Highly dispersed platinum honeycomb reforming catalysts: Sintering behavior and activity

The influence of chlorine regulation by steam treatment and of operation conditions in the dehydrogenation of methylcyclohexane (MCH) on the dispersity of chlorided Pt/-Al₂O₃ honeycomb catalysts has been investigated by means of transmission electron microscopy (TEM). The loss of surface chlorine greatly promotes the sintering of small Pt crystallites (<20 Å), while the reaction testing does not affect the high dispersities of the catalysts. An original evidence of the antipathetic structure sensitive character for the dehydrogenation of MCH on highly dispersed Pt catalyst is provided.

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Pt/-Al₂O₃ . Pt (<20 Å), .

     

Geometric effects in methylcyclopentane hydrogenolysis on platinum catalysts

Methylcyclopentane hydrogenolysis was studied at 493 K over variously dispersed platinum catalysts. The relative contributions of the predominant hydrogenolysis mechanisms are correlated to the particle size in agreement with a simple geometric model.

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493 . .

     

Catalytic oxidation of ascorbic acid by molecular oxygen in aqueous pyridine in the presence of Co2+, Ni2+, Mn2+ and Zn2+ ions

In aqueous pyridine solutions, Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ effectively catalyze the oxidation of ascorbic acid by molecular oxygen. A kinetic expression consistent with the experimental data is given and a possible mechanism proposed.

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- , , . , . .

     

Vapor phase oxidation of 2-methylpyridine on vanadyl polyphosphates

Vanadyl -and -polyphosphates in vapor phase oxidation of 2-methylpyridine show comparable activity and selectivity to the formation of pyridine-2-carboxaldehyde as traditional vanadium-molybdeum oxide catalysts. A redox mechanism for the reaction of 2-methylpyridine oxidation on vanadyl polyphosphates is suggested with interaction between 2-methylpyridine and oxygen of the catalyst lattice as the rate-determining step.

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- - 2- -- . - 2- . - 2- .

     

Infrared spectroscopic studies of H2S adsorption on γ-Al2O3

IR spectra of H₂S adsorbed in various quantities on -Al₂O₃ have been studied. The method of spectral probes has been used to determine the extent of H₂S blocking of Lewis acid and basic centers.

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- , -Al₂O₃. .

     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

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, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

Kinetics and mechanism of elimination of methoxyphenethyl chlorides in the gas phase

The kinetics for the gas phase elimination of o-and m-methoxy-2-phenylethyl chlorides have been investigated over the temperature range of 390-464°C and pressure range of 38–119 Torr. The reactions in seasoned vessels and in the presence of the free radical inhibitor propene, are homogeneous and unimolecular and follow a first-order rate law. The o-anisyl and p-anisyl substituents at the -position of ethyl chloride assist anchimerically the elimination processes. The formation of a cyclic product, benzodihydrofuran, from o-methoxy-2-phenylethyl chloride suggests an intimate ion pair mechanism operating in this reaction.

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- --2- 390–464°C 38–119 . - , , , . - - - . , , --2- , .

     

Study of thermal behaviour of some derivatives of triphenylamine,with a view to obtaining new stationary phases for gas chromatography

A study was carried out upon the thermal behaviour of eight derivatives of triphen-y l amine, i. e. trinitrotriphenylamine; triaminotriphenylamine; triaminotriphenylamine chlorhydrate, tetraphenylborate and picrate; and a trisazo derivative and its compound with Be(II) and U(VI). The aim of this study was to find compounds with satisfactory thermal stability for use as stationary phases in gas chromatography.

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Zusammenfassung Eine umfassende Untersuchung zum thermischen Verhalten von acht Triphenylaminderivaten, d. h. Trinitrotriphenylamin, Triaminotriphenylamin, Triaminotriphenylamin Chlorhydrat, Tetraphenylborat und Pikrat, sowie ein Trisazoderivat und seine Verbindungen mit Be(II) und U(VI) wurde durchgeführt. Der Zweck dieser Studie war Verbindungen befriedigender Thermostabilität zum Einsatz als stationäre Phasen in der Gaschromatographie zu finden.

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: , , -, , () U(VI). .

