Thermogravimetry of copper and copper oxides (Cu2O-CuO)

The thermogravimetry of mixtures of metallic copper and copper oxides was studied. The experiments were performed by heating the samples in air to 700–800° to transform all the components to copper(II) oxide, and continuing the heating in nitrogen to 1050–1100° when the dissociation of copper(II) oxide to copper(I) oxide is complete. The identification of the components and their quantitative determination were carried out by determining the shape, size, and ratio of the segments of the curves obtained during the heating. The method can be used for quantitative analysis of mixtures of copper and/or copper oxides.

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Zusammenfassung Gemische von metallischem Kupfer und Kupferoxiden wurden thermogravimetrisch untersucht. Zur Überführung aller Komponenten in Kupfer(II)-oxid erhitzte man sie in Luft auf 700–800°, um daraufhin bis zur vollständigen Dissoziation des Kupfer-(II)-oxids zu Kupfer(I)-oxid unter Stickstoff die Temperatur bis auf 1050–1100° zu steigern. Die Identifizierung der Komponenten und ihre quantitative Bestimmung erfolgten durch die Form, Größe und die Verhältnisse der verschiedenen Abschnitte der erhaltenen Kurven. Diese Methode ist zur quantitativen Bestimmung von Gemischen aus Kupfer und Kupferoxid sowie von Kupferoxiden geeignet.

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Résumé Étude thermogravimétrique de mélanges du cuivre métallique et d'oxydes de cuivre. Les échantillons sont d'abord chauffés dans l'air jusqu'à 700–800° jusqu'à ce que tous les constituants soient transformés en oxyde de cuivre(II); le chauffage est ensuite poursuivi dans l'azote jusqu'à 1010–1100°, où la dissociation de l'oxyde de cuivre(II) en oxyde de cuivre(I) est complète. Les constituants ont été identifiés et dosés en utilisant la forme, la dimension et les proportions des différentes parties des courbes pendant le chauffage. La méthode peut être utilisée pour l'analyse quantitative de mélanges de cuivre et ou d'oxydes de cuivre.

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. 700–800: ( (), 1050–1100° [ () (I)]. , , . / .

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The author wishes to acknowledge the financial assistance provided by the Technion — Israel Institute of Technology.The author wishes also to thank Dr. R. F. Tylecote (University of Newcastle Upon Tyne, England) for very helpful comments and useful discussions of this investigation and to Mrs. N. Leder for chemical analyses.     

Kinetics of homogeneous hydrogenation of cyclohexene catalyzed by complexes of rhodium and iridium with a terdentate ligand

Complexes of the composition MC1HN (CH₂CH₂AsPh₂)₂ (M= =Rh(I), Ir(I) were used as catalysts for the homogeneous hydrogenation of cyclohexene over the temperature range 20–50 °C and 0.4 to 1 atm hydrogen partial pressure. The dependence of rate of hydrogenation on temperature, hydrogen concentration, catalyst concentration and substrate concentration is reported. The activation parameters of the reaction, H* and S* have been evaluated.

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MC1HN (CH₂CH₂AsPh₂)₂ (M=Rh(I) Ir(I) 20–50°C 0,4 1 atm. , , . H^* S^*.

     

Reactivity of coordinated O2? ion-radicals in the oxidation of organic compounds

By the flow ESR method, the rates of the reaction of the radical complex Ti(IV)(O ₂ ^– ) with some aromatic compounds in aqueous solution have been measured. An elementary step of these reactions seems to be one-electron oxidation with the formation of a substrate cation-radical.

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- Ti(IV)(O ₂ ^– ) . - -.

     

Tunnel recombination of surface and bulk radiation defects in finely dispersed CaO at 4.2 and 77 K

Recombination of radiation defects in CaO is shown to occur through electron tunneling from surface F_s ⁺ to V^–-center stabilized in the bulk.

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, CaO F_s ⁺- V^–-, .

