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 , .

     

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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- , . . , - .

     

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. .

     

Nonempirical SQM FF calculation of vibrational spectra for the acetonitrile molecule coordinated to Lewis acids BF3 and BCl3

In terms of SQM FF methods, nonempirical quantumchemical calculations of vibrational spectra for acetonitrile molecule coordinated to Lewis acids BF₃ and BCl₃ were carried out. Scaling factors were obtained from the conditions to reproduce vibrational spectra of CH₃CN and CD₃CN molecules. Contribution of the increase in the power force constant and the kinetic effect of the NB bond to the shift of _CN and _CC under coordination has been determined.

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SQM FF BF₃ BCl₃. CH₃CN CD₃CN. NB _{CN CC} .

     

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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. -, , — . , . - ( ) ( ) . , . : , . , , , - . . , .

     

Exchange kinetics of amino acid anions in solutions of ternary copper(II) complexes with diethylenetriamine

Rate constants for the chemical exchange of some amino acid anions in solutions of copper(II) ternary complexes with diethylenetriamine have been determined by the NMR method. The coordination of amino acid anions in ternary and binary species is different and ligand substitution in the Cu(II) complexes follows an associative mechanism.

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- (II) . - (II).

     

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 ⁺ - . - .

     

X-ray diffraction study of palladium catalysts. Influence of the preparation method on the dispersity of metallic phase

Influence of different methods of catalyst preparation on their phase composition and the crystallite dispersity has been demonstrated.

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.

     

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 , .

     

n-Hexane dehydrocyclization over Pt?Ni supported on alumina catalysts

Pt–Ni/-Al₂O₃ catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.

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Pt–Ni/-Al₂O₃ -. Ni . Ni , .

     

Synthesis and thermal study of some adducts of morpholine with nickel(II) nitrite,sulphate and perchlorate

The preparations of the nickel-morpholine (Morph) complexes Ni(NO₂)₂·3Morph and Ni(ClO₄)₂·4Morph·2H₂O are described. The thermal treatment of this perchlorate and of NiSO₄·2Morph led to the isolation of Ni(ClO₄)₂·2Morph·2H₂O and NiSO₄·Morph. The magnetic moments, diffuse reflectance spectra and infrared spectra of these compounds are all compatible with a pseudo-octahedral environment around the nickel atom.

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Zusammenfassung Die Darstellung der Nickel-Morpholin(Morph)-Komplexe Ni(NO₂)₂·3Morph und Ni(ClO₄)₂·4Morph·2H₂O wird beschrieben. Die thermische Behandlung dieses Perchlorates und von NiSO₄·2Morph ergibt Ni(ClO₄)₂·2Morph·2H₂O und NiSO₄Morph. Magnetisches Moment sowie diffuse Reflektionsspektren und Infrarotspektren dieser Verbindungen sind kompatibel mit einer pseudooktaedrischen Koordination des Nickelatoms.

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, () : Ni(NO₂)₂·, NiSO₄·2 Ni(ClO₄)₂·4·2H₂O. NiSO₄· Ni(ClO₄)₂·2·2H₂O. , , .

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The authors are indebted to Consejeria de Cultura y Educación de la Comunidad Autónoma de Murcia for financial support.     

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 , . , .

     

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 . .

     

Methanol transformations on zirconium phosphate, CuX zeolite and their mixtures

It has been revealed that the mixtures of CuX zeolite and zirconium phosphate are more active catalysts for the oxidative dehydration of methanol than the individual components.

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- .

     

Thermal properties of some metal chelates of di-isobutyldithiocarbamic acid

The thermal properties of some metal chelates of di-isobutyldithiocarbamic acid have been investigated in an inert atmosphere, with a view to applying them to gas chromatographic separation. In spite of the slight decomposition occurring during volatilization, most of the metal chelates may be successfully separated by gaschromatography on short nonpolar glass capillary or fused silica columns. There is no clear correlation between the gaschromatographic behaviour and the thermal stability of the metal chelates studied here.

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Zusammenfassung Die thermischen Eigenschaften einiger Metallchelate der Di-isobutyl-dithiocarbaminsäure wurden in einer inerten Atmosphäre hinsichtlich der Möglichkeiten ihrer gaschromatographischen Trennung untersucht. Trotz der während der Verflüchtigung eintretenden geringfügigen Zersetzung kann der grösste Teil der Metallchelate durch Gaschromatographie erfolgreich in kurzen nichtpolaren Glaskapillarkolonnen oder in mit geschmolzenem SiO₂ bedeckten Kolonnen getrennt werden. Es besteht keine eindeutige Korrelation zwischen dem gaschromatographischen Verhalten und der thermischen Stabilität der untersuchten Metallchelate.

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. , . .

     

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 -, , -.

     

The pyrolysis of polymers and identification of the soot adsorbed components

Various polymers like polyethylene, polyvinyl chloride, polyamide 6 and polypropylene were burnt in an open flame furnace according to DIN 4102. The generated soot particles were collected on glass fiber filters followed by elution with tolouene. A great part of the soot extract adsorbed compounds could be identified by means of gaschromatographic and mass spectrometric analysis. For polyvinyl chloride and polystyrene mainly aromatic combustion products like naphthalene, phenanthrene, pyrene and chrysene were detected in contrast to polyethylene and polypropylene which form aliphatic and olefinic products. In the chromatograms these components are often interfered by superimposition of the aromatics. The extractions of the sample receiver with nitromethane lead to the separation of the aromatic — from the aliphatic compounds. Monomeric and dimeric-caprolactam were mainly formed by burning polyamide 6.

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Zusammenfassung Verschiedene Kunststoffe wie zum Beispiel Polyethylen, Polyvinylchlorid, Polyamid 6 und Polypropylen wurden in offener Flamme in 'Anlehnung an DIN 4102 verbrannt. Die dabei entstehenden Russpartikel wurden auf Glasfaserfiltern gesammelt und mit Toluol extrahiert. Durch gaschromatographische und massenspektrometrische Untersuchungen konnten die Hauptbestandteile des Russextraktes analysiert werden. Bei Polyvinylchlorid und Polystyrol handelt es sich vorwiegend um aromatische Verbindungen, wie zum Beispiel Naphthalin, Phenanthren, Pyren und Chrysen. Die Hauptkomponenten des extrahierten Russes von Polyethylen und Polypropylen bestanden aus aliphatischen und olefinischen Produkten, die im Chromatogramm die aromatischen überdeckten. Durch Ausschütteln der Probenvorlage mit Nitromethan konnte eine Trennung der aromatischen von den aliphatischen erreicht werden. Bei der thermischen Zersetzung von Polyamid 6 wurden als Hauptabbauprodukte das Mono und Dimere des -Caprolactams gebildet.

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80–120° 1, 3, 5-- /3, 5--. -4- / / 1330/ / -/. / / . , -. 1330 - . - .