A model of reaction front propagation in crystals

A spatio-temporal model of anisotropic propagation of the dehydration front in Na₃P₃O₉ · 6H₂O single-crystals is discussed. It is based on the assumption that dehydration proceeds as a periodic displacement of the reaction front from one reacting elementary block to another, and that experimentally fixed dehydration patterns are composed of a multitude of elementary patterns having the same shape. The model can be applied to other crystals.

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Zusammenfassung Ein Zeit- und Raummodell der anisotropischen Fortschreitung der Dehydratationsgrenzfläche in Na₃P₃O₉ · 6H₂O Einkristallen wird diskutiert. Das Modell ist auf einer Annahme begründet, dass die Wasserabspaltung als eine periodische Propagation der Reaktionsgrenzfläche von einem reagierendem Elementarblock zu anderem verläuft und dass die experimentell fixierte Entwässerungsfiguren aus einer Menge von Elementarfiguren von identischer Form zusammengestellt sind. Das Modell kann auf andere Kristallen verbreitet werden.

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- Na₃P₃O₉· 6₂. , , . .

     

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) .

     

Reactivity of finely dispersed iron (III) oxides and oxide hydroxides in solid-state reactions

The kinetics of the reaction of-Fe₂O₃ (hematite) with K₂CO₃ was studied at 600–800 °C for hematite samples prepared in different ways. The results demonstrated that the hematite reactivity is not a simple function of the specific surface area (or particle size), but depends significantly on the sample preparation history, especially at lower reaction temperature. The effect of low-temperature sintering on the hematite reactivity is discussed.

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Zusammenfassung Die Kinetik der Reaktion unterschiedlich präparierter-Fe₂O₃- (Hämatit-) Proben mit K₂CO₃ bei 600–800 °C wurde untersucht. Die Ergebnisse zeigen, dass die Reaktivität des Hämatits keine einfache Funktion der spezifischen Oberfläche (bzw. Teilchengrösse) ist, sondern deutlich von der Vorgeschichte der Probe, insbesondere bei tieferer Temperatur, abhängt. Der Einfluss des Tieftemperatursinterns auf die Reaktivität des Hämatits wird diskutiert.

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600–800° (-₂₃) . , ( ), , , «» . .

     

Variations in electronic state of silver catalysts for methanol oxidation

Variations in the electronic state of silver catalysts for methanol oxidation under the effect of the reaction medium have been studied, using diffuse reflectance spectroscopy. The nature of active centers-Ag⁺ cations, Ag _n ⁺ complexes and clusters of various sizes for bulk and supported catalysts are shown to be identical.

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. - Ag⁺, Ag _n ⁺ .

     

Radiation induced oxidation of ethyldichlorosilane

It has been revealed that the radiation induced oxidation of ethyldichlorosilane by oxygen produces practically one reaction product, namely chlorine-containing disiloxane. A reaction mechanism involving the formation of silyl hydroperoxide as one of the steps is suggested.

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, — . , .

     

Active state of copper in catalysts for low-temperature methanol synthesis

Copper-containing catalysts have been investigated in low-temperature methanol synthesis. It is shown that the active component of the catalyst is the copper ion and not the metallic copper as is supposed previously.

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, , , .

     

Influence of Pr ions on the properties of Pd/SiO2 and Pt/SiO2 catalysts in oxidation of n-butane

It has been established that (M_VIII+Pr)/SiO₂ catalysts (M_VIII=Pd or Pt) obtained from organometallic precursors, have increased the dispersity of Pt, but their TN in deep oxidation of n-butane is by 3–6 times lower than that of unmodified M_VIII/SiO₂.

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(M_VIII+Pr)/SiO₂ ( M_VIII=Pd, Pt), , Pt, 3–6 - M_VIII/SiO₂.

     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

Studies of n-octane transformations on zeolites under hydrocracking conditions in a two-reactor flow-circulation system

Transformations of n-octane under hydrocracking conditions in a two-reactor flow-circulation system have been studied. It has been established that at high hydro-dehydrogenation activity of zeolite catalysts the reaction mechanism involves an initial step of paraffin dehydrogenation on a metal component and subsequent steps of cracking, isomerization and disproportionation of intermediate olefins on an acid component. Sodium content in zeolite determines the paraffin hydrocracking selectivity.

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- - . , - , . .

     

Study of hydroisomerization of n-hexane on natural mordenite catalyst

A mordenite-containing rock sample from the Tokaj Mountains (Hungary) and its various forms modified by chemical treatment have been tested for catalytic properties during isomerization of n-hexane. Addition of Pt to the catalyst leads to a sharp decrease in the rate of cracking and in the rate of deactivation and this results in a catalyst of high selectivity for hexane isomers.

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(), , , , -. Pt , .

     

Reactivity of oxidized substances and its correlation with catalyst properties in deep oxidation reactions

In terms of the donor-acceptor interaction concept /1/ the relative reactivity (RR) of organic and inorganic compounds and its correlation with catalyst properties in deep oxidation reactions are treated. RR and relative activity of the catalysts are shown to change depending on the predominant character (acceptor or donor) of reactant-catalyst interaction.

