Combined pulse microcatalytic and ESR studies of butylene oxidation on V-Mg oxide catalysts

Abstract The behavior of V–Mg oxide catalysts in both steady and non-steady state butylene oxidation has been examined.

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, .

     

Quality control of the cure process of thermosetting resins by means of differential scanning calorimetry

Calorimetric and rheological characterizations of thermosetting resin formulations containing a novalac epoxy resin hardened with 60 to 120 parts per hundred of methylated maleic acid adduct anhydride are described. The calorimetrically determined epoxy conversion has been related to the gelation limits theoretically calculated from Flory's non-linear copolymerization theory and experimentally verified in rheological tests.

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Zusammenfassung Die kalorimetrische und rheologische Charakterisierung der Ansätze von hitzhärtbarem Harz wird beschrieben. Die Ansätze enthalten ein mit 60–120% methyliertem Maleinsäure-Adduktanhydrid gehärtetes Novolackepoxidharz. Die kalorimetrisch bestimmte Epoxid-konversion wurde auf die theoretisch aus der nicht-linearen Flory'schen Kopolymerisationstheorie berechneten und experimentell durch rheologische Tests bestätigten Erstarrungsgrenzen bezogen.

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, - . -, , , .

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Financial and scientific support by the CNR Progetto Chimica Fine e Secondaria and the Societa Italiana Resine (SIR) is gratefully acknowledged.     

Frequencies, anharmonicities, and dissociation energies of OH groups in H-mordenite

Harmonic frequencies, anharmonicities and dissociation energies of surface hydroxy groups in H-mordenite have been determined. The application of the Lippincott-Schroeder potential function for similar problems is proposed.

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, -. - .

     

Gas diffusion during the thermal analysis of pyrite

Maximum rates of weight loss were measured during thermal analysis experiments involving the oxidation of thin layers of pyrite particles (<37 to 212–300 m screen size fractions) in oxygen-containing atmospheres (10–100%). The experimentally determined rates were compared with those calculated for several diffusion-based models. Good agreement was obtained with the model involving gas diffusion in the crucible.

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Zusammenfassung Maximale Geschwindigkeiten des bei der Oxydation von in dünnen Schichten aufgebrachten Pyritteilchen (< 37 bis 212–300 m Teilchengröße) in 10–100 Sauerstoff enthaltenden Atmosphären auftretenden Gewichtsverlustes wurden im Verlaufe von thermoanalytischen Experimenten gemessen. Die erhaltenen Werte werden mit denen für einige, die Diffusion berücksichtigenden Modelle berechneten verglichen. Gute Übereinstimmung wurde bei dem die Gasdiffusion im Tiegel berücksichtigenden Modell erhalten.

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37 212–300 10 100%. . , .

     

A TPR study of SiO2-supported Ru?Ag catalysts

A H₂ chemisorption and TPR study of Ru–Ag/SiO₂ catalysts reveals that after oxidation at 373 K this systems behaves like Ru–Cu/SiO₂. High temperature oxidation, however, does not result in the separation of the metal like in the Ru–Cu case but in the redispersion of Ag on top of the Ru particles.

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H₂ Ru–Ag/SiO₂ , 373 Ru–Cu/SiO₂. , , , Ru–Cu, Ag Ru.

     

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.     

Calculation of the mass transfer coefficient with a chemical reaction in a gas-liquid system

A solution of the problem of mass transfer in a turbulent boundary layer has been obtained with a first-order chemical reaction occurring in the liquid phase. The dependence of the enhancement factor for absorption and of the mass transfer coefficient on the model parameters can be used for building up a hierarchic model of the gas-liquid reactor.

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Modelling of self-oscillations in the combustion of n-heptane-isooctane mixtures

A mathematical model has been constructed to describe the self-oscillation regime of the cool-flame combustion of an n-heptane-isooctane mixture. The character of the dependence of the amplitude and oscillation period on the temperature and mixture composition is in a qualitative agreement with the similar experimental data.

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, --. .

     

A comparative study of uncatalyzed and catalyzed oscillatory behavior of different mono-and dihydroxybenzoic acids in acidic bromate

Optimum and boundary conditions for uncatalyzed and catalyzed temporal oscillations in the redox potentials in the oxidation of mono- and dihydroxybenzoic acids in acidic bromate (H₂SO₄) have been established and compared. The number and relative positions of the functional groups, in the aromatic ring have been found to influence the oscillatory behavior. Ferroin has been found to enhance the oscillatory behavior considerably as compared to Ce(IV) and Mn(II). A probable explanation of the oscillatory behaviour of these system is suggested.

