Changes in the acid-strength distribution and the catalytic selectivity of H,Na?MOR

Acidities of synthetic H,Na–MOR samples decationized to different degrees have been characterized by differential adsorption heat distribution of ammonia. A fairly good correlation has been found between the number of acid sites of different strengths and the catalytic activity as well as the selectivity for xylene isomerization and disproportionation. The results are correlated with the mechanism of these reactions.

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H,Na–MOR, , - . , . .

     

Mo(V)/SiO2 supported catalysts for the epoxidation of allyl chloride

New Mo(V)/SiO₂ supported catalysts as the products of settlement of MoO(OH)₃ on silica were obtained and ESR examined. Catalytic activity in epoxidation of allyl chloride with cumene hydroperoxide was found.

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MoO(V)/SiO₂, MoO(OH)₃ S O₂. .

     

Modification of the catalytic and chemisorptive properties of Pt/SiO2 catalysts by high temperature reduction and restoration by O2?H2 treatments

The reduction of Pt/SiO₂ at 1100 K results in a decrease of the quantity of absorbed hydrogen and of the catalytic activity in benzene hydrogenation, ethane hydrogenolysis and neopentane isomerization, which cannot be accounted for by metal sintering. O₂ treatment followed by reduction at moderate temperature restores the usual properties of the catalyst. This behavior is similar to that observed on Pt/TiO₂ catalysts, the difference lying in the temperature at which the phenomenon appears.

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Pt/SiO₂ 1100 , , . O₂ , . Pt/TiO₂ , .

     

Oscillatory phenomena during ammonia oxidation in the presence of a PtRh catalyst

The paper describes oscillatory phenomena observed during ammonia oxidation on a PtRh catalyst in a single pellet reactor. The phenomena consist in periodical changes of the catalyst temperature and a periodical initiation of the reaction in the gas phase. They are interpreted via coupling of the catalytic dissociation and homogeneous oxidation of ammonia.

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, PtRh . . .

     

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.     

Toluene and m-xylene complexes of the chlorine atom: Reactivity toward toluene and m-xylene

Rate constants for the reactions of toluene-chlorine complex+toluene (k=5.1×10⁵ dm³ mol^–1 s^–1) and m-xylene-chlorine complex+m-xylene (k=6.8×10⁴ dm³ mol^–1 s^–1) have been measured in laser flash photolysis experiments using nitrogen trichloride as chlorine atom source in carbon tetrachloride solvent at room temperature. We found that the stability of the chlorine atom complexes increases while the reactivity decreases with increasing methyl substitution.

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(k=5,1×10⁵ ·^–1·^–1) - (k=6,8×10⁴ ·^–1·^–1) . .

     

Kinetics of the homogeneous catalytic hydrogenation of methacrylic acid in the presence of pentacyanocobaltate(II)

The kinetics and mechanism of the pentacyanocobaltate(II)-catalyzed hydrogenation of methacrylic acid has been investigated by a non-linear programming technique. Three kinetic models have been examined. The best results were obtained with the equation based on a mechanism involving free radicals and organocobalt intermediates.

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(II) . . , .

     

Variation of the surface potential of zinc oxide under illumination

Spectral and kinetic dependences of the decrease in the surface potential (SP) of ZnO under illumination and processes of SP relaxation in the dark have been studied. A significant contribution to the decrease of SP in the less-than-bandgap light absorption region is shown to be due to the photodissociation of specific surface bonds with the formation of localized Zn _s ⁺ and O _s ^– .

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() ZnO . , Zn _s ⁺ O _s ^– .

     

The preparation and thermal analysis studies on some first row transition metal complexes of 2-aminopyrimidine

Complexes of 2-aminopyrimidine with the chlorides, bromides and iodides of cobalt(II), zinc(II) and also with the chlorides and bromides of manganese(II), nickel(II) and copper(II) have been prepared. The chloride complex of iron(II) was also obtained. The stereochemical configurations of the complexes were deduced using spectral and magnetic properties. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis.

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Zusammenfassung Komplexe von 2-Aminopyrimidinen mit den Chloriden, Bromiden und Jodiden von Kobalt(II), Zink(II) und den Chloriden und Bromiden von Mangan(II), Nickel(II) und Kupfer(II) wurden hergestellt. Der Chloridkomplex von Eisen(II) wurde ebenfalls erhalten. Die stereochemischen Konfigurationen der Komplexe wurden aus spektralen und magnetischen Eigenschaften abgeleitet. Die Zersetzung der Komplexe wurde durch Thermogravimetrie und Differentialthermoanalyse untersucht.

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Résumé Les complexes de l'amino-2 pyrimidine avec les chlorures, bromures et iodures de cobalt(II), zinc(II) ainsi qu'avec les chlorures et bromures de manganèse(II), nickel(II) et cuivre(II) ont été préparés. Le complexe formé avec le chlorure de fer(II) a aussi été obtenu. Les configurations stéréochimiques des complexes ont été déduites des propriétés spectrales et magnétiques. La décomposition thermique des complexes a été étudiée par thermogravimétrie et analyse thermique différentielle.

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2- , (II) (II), (II), (II) (II). (II). . .

     

Rapid chromatographic method to determine surface concentration of hydroxy groups on silicon and aluminium oxides using dimethylzinc

A rapid chromatographic method to determine the surface concentration of hydroxy groups on silicon and aluminium oxides using dimethylzinc is proposed. The dependence of their concentration over domestic silica gels and -Al₂O₃ on the dehydration temperature has been studied. The results are compared with the literature data.

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. -Al₂O₃ . .

