Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.

     

A gradientless flow microreactor

A simple flow microreactor can perform as a gradientless microreactor under suitable conditions so that, thanks to molecular diffusion, the reactant concentration is leveled out considerably. This was demonstrated on the basis of a mathematical analysis of the reactant concentration distribution in a flow reactor and the observation was confirmed experimentally. A simple flow microreactor was designed and its gradientless property was verified using carbon dioxide hydrogenation as a test reaction.

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. . , . , .

     

Calorimetric studies of the properties of Pd/Al2O3 with different metal contents

Hydrogen on Pd/Al₂O₃ catalysts (1,2,4% Pd) is sorbed in three forms with a heat of 152.6–2.1 kJ/mol. Metallic surface of the catalysts has been measured by the amount of adsorbed oxygen, whose adsorption heat varies in the range of 313.7–3.4 kJ/mol. Catalytic activity and selectivity of Pd/Al₂O₃ was studied in isoprene hydrogenation.

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Pd/Al₂O₃- 152,6–2,1 /. , 313,7–3,4 /. Pd/Al₂O₃ .

     

Measurement of adsorption heats of nitrogen on metal nitrides

Adsorption heats q and activation energies of the nitrogen exchange on several metal nitrides have been compared. For the systems capable of changing readily their composition upon varying conditions, the isotope exchange is suggested to be the most reliable method of the determination of q.

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. , , , .

     

Influence of water activity on the rate of dihydrogen oxidation by metal complexes in aqueous solutions of electrolytes

Strong interaction of Pt with a TiO₂ support (reductive high-temperature treatment) is shown to increase the catalytic activity due to a decrease in CO coverage of the active Pt surface.

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, TiO₂- ( ) .

     

State of components in group IV A metal modified nickel catalysts prepared via decomposition of metal complexes

The dispersity and state of components in (M+Ni)/SiO₂ catalysts (M=Ge, Sn, Pb), prepared via the reduction of anchored complexes, have been studied by chemisorption and electron microscopy. High dispersity of metallic particles (6Å) has been revealed. According to Mössbauer spectroscopy, in (Ni+Sn)/SiO₂ catalysts reduced at 873 K, a partial reduction of Sn to the metallic state is observed.

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(M+Ni)/SiO₂ ( M=Ge, Sn, Pb), , , - . 873 ° K (Sn+Ni)/SiO₂ , , , 6 Å.

     

Conversion of C1?C2 alkanes over manganese catalysts reoxidized by carbon dioxide and oxygen

Reoxidation of Mn-containing catalysts by oxygen and carbon dioxide in the conversion of C₁–C₂ alkanes has been studied. Reoxidation of these catalysts by carbon dioxide and oxygen added at a certain ratio permits to obtain optimum degree of surface oxidation, ensuring the high selectivity of conversion of C₁–C₂ alkanes to C₂H₄.

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Mn- C₁–C₂. , Mn- , C₁–C₂ C₂H₄.

     

Thermal analysis — A guide to the optimization of sintering processes

During the sintering of multicomponent disperse systems prepared from mixtures of the components, a variety of solid-state reactions, phase formation or dissolution, and the occurrence of a liquid phase determine the densification and the final microstructure of the material.The results are presented of investigations on the systems WC-Co and Fe-Si, through the simultaneous application of dilatometry, differential thermal analysis and thermogravimetry, coupled with metallographic and microprobe analysis.

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Zusammenfassung Beim Sintern vielkomponentiger Systeme, die aus Gemischen der Komponenten hergestellt werden, bestimmt eine Vielzahl von Festkörperreaktionen, Neubildung und Auflösung von Phasen und das Auftreten von flüssigen Phasen die Verdichtung und die erreichbare Mikrostruktur des Materials.Ergebnisse der Untersuchung in den Systemen WC-Co und Fe-Si durch kombinierten Einsatz von Dilatometrie, TG-DTA, metallographischen und Mikrosonden-Untersuchungen werden mitgeteilt.

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, , , . WC- Fe-Si , , .

     

Thermal stability of poly(β-bromostyrene) and copolymers of β-bromostyrene with methyl methacrylate

The thermal stabilities of poly(-bromostyrene), poly-(methyl methacrylate) homopolymers and copolymers of-bromostyrene-methyl methacrylate covering the entire composition range were studied using TG analysis. At each extreme of the composition range, incorporation of comonomer units results in a copolymer more stable than the brominated homopolymer. Maximum stability occurs for compositions of approximately 62 mole percent-bromostyrene. The formation of the anhydride structure among the degradation products leads to the stability of the copolymers.