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- - (H₂SO₄). . , Ce(IV) Mn(II), . .

     

Free radical additions to the C=O bond of formaldehyde

The reactions between formaldehyde and n-propyl radicals were studied at 333 and 363 K. Addition to the C=O bond was found to be several times faster than abstraction of the formyl hydrogen atom. With a TST estimate of log(A/dm³ mol^–1 s^–1)=7.9±0.5, 28.0±2.1 kJ mol^–1 was obtained for the activation energy of the addition reaction.

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- 333 363 . C=O . 28.0±2.1 ^–1 , lg(A/ ^{–1 –1})=7.9±0.5 .

     

Development of phase composition for mixed Ni?Cu chromite catalysts. Conversions under calcination

IR spectroscopic and X-ray studies of variations in the composition of Ni, Cu and (Ni+Cu) ammonium chromates under thermal treatment show that the Ni–Cr system consists of spinel and NiO, and Cu–Cr systems consist of the spinel CuCr₂O₄ only. In mixed Ni–Cu–Cr systems part of Ni- and Cu-containing components remain independent and part of them form common Ni+Cu phases.

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Ni-, Cu- (Ni+Cu)- . , Ni–Cr NiO, Cu–Cr — CuCr₂O₄. Ni–Cu–Cr Ni- Cu- , Ni+Cu .

     

ESR study of free radicals chemically generated at high pressure

Free radicals generated by the thermal decomposition of benzoyl peroxide in polyacrylnitrile were studied by the ESR method at 700 MPa between 100 and 130°C. The formation and decay of macroradicals were investigated and the mechanism of macroradical generation is discussed.

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700 MPa 100 130°C. .

     

Influence of neodymium content on the catalytic properties of zeolite NDHNaY

The influence of neodymium content on the catalytic properties of a HNaY zeolite was investigated using the cracking of n-heptane as model reaction. Neodymium zeolites were found to be more active for cracking and hydrogen transfer reactions than zeolites containing lanthanum, cerium or praseodymium.

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HnaY . , , , .

     

Non quasi-stationary state pyrolysis. Induction period of neopentane pyrolysis

The principle of an apparatus using an isothermal continuous flow stirred tank reactor to study homogeneous gas phase reactions at space times of the order of 1 sec is given. With this apparatus, the induction period of neopentane pyrolysis (as an example) has been clearly shown.

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, , 1 . , , .

     

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     

Ceramics — new applications in a traditional field of thermal analysis

Ceramics is by tradition one of the main fields of application for methods of thermal analysis. Changing technology and environmental problems have provided new reasons for the extensive use of highly-developed TA instrumentation. It is shown that TA can solve difficulties in production processes, provide new information for the optimum use of raw materials and select further fields of application for ceramics.

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Zusammenfassung Die Keramik ist traditionsgemäss ein Hauptanwendungsgebiet der thermoanalytischen Methoden. Veränderungen in der Technologie und in dem Umweltschutzproblemen geben neuen Anlass für die extensive Anwendung hochentwickelter TA-Geräte. Es wird gezeigt, dass die TA Schwierigkeiten im Produktionsprozess lösen kann, neue Informationen über den optimalen Gebrauch von Rohmaterialien liefert und weiters Anwendungsgebiete für die Keramik erschliesst.

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. . , TA .

     

Effect of protonation on hydroconversion of n-dodecane over Ni/ZSM-5 catalysts

The amount and distribution of acid sites are responsible for both conversion and product distribution in hydroconversion of n-dodecane over Ni/ZSM-5 catalysts. Catalytic stability is also related to the protonation degree of the samples.

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, - Ni/ZSM-5. .

     

Dynamics of chemical reactions and nonphysical steady states

Data on the position of nonphysical (lying beyond the region of determination) steady states are shown to be of use for understanding the dynamic behavior of chemical reactions, in particular, the reasons for slow relaxations.

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Conversion of pentane to isopentane and isopentane to isobutane catalyzed by a solid superacid in the vapor phase /1/

The title reactions were studied with a solid superacid, which was prepared by exposing Zr(OH)₄ to 1 N H₂SO₄, followed by calcination at 650°C in air. Pentane and isopentane were converted into isopentane and isobutane, respectively, the selectivities being 84% under short contact conditions at 80°C.

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, - Zr(OH)₄ 1 N- H₂SO₄ 650°C . , , 84% 80°C.