     

The thermal decomposition of cerium(III) nitrate

The thermal decomposition of anhydrous Ce(NO₃)₃ has been studied. The thermal decomposition reaction is described by the second order kinetic equation, [1/(1–)]–1=kt. The apparent activation energy was determined asE _a=104 kJ mol^–1 while the enthalpy of the reaction was estimated asH _r=111.1 kJ mol^–1. The decomposition reaction differs from that observed for Nd(NO₃)₃.

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Zusammenfassung Die thermische Zersetzung von wasserfreiem Ce(NO₃)₃ wurde untersucht. Die thermische Zersetzung wird durch die Geschwindigkeitsgleichung zweiter Ordnung[1/(1–)]–1=kt, beschrieben. Für die scheinbare Aktivierungsenergie wurde ein Wert von 104 kJ mol^–1 und für die Enthalpie der Reaktion ein Wert von 111,1 kJ mol^–1 ermittelt. Die Zersetzungsreaktion unterscheidet sich von der für Nd(NO₃)₃.

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. : [1/(1–)]– 1=kt. a, 104 · ^–1, H _r, 111.1 · ^–1. .

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The authors wish to thank the Council for Scientific and Industrial Research and the University of Pretoria for financial assistance.     

Study of selective dissociation in C6F5H?C6F5D mixtures induced by intense CO2 laser pulses

Irradiation of a C₆F₅H–C₆F₅D mixture at 1 Torr by a tunable CO₂ pulse laser brings about chiefly dissociation of one component depending on the frequency of emission absorbed by the proper molecules. The addition of radical acceptors increases the selectivity by suppressing secondary reactions.

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C₆F₅H C₆F₅D 1 CO₂-, , . .

     

Discrimination of active sites for ethylene homologation and ethylene metathesis on molybdena silica catalyst

Active sites for ethylene homologation (3C₂H₄2C₃H₆) and ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) were discriminated by adding platinum to a reduced molybdena silica catalyst, and the former was presumed to be composed of several molybdenum species, while the latter was presumed to be composed of one molybdenum species.

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(3C₂H₄2C₃H₆) (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . , , .

     

Sintering of supported palladium

Sintering results of Pd supported on carbon black at 723–973 K, in water vapor, in H₂ and under high vacuum are reported. They are compared with sintering data of Pd on other supports. The observed sequences are: SiO₂C>sepioliteAl₂O₃>AlPO₄ and H₂O>high vacuum>H₂.

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Pd 723–973 , , H₂ . Pd . : SiO₂Al₂O₃>AlPO₄ H₂O> >H₂.

     

A variational formulation of the rate equations for closed chemical systems

This paper presents a variational formulation of the kinetic equations corresponding to a closed chemical system.

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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 . .

     

Influence of dehydration conditions on the state of nickel in Y-zeolites

Infrared spectroscopic studies have revealed that the presence of water in dehydrated samples of Ni-containing Y-zeolites rises the number of nickel cations accessible for CO adsorption in NiNH₄Y and leads to their partial screening in NiNaY.

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- , CO NiNH₄Y NiNaY.

     

On the deactivation of Fe2O3?MoO3/SiO2 catalysts in the oxidation of methanol to formaldehyde

The deactivation behavior of Fe₂O₃–MoO₃/SiO₂ catalysts with different Fe₂O₃+MoO₃ content in the oxidation of methanol to formaldehyde is investigated. A simplified reaction-deactivation kinetic model is presented and used to compare and discuss the different behaviors.

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Fe₂O₃–MoO₃/SiO₂ Fe₂O₃+MoO₃ . : -.

     

A study of thermal preparation OF c-Mn2P4O12

With the application of thermogravimetry under quasi-isothermal-isobaric conditions, the reaction course of the calcination of Mn(H₂PO₄ · H₂O to give dimanganese cyclotetraphosphate has been studied. Isothermal calcination was also carried out in an electric furnace at various temperatures (200 min). The reaction products were analyzed by chromatography, IR and NMR spectrocopy, and X-ray diffraction analysis. The compositions of the calcinates were determined through extraction with various inorganic and organic solvents.

