Investigation of toluene formation on Pt/Al2O3 catalyst in n-hexane dehydrocyclization

Formation of toluene, a chain lengthening product, has been observed on Pt/Al₂O₃ catalyst in n-hexane dehydrocyclization. Toluene formation is influenced by the catalyst pretreatment processes and the reaction temperature. A correlation has been found between the ageing phenomena and toluene formation.

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- Pt/Al₂O₃ — . . .

     

Mass spectrometric method to determine the mode of carbon-metal bonding during catalytic hydrogenolysis of hydrocarbons

A new method based on high-resolution mass-spectrometry has been developed to distinguish between the modes of adsorption of ethane (i.e. 1,2- or 1,1-diadsorbed form) on the catalyst surface. It has been established that under the conditions of H-D exchange, the 1,2-diadsorbed mode is operative, whereas at higher temperatures this interaction can be converted into 1,1-attachment.

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, - , (.. 1,2- 1,1- ) . , H-D 1,2- , 1,1-.

     

Theoretical study of the formation of adsorbed dicarbonyl species

The formation of mono- and dicarbonyl species during CO adsorption has been theoretically studied in order to obtain a mathematical model of the adsorption isotherms. The dependences proposed describe well the results of other authors and allow better utilization of the experimental data.

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- CO . .

     

Pyrolysis of propane in the presence of ethylene

Pyrolysis of propane in the presence of ethylene and ethylene labeled with¹⁴C has been studied in the temperature range 773–1019 K. The disappearance of the inhibiting effect of ethylene on the thermal decomposition of propane with increasing temperature was observed.

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¹⁴C 773–1019 . .

     

Kinetics of decomposition of hydrogen peroxide on Fe(III)?Al(III) hydroxide-oxide systems

The kinetics of decomposition of hydrogen peroxide have been studied on mixed Fe(III)–Al(III) hydroxide and oxide catalysts. While iron hydroxide possesses considerable catalytic activity, aluminium hydroxide has very little activity. The rate of decomposition on mixed hydroxides increases with increasing concentration of aluminium hydroxide up to about 1.5 mol% and decreases thereafter. The mixed oxides possess negligible activity compared to the corresponding hydroxides. The energy of activation, as calculated from the Arrhenius equation, is 10.1 kcal/mol for sample S4, containing 1.52 mol% of alumina. The rate of decomposition of S4 increases with increasing pH up to 6.8 and decreases thereafter. The rate is first order in all these cases. A suitable mechanism is suggested.

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Fe(III)–Al(III). , . , 1,5 , . . , , 10,1 / S4, 1,52 . S4 pH 6,8, . . .

     

Oxidative conversion of butane and pentane on superacid catalysts

Catalytic properties of AlBr₃, AlBr₃–CuCl₂ and AlBr₃–NiSO₄ in liquid-phase conversion of butane and pentane have been examined. A possibility for the oxidative condensation has been revealed due to both the stoichiometric reduction of Ni²⁺ and Cu²⁺ ions entering into the composition of superacid catalysts, and the catalytic oxidation in the presence of bromine as an oxidant. Nature of the centers responsible for the oxidative condensation of lower paraffins is discussed.

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AlBr₃; AlBr₃–CuCl₂; AlBr₃–NiSO₄ . , Ni²⁺, Cu²⁺, , . , .

     

IR spectroscopic studies of H2S adsorption on acid and base catalysts

IR spectra of H₂S adsorbed on various types of catalysts have been studied by monitoring changes in the properties of their surfaces from the spectra of probe molecules. It is shown that H₂S is adsorbed only dissociatively on basic centers (BC); on proton centers (PC) it forms H-complexes, while with the participation of strong Lewis acid centers (LAC), it is adsorbed both associatively and dissociatively.

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- H₂S , -. , H₂S (), () -, ()- , .

