Thermogravimetric study of diatomites

The thermal curves of diatomites (kieselguhrs) in air display different profiles, depending on the type and quantity of impurities (carbonates, clays, etc.) present. TG and DTG runs can be used for a quick diagnosis of quality, but also give a nearly quantitative picture of the silica content of these minerals.

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Zusammenfassung In Abhängigkeit von Art und Menge der Verunreinigungen (Karbonate, Tonerde usw.) weisen die thermischen Kurven von Diatomiten (Kieselguhr) in Luft unterschiedlichen Verlauf auf. Einfache TG- und DTG-Untersuchungen können als Schnelldiagnose zur Bestimmung der Qualität benutzt werden und geben ausserdem noch ein nahezu quantitatives Bild über den Silikatgehalt dieser Mineralien.

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( ) , (, . .). , .

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The authors acknowledge the financial support of this work by the Comisión Asesora de Investigatión Cientifica y Técnica, Spain, through Project No. PR84-0151.     

A method for the treatment of experimental data. Kinetic system comprising two irreversible first order consecutive reactions

A method is proposed for the treatment of data from a kinetic system comprising two irreversible first order consecutive reactions (ABC). It is based on the solving of contrary propositions for an ordinary differential equation.

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(ABC). .

     

Effect of preparation conditions on the properties of carbon-supported nickel catalysts

Carbon-supported Ni catalysts were prepared from nickel nitrate or chloride. Characterization was carried out by H₂ and CO chemisorption, XRD and TEM. Catalysts were further tested in the hydrogenolysis of n-butane.

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, , . H₂ CO, ., -.

     

Reactions of isoflavone and 2-hydroxyisoflavanone with sodium ethoxide in anhydrous ethanol

Recent observation /1,4/ on the existence and unreactivity of IV under basic conditions, as well as its part in the inhibitory effect on the decomposition into deoxybenzoin is unequivocally proved by comparing the decompositions of I and VI. It is also shown that the decomposition of I is detemined neither by the character of the solvent nor by the nucleophilic character of the reactant, but by the possibility of the formation of IV.

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IV , I VI. , I . , , IV.

     

DSC characterization of ZSM-5/MgO/Al2O3 catalysts

The physico-chemical characterization of magnesium-modified ZSM-5 zeolite catalysts has been performed by differential scanning calorimetry. Evidence has been found of the formation of magnesium oxide and the magnesium spinel phase in alumina-bonded ZSM-5 catalysts. DSC proved a suitable technique for characterization of these systems.

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Zusammenfassung Mg-modifizierte ZSM-5-Zeolithkatalysatoren wurden durch DSC charakterisiert. Es wurden Beweise für die Bildung von Magnesiumoxid und Magnesiumspinell in ZSM-5/Aluminiumoxid-Katalysatoren gefunden. DSC hat sich zur Characterisierung dieser Systeme als geeignet erwiesen.

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- 3CM-5, . - - . .

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This work was carried out within the Progetto finalizzato Energetica 2 of the National Research Council of Italy.     

Nonempirical calculations of water adsorption on bridged structural fragments of aluminosilicate

Within the discussion of the possibility to apply semiempirical methods for chemisorption calculations, nonempirical calculations of two types of adsorption complexes of H₂O molecule with bridged structural fragments of aluminosilicate have been carried out.

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, .

     

M?ssbauer spectroscopic studies of passivated layers of iron-containing catalysts for ammonia synthesis

Combined conversion electron (CEMS) and transmission -ray (MS) Mössbauer spectroscopy was used to study the structure of passivated layers of promoted and unpromoted iron-containing catalysts. In both catalysts the oxide-coated films were found to consist of small paramagnetic (at 300 K) clusters of ferric oxide.

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. , ( 300 ) .

     

Exchange kinetics of amino acid anions in solutions of ternary copper(II) complexes with diethylenetriamine

Rate constants for the chemical exchange of some amino acid anions in solutions of copper(II) ternary complexes with diethylenetriamine have been determined by the NMR method. The coordination of amino acid anions in ternary and binary species is different and ligand substitution in the Cu(II) complexes follows an associative mechanism.

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- (II) . - (II).

     

Temperature effects on coprecipitated Al,Fe-hydroxides during hydrothermal transformations

Studies of the hydrothermal behaviour of coprecipitated Al, Fe-hydroxides with aluminium contents from 5 to 50 mol% reveal that the temperature of the hydrothermal process strongly affects the reciprocal influence of Al(III) and Fe(III) ions on the direction of transformation of the initially amorphous gels.It has been found by X-ray diffraction analysis and IR spectroscopic investigations that at 373 K, up to 10 mol% Al, well-crystallized Al-substituted hydrohematite is formed; at 15–25 mol% Al the crystallinity falls off and the products are amorphous; and at 27.5–50 mol% Al the poorly-crystallized hydrohematite appears, accompanied by different crystalline aluminium trihydroxides, the equilibria of which depend essentially on the AlFe ratio and on the pH of the medium.The hydrothermal process carried out at 413 K yields the Al-substituted protohematite for samples with 15–50 mol% Al, whereas the unique crystalline phase of Al-hydroxide is a well-crystallized boehmite.

