depending upon the nature of M_I. The formation of a sulfide bimetallic species (SBMS) is suggested.

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M_I/SiO₂, M_I/WS₂, (M_I,W)/SiO₂ (Ni, M_II)/SiO₂, M_I — , M_II–Nb, Mo, W, Re. - M_I. .

     

Studies on the active sites for dehydrocyclization reaction over Pt?Al2O3 catalysts

The work represents a search for direct evidence of the existence of low temperature and high temperature active sites over Pt–Al₂O₃ for dehydrocyclization reaction. It is suggested that the former consists of dispersed metallic Pt and the latter of super-dispersed metallic Pt or isolated atomic Pt and ionic Pt.

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- - Pt/Al₂O₃ . , Pt, Pt, Pt.

     

Hydrogenation of nitric oxide on platinum black in acidic solution

By comparison of the catalytic hydrogenation and electrochemical reduction of NO on platinum black catalysts it has been shown that the hydrogenation of NO to ammonia and to hydroxylamine occurs in the diffusion controlled region only.

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NO , NO .

     

Mechanism of methane photooxidation on V/SiO2 catalyst

CH₄ photooxidation on V/SiO₂ catalyst in the presence of gaseous oxygen has been studied by the mass-spectometric method. It has been established that CO₂ forms due to the interaction of CH₄ with surface oxygen anions bonded to vanadium ions. Photodecomposition of V⁴⁺O ₂ ^– species formed in O₂ adsorption on reduced vanadium ions leads to the reoxidation of the latter.

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- CH₄ V/SiO₂ . , CO₂ CH₄ , . V⁴⁺O ₂ ^– O₂ , .

     

Study of nitric oxide interaction with the Pt(100) surface by electron energy loss spectroscopy

The adsorption and dissociation of nitric oxide on the Pt(100) surface have been studied using Electron Energy Loss Spectroscopy.

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Pt(100).

     

Etude enthalpique de l'interaction du chelate Eu(DPM)3 avec une serie de pyridines en solution

Résumé Les constantes d'équilibre et les variations d'enthalpie entre une série de pyridines méthylées et le chélate tris(dipivaloylméthanato) europium (III) ont été déterminées à 36° dans le chloroforme par des mesures calorimétriques. Nous constatons que la chaleur de complexation de l'adduit 1/1 est sensible à l'encombrement stérique du ou des méthyles en de l'hétéroatome. Cependant, lorsque le rapport des concentrations entre la base et le chélate est supérieur à l'unité, l'enthalpie de la réaction est modifiée. Dans ce cas, nous attribuons cette modification à l'existence d'un équilibre supplémentaire entre le chélate et les bases conduisant à la formation de l'adduit 1/2.

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Equilibrium constants and enthalpy changes are reported between a series of substituted methylpyridines and the chelate tris(dipivaloylmethanato)europium(III) in chloroform solution at 36° as obtained by calorimetric measurements. The 11 adduct enthalpies are ordered in agreement with the electronic and steric effects of the methyl group in a to the heteroatom. Some anomalies are observed when the concentration ratio between ligand and chelate is higher than unity. These findings conform with the hypothesis of the existence of a supplementary equilibrium which may be assigned to the formation of the 12 adduct.

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Zusammenfassung Es wird über durch kalorimetrische Messungen ermittelte Gleichgewichtskonstanten und Enthalpie-Änderungen zwischen einer Reihe substituierter Methylpyridine und dem Tris(dipivaloylmethanato)-Europium (III) Chelat in Chloroform bei 36° berichtet. Die 1/1 Addukt-Enthalpien befinden sich in Übereinstimmung mit dem elektronischen und sterischen Effekt der Methylgruppe im a des Heteroatoms. Einige Anomalien werden beobachtet, wenn das Konzentrationsverhältnis zwischen dem Liganden und dem Chelat höher als eins ist. Diese Feststellungen sind im Einklang mit der Hypothese der Existenz eines supplementären Gleichgewichts und können der Bildung des 1/2-Adduktes zugeordnet werden.

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, , // () 36°. 11 , - . , . . . 12.

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Les auteurs souhaitent exprimer ici leurs remerciements au Docteur J. F. Gal pour l'intérêt qu'il a porté á ce présent travail.     

Investigation of catalysts for thermal conversion of alkaline salts of benzenecarboxylic acids

Thermal decomposition of cadmium and zinc salts of benzenecarboxylic acids as catalysts for the thermolysis of alkaline salts of the same acids have been studied.

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Determination of the surface hydroxy groups on alumina and silica-alumina catalysts by dimethylzinc

The earlier proposed pulse flow method for the determination of surface OH groups based on the reaction of gaseous dimethylzinc tetrahydrofuranate with active hydrogen was applied to alumina and silica-alumina catalysts. The concentrations of OH groups found by this method are in a good agreement with the published data, obtained by deuterium exchange and gravimetry.

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, , OH, , - . OH, , , .

     

Ba(OH)2 as catalyst in organic reactions, III. The structure of adsorbed ylids

The nature of adsorbed sulfonium and phosphonate ylids on a new barium hydroxide catalyst (C-200) is analyzed by IR. The catalytic activity of C-200 in solid-liquid phase transfer conditions is explained by these IR studies.

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(C-200) . C-200 - .

     

Recombination of polyatomic ester peroxy radicals in solution

Termination rate constants of peroxy radicals of seven polyatomic esters in benzene and perflouorooctane media have been measured by pulse photolysis. Recombination of peroxy radicals for all esters examined proves to be diffusion controlled. Reactivity of peroxy radicals in the termination reaction grows with increasing number of ester groups.

