Effects of radioactivity on surfaces: I. Influence of Cr-51 on the catalytic activity of chromium catalysts

Chromium catalysts were prepared on monolith supports, some of them with radioactive Cr-51 in the surface. The dehydrogenation-hydrogenation reaction of cyclohexene was used to compare the catalytic activities of the radioactive and inactive catalysts. Differences were observed in the distribution of the main products at low temperatures and of the byproducts also at high temperatures.

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, Cr-51. - . , — , .

     

Influence of the thermal treatment of platinum alumina catalysts with exhaust gases on their activity in cyclopropane hydrogenation

The activity of platinum/alumina catalysts in cyclopropane hydrogenation has been investigated. Catalysts heated in exhaust gases are considerably less active in cyclopropane hydrogenation as compared to samples calcined in air. A relatively stable modification of the metallic surface is formed, probably as a result of coke or poison deposition.

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- . , , , , , . , , .

     

Differential thermal analysis of the phase transition of dicalcium orthosilicate Ca2SiO4 under a reducing atmosphere

The transformation of Ca₂SiO₄ was investigated with regard to the disintegration of the sinter in alumina manufacturing. DTA was applied to study the effect of the reducing atmosphere upon the course of the polymorphic transitions of Ca₂SiO₄, and particularly the self-disintegration process. Pure synthetic dicalcium orthosilicate and blends of pure components from the system CaO-Al₂O₃-SiO₂-Fe₂O₃ were compared with technological mixtures of limestone and fly ash. Data obtained from the DTA runs allowed the specification of technical parameter for both firing and cooling of the sinter.

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Zusammenfassung Die -Umwandlung in Ca₂SiO₄ wurde im Hinblick auf den Zerfall von Sinter in der Tonerdeproduktion untersucht. Mittels DTA wurde der Einfluß einer reduzierenden Atmosphäre auf den Verlauf der polymorphen Umwandlungen von Ca₂SiO₄ und insbesondere auf den Zerrieselungsprozeß verfolgt. Reines synthetisches Ca₂SiO₄ und Gemische reiner Komponenten des Systems CaO-Al₂O₃-SiO₂-Fe₂O₃ wurden mit technischen Mischungen aus Kalk und Flugasche verglichen. Die Ergebnisse von DTA-Versuchen erlauben die Spezifizierung der technischen Bedingungen für das Brennen und Abkühlen des Sinters.

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. , , . -l₂₃-SiO₂-F23 . .

     

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 ) .

     

Nature of intermediates in the synthesis of hydrocarbons from methanol

According to the GC-MS analysis of the composition of liquid hydrocarbons obtained in methanol conversion on ZSM-5 zeolites and the selectivity of cyclohexene conversion on these catalysts, the sequence of the aromatization reaction steps is discussed.

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-- , ZSM-5, .

     

Bauxites as hydrotreatment catalysts

The effects of calcination temperature on structural and textural characteristics of two Greek bauxites were examined by different physicochemical techniques. Although the above minerals exhibited lower activity than a commercial CoMo/Al₂O₃ catalyst, they were evaluated as possible hydrotreating catalysts.

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. , CoMo/Al₂O₃, , .

     

Study of the combustion of a fire retardant coating by thermal analysis and different complementary techniques

An intumescent fire retardant coating can effectively control fire spread and damage. Its dual purpose is to confine the surface spread of flame to the boundaries of an already established fire, and to retard the penetration of heat and flame to and through the coated surface. Our composition expanded and provided an insulation layer between the flame source and the combustion substrate, and liberated a quantity of primarily non-flammable decomposition products which tended to extinguish the flame. The main ingredients of the coating were cellulose acetate butyrate and HMDI (Desmodur N) for Polyurethane, and Chlorowax-70 (chlorinated paraffins) as fire retardant component. This fire retardant coating was applied to wood panels, and tested in a 2-foot tunnel, its flame spread rating being measured. The effects of three parameters of interest were investigated: the type of wood used, the percentage of Chlorowax, and the coating thickness. It was found of interest to study the oxidation of the coating using different techniques, e.g. flash pyrolysis under oxygen and GC/MS for analysis of the decomposed products. Combustion studies of the coating were also conducted using DSC and thermogravimetry, either with the scanning mode or under isothermal conditions. Comparisons were made between the results obtained from pyrolysis and combustion.

