Kinetics of the catalytic transformation of isobutene into methacrylonitrile with NO on supported nickel oxide aerogel

Kinetic studies of the nitroxidation of isobutene by NO show that the reaction follows a redox mechanism in the temperature range of 300–400°C. This mechanism implies an interaction between dehydrogenated isobutene -allyl radical and atomic nitrogen due to the decomposition of NO by the reduced catalyst, which is then reoxidized.

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NO , 300–400°C. - , NO , .

     

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. .

     

Alkylation of toluene with ethylene on HZSM-5

Alkylation of toluene with ethylene on unmodified large-crystal HZSM-5 has been studied in a flow system at 673 K, atmospheric pressure. The yield of ethyltoluenes increased and that of benzene and xylenes decreased with time on stream. This change in yields was accelerated by increasing the ethylene content of feed and by pretreating the catalyst with ethylene. Selectivity for toluene ethylation increase with increasing space velocity.

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HZSM-5 673 . - , . - - -. .

     

Influence of structural promoters on reduction dilatograms of iron catalyst

In each reduction step, changes in the catalyst pellet volume during reduction of precipitated iron catalysts are determined by the concentration of structural promoters and the reaction temperature.

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, , .

     

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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- , . . , - .

     

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- . , , , , . , , , , .

     

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. .

     

Study of the combustion of a fire retardant coating by thermal analysis and different complementary techniques

An intumescent fire retardant coating can effectively control fire spread and damage. Its dual purpose is to confine the surface spread of flame to the boundaries of an already established fire, and to retard the penetration of heat and flame to and through the coated surface. Our composition expanded and provided an insulation layer between the flame source and the combustion substrate, and liberated a quantity of primarily non-flammable decomposition products which tended to extinguish the flame. The main ingredients of the coating were cellulose acetate butyrate and HMDI (Desmodur N) for Polyurethane, and Chlorowax-70 (chlorinated paraffins) as fire retardant component. This fire retardant coating was applied to wood panels, and tested in a 2-foot tunnel, its flame spread rating being measured. The effects of three parameters of interest were investigated: the type of wood used, the percentage of Chlorowax, and the coating thickness. It was found of interest to study the oxidation of the coating using different techniques, e.g. flash pyrolysis under oxygen and GC/MS for analysis of the decomposed products. Combustion studies of the coating were also conducted using DSC and thermogravimetry, either with the scanning mode or under isothermal conditions. Comparisons were made between the results obtained from pyrolysis and combustion.

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Zusammenfassung Ein schwellender feuerhemmender Überzug kann Ausbreitung und Schäden von Feuer wirksam einschränken und wird zwei Zwecken gerecht: Verhinderung der Ausbreitung von ausgebrochenem Feuer und Schutz der überzogenen Oberfläche vor Hitze- und direkter Flammeneinwirkung. Die beschriebene Komposition quillt und bildet eine Isolationsschicht zwischen der Flammenquelle und dem brennbaren Material, liefert zugleich aber auch eine gewisse Menge von nichtbrennbaren, die Flamme erstickenden primären Zersetzungsprodukten. Die Hauptbestandteile des Überzugs sind Celluloseacetat und -butyrat und HMDI (Desmodur N) für Polyurethan sowie Chlorowax-70 (chlorierte Paraffine) als feuerhemmende Komponente. Dieser feuerhemmende Überzug wurde auf Holzplatten aufgebracht und in einem 2ft-Tunnel getestet, wobei die Flammenausbreitungsgeschwindigkeit gemessen wurde. Der Einfluß von drei interessierenden Parametern wurde untersucht: Typ des benutzten Holzes, Anteil von Chlorowax und Überzugsschichtdicke. Es erwies sich als interessant, die Oxydation des Überzugmaterials mit verschiedenen Techniken zu untersuchen, z.B. durch Schnellpyrolyse und Analyse der Zersetzungsprodukte mittels GC/MS. Verbrennungsuntersuchungen des Überzugmaterials wurden auch mittels DSC und Thermogravimetrie entweder nach der scanning-Arbeitsweise oder unter isothermen Bedingungen ausgeführt. Die bei Pyrolyse und Verbrennung erhaltenen Ergebnisse werden miteinander verglichen.

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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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. , , .

     

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.     

Comparative discussion of NH

A comparative study of NH ₄ ⁺ formation on aluminosilicate surface and in an aqueous solution of hydrochloric acid has been carried out in the framework of the nonempirical method with a STO-3G basis. It is suggested that the compensation mechanisms of energy consumptions to form protonated species in both cases are similar.

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-3 - NH ₄ ⁺ - . - .

     

Redistribution kinetics of isotope molecules due to reversible bimolecular reactions with several atomic channels

Isotope kinetic equations for reversible bimolecular reactions describe the rearrangement of atoms in activated complexes. It has been established from the model reaction CH₄+HCH₃+H₂ that the isotopic homoexchange of methane via two atomic channels is given by one set of equations with different sets of parameters.

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- . CH₄+HCH₃+H₂ , .

