The consistency of repeated H2?O2 titration cycles on supported Pt catalysts

H₂ and O₂ uptakes at 296 K on a Pt/Al₂O₃ catalyst remained constant during repeated H₂–O₂ titration cycles conducted in a high vacuum adsorption system. Previously reported variations in these uptakes are attributed to adsorption of contaminants during desorption conditions. Also, it was found that nearly 40% of the H₂ adsorbed could be removed by degassing at 296 K for 1 hr.

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H₂ O₂ 296 Pt/Al/₂O₃ H₂–O₂, . . , 40% H₂ 1 296 .

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Radiolysis of nitrous oxide adsorbed on alumina ionic mechanism of radiolysis of nitrous oxide on alumina with small surface areas

A mechanism is proposed for the radiolysis of adsorbed N₂O describing the experimental dependences of the radiation-chemical yields of O _st ^– and N₂ on N₂O coverages.

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N₂O, - O _st ^– N₂ N₂O.

     

Thermal and photochemical stability of polystyrene and its blends with polyvinyl chloride

The influence of some irregularities in polystyrene (PS) and polyvinyl chloride (PVC) chains on their thermal stability was investigated. UV irradiation caused an increase in the content of these irregularities in the polymers. It was found that the presence of carbonyl groups and crosslinking of the polymer chains hamper the thermal dehydrochlorination of PVC and the total decomposition of both polymers. On the other hand, weak peroxy linkages (which facilitate degradation processes) and conjugated double bonds decrease the temperature of total decomposition of PS and PVC blends.

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Zusammenfassung Es wurde der Einfluß von Unregmlmäßigkeiten in Polystyrol (PS)- und Polyvinylchlorid (PVC)-Ketten auf deren thermische Stabilität untersucht. UV-Bestrahlung verursacht ein Ansteigen des Gehaltes an Unregelmäßigkeiten in den Polymeren. Es wurde festgestellt, daß die Gegenwart von Carbonylgruppen und Querverbindungen der Polymerketten die thermische Dehydrochlorierung von PVC und eine vollständige Zersetzung beider Polymere verhindern. Andererseits senken Peroxidverknüpfungen (die die Degradierungsvorgänge erleichtern) und konjugierte Doppelbindungen die Temperatur für eine vollständige Zersetzung von PS und PVC Gemischen.

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. - . , . , , , .

     

IR-spectroscopic studies of strength and concentration of acid centers on V2O5/Al2O3 catalysts

The strength of protonic sites and the concentration of acid centers in V₂O₅/Al₂O₃ catalysts have been estimated according to pyridine and ammonium adsorption.

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V₂O₅/Al₂O₃.

     

Routes of catalytic oxidation of o-xylene to phthalic anhydride

Relative reactivity of o-xylene, o-tolualdehyde, phthalide, and phthalane and the rate of phthalic anhydride formation from them have been determined. The main route of o-xylene oxidation to phthalic anhydride is due to the o-arrangement of methyl groups, proceeding through bicyclic products, such as dihydrobenzofuran (phthalane) and 3,4-benzofuran.

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-, - , , . - - : () 3,4-.

     

Gradient systems are cross-catalytic

If the kinetic differential equation of a chemical mechanism is a gradient system, the mechanism is essentially cross-catalytic. Consequently, rather few conservative (in the Horn-Jackson sense) mechanisms have a kinetic differential equation of the gradient type. Relations with thermodynamics are only briefly mentioned.

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, , , . ( -) . .

     

X-ray and thermal studies of ferroelectric Dy2(MoO4)3

Dysprosium molybdate, Dy₂(MoO₄)₃, displays a ferroelectric phase transition at 145 °C. The X-ray and thermal (DTA, TG and DSC) properties of this compound have been studied. The X-ray study confirmed the ferroelectric phase in the orthorhombic space group Pba2. Thermal analysis demonstrated the existence of a ferroelectric and another phase transition in this compound.

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Zusammenfassung Dysprosiummolybdat, Dy₂(MoO₄)₃ (Abk.: DMO), ein Vertreter der Seltener-denmolybdatreihe zeigt bei 145 °C einen ferroelektrischen Phasenübergang. Röntgendiffraktion und thermische Eigenschaften (DTA, TG, DSC) der genannten Verbindung wurden untersucht. Auf Grund der Röntgendiffraktionsuntersuchung gehört die ferroelektrische Phase in die orthorhombische Raumgruppe Pba2. Mittels Thermoanalyse konnte bei dieser Verbindung die Existenz ferroelektrischer und anderer Phasenübergänge nachgewiesen werden.

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145 °C. (, ) . , Pba2. .

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The authors wish to thank Prof. A. Paul and Mr. R. Bhatnagar for their kind help in some of the experimental work. One of us (MR) gratefully acknowledges a Fellowship from DST, Government of India.     

Interdependence between the dispersion of a solid decomposition product and its formation rate

In an analysis of the possible mechanism and kinetics of a thermal decomposition reaction with the formation of a solid product, the following features were considered: the collective rearrangement character of the transformation; the formation of a product with a different non-equilibrium defectiveness and free energy; the free energy relationship in the series of processes leading to products with different dispersions; the formation of intermediate structures; and the spinodal character of their decomposition. Relationships are presented between the rate of solid product formation, the process temperature, and the surface area and size of the particles.

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Zusammenfassung In einer Analyse des möglichen Mechanismus und der Kinetik einer unter Bildung eines festen Produktes verlaufenden thermischen Zersetzungsreaktion werden folgende Besonderheiten erörtert: der kollektive Umordnungscharakter der Umwandlung, die Bildung eines Produktes mit unterschiedlicher Nichtgleichgewichts-Gitterstörung und unterschiedlicher freier Energie, die Beziehung der freien Energie in zu Produkten unterschiedlicher DispersitÄt führenden Prozessen, die Bildung intermediÄrer Strukturen und der spinodalen Charakter ihrer Zersetzung. Beziehungen zwischen der Bildungsgeschwindigkeit des festen Produktes, der Temperatur des Prozesses und der OberflÄchengrö\e und Grö\e der Partikel werden angegeben.

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: ; ; , ; . , , .

     

On the catalytic system MgO?Na

Acid-base and radical properties of two sets of MgO–Na catalysts have been studied. The catalysts were prepared (I) by impregnation of MgO with NaOH in aqueous solution, and (II) by evaporation of metallic sodium onto a MgO surface. The catalyst prepared by the second method was much more basic than pure MgO (H_o=35) and showed a high activity in olefin isomerization.

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- MgO–Na. 1) MgO (NaOH) 2) MgO. , , , MgO(H₀=35), .