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Zusammenfassung Untersuchungen des hydrothermalen Verhaltens von kopräzipierten Al, Fe-Hydroxiden mit Aluminiumgehalten von 5–50 mol% haben ergeben, daß die Temperatur des hydrothermalen Prozesses den gegenteiligen Effekt von Al(III)- und Fe(III)-Ionen auf die Richtung der Umwandlung der anfänglich amorphen Gele wesentlich beeinflußt. Durch Röntgendiffraktion und IR-Spektroskopie wurde ermittelt, daß bei 373 K bis zu 10 mol% Al gut kristallisierter, Al-substitutierter Hydrohämatit gebildet wird. Bei 15–25 mol% Al sind die Produkte amorph und bei 27,5–50 mol% Al liegt schlecht kristallisierter Hydrohämetit vor, begleitet von verschiedenen kristallinen Aluminiumtrihydroxiden, deren Gleichgewicht im wesentlichen vom Al/Fe-Verhältnis und vom pH des Mediums abhängt. Der bei 413 K. ausgeführte hydrothermale Prozeß ergibt Al-substituiertes Protohämatit für Proben mit 15–50 mol% A, während ein gut kristallisierter Boehmit die einzige kristalline Al-Hydroxidphase ist.

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5 50 , . , 373 10 , . 15 25 , , 27,5–50 — . , , , AlFe pH . , 413 15–50 , , .

     

IR study of adsorbed piperidine dehydrogenation on oxidic or sulfided Ni?W/Al2O3 catalysts

IR spectroscopy has been used to follow the transformation at different temperatures of piperidine chemisorbed on oxidic or sulfided Ni–W/Al₂O₃ catalysts. Formation of an intermediate species, possibly tetrahydropyridine, and pyridine is evidenced. Their formation temperature on the sulfided samples accounts for the catalyst activity in pyridine hydrogenation under H₂ pressure.

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- , Ni–W/Al₂O₃, . , , . .

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This work was supported by the Groupement scientifique Hydrotraitement catalytique (CNRS-IFP, TOTAL. ELF).     

Methane synthesis from CO/H2O mixture on supported nickel catalysts, II. Surface species in CO?H2 and CO?D2O interaction by IR spectroscopy

The species resulting in CO, CO+H₂ or CO+D₂O adsorption on supported Ni catalysts were followed by IR spectroscopy and their role in methane synthesis mechanism is discussed.

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- , CO, CO+H₂ CO+D₂O . .

     

ESR spin-trapping study of the radicals produced in the photochemical reaction of Cr, Mo, W hexacarbonyls with carbon tetrachloride

The effect of UV and visible light on the catalytic reaction has been investigated in the systems containing Cr, Mo and W hexacarbonyls, nitrone and nitroso type of spin-traps in carbon tetrachloride. Under these reaction conditions not only radical CCl ₃ ^. but also dialkyl-, diphenyl- and acyl-phenylnitroxides have been trapped.

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, Cr, Mo W, . CCl ₃ ^. , , .

     

Studies of dynamic properties of heterogeneous catalytic reactions in a closed isothermal gradientless system over biographically inhomogeneous catalyst surface

The dynamics of a closed isothermal system of constant volume consisting of an ideal gaseous mixture and particles adsorbed over the biographically inhomogeneous catalyst surface, has been studied. The existence, uniqueness and asymptotic stability of the point of detailed equilibrium in each positive reaction simplex has been proved.

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, , . , , .

     

Thermal analysis of carbon anti-burn-on disperse systems used in foundries

Anti-burn-on disperse systems for foundry use, containing carbon (graphite or anthracite after different pretreatments, or mixtures thereof) in carboxymethylcellulose-water, were studied by TG-DTA. Thermal effects are attributed to the evaporation of water, the evolution of other volatiles and the beginning of ignition. TG is useful for determination of the water content.

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Zusammenfassung Oxidationshemmende Dispersionen für die Giesserei, die aus Kohle (Graphit, Anthrazit verschiedener Vorbehandlung bzw. Gemische daraus), Carboxymethylcellulose und Wasser bestehen, wurden durch TG-DTA untersucht. Die thermischen Effekte werden der Verdampfung von Wasser, dem Entweichen anderer flüchtiger Produkte und der beginnenden Verbrennung zugeordnet. Der Wassergehalt kann mittels TG bestimmt werden.

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(, ), , - — . , . .