     

Theoretical models of calorimetric systems

In the present paper the dynamic properties of nonisothermal-nonadiabatic calorimeters have been analysed. In these calorimeters the thermal effect produced is partly accumulated in the calorimetric vessel, and partly transmitted to the shield with constant temperature. The generalized equation of the heat balance and the equation of the dynamics have been given for this type of calorimeter. The dependence between the course of the thermal effectQ in timet as a function of the temperature changes of the calorimeter has been presented. DependencesQ(t)=f[(t)] for a calorimeter with different domain configurations distinguished in it, and with different mutual locations of heat sources and temperature sensor have been given. Practical application of the considerations presented has been given.

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Zusammenfassung Die Eigenschaften der sog. nicht-isotherm-nicht-adiabatischen Kalorimeter werden analysiert. In diesen Kalorimetern wird der ausgelöste thermische Effekt teils im Kalorimetergefäß gespeichert und teils dem Konstanttemperaturschild übertragen. Die verallgemeinerte Gleichung des Wärmegleichgewichts und die Gleichung der Dynamik werden für diesen Kalorimetertyp mitgeteilt. Die Abhängigkeit zwischen dem Verlaufe des thermischen EffektesQ in der Zeitt als Funktion der Temperaturänderungen des Kalorimeters werden ebenfalls mitgeteilt. Die AbhängigkeitenQ(t)=f[(t)] werden für ein Kalorimeter mit verschiedenen Bereichskonfigurationen, verschiedenen gegenseitigen Störungen der Wärmequelle und des Temperatursensors angegeben. Es wird auch die praktische Anwendung der beschriebenen Anordnungen gezeigt.

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Résumé Les propriétés dynamiques des calorimètres appelés non-isothermes/non-adiabatiques sont examinées dans cet article. Dans ces calorimètres, l'effet thermique étudié est, en partie, accumulée dans la cellule calorimétrique et, en partie, transmis à la gaine à température constante. On donne l'équation générale du bilan thermique et l'équation de la thermocinetique pour ce type de calorimètre. L'évolution de l'effet thermiqueQ pendant le tempst est exprimée en fonction des variations de température du calorimètre en tempst. Les relationsQ(t)=f[(t)] sont données pour un calorimètre avec différentes configurations et différentes altérations mutuelles des sources de chaleur et des détecteurs de température. On donne également une application pratique des considérations présentées.

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- . , . . Q t . Q(t)=f[(t)] . .

     

Analysis of thermal processes: The exponential integral

Thermal processes can often be characterized by peak reaction temperatures, pre-exponentials, and activation energies, as well as by other parameters. Values of the exponential integralEi(–x), or of a related integralI(x), where the numeric argumentx is a function of activation energy and temperature, are essential to the analyses of many of these processes. It is shown that the use of only the first term of the concomitant asymptotic series to approximate these integrals can result in less reliability than the uncertainty in thermal reaction data. Hence, values ofI(x) which are accurate to 4 significant digits over the range ofx from 15 to 50 are presented.

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Zusammenfassung Thermische Vorgänge können oft durch Spitzenreaktionstemperaturen, präexponentiellen Faktoren, Aktivierungsenergien oder andere Parameter gekennzeichnet werden. Werte des exponentiellen IntegralsEi(–x) oder eines entsprechenden IntegralsI(x), wobeix die Funktion von Aktivierungsenergie und Temperatur ist, sind wichtig zur Analyse vieler dieser Prozesse. Es wurde gezeigt, daß die Benutzung nur des ersten Gliedes der sich nähernden asymptotischen Serie zur Approximation dieser Integrale in geringerer Verläßlichkeit resultiert als die Unsicherheit der thermischen Daten. Werte vonI(x), die genau auf 4 signifikante Zahlenwerte über den Wert vonx von 15 bis 50 zutrafen, wurden vorgelegt.

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, , . Ei(–x), I(x), , . I() 4-4- x 15 50.

     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

Some remarks about butene-1 transformations on NaHY zeolite

Comments are given on the paper Alternative Interpretation of Infrared Spectra of the Zeolite NaHY+Butene-1 System of Forster and Seelemann /2/. Our previous paper /1/ was partly revised but the usefulness of comprehensive studies by infrared and temperature-programmed desorption methods has been emphasized.