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Mechanism of o-xylene conversion on magnesium modifications of Y zeolite

o-Xylene conversions has been investigated in the presence of MgNaY zeolites with different Si/Al ratios and degrees of exchange. Disproportionation proceeds to a higher degree than does isomerization. The distribution of reaction products is attributed to geometric factors. The results are in agreement with a monomolecular mechanism of isomerization.

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- MgNaY Si/Al . , , . . .

     

Immobilized sol of cobalt(III) hydroxide as an efficient catalyst of water oxidation to dioxygen by the Ru(bpy)33+ complex

Catalysts of water oxidation to dioxygen by Ru(bpy) ₃ ³⁺ have been obtained by immobilization of colloidal Co(III) hydroxide on supports of the hydroxide types. These supports are found to be able either to enhance (Al(III), Bi(III), Sn(IV) and Ce(IV) hydroxides) or to weaken (Fe(III) and Mn(IV) hydroxides) the catalytic efficiency of the initial sol. The possible nature of the influence of the support is discussed.

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Ru(bpy) ₃ ³⁺ Co(III). - , ( Al(III), Bi(III), Sn(IV), Ce(IV)), ( Fe(III), Mn(IV)) . .

     

Determination of the strength of aprotic acidic centers on catalyst surfaces from the IR spectra of adsorbed carbon monoxide

Correlations between the adsorption heats of carbon monoxide on aprotic acidic centers and the v _CO values in IR spectra have been studied. In the case of aprotic centers formed by cations of non-transition metals, v _CO is shown to be linearly dependent on the adsorption heat.

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v _CO . , , , v _CO .

     

Measurements of thermal conductivity and specific heat of dilute metallic alloys in the form of small samples by electrical method

The method of determining the thermal conductivity depends upon a relation between the maximum temperature ( _m ) attained for a given current and potential difference (V) in a current carrying specimen. Heat is assumed to enter and leave specimen only through the surfaces through which electric current enters and leaves, other surfaces being insulated against flow of both heat and electricity. The plane ends of the rod were taken to be isothermal and equipotential surfaces held at a constant temperature.For the measurement of the specific heat, a homogeneous constant Joule heating is imposed. The initial slope of ( _m ) as a function of time is inversely proportional of heat capacity regardless of heat losses. Measurements on dilute Ni base Cr alloy sample up to 360 °C.

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Zusammenfassung Die Methode zur Bestimmung der Wärmeleitfähigkeit hängt vom Verhältnis zwischen der bei einer bestimmten Stromstärke erreichten Maximumtemperatur ( _m ) und dem Spannungsabfall an einem stromdurchflossenen Prüfling ab. Es wird davon ausgegangen, daß die Wärme nur an den Flächen in die Probe gelangt bzw. diese verlässt, an denen auch der elektrische Strom ein- bzw. austritt, da die übrigen Oberflächen gegen Strom- und Wärmefluss isoliert wurden. Die planen Enden des Messstabes wurden bei konstanter Temperatur gehalten und als isotherme bzw. äquipotentiale Flächen angesehen.

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( _m ), (V) . , , , . , , . . _m , , . Ni-Cr 360°.

     

Compounds responsible for the deactivation of H-USY zeolite during the alkylation of phenol with methanol

H-USY deactivates very rapidly during the alkylation of phenol with methanol at 200°C. The retention in the pores of compounds resulting from successive O- and C-alkylation of phenol (such as polymethylphenols and polymethylanisoles) is responsible for this deactivation. The retention of these compounds in the pores is not due to their steric blockage but to their low volatility and their strong adsorption.

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H-USY 200°C. , - - , ( -). , .

     

Preparation,spectral and thermal studies of neodymium zirconyl oxalate hexahydrate

Neodymium zirconyl oxalate (NdZrOX) is prepared and characterized by chemical analysis and ir spectral studies. Its thermal decomposition has been investigated by using DTA, TG, DTG, X-ray diffraction and ir spectroscopy. On the basis of thermogravimetry and isothermal studies a probable mechanism for the decomposition is proposed. The decomposition proceeds mainly through three stages: i) dehydration between RT-413 K, ii) decomposition of oxalate between 413–943 K and iii) decomposition of the carbonate between 1028–1235 K to give a mixed oxide. The ir spectra and X-ray diffraction studies are made for identification of the intermediates. X-ray diffraction studies of the end product indicates that it belongs to cubic crystal system witha=11.520 Å.

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Zusammenfassung Neodymzirkonyloxalat (NdZrOX) wurde dargestellt und durch chemische Analyse und IR-spektroskopische Untersuchungen charakterisiert. Die thermische Zersetzung dieser Verbindung wurde mittels DTA. TG, DTG, Röntgendiffraktometrie und IR-Spektroskopie untersucht. Basierend auf Ergebnisse der Thermogravimetrie und isothermer Methoden wird ein möglicher Zersetzungsmechanismus vorgeschlagen. Die Zersetzung verläuft im wesentlichen über drei Stufen: i) Dehydratisierung zwischen Zimmertemperatur und 413 K, ii) Zersetzung des Oxalats zwischen 413 und 943 K und iii) Zersetzung des Carbonats zwischen 1028 und 1235 K unter Bildung eines Mischoxides. IR-spektroskopische und röntgendiffraktometrische Untersuchungen wurden zur Identifizierung der Zwischenprodukte ausgeführt. Die röntgendiffraktometrische Untersuchung des Endproduktes ergibt eine kubische Zelle mita= 11.520 Å.

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-. , , , . . , , : / 413 , / 413943 / 1028–1235 . - . - , =11.520 Å.

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One of the authors (VBR) is grateful to CSIR (India) for the senior research fellowship.