     

Thermal decompositions of kaolinite intercalation compounds

Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.Decomposition of the potassium acetate intercalation compound proceeds simultaneously with the dehydroxylation of kaolinite at an extrapolated onset temperature of 360 °C. The high-temperature reactions (dehydroxylation and transformation) of kaolinite obtained through the decomposition of intercalation compounds with volatile intercalation agents depend on the conditions applied during decomposition.

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Zusammenfassung Mittels Röntgenbeugung und thermischer Analyse (simultane TG-DTG-DTA und quasi-isotherme-quasi-isobare TG) konnte gezeigt werden, daß das molare Verhältnis Einlagerungsmedium/Kaolinit in allen Einlagerungsverbindungen etwa 1 ist. In gesättigter Atmosphäre des jeweiligen Einlagerungsmediums ist die Einlagerungsverbindung stabil bis über 150 °C. Die Zersetzung der Kaliumacetat-Einlagerungsverbindung läuft zusammen mit der Dehydroxylation des Kaolinits bei einer extrapolierten onset-Temperatur von 360 °C ab. Die Hochtemperaturreaktionen (Dehydroxylation, Phasenneubildung) von Kaolinit, der aus der Zersetzung von Einlagerungsverbindungen mit flüchtigen Einlagerungsmedien erhalten würde, werden von den Zersetzungsbedingungen beeinflußt.

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- ( , , ) , - 1. , , 150°. — ** 360°, ** . , , .

     

Thermal decompositions of [Co(py)4Cl2]2PbCl6 and [Ru(dipy)3]PbCl6

The thermal decompositions of [Co(py)₄.Cl₂]₂PbCl₆ and [Ru(dipy)₃]PbCl₆ were examined by dynamic thermoanalytical methods and under isothermal conditions permitting quantitative determination of some of the reaction products. A comparative study of the corresponding chloride salts was also performed. Both groups of compounds decompose with the liberation of chlorine and organic ligands (and H₂O in the case of the hydrates of the chlorides), and the process is accompanied by the simultaneous transitions Pb(4 +)Pb(2 +) and Co(3 +) Co(2 +). The ruthenium complex salts initially decompose without a change in the oxidation state of the Ru atom, but upon thermal treatment of the hexachloroplumbate certain chlorination products of the organic ligands are formed.

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Zusammenfassung Mit Hilfe dynamischer thermoanalytischer Methoden und unter die quantitative Bestimmung einiger Reaktionsprodukte ermöglichenden isothermen Bedingungen wurde die thermische Zersetzung von [Co(py)₄Cl₂]₂PbCl₆ und [Ru(dipy)₃]PbCl₆ untersucht. Eine vergleichende Betrachtung der korrespondierenden Chloride wurde ebenfalls durchgeführt. Die Zersetzung beider Verbindungsgruppen geschieht unter Freisetzung von Chlor und organischen Liganden (bei den Hydraten der Chloride auch von Wasser) und ist von den übergängen Pb(4 +) Pb(2 +) bzw. (Co(3 +) Co(2 +) begleitet. Die Komplexsalze des Rutheniums zersetzen sich anfangs ohne Änderung der Oxydationsstufe des Rutheniumatoms, es bilden sich allerdings infolge von Wärmezufuhr aus dem Hexachloroplumbat verschiedene Chlorprodukte der organischen Liganden.

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[Co(py)₄l₂]₂PbCl₆ [Ru(dipy)₃]PbCl₆ , . . , . . , .

     

Kinetic isotope effect in trans-alkylation with ethylbenezene

Kinetic isotope effect (KIE) measurements in the trans-alkylation of toluene and benzene with ethylbenzene in hexane in the presence of AlBr₃ at 313 K indicate that deuterium in the toluene methyl group causes a small inverse KIE characteristic for a -complex transiton state. The small direct KIE found for the reaction with C₂D₅C₆H₅ does not agree with a mechanism involving alkyl-and -phenylalkyl cations.

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() - AlBr₃ 313 . , , - C₂D₅C₆H₅ , - -.

     

SEM-EDAX investigations of use-related microstructural changes in an ammonia synthesis catalyst

Changes in the topography and distribution of the chemical constituents in the microspaces of oxide type catalysts and prereduced catalysts have been investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX) before and after six years of use in industrial ammonia synthesis reactors.

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6- .

     

Selective hydrogenation of fatty oils on alloyed Ni?Al catalyst. I. Kinetic model

On the basis of literature data concerning the reaction mechanism, a kinetic model for the selective hydrogenation of cotton-seed oil on the S-3 commercial alloyed Ni–Al catalyst is suggested. Its parameters have been identified according to the experimental data obtained in an agitated slurry reactor at T=140–200°C and P=0.2–0.8 MPa.

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, C-3. , , t=140–120°C, P=0.2–0.8 .