Damped concentration oscillations in the oxidation of the reduced forms of heteropolyacids

Concentration oscillations of reduced forms of phosphorus-molybdenum, silicon-molybdenum, and silicon-tungsten heteropolyacids of the 12th row have been induced by the pulse radiolysis of their 5×10^–2M aqueous solutions. Appearance of these oscillations seems to be related to the reaction of reduced forms of heteropolyacids with hydrogen peroxide which is also produced during water radiolysis.

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-, 12- , 5·10^–2M . , -, - , .

     

Calorimetric measurement of structural relaxation in chalcogenide and metallic glasses

Some special characteristics of the structural relaxation (SR) in chalcogenide and metallic glasses are presented and the current theories dealing with the physical nature of the SR are recalled. The type of experiments used to measure SR by differential scanning calorimetry are reviewed and some rules to be taken into account when measuring calorimetrically the SR are stressed.

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Zusammenfassung Es werden einige spezielle Charakteristiken der Strukturrelaxation (SR) von Chalkogeniden und Metallgläsern vorgestellt und die gegenwärtigen Theorien über die physikalische Natur der SR zitiert. Die Art von Experimenten zur Messung von SR mittels DSC wurden kritisch besprochen und einige inbetrachtzuziehende Regeln für die kalorimetrische Bestimmung der SR hervorgehoben.

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. , . , . , .

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This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) project MAT88-0439.     

Participation of molecular oxygen in the formation of complete oxidation products via a concerted mechanism

A comparison is given between the rate of catalytic reactions and that of decomposition of surface compounds under the influence of molecular oxygen of different isotopic composition in reactions of complete oxidation of n-butane and 1-hexene on zinc oxide and cuprous oxide. It has been shown that the rates of accumulation of products containing heavy oxygen are much smaller than those theoretically expected from the heavy isotope concentration in molecular oxygen. A conclusion is drawn that molecular oxygen is not directly incorporated into the reaction products but promotes decomposition of the surface compounds by oxidizing the surface sites where these compounds are stabilized.

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

     

Effect of discontinuous irradiation in the radiolysis of heavy metal azides

A decrease in the steady-state rate of radiation gas evolution from silver and thallium azides under discontinuous irradiation has been revealed and the critical time for the darkening period (0.1 s) has been determined. This effect is not observed for lead and cadmium azides. An interpretation for the effect of discontinuous irradiation is suggested.

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. ( .І ). . .

     

Exchange kinetics of amino acid anions in solutions of ternary copper(II) complexes with diethylenetriamine

Rate constants for the chemical exchange of some amino acid anions in solutions of copper(II) ternary complexes with diethylenetriamine have been determined by the NMR method. The coordination of amino acid anions in ternary and binary species is different and ligand substitution in the Cu(II) complexes follows an associative mechanism.

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- (II) . - (II).

     

Experimental study of the bifurcation diagram in the Belousov-Zhabotinskii reaction

In the citric acid-Mn²⁺–H₂SO₄–KBrO₃ system a hysteresis phenomenon in the switching on and off of the oscillations has been observed. The possible bifurcation diagrams of the system are discussed.

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-Mn⁺²–H₂SO₄–KBrO₃ . .

     

The role of adsorption calorimetry in the study of surface phenomena

After a short survey of the development of adsorption calorimetry, the current position of this method is demonstrated in the light of some more recent results. A critical analysis is made of the areas in which adsorption calorimetry could be successfully applied in the future, either alone or, preferably, in combination with other techniques.

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Zusammenfassung Nach einem kurzen Überblick über die Entwicklung der Adsorptionskalorimetrie wird die augenblickliche Bedeutung dieser Methode an Hand einiger neuerer Ergebnisse demonstriert. Es wird kritisch analysiert, in welchen Gebieten die Adsorptionskalorimetrie in Zukunft erfolgreich eingesetzt werden kann, sei es allein, oder zweckmäßigerweise in Verbindung mit anderen Techniken.

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Résumé Après une brève revue du développement de la calorimétrie d'adsorption, on montre la position actuelle de cette méthode à la lumière de quelques résultats plus récents. On donne une analyse critique des domaines dans lesquels la calorimétrie d'adsorption pourraît être appliquée avec succès, seule ou, de préférence, en combinaison avec d'autres techniques.