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Zusammenfassung Die thermische Stabilität von-Bromstyrol- und Methylmethacrylat-Homopolymeren sowie von sich über den ganzen Zusammensetzungsbereich erstreckenden-Bromstyrol/Methylmethacrylat-Kopolymeren wurde thermogravimetrisch untersucht. An beiden Enden des Zusammensetzungsbereichs führt der Einbau von Komonomereinheiten zu einem Kopolymer, das stabiler als das bromierte Homopolymer ist. Maximale Stabilität wird bei einem Gehalt von etwa 62 Mol-%-Bromstyrol erreicht. Die Bildung der Anhydridstruktur führt zur Stabilität des Kopolymers.

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/-, - . , . - 62%. .

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Presented at the World Conference of Thermal Analysis, held in Bad Hofgastein (Austria), 1985.     

Simple catalytic mechanism permitting a multiplicity of catalyst steady states

The conditions of the existence of several steady states for a three-step mechanism, viz. a catalytic trigger (consecutive), are discussed.

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- ().

     

Oxidation of carbon monoxide with nitrous oxide over CeO2

With the help of the transient response method and fluorescence spectroscopy, it has been revealed that the title reaction proceeds by the catalyst redox transformation Ce(III)Ce(IV) over CeO₂ in great contrast to previous observations over MgO. , Ce(III)Ce(IV) CeO₂ MgO.     

DTA-controlled reactions and phase relations in the ternary system Sn-Te-I

The system Sn-Te-I was investigated by DTA and X-ray powder methods. No intermediate ternary phase exists in the respective phase diagram. Reactions of the components on pseudobinary joins are easily explained by the phase relations. Liquidus isotherms of the ternary system are given.

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Zusammenfassung Das System Sn-Te-I wurde durch DTA- und Röntgenmethoden untersucht. In dem Phasendiagramm existiert keine intermediäre Ternärphase. Die Reaktionen der Komponenten der pseudobinären Koppelungen können durch die Phasenverhältnisse leicht erklärt werden. Flüssigkeitsisothermen des Ternärsystems werden gegeben.

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Résumé Le système Sn-Te-I a été étudié pa ATD et rayons X sur poudre. Il n'existe pas de phase ternaire intermédiaire dans le diagramme de phases correspondant. Les réactions des composants en systèmes pseudobinaires s'expliquent facilement par les relations de phases. Les isothermes des liquidus du système ternaire sont données.

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Sn--I. . . .

     

Application of thermal analysis for quantitative nitrogen determination in fertilizers

DSC and DTA techniques have been used to determine nitrogen present in the form of ammonium nitrate in fertilizers. The optimum conditions for the investigations were determined for both techniques. By determining peak area, i.e. the enthalpy of the ammonium nitrate crystal transformation II I, it was possible to determine the nitrogen content in ammonium nitrate and in lime ammonium nitrate by DSC with average deviations of 0.44 and 0.91%,respectively. Using DTA and the enthalpy of the ammonium nitrate crystal transformation IV III, the average deviation of nitrogen determination in lime/ammonium nitrate was 1.09%.

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Zusammenfassung DSC und DTA wurden zur Bestimmung des in Düngemitteln in Form von Ammoniumnitrat vorliegenden Stickstoffs benutzt. Für beide Techniken wurden die optimalen Untersuchungsbedingungen ermittelt. Durch Bestimmung der Peakfläche, d. h. der Enthalpie der Kristalltransformation II I des Ammoniumnitrats konnte der Stickstoffgehalt in Ammoniumnitrat und in Kalk/Ammoniumnitrat mittels DSC mit mittleren Abweichungen von 0.44 bzw. 0.91% bestimmt werden. Aus der Kristalltransformation IV III des Ammoniumnitrats ergibt sich bei Benutzung der DTA-Methode eine mittlere Abweichung von 1.09% für die Stickstoffbestimmung in Kalk/Ammoniumnitrat.

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, . . , , (III) , — . , , 0,44 0,91%. IVIII , - 1,09%.

     

Thermal decomposition of peroxypropionyl nitrate: Kinetics of the formation of nitrogenous products

The Arrhenius expression for reaction 1, CH₃CH₂COO₂NO₂CH₃CH₂COO₂+NO₂, has been determined to be k=2×10¹⁵ exp (–12800/T)·s^–1. The free radical mechanism is the exclusive thermal decomposition mechanism of PPN. The main nitrogenous decomposition products of pure PPN are ethyl nitrate, nitrogen dioxide and methyl nitrate. In the presence of NO, ethyl nitrite is the major organitrogen product.

