Evidence of blockage of PtH offretite channels by platinum crystallites

The introduction of platinum in a protonic offretite causes a decrease of its activity for m-xylene isomerization and an increase of its constraint index. This is due to the blockage of the offretite channels by small platinum crystallites (<8 Å), as confirmed by the study of m-xylene adsorption.

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- . (<8 Å), -.

     

Catalytic properties of phosphorus-containing rhenium complexes in the hydrogenation of hexene-1

Rhenium (V, VI) complexes with organophosphorus ligands proved to be catalytically active in hexene-1 hydrogenation. The kinetics of this process catalyzed by ReOCl₃(PPh₃)₂ has been examined. The organic ligand in the coordination sphere of rhenium complexes was found to affect selectivity to olefin bonds or nitro groups in the hydrogenation of hydrocarbons.

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(V, VI) -1. , ReOCl₃ (PPh₃)₂. , .

     

Effect of the medium in hexacyanoferrate (III)-iodide and peroxodisulfate-iodide reaction

The kinetics of the two reactions hexacyanoferrate (III)-iodide and peroxodisulfate-iodide in several isodielectric water-cosolvent mixtures have been studied. The results can be rationalized as a consequence of the cosolventwater interaction.

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(III) -. -.

     

Thermometrische und Enthalpimetrische Titrationsmethoden

Zusammenfassung Ausgehend von der allgemeinsten Form der Wärmeleistungsbilanzgleichung für thermometrische und enthalpiemetrische Titrationsmethoden werden die Möglichkeiten dieser Methoden in der analytischen Chemie und im Bereich der Stoffdatenbestimmung aufgezeigt und kritisch gewürdigt. Der Bedarf an zuverlässigen Stoffdaten erschließt den thermometrischen und enthalpiemetrischen Titrationsmethoden im Bereich der Thermo chemie der Lösungen neue Anwendungsgebiete.

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Starting from the most general form of the balance equation of thermal performance for thermometric and enthalpimetric methods of titration, the possibilities of these methods in analytical chemistry and in the field of determining data on materials are demonstrated and critically appreciated. The demand for reliable data on materials opens new fields of application of thermometric and enthalpimetric titration methods in the sphere of the thermal chemistry of solutions.

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Résumé A partir de la forme la plus générale de l'équation du bilan de puissance calorifique pour les méthodes de titrages thermométriques et enthalpimétriques, on montre les possibilités de ces méthodes en chimie analytique et dans le domaine de la détermination des données des substances et on en donne une appréciation critique. Les exigences sur les données sûres relatives aux constituants ouvrent aux méthodes de titrations thermpmétriques et enthalpimétriques de nouveaux domaines d'application dans le domaine de la thermochimie en solution.

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, , . .

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Vorgetragen anläßlich des II. Seminars Thermometrische Analyse (II. Thermometriás Szeminárium) Budapest, 2–7 September 1980.

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Teile dieser Arbeit sind Ergebnisse, die im Rahmen eines vom Bundesministerium für Forschung und Technologie gef6rderten Forschungsprogramms der DECHEMA (F91-J) am Lehrstuhl für Chemie VI der Universität Regensburg erhalten wurden. Herrn Prof. Dr. R. Wachter, Universität Regensburg, danke ich für Diskussionen und Hinweise.     

Periodic thermal instability during the differential thermal analysis of pyrite

The cause of oscillations in high resolution DTA curves was investigated using simultaneous TG supported by microscopic and XRD examination of quenched samples. The latter techniques showed the instability resulted from the sequential ignition of individual or small groups of particles. This behaviour was different to that observed in our earlier isothermal tests where the oscillations were caused by periodic cracking of the oxide film.

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Zusammenfassung Die Ursache von Oscillationen in hochaufgelösten DTA-Kurven wurde durch TG und gleichzeitige Ausführung von mikroskopischen und XRD-Untersuchungen von abgeschreckten Proben erforscht. Die zuletzt genannten Techniken lassen eine Instabilität erkennen, die auf eine regelmässig aufeinanderfolgende Verbrennung von individuellen oder kleinen Gruppen von Partikeln zurückzuführen ist. Dieses Verhalten unterscheidet sich von dem, das in unseren früheren isothermen Testversuchen beobachtet wurde, bei denen die Oscillationen durch periodisches Zerreissen des Oxidfilms verursacht wurden.

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- . , . , .

     

Cross-linking and gel formation in the thermal degradation of PVC

Cross-linking in the thermal degradation of PVC was investigated by measuring the dependence of number-average molecular weight, gel fraction, molecular weight distribution and intrinsic viscosity on degradation time. A linear relationship was found between the cross-linking density and reaction time. Only one fifth of the polyene sequences formed participate in the cross-linking process.

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- , , . . .

     

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 question of thermal decomposition of pyrite

The thermal decomposition of monomineral pyrite was studied in an inert atmostphere. From an analysis of the values of the thermal effects, an interpretation of the hree physicochemical processes recorded in the thermoanalytical curves is proposed.