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- /1/ (OPC) . , OPC .

     

PMR study of the lifetime of complexes with a strong hydrogen bond at low temperatures

The kinetics of formation and cleavage of hydrogen bonds in complexes of carboxylic acids with proton acceptors have been studied by PMR spectroscopy over the range –100 to 150°C. The activation parameters of the processes have been measured.

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¹H –100° ÷–155°C . .

     

On the complex influence of the experimental parameters and the properties of the substances on the representation of solid-liquid transitions studied with a differential scanning calorimeter

Due to the increasing importance of quantified results of dynamic calorimetric measurements, the influence of single experimental parameters has been studied by some authors. We found that these results can be represented correctly only in a complex form. According to this experience, the experimental parameters were changed on the basis of statistically planned experiments. The numerous measurements were carried out with samples of indium, 1,3-dinitrobenze and polyethylene prepared in different ways. The results were evaluated in a complex form. The evaluation of the experimental data revealed a significant influence of the substance properties and the experimental parameters.

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Zusammenfassung Die zunehmende Bedeutung quantifizierbarer Ergebnisse von dynamischen kalorimetrischen Messungen veranlasste die Autoren [1–9] zur Untersuchung des Einflusses einzelner experimenteller Parameter. Nach unseren Erfahrungen können diese Ergebnisse nur in komplexer Form dargestellt werden. Entsprechend wurden die Versuchsbedingungen nach einem statistischen Plan variiert. Zahlreiche Messungen wurden mit unterschiedlich präparierten Indium-, 1,3-Dinitrobenzen- und Polyethylen-Proben durchgeführt und die Ergebnisse in komplexer Form ausgewertet. Dabei zeigte sich ein signifikanter Einfluss der Probeneigenschaften und der Versuchsbedingungen.

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, . , . , . , 1,3- , . , , .

     

Unimolecular decomposition of CF3OF-calculation by reduced Kassel integral in factorized form

The fall-off curves were calculated for the unimolecular decomposition of the trifluoromethyl hypofluorite at 475.8, 496.9 and 507.3 K by means of the Reduced Kassel Integral in Factorized Form.

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475,8,496,9 507,3 .

     

Study of the thermal decomposition of solids in a fluidized bed, III

The influence of the air humidity upon the thermal decomposition of diammonium hydrogen phosphate was studied in a fluidized bed, under isothermal conditions. It was found that the increase of the decomposition rate is influenced directly by the partial pressure of the water vapour in the air, and indirectly by the working temperature. The moisture effect is explained by the salt hydrolysis in the water condensed on the grain surface. The energy of activation of the thermal decomposition decreases when the air humidity increases.

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Zusammenfassung Der Einfluß der Luftfeuchtigkeit auf die thermische Zersetzung des Diammoniumhydrogenphosphats wurde in fluidisiertem Bett unter isothermen Verhältnissen studiert. Die Zunahme der Zersetzungsgeschwindigkeit war direkt proportional dem partialen Wasserdampfdruck in der Luft und indirekt proportional der Arbeitstemperatur. Diese Wirkung wird durch Salzhydrolyse in dem kondensierten Wasser an der Kernoberfläche erklärt. Die Aktivierungsenergie der thermischen Zersetzung nimmt mit zunehmendem Feuchtigkeitsgehalt ab.

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Résumé On a étudié l'influence de l'humidité atmosphérique sur la décomposition thermique de (NH₄)₂HPO₄ en lit fluidisé, en conditions isothermes. La pression partielle de la vapeur d'eau dans l'air intervient directement sur l'augmentation de la vitesse de décomposition et exerce une action indirecte sur la température de travail. On a expliqué l'effet de l'humidité par l'hydrolyse du sel dans l'eau condensée à la surface des grains. La valeur de l'énergie d'activation de la décomposition thermique diminue quand l'humidité atmosphérique augmente.

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. , , , , . , .

     

Thermal curve interpretation by spectral resolution into the basic set of rectangular pulse curves

A new numerical method for the determination of thermokinetics is proposed. This is based on the spectral resolution of a thermal curve into the basic set of unit rectangular pulse curves orthogonalized by Löwdin's transformation. A numerical example shows that the present method can be successfully applied to experimental curves.

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Zusammenfassung Eine neue numerische Methode zur Bestimmung von Thermokinetika wird vorgeschlagen. Sie beruht auf der spektralen Auflösung einer thermischen Kurve in die Grundfolge von Einheiten rechteckiger Pulskurven, welche durch eine Löwdins Transformation orthogonalisiert worden sind. Ein numerisches Beispiel zeigt, dass diese Methode bei experimentellen Kurven mit Erfolg eingesetzt werden kann.

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ë- . , .

     

Peculiarities of propylene metathesis over catalysts prepared by anchoring of Mo(V) oxalate to γ-Al2O3

Propylene metathesis over catalysts prepared by coordination of Mo(V) oxalate to -Al₂O₃ has been studied.

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, (V) -Al₂O₃.