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CH₃CH₂COO₂NO₂CH₃CH₂COO₂+NO₂ : k=2·10¹⁵exp (–12800/T) ^–1. () - . , . NO .

     

The reaction between nitrous oxide and carbon monoxide over magnesium oxide

The title reaction was carried out with the help of the transient response method over MgO. It was concluded that no catalyst reduction occurred over this catalyst and the reaction proceeded through the reaction between adsorbed nitrous oxide and adsorbed carbon monoxide without participation of MgO oxygen.

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MgO. , - MgO.

     

Thermochemistry of Carbonization of Polypyromellitimide

The mechanisms of thermal degradation processes in polypromellitimide films were investigated by mass-spectrometric thermal analysis and high-resolution NMR spectroscopy in the solid state. Both the structures of the solid residues of pyrolysis products of the PM polyimide and the process of carbonization proper up to 1200° were studied. It was established that the breaking of the C_ar-O-C_ar bond in the diamine moiety is not the primary act of degradation of the molecular structure of the polymer, as might be expected on the basis of the value of the bond energy. The process of intermolecular crosslinking following polymer degradation under high-temperature conditions is completed by the formation of a complex nitrogen-containing heterocyclic structure.

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Zusammenfassung Der Mechanismus der in Polypyromellitfilmen ablaufenden thermischen Zersetzungsprozesse wurde durch massenspektrometrische thermische Analyse und hochauflösende Festkörper-NMR-Spektroskopie untersucht. Sowohl die Struktur des festen Rückstandes des Pyrolyseproduktes des PM-polyamids als auch der Prozeß der Verkokung bis 1200 °C wurden Untersucht. Es wurde festgestellt, daß das Aufbrechen der Bindung C _ar ,-O-C _ar im Diaminteil nicht der primäre Schritt der Zersetzun der molekularen Struktur des Polymers ist, wie nach dem Wert der Bindungsenergie zu erwarten wäre. Der auf die Hochtemperatur-Polymerzersetzung folgende Prozeß der intermolekularen Vernetzung endet mit der Bildung einer komplexen stickstoffhaltigen heterozyklischen Struktur.

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- (MTA) (MP BPTT) , 1200 °C. . , C _ap -C _ap , , .

     

New models of monooxygenase on the basis of Sn(II) compounds

The data on the selectivity of various C–H bonds and the stereochemical course of the reaction in the known chemical systems simulating monooxygenase, do not agree with the oxenoid mechanism postulated for these reactions, but correspond to the interaction of saturated hydrocarbons with the OH radical intermediate. On the basis of organic compounds of Sn(II) in aprotic media, new systems have been developed which selectively oxidize alkanes to alcohols in the presence of O₂ in the coupled process and display many characteristics of the oxenoid reactions.

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C–H , , , , . (II) , .

     

Preparation and characterization of iron(II) complexes of ethylene glycol

Nine iron(II) ethylene glycol sulphate complexes were prepared. Their compositions were determined by standard analytical methods. They were characterized by means of temperature-dependent magnetic susceptibility and Mössbauer spectroscopic measurements. On the basis of the patterns of their thermal decompositions, the complexes could be classified into three groups.

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Zusammenfassung Neun Eisen(II)-ethylenglykol-sulfat-Komplexe wurden dargestellt. Die Zusammensetzung dieser Komplexe wurde nach analytischen Standardmethoden bestimmt. Die Verbindungen wurden durch Messungen der temperaturabhängigen magnetischen Susceptibilität sowie mittels Mössbauer-Spektroskopie charakterisiert. Nach dem Verhalten bei der thermischen Zersetzung konnten diese Komplexe in drei Gruppen klassifiziert werden.

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, . . , .

     

Changes in iron oxidation state and surface composition of iron-chromium catalyst reduced by hydrogen

X-ray photoelectron spectroscopic studies of the reduction of iron-chromium catalysts have been carried out to determine changes in the relative surface concentrations of iron(II) and (III) oxides and metallic iron and in its surface composition at 100–500°C.

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(II), (III) 100–500°C. .

     

Hydrogen formation in silane oxidation

From mass-spectrometric data, it has been established that the main gaseous product of silane oxidation by oxygen at low pressures is molecular hydrogen. Isotopic analysis of the hydrogen formed in the oxidation of SiH₄+SiD₄ mixtures indicates that not less than 20% hydrogen is generated by a molecular mechanism.

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- , . , SiH₄+SiD₄ , 20% .