     

Particle size dependence for CO chemisorption on supported Ru catalysts

The stoichiometry of CO chemisorption on highly dispersed zeolite-supported Ru has been investigated. This stoichiometry, which can be expressed as CO/H, increases with decreasing Ru particle diameter. For diameters <1.6 nm this ratio approached a limiting value of 4–5, indicating the formation of surface carbonyls. No direct influence of the support on this ratio could be detected.

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CO Ru, . , CO/H, Ru. <1,6 n 4–5, . .

     

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 . .

     

TG and TGT investigations of the decomposition of nitrocellulose under quasi-isothermal conditions

A derivatographic study was made of the influence of the slow heat transport between the sample and its surroundings upon the courses of exothermic transformations. It was found that if the sample was placed in a thin film layer on the multiplate sample holder and the quasi-isothermal heating technique was applied, then the rate of the decomposition could already be regulated at will, up to a certain limit. Under the conventional thermoanalytical conditions the same sample decomposed in an explosion-like way. The examinations were supplemented with thermo-gas-titrimetric (TGT) measurements.

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Zusammenfassung Die Autoren untersuchten mit dem Derivatographen die Wirkung der langsamen Wärmeübertragung zwischen Probe und Umgebung auf den Verlauf exothermer Umwandlungen. Es wurde festgestellt, daß bei Auftragung der Probe in einer dünnen Filmschicht auf den Mehrplatten-Probenbehälter und bei Anwendung einer quasi-isothermen Aufheiztechnik die Zersetzungsgeschwindigkeit bis zu einer gewissen Grenze bereits nach Belieben gesteuert werden kann. Dieselbe Probe wird unter den üblichen thermoanalytischen Bedingungen explosionsartig zersetzt. Die Autoren ergänzten ihre Prüfungen auch mit thermogas-titrimetrischen (TGT) Messungen.

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Résumé Les auteurs ont étudié à l'aide d'unDerivatograph l'influence du transfert de chaleur lent entre l'échantillon et son environnement, sur l'allure des transformations exothermiques. Les résultats montrent que si l'échantillon est placé sous forme de films minces sur le support multiplaques et s'il est chauffé en régime quasi-isotherme, la vitesse de la décomposition peut-être contrôlée, jusqu'à une certaine limite, à volonté. Si l'on applique les conditions habituelles de l'analyse thermique, le même échantillon se décompose de manière explosive. Les auteurs ont complété leurs études en effectuant également l'analyse titrimétrique des gaz émis.

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

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The authors wish to thank Prof. E. Pungor for valuable discussions.     

Kinetics of oxidation of methanol by chlorine dioxide

The kinetics of oxidation of methanol by chlorine dioxide has been investigated at 35 °C. The reaction is first order with respect to both substrate and chlorine dioxide. Molecular chlorine dioxide is the principal oxidant. The influence of various factors, e.g. ionic strength, inorganic salts, D₂O and temperature on the initial rate has been studied. The activation parameters have been calculated and a mechanism involving hydride abstraction has been suggested.

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35 °C. , . . , . , , D₂O , . , .

     

Effect of electronic interaction between metal and support: How the nature of Ru/Al2O3 is modified

It is a well known fact that when supported on different supports, a transition metal may show different catalytic behavior. In some cases it is claimed that the differences in the acidity of supports are due to this phenomenon. In this work, by adding increasing amounts of MgO to Al₂O₃, the number of acid sites and hence the acidity of Al₂O₃ were monotonically decreased. The behavior of Ru supported on these mixed supports was investigated with IR, and it is concluded that the interaction between metal and acid sites on the surface is the most important factor for the changing properties.

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, , . . Al₂O₃ MgO Al₂O₃. Ru -, , -.

     

Thermische Zersetzung des Kaliumhexacyanoferrats (II)

Zusammenfassung Es wurde festgestellt, daß unter Luftzutritt die Grenze der thermischen Beständigkeit des K₄[Fe(CN)₆] bei 200° liegt. Die Zersetzung des Komplexes führt im Temperaturbereich von 200° bis 350° zu ferromagnetischen Intermediären. Der Ferromagnetismus der erwärmten Präparate konnte mit der Bildung von-Fe₂O₃ erklärt werden. Bei 250° besteht die vorherrschende kristalline Phase aus Kaliumkarbonat.

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It has been found that the limit of thermal stability of K₄[Fe(CN)₆] in air is 200°. The decomposition of the complex in the temperature range of 200°–350° leads to ferromagnetic intermediates. The ferromagnetism of these products could be explained by the formation of-Fe₂O₃. At 250° the crystalline phase consists mainly of potassium carbonate.

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Résumé On a établi que la limite de la stabilité thermique de K₄[Fe(CN)₆] en présence d'air s'élève à 200°. Entre 200 et 350°, la décomposition du complexe donne des produits intermédiaires ferromagnétiques. Ce ferromagnétisme s'explique par la formation de-Fe₂O₃. A 250°, la phase cristalline dominante est constituée par du carbonate de potassium.

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, K₄[Fe(CN)₆] , 200°. 200°–350° . -Fe₂O₃. 250° .