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. , , / .

     

Kinetics of reactions in solution: Method for the treatment of data from non-isothermal chemical kinetic experiments

A new method is proposed for the treatment of kinetic data derived from non-isothermal kinetic experiments for the determination of the parameters of the Arrhenius equation. The results obtained from its application show the excellent precision of this method.

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. , , .

     

Oxidation of organic sulfides and sulfoxides by oxygen in the presence of copper complexes

In liquid-phase oxidation of sulfides and sulfoxides by air oxygen in acetone solution a high catalytic activity is shown by copper(II) phenolates containing electrodonor substituents in their benzene ring. Reactivity of aliphatic sulfides with R=C₁–C₅ in sulfoxide formation is 5–10 times higher than that of petroleum sulfides. Oxidation rate of sulfides to sulfoxides is by an order of magnitude higher than that of sulfoxides to sulfones.

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(II), - . R=C₁–C₅ 5–10 , . .

     

Pore diffusion inhibition of reactions in a nonisothermal porous catalyst grain

An efficiency factor for the joint process of steady-state reaction and pore diffusion has been determined as a Taylor sequence over the thickness of a nonisothermal porous catalyst grain. Relations permitting to estimate the nonuniformity of temperature distribution in the catalyst grain for arbitrary kinetics are suggested.

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. , .

     

Selective catalytic hydrogenation of double bonds in unsaturated furan ketones

In the hydrogenation of unsaturated furan ketones in solvents at atmospheric pressure and room temperature the Raney Pd–Al catalyst is highly active and selective towards the hydrogenation of double bonds. The only reaction products are the respective saturated ketones.

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, Pd–Al . . .

     

Catalytic properties of V?Mo?O systems in acrolein oxidation

Catalytic properties of V–Mo–O systems have been studied in acrolein oxidation. When catalysts are activated in reaction mixtures at 673 K, then a solid solution of molybdenum oxides in reduced vanadium oxides is formed, which is responsible for deep oxidation. Also, several compounds are produced, which by their activity and selectivity to acrylic acid formation are arranged in the sequences VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, and VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅, respectively.

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V–Mo–O . 673 K , , , : VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, : VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅.

     

Strength and accessibility of Br?nsted acid sites in synthetic H,Na?MOR

Changes in the acid strength of synthetic H, Na–MOR ion exchanged to different degrees have been characterized by IR spectroscopy. A distinct shift in the frequency of the 3600 cm^–1 band was observed increasing the degree of ion exchange. The accessibility of these sites is also revealed.

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H,Na-MOR , . 3600 cm^–1. .

     

Springer in the International Year of Chemistry 2011

Announcement

Springer in the International Year of Chemistry 2011     

Effect of Sn addition on the catalytic properties of the metallic phase in Pt?Sn/Al2O3 catalysts

Platinum-tin/alumina supported catalysts have been studied. The TPR results show an assisted reduction of tin by platinum. The effect of alloying in cyclohexane dehydrogenation, o-xylene hydrogenation and cyclopentane hydrogenolysis is discussed.

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- , . . , - .

     

Springer in the International Year of Chemistry 2011

Announcement

Springer in the International Year of Chemistry 2011     

Springer in the International Year of Chemistry 2011

Announcement

Springer in the International Year of Chemistry 2011     

Studies of the state and catalytic properties of platinum and tin in prereduced Pt?Sn/ZnAl2O4 and Pt?Sn/MgAl2O4 catalysts

X-ray diffraction and Mössbauer spectroscopy studies indicate that the thermal pretreatment of Pt–Sn catalysts supported on ZnAl₂O₄ and MgAl₂O₄ spinels, in the reduction medium leads to the formation of coarse-disperse particles of PtSn, Pt₂Sn₃ and PtSn₂ alloys, which deactivate the catalysts.

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, Pt–Sn , ZnAl₂O₂ VgAl₂O₄ , PtSn, Pt₂Sn₃ PtSn₂. .

     

Focus on H/D exchange of proteins in solution

Editorial

Focus on H/D exchange of proteins in solution     

Springer in the international year of chemistry 2011

Announcement

Springer in the international year of chemistry 2011