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Zusammenfassung Ein schwellender feuerhemmender Überzug kann Ausbreitung und Schäden von Feuer wirksam einschränken und wird zwei Zwecken gerecht: Verhinderung der Ausbreitung von ausgebrochenem Feuer und Schutz der überzogenen Oberfläche vor Hitze- und direkter Flammeneinwirkung. Die beschriebene Komposition quillt und bildet eine Isolationsschicht zwischen der Flammenquelle und dem brennbaren Material, liefert zugleich aber auch eine gewisse Menge von nichtbrennbaren, die Flamme erstickenden primären Zersetzungsprodukten. Die Hauptbestandteile des Überzugs sind Celluloseacetat und -butyrat und HMDI (Desmodur N) für Polyurethan sowie Chlorowax-70 (chlorierte Paraffine) als feuerhemmende Komponente. Dieser feuerhemmende Überzug wurde auf Holzplatten aufgebracht und in einem 2ft-Tunnel getestet, wobei die Flammenausbreitungsgeschwindigkeit gemessen wurde. Der Einfluß von drei interessierenden Parametern wurde untersucht: Typ des benutzten Holzes, Anteil von Chlorowax und Überzugsschichtdicke. Es erwies sich als interessant, die Oxydation des Überzugmaterials mit verschiedenen Techniken zu untersuchen, z.B. durch Schnellpyrolyse und Analyse der Zersetzungsprodukte mittels GC/MS. Verbrennungsuntersuchungen des Überzugmaterials wurden auch mittels DSC und Thermogravimetrie entweder nach der scanning-Arbeitsweise oder unter isothermen Bedingungen ausgeführt. Die bei Pyrolyse und Verbrennung erhaltenen Ergebnisse werden miteinander verglichen.

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. -, , — . , . - ( ) ( ) . , . : , . , , , - . . , .

     

Some remarks about butene-1 transformations on NaHY zeolite

Comments are given on the paper Alternative Interpretation of Infrared Spectra of the Zeolite NaHY+Butene-1 System of Forster and Seelemann /2/. Our previous paper /1/ was partly revised but the usefulness of comprehensive studies by infrared and temperature-programmed desorption methods has been emphasized.

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: NaHY+-1. [2]. [1] , - .

     

Catalytic decomposition of isopropyl alcohol on iron(II) sulfide

The decomposition of isopropyl alcohol on troilite (FeS) which was thermally activated at 873, 973 and 1073 K, is described in this paper. The catalyst subjected to thermal activation exhibits improved activity, which increases with temperature of activation. It has been observed that the apparent activation energy E and the preexponential factor A have a compensating effect. The experiments involving the preadsorption of pyridine have shown that this substance is preferentially and irreversibly adsorbed on hydrogenation active centers.

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(FeS), 873, 973 1073 . , , , . . , .

     

Measurements and calculations of stresses in metal-ceramic systems

Deflection changes dependent on temperature and thickness of ceramics have been measured on ceramic-coated metal strips, using a modified commercial dilatometer.The deflections are not only dependent on the difference in the thermal expansion coefficients of the two materials, but are also influenced by the thickness ratio of the ceramic to the metal. The stresses existing in the ceramic have been calculated for the surface layer and for the layer in the transition zone ceramic/metal. The results have shown that there is no proportional relation between the value of deflection and the stresses in the ceramic; however, the maxima in the deflection curves coincide with the peaks shown in the stress curves. From a certain thickness ratio of ceramic to metal — determined by the Young's moduli of the materials — tensile stresses in the surface of the ceramic occur even at the higher expansion coefficient of the metal.

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Zusammenfassung An mit Keramik beschichteten Metallstreifen wurden in einem modifizierten, handelsüblichen Dilatometer Ausbiegungsänderungen in Abhängigkeit von der Temperatur und der Keramikdicke gemessen. Die Verformungen hängen nicht allein von der Differenz der thermischen Ausdehnungskoeffizienten der beiden Werkstoffe ab, sondern werden auch durch das Dickenverhältnis von Keramik zu Metall beeinflusst. Die in der Keramik vorhandenen Spannungen wurden für die Oberflächenschicht und für die Schicht in der Grenzzone Keramik/Metall berechnet. Die Ergebnisse haben gezeigt, daß kein proportionaler Zusammenhang zwischen der Grösse der Ausbiegung und den Spannungen in der Keramik vorhanden ist. Maxima in den Ausbiegungskurven fallen jedoch mit ausgezeichneten Punkten in den Spannungskurven zusammen. Ab einem durch die Elastizitäts-Moduln der Werkstoffe bestimmten Dickenverhältnis von Keramik zu Metall treten auch bei einem grösseren Ausdehnungskoeffizienten des Metalls Zugspannungen in der Oberfläche der Keramik auf.