     

Formation and thermal decomposition of silicon oxynitride compounds II

In studies on the reactions of silicon oxynitride, Si₂N₂O, with lithium oxide and of lithium metasilicate with lithium nitride, the formation of a previously unknown compound with stoichiometry Li₅SiNO₃ has been observed.

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Zusammenfassung Eine bisher unbekannte Verbindung der Zusammensetzung Li₅SiNO₃ wurde bei Reaktionen von Siliciumoxynitrid (Si₂N₂O) mit Lithiumoxid und von Lithiummetasilikat mit Lithiumnitrid erhalten.

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(Si₂N₂O) , Li₅SiNO₃.

     

Influence of chemical non-steady-state on SO2 conversion in fluidized catalyst bed

The effect of the influence of catalyst non-steady-state on SO₂ conversion ion a fluidized catalyst bed has been studied depending on the ratio of relaxation time for the catalytic reaction step to the characteristic time of particles diffusion.

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.

     

Catalytic properties of sodium-containing silica gel in n-heptane decomposition

n-Heptane decomposition reactions on silica catalysts containing various amounts of sodium ions were studied. Ethylene, methane and propylene as well as unbrached -olefins were the main reaction products. The comparison of the experimental and theoretical results suggests a free-radical reaction mechanism.

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- , . , , -. - .

     

Photoadsorption, photooxidation and photodecomposition of simple molecules on alkali halide surfaces

Data have been obtained on the activities of 19 alkali halides in photoadsorption of O₂ and CO₂, photooxidation of H₂ and CO and photodecomposition of H₂O and CO₂.

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19 O₂ CO₂, H₂ CO H₂O CO₂.

     

ESR studies of molybdenum in Ti?Mo heteropoly acid supported on TiO2

ESR studies indicate that in Ti–Mo heteropoly acid supported on TiO₂, two types of Mo⁵⁺ ions are observed, corresponding to stabilization of the heteropoly blue with various degrees of interaction with the surface. , - TiO₂ Mo⁵⁺, .     

Quantitative analysis of binary antioxidant mixtures

Quantitative analysis of individual inhibitors and their binary mixtures has been carried out. It has been established that the effect of binary mixtures (additive, synergistic or antagonistic) depends on the structure, concentration ratios and activity of their components. The conditions of the synergistic effect have been determined.

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, , . , , . , .

     

Thermal analysis of some lignin model compounds

Compounds acting as model biphenyl and phenylcoumarane structural units in the lignin molecule (dehydrodivanillin and dehydrodiisoeugenol) were investigated by thermal analysis. The results were compared with previously obtained data on the thermal degradation of model phenylpropane monomer units of lignin. It was found that the mechanism of thermal degradation of these models and the thermal stabilities of the bonds depend on the structure. The thermal stability of the models increases in the absence of reactive functional groups in the side chain.

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Zusammenfassung Modellverbindungen mit Biphenyl und Phenylcumaran Bindungen im Lignin wie Dehydrodivanillin und Dehydrodiisoeugenol wurden einer thermoanalytischen Prüfung unterworfen und die Ergebnisse mit jenen der thermischen Zersetzung von Phenylpropan-monomeren Modellen des Lignins verglichen. Es wurde festgestellt, daß der Mechanismus der thermischen Zersetzung und die thermische Stabilität der Bindungen strukturabhängig sind. Die thermische Stabilität der Modelle nahm mit Abwesenheit reaktionsfähiger funktioneller Gruppen an der Seitenkette ab. Die Bindung vom Typ des Phenylcumarans ist thermisch am stabilsten. Das Zerreissen der Bindungen scheint durch einen Mechanismus durch freie Radikale zu erfolgen.

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Résumé Étude thermique de composés modèles pour les liaisons structurales de type diphényle et phénylcoumaranne dans la molécule de lignine (déhydrodivanilline et déhydrodiisoeugénol). Comparaison des résultats avec ceux obtenus précédemment dans le cas de la dégradation thermique de composés servant de modèles pour les unités monomères de phénylpropane dans la lignine. Détermination du mécanisme de la dégradation thermique de ces modèles et de la stabilité thermique des liaisons suivant la structure. La stabilité thermique augmente en l'absence de groupes fonctionnels réactifs dans la chaîne latérale. La liaison de type phénylcoumaranne est thermiquement la plus stable. On suppose un mécanisme avec radical libre pour la rupture des liaisons structurales.

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, ( ). . , - . . . - .

     

Interaction between propene and CoNaX zeolite and exchange of propene hydrogens

Interaction of propene with CoNaX and NaX zeolites and exchange of propene hydrogens with CoNaX zeolite was studied at the temperature of the IR beam and at 300°C by means of IR and MS analysis. In addition, the heats of adsorption were measured. The structure of adsorbed propene complexes was found to be influenced by the presence of Co²⁺ ions. The mechanism of the exchange is discussed and the properties of the OH groups of HY, HX and CoNaX zeolites are compared.

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CoNaX NaX CoNaX 300°C . . , Co²⁺ . OH , CoNaX .

     

On a diffusion model of a catalytic reaction

A model to describe a catalytic reaction with simultaneous diffusion is analyzed. The possibility of formation of periodic structures in space is shown.

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, . .

     

Modification of HY-zeolite with trifluoromethane

H-form of Y-type zeolite was modified by means of thermal treatment (450 °C) with trifluoromethane. Fluorine can be introduced into the zeolite phase using this method. However, the crystallinity and catalytic activity (cumene cracking) of the resulting sample is lower than that of the initial HY-zeolite.

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- (450°C) . ѕ. , ( ) , -.