     

On the nature of surface sites for heterolytic dissociation of hydrogen on Al2O3

A quantum-chemical analysis of the models for geminal OH groups of Al₂O₃ and of the processes of their dehydroxylation with further dissociative chemisorption of hydrogen has been carried out. Calculations were performed by the SCF MO LCAO method using STO-3G basis set in terms of the cluster approach.

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OH- Al₂O₃ . , STO-3G .

     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

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Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

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, , , . . , . , , . , .

     

Oxygen chemisorption and activity studies on unpromoted and promoted TiO2 supported tungsten sulfide catalysts

Low temperature oxygen chemisorption (LTOC) has been applied to characterize unpromoted and promoted tungsten sulfied catalysts supported on TiO₂. LTOC, hydrodesulfurization and hydrogenation are found to correlate with the W loading.

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() - TiO₂ . , - W .

     

Mechanism of the liquid-phase oxidation of diethyl sulfide catalyzed by heteropoly acids

It has been established that in the oxidation of diethyl sulfide by¹⁸O₂ in CH₃C¹⁶O₂H–H₂ ¹⁶O solution at 369 K catalyzed by heteropoly acids, sulfoxide and sulfone with 44–54%¹⁸O enrichment are formed. The process is accompanied by isotope exchange of molecular oxygen.

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, ¹⁸O₂ CH₃C¹⁶O₂H–H₂ ¹⁶O 369 ¹⁸O 44–54%, .

     

Isomerization and dehydrobromination of 1-bromo-2-methylpropane on alumina modified with alkali halides

The kinetics of the dehydrobromination of 1-bromo-2-methylpropane on alumina modified with NaI and KI have been investigated. A mechanism for the isomerization reactions on alumina modified with alkali halides is proposed in order to explain the catalytic behavior of iodide ion as compared with that of chloride and bromide ions, reported in a previous paper.

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1--2- , NaJ KJ. , , , , .

     

A new method of DTA: Theory and practice

A novel differential thermoanalytical technique is described and discussed with regard to function, operation, performance, theory and application. Information is provided about the nature of the internal processes taking place at the time of absorption or release of energy. Notable features of the technique include high sensitivity and independence of a reference sample.

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Zusammenfassung Eine neue differentialthermoanalytische Technik wird hinsichtlich ihrer Funktion, Arbeitsweise, Leistung, Theorie und Anwendung beschrieben. Es wird über die Beschaffenheit der inneren Vorgänge bei der Energie-Absorption oder -Freisetzung berichtet. Vorteile der neuen Technik sind die hohe Empfindlichkeit und die Unabhängigkeit von der Referenzprobe.

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Résumé On décrit et discute une nouvelle technique d'ATD en considérant sa fonction, son utilisation, ses possibilités, sa théorie et son application. On indique les processus internes qui se produisent lors de l'absorption ou de la libération d'énergie. Les principales caractéristiques de la technique se rapportent à la sensibilité élevée et à l'indépendance de l'échantillon de référence.

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, , , , , . .

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We wish to acknowledge support of this research by the National Research Council of Canada and Dalhousie University, Halifax.     

TPD studies of hydrogen adsorption on group VIII metals

Hydrogen desorption proceeds in several temperature regions and differs by its order of magnitude and activation energy. Differential curves of adsorbed hydrogen distribution with respect to the desorption activation energy, dN/dE (E), show a considerable inhomogeneity of adsorbed atomic species and the energetic homogeneity of molecular species.

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. dN/dE (E) .

     

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 .

     

Modification of catalytic properties of silica-supported rhodium

A sharp change in the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion has been found for catalysts prepared via interaction between Rh(CO)₂Cl₂ and silica modified by Sn, Pb, Mo and W ions.

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, Rh(CO)₂Cl₂ , Sn, Pb, Mo W, , , -.

     

Iron-chromium catalysts in the conversion of methanol with water vapor

The catalytic properties of iron-chromium catalysts in methanol conversion with water vapor were studied. The activity of the catalysts is shown to depend on the method of preparation and their Cr₂O₃ content. The Cr₂O₃ admixture is found to play the role of a stabilizer of the active surface.

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. Cr₂O₃. Cr₂O₃ .