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Zusammenfassung Die thermische Zersetzung von monomineralem Pyrit wurde in inerter Atmosphäre untersucht. An Hand der Analyse der Werte der thermischen Effekte wird eine Beschreibung dreier, in den thermoanalytischen Kurven festgehaltener physikalischchemischer Vorgänge vorgeschlagen.

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Résumé On a étudié la décomposition thermique de la pyrite, en atmosphère inerte. On propose une interprétation des trois processus physicochimiques enregistrés sur les courbes thermoanalytiques, qui repose sur l'analyse des effects thermiques.

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- , .

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Oxidation of ethanol on platinum/alumina and copper oxide catalysts

The oxidation of ethanol on CuO, CuO/Al₂O₃ and Pt/Al₂O₃ catalysts has been studied at various concentrations of alcohol, oxygen and water vapor in the reaction mixture. The reaction order and activation energies have been determined for both complete and partial oxidation processes. A consecutive oxidation scheme is suggested.

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CuO, CuO/Al₂O₃ Pt/Al₂O₃ , . . .

     

The effect of preparation conditions on the activity and stability of copreciptitated Ni/Al2O3 catalysts for the methanation of carbon monoxide

The activities and stabilities of coprecipitated Ni/Al₂O₃ methanation catalysts depend markedly on their preparation and pretreatment. The results are discussed in relation to the structure of the precipitate and to changes which occur during calcination and reduction.

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Ni/Al₂O₃ . , .

     

High-temperature X-ray diffraction studies of the formation of V?Mo?O catalyst

High-temperature X-ray diffraction analysis in the temperature range of 553–823 K was used to study the formation and the region of thermal stability of VMo₃O₁₁ being an active component of the V–Mo–O catalyst for acrolein oxidation to acrylic acid.

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553–823 K VMo₃O₁₁, V-Mo-O .

     

Conversion of furan compounds in the presence of polymeric gel-immobilized catalysts

Based on studies of catalytic oligomerization of furyl alcohol, 2-furfurylydeneacetone and tetrachlorofuran in the presence of gel-immobilized complexes (GIC) Al(OPh)₃, BF₃ and Ti(OBu)₄, an oligomerization mechanism is suggested and supported experimentally.

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(), 2- () () - (), Al(OPh)₃, BF₃ Ti(OBu)₄. .

     

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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, , , .

     

IR spectra of NO and NO+CO mixtures adsorbed on Fe2O3

The interaction of NO and NO+CO mixtures with Fe₂O₃ has been studied by IR spectroscopy. The conclusion has been made that adsorption bands in the region of 1200–1700 cm^–1 belong to nitrite-nitrate structures, the band at 1810 cm^–1 characterizes catalytically active particles of NO adsorbed on reduced surface sites, Fe²⁺, the bands at 2210 and 2240 cm^–1 are due to vibrations of gaseous N₂O.

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- NO NO+CO Fe₂O₃. , 1200–1700 ^–1 - ; 1810 ^–1 NO, , Fe²⁺; 2210 2240 ^–1 N₂O.

     

Pt(alizarine)2 complex adsorbed on titanium dioxide as a sensitizer in photocatalytic evolution of dihydrogen

Pt(alizarine)₂ complex adsorbed on the surface of titanium dioxide has been found to cause spectral sensitization of the photocatalytic activity of TiO₂. Adsorption of the complex provides simultaneously sensitization of the photoprocess and catalysis of dark steps of dihydrogen formation.

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, Pt()₂ TiO₂. , , .

     

Hydrogenation of ethylene on gadolinium X, Y and L-type zeolites

It is shown that Gd-zeolites have a catalytic activity towards ethylene hydrogenation at 1 atm. This activity decreases with an increase in the SiO₂/Al₂O₃ ratio from 2.2 to 6.1 and 4.1, i.e. upon going from an X type zeolite to Y and L. For these types of zeolite the activity grows with an increase in Gd³⁺ content from 50 to 80%. Oxygen addition to the reaction mixture stabilizes the catalytic activity of zeolites.

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, qv 1 . , SiO₂/Al₂O₃ 2,2 6,1 4,1, .. X Y L. , 50 80%. .

     

An investigation on the effects of additives during the thermochemical decomposition of phosphogypsum under isothermal conditions

A study was made of the isothermal kinetics of phosphogypsum in the presence of additives and in a reducing gaseous medium.

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Zusammenfassung Es wurden isotherme kinetische Untersuchungen an Phosphogips in Gegenwart von Zusätzen sowie m reduzierender Atmosphäre durchgeführt.

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- .

     

The influence of CSH phase nuclei on Ca3SiO4Cl2 hydration

The influence of CSH phase nuclei on calcium chlorosilicate hydration has been studied by means of calorimetry, QXRD, DTA and TG methods.

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Zusammenfassung Mittels kalorimetrischen, QXRD-, DTA- und TG-Verfahren wurde der Einfluß von CSH Phasenkörpern auf die Hydratierung von Kalziumchlorosilikat untersucht.

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, , .

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C=CaO, S=SiO₂, H=H₂O