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: NaHY+-1. [2]. [1] , - .

     

Interaction of butylamines with protonic centers of HNaY zeolite

IR-spectroscopic studies of the interaction of tert-, sec- and n-butylamine with HNaY protonic centers at 373–725 K and P_amine=0.13–13.3 kPa indicate that the deamination proceeds through intermediate butylammonium ions whose decomposition is the rate-determining step and can provide directly ammonium ions. The temperature of incipient reaction increases in the series: tert-

- -, - - 373 723 0,13 13,3 . , . . : -<-<-.

     

Influence of hydrogen on the aromatization of ethane over Pt/H-ZSM-5 zeolite

Hydrogen influences the activity and selectivity of a Pt/H-ZSM-5 zeolite in ethane aromatization by favoring hydrogenolysis and suppressing dehydrogenation and coking. H₂ formed during the reaction inhibits the aromatization activity.

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Pt/H-ZSM-5 , . H₂, , .

     

Study of the solid solution of MoO3 in Fe2V4O13

Differential thermal and phase X-ray analyses have shown that MoO₃ and Fe₂V₄O₁₃ form a solid substitution solution, in which Mo⁶⁺ ions are incorporate into the crystal lattice of Fe₂V₄O₁₃ in place of V⁵⁺ ions. The solubility limit of MoO₃ in Fe₂V₄O₁₃ at ambient temperature is 18 mole % of MoO₃. The phase equilibria in the system Fe₂V₄O₁₃-FeVMoO₇, were also studied. Results are presented in the form of a phase diagram.

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Zusammenfassung Durch DTA und Röntgenphasenanalyse wurde gezeigt, daß MoO₃ und Fe₂V₄O₁₃ Substitutionsmischkristalle bilden, in denen Mo⁶⁺-Ionen anstelle von V⁵⁺-Ionen in das Kristallgitter von Fe₂V₄O₁₃ eingebaut sind. Die Löslichkeitsgrenze von MoO₃ in Fe₂V₄O₁₃ beträgt bei Umgebungstemperatur 18 Mol-% MoO₃. Ebenfalls wurden die Phasengleichgewichte im System Fe₂V₄O₁₃-FeVMoO₇ untersucht. Die Ergebnisse sind in Form eines Phasendiagramms dargestellt.

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- , ₃ Fe₂V₄O₁₃ , o⁶⁺ V^5– Fe₂V₄O₁₃. ₃ Fe₂V₄O₁₃ 18 %. Fe₂V₄O₁₃-FeVMoO₇ .

     

A study of the thermal decomposition ofc-Fe2P4O12

The conditions of preparation of diferrous cyclo-tetraphosphate (tetrametaphosphate) have been followed by thermal decomposition (dehydration) of the phosphorus compound obtained from a mixture of iron and phosphoric acid. The methods of non-isothermal TA and analysis of the calcinates prepared under the same conditions in an electric furnace have been used to determine the temperatures of the individual dehydration and condensation reactions, the temperature regions of the existence of intermediates, and the conversion degree of the calcinate into the final product. It has been shown that the reactions are affected in a distinctly favourable way by increased water vapour pressure in the area of the products being formed.

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Zusammenfassung Die Bedingungen für die Darstellung verschiedener Zyclotetraphosphate (Tetrametaphosphate) durch thermische Zersetzung (Dehydratierung) einer aus einem Gemisch von Eisen mit Phosphorsäure gewonnenen Phosphorverbindung wurden untersucht. Zur Bestimmung der Temperaturen der einzelnen Dehydratierungs- und Kondensationsreaktionen, der Temperaturbereiche für die Existenz von Zwischenprodukten sowie des Konvertierungsgrades der Kalzinate zu den Endprodukten wurden nicht-isotherme TA-Methoden und auch eine Untersuchung der unter gleichen Bedingungen in einem elektrischen Brenner gefertigten Kalzinate angewendet. Es wurde gezeigt, daß die Reaktion auf eindeutig bevorzugte Weise durch erhöhten Wasserdampfdruck über den zu fertigsenden Produkten beeinflußt wird.

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