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Zusammenfassung Der Verlauf der Dimangan-cyclotetraphosphat ergebenden Kalzinierung von Mn(H₂PO₄)₂ · H₂O wurde thermogravimetrisch unter quasi-isothermen-isobaren Bedingungen untersucht. Isotherme Kalzinierung wurde auch im elektrischen Ofen (200 min) bei verschiedenen Temperaturen ausgeführt. Die Reaktionsprodukte wurden chromatographisch, IR- und NMR-spektroskopisch sowie röntgendiffraktometrisch analysiert. Die Zusammensetzung der kalzinierten Produkte wurde via Extraktion mit verschiedenen anorganischen und organischen Lösungsmitteln bestimmt.

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Mn(H₂PO₄ · H₂O. . . - , - - . .

     

A simplified View of δ → δ* Transition Energies in Compounds with multiple metal-metal bonds: The isolated δ — δ* manifold model

The energetics of the * transition in quadruply bonded complexes are investigated using a very simple valence-bond formalism, called the isolated * manifold (IDDM) model. In this model all electrons except for those that occupy the or * molecular orbitals are ignored, as are explicit metal-ligand interactions. The resulting equations allow the calculation of transition energies very inexpensively, albeit with poor quantitative agreement: the * transition in prototypical quadruple-bond systems is predicted to occur at energies greater than 70,000 cm¹. The model incorporates configuration interaction between the two¹ A _1g configurations (|| and |**|) to roughly the same extent as do correlated all-electron calculations. The application of the method to systems that involve relative changes in * transition energies, such as the torsional twisting of quadruple bonds, is more successful quantitatively.     

Etude des transitions de phase du sulfate dibasique de plomb PbSO4, 2PbO: Influence de la vitesse de montee en temperature et de L'histoire thermique

Basic lead sulfate, PbSO₄·2PbO, was studied by means of DTA, X-ray diffraction and scanning electron microscopy. DTA runs at different heating rates showed that two kinds of thermal evolution are possible for PbSO₄·2PbO. IfT<40 deg h^–1, we have the normal process according to the following transitions: IfT>40 deg h^–1 the-PbSO₄·2PbO phase appears at 440 C, but is unstable and breaks down into monobasic and tetrabasic lead sulfates. Reaction enthalpies were evaluated and correlated with the cell volume variations determined by X-ray diffraction. An interpretation of the existence of two types of process is proposed.

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Zusammenfassung Basisches Bleisulfat PbSO₄·2PbO wurde mittels DTA, Röntgendiffraktometrie und Scanningelektronenmikroskopie untersucht. DTA-Versuche mit unterschiedlichen Aufheizgeschwindigkeiten haben gezeigt, da\ PbSO₄·2PbO auf zwei verschiedene Weisen thermisch gebildet werden kann. Bei¯T<40·h^–1 verlÄuft der normale Proze\ entsprechend den Reaktionsgleichungen Bei¯T>40 h^–1 tritt die-PbSO₄· 2PbO-Phase bei 440 C auf, ist jedoch instabil und zerfÄllt zu monobasischem und tetrabasischem Bleisulfat. Die Reaktionsenthalpien wurden bestimmt und mit den röntgendiffraktometrisch ermittelten VerÄnderungen des Elementarzellenvolumens in Beziehung gesetzt. Die Existenz von zwei Typen des Prozesses wird interpretiert.

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, - PbSO₄·2PbO. , , . 40 /. « » : 40/ 440 C PbSO₄·2PbO, , , . , - . .

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Nous remercions F. Chapuis et M. Andréani (Lab. Matériaux, E. C. F.) qui ont réalisés les clichés de microscopie.     