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Résumé On a mesuré, sur des bandes de métal recouvertes de céramique et en se servant d'un dilatomètre commercial modifié, les changements de déflection qui dépendent de la température et de l'épaisseur des céramiques.Les déflections dépendent non seulement de la différence des coefficients de dilatation thermique des deux matériaux, mais aussi du rapport des épaisseurs respectives de la céramique et du métal. Les contraintes existant dans la céramique ont été calculées pour la couche superficielle et pour la couche de la zone de transition céramique/métal. Les résultats ont montré qu'il n'y a pas de relation de proportionnalité entre la valeur de la déflection et les contraintes dans la céramique; cependant, les maximums des courbes de déflection coïncident avec les pics des courbes de contrainte. A partir d'un certain rapport d'épaisseur de la céramique au métal — déterminé par les modules d'Young des matériaux — les contraintes d'allongement à la surface de la céramique se produisent même si le métal possède un coefficient de dilatation plus élevé.

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. , . /. , . , . , , , .

     

A temperature programmed desorption study of H2 from supported nickel catalyst

The chemisorption of hydrogen on Ni/SiO₂ has been studied by measuring temperature programmed desorption on various samples under various experimental conditions. Two peaks are found, which can be related to a weakly and to a strongly bound species of chemisorbed hydrogen. Their analysis has been performed by a method which makes possible to determine whether a certain kinetic model can describe the entire desorption process or to assign a clear meaning to the corresponding kinetic parameters.

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Ni/SiO₂ - . . , , , , .

     

Study of platinum black in a high-temperature X-ray camera

The behavior of platinum black is tested in a high-temperature X-ray camera. In the presence of hydrogen and at a temperature of over 400°C a new tetragonal modification of platinum has been found with lattice constants: a_o=0.403 nm and c_o=0.348 nm.

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. 400°C a_o=0,403 c_o=0,348.

     

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.

     

Simultaneous oxidation of CH4 and SO2 over vanadium and palladium containing catalysts

The kinetics of deep oxidation of CH₄ and SO₂ over complex vanadium catalysts with and without palladium additives and over silica-supported palladium has been studied. Sulfur dioxide increases the rate of CH₄ oxidation, not affecting the reaction mechanism, whereas CH₄ does not effect SO₂ oxidation on the catalysts studied.

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, , . , , .

     

Beckmann rearrangement of cyclohexanone oxime p-toluenesulfonate on acidic catalysts

The Beckmann rearrangement of cyclohexanone oxime p-toluenesulfonate has been studied using several catalysts. The reaction is catalyzed by weakly acidic sites and seems to occur by way of O-(p-toluenesulfonyl)--caprolactim.

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- -, . - -(-)--.

     

Transalkylation of phenols over heteropoly acids

Transalkylation of 2,6-di-tert-butyl-4-R-phenols over solid heteropoly acids (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₃PW₁₂O₄₀/SiO₂, H₄SiW₁₂O₄₀/SiO₂) in the presence of toluene or o-xylene as acceptors of a tert-butyl group at 100–140 °C produces 4-R-phenols with 92–98% yield (R = H, alkyl, aryl, etc.). HPAs are effective catalysts for the transalkylation of p-cresol and 2, 6-ditert-butyl-4-methylphenol.

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2,6----4-R- (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₃PW₁₂O₄₀/SiO₂, H₄SiW₁₂O₄₀/SiO₂) 0- - 100–140°C 4-R- 92–98% (R = H, , ..). - 2,6----4-.

     

Studies on the V?Ti?O system obtained by thermal decomposition of vanadyl and titanyl oxalates in argon atmosphere

The V–Ti–O system as a product of thermal decomposition of vanadyl and titanyl oxalates at 873 and 1173 K in argon atmosphere was studied by X-ray diffraction and infrared spectroscopy. The results obtained, the analysis and surface measurement data suggest that a V³⁺–V⁴⁺–Ti⁴⁺–O solid solution is formed. Spectroscopic measurements reveal the presence of a V=O bond in the system obtained at 873 K.

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V–Ti–O, 873 1173 - . , , V⁺³–V⁺⁴–O . V=O , 873 .

     

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. , - - , ( -). , .

     

Rh/nylon catalysts for partial hydrogenation of benzene to cyclohexene

Hydrogenation of benzene on Rh/nylon produced cyclohexene with a high selectivity. The influence of contact time, pretreatment of catalyst and rhodium salt precursors have been studied. Samples prepared from Rh(III) were found more selective than catalysts obtained from Rh(I). It is suggested that electron deficient metal sites are responsible for cycloolefin formation.

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Rh/ . , . , Rh(III) , , Rh(I). , .