Oxygen adsorption on silver-gold alloy

Oxygen adsorption on Ag/Au alloys has been studied by field-emission microscopy (FEM). A decrease in the silver concentration of alloy is accompanied by a drastic fall in its ability to absorb oxygen. Using the interacting bonds method (IBM), the adsorption heat of atomic oxygen on the (100) plane of the silver-gold alloy has been calculated.

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. , . (100) .

     

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. - . , — , .

     

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. , - - , ( -). , .

     

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

     

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

     

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 . , , , . . , .

     

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, , .

     

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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- . , , , , , . , , .

     

Effect of addition of intermetallic componds on the catalytic activity of La2CuO4

Decomposition of nitrous oxide has been studied on pure La₂CuO₄, La₂CuO₄ with 5 wt.% CaNi₅ and La₂CuO₄ with 5 wt.% NiO in the temperature range 200–480°C at 200 Torr initial pressure of reactant gas. The addition of 5 wt.% CaNi₅ decreases the energy of activation drastically in comparison with La₂CuO₄. The results are explained on the basis of the dispersity of Ni/NiO on La₂CuO₄.

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La₂CuO₄ 5.% CaNi₅ 5 .% NiO , 200–480°C 200 . 5 . % CaNi₅ . Ni/NiO La₂CuO₄.

     

Kinetics and mechanism of TI(III) oxidation of cellobiose in acidic medium

TI(III) oxidation of cellobiose in the presence of H₂SO₄ in aqueous acetic acid is first order in each reactant and is acid catalyzed. TI(OAc) ₂ ⁺ is the active species. Products identified are gluconic acid and glucose. A mechanism consistent with the temperature, solvent, acidity and salt effects is been proposed.

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TI(III) H₂SO₄ . TI(OAc) ₂ ⁺ . . , , , .

     

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 ) .

     

CO2 hydrogenation on iron-containing mono- and bimetallic catalysts

The effect of chemical composition of supported, ironcontaining mono- and bimetallic catalysts on the mechanism of CO₂ adsorption and hydrogenation has been studied. It is shown that at 673 K the conversion degree of CO₂ decreases in the sequence Co/Al₂O₃> Co–Ni/Al₂O₃>Ni/Al₂O₃.

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CO₂. , 673 Co/Al₂O₃> Co–Ni/Al₂O₃>Ni/Al₂O₃ .

     

Characteristics and surface morphology change of modified PtRh 10 gauze of HCN synthesis

The modification of PtRh10 gauze catalysts by coating their surfaces with a thin film of PtRh/Al₂O₃ is reported. The investigation of the activity, selectivity and morphological change of the surface of the catalyst for standard gauzes and those covered with a thin film, applied in the HCN synthesis is deseribed.

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PtRh 10 PtRh–Al₂O₃. , HCN.

     

Исследование роли фосфиновых комплексов никеля различных степеней окисления в каталитической димеризации олефинов

Ni(II), Ni(I) Ni(O) . , , , Ni(O) Ni(I) - Ni(I) Ni(II) Ni(O).

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The interaction of organoaluminium compounds with phosphine complexes of Ni(II), Ni(I) and Ni(0) has been studied under the conditions of catalytic propylene dimerization. The active complexes are formed from Ni(II) compounds, the regeneration of the latter is ensured by repeated reduction, oxidation of Ni(0) to Ni(I), and by disproportionation of Ni(I) into Ni(II) and Ni(0).

     

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 - . . , , , , .

     

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 . .

     

Novel type of oscillatory chemical reactions

Chemical oscillations occur during the uncatalyzed oxidation of a number of phenol and aniline derivatives by acidic bromate.

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.

     

Effect of the active component concentration in supported catalyst on the selectivity

The selectivity of heterogeneous catalytic reactions can be controlled by varying the concentration of a catalytically active component supported on a carrier. This has been confirmed by data for o-xylene oxidation on vanadium pentoxide supported on alumina.

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- . - , .