The structures and thermal decomposition of cupric mono,di and trichloracetates

Magnetic moment measurements and ultra-violet diffuse reflectance spectroscopy have been used to investigate the structure of the chloroacetates of copper(II). These studies indicate that cupric monochloroacetate dihydrate is dimeric and cupric trichloracetate tetrahydrate is monomeric. Cupric dichloracetate tetrahydrate forms an intermediate case. The thermal decomposition of these compounds under nitrogen has been studied using thermogravimetry and differential thermal analysis, together with analysis of the products of the decomposition. The major organic product formed in the thermal decomposition of the mono- and dichloracetates is the corresponding chlorinated acetic acid; the solid inorganic product is cuprous chloride. Thermal decomposition of the trichloracetate yields cupric chloride and a mixture of trichloracetic acid and trichloracetyl chloride.

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Zusammenfassung Messungen des magnetischen Momentes sowie diffuse UV-Remissionspektroskopie wurden zur Untersuchung der Struktur der Kupfer(II)-chloracetate eingesetzt. Die Ergebnisse deuten darauf hin, daß Kupfermonochloracetat-Dihydrat dimer und Kupfertrichloracetat-Tetrahydrat monomer ist. Das Kupferdichloracetat-Tetrahydrat bildet hierbei eine Zwischenstufe. Die thermische Zersetzung dieser Verbindungen wurde in Stickstoffatmosphäre unter Anwendung der Thermogravimetrie und Differentialthermoanalyse untersucht, bei gleichzeitiger Analyse der Zersetzungsprodukte. Das bei der thermischen Zersetzung des Mono- und Dichloracetats gebildete organische Hauptprodukt ist die entsprechende chlorierte Essigsäure; der feste anorganische Rückstands das Kupfer(I)-chlorid. Die thermische Zersetzung des Trichloracetats ergibt Kupfer(II)-chlorid sowie eine Mischung von Trichloressigsäure und Trichloracetylchlorid.

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Résumé La mesure du moment magnétique et la spectroscopie de réflexion diffuse dans l'U. V. sont utilisées pour étudier la structure des chloroacétates de cuivre (II). Les résultats indiquent que le monochloroacétate de cuivre (II) dihydraté est dimère et que le trichloroacétate de cuivre (II) tétrahydraté est monomère. Le dichloroacétate de cuivre (II) tétrahydraté représente un cas intermédiaire. La décomposition de ces composés dans l'azote a été suivie par thermogravimétrie et analyse thermique différentielle, en analysant simultanément les produits de décomposition. Le principal produit organique formé lors de la décomposition thermique des mono et dichloroacétates est l'acide chloroacétique correspondant; le produit solide inorganique est le chlorure de cuivre (I). La décomposition thermique du trichloroacétate fournit le chlorure de cuivre (II) et un mélange d'acide trichloracétique et de chlorure trichloroacétylique.

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(II). , (II) , (II) - . (II) . , , . , - , , (I). (II) (II) .

     

Hydrogenation of carbon monoxide catalysts prepared by pyrolysis of Co2(CO)8 on various oxide supports

Catalysts prepared by pyrolysis of Co₂(CO)₈ on oxide supports have been studied in the hydrogenation of CO. It is shown that MgO and -Al₂O₃-based catalysts are less active than those supported on SiO₂, TiO₂ and ZrO₂. The application of -Al₂O₃ as a support increases the relative yield of light hydrocarbons.

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, Co₂(CO)₈ , CO. , MgO -Al₂O₃ SiO₂, TiO₂ ZrO₂. -Al₂O₃ .

     

Molybdenum hexacarbonyl catalyzed photooxygenation of cyclohexane by air dioxygen in acetonitrile solution

ESR and XPS investigations on Cu/–Al₂O₃ catalysts with various amounts of Cu loading are reported. Experimental data are related to the surface structure and dispersed state of catalysts. The results show that ESR can be used as a means of charaterizing monolayer dispersed state for paramagnetic supported catalysts.

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Cu/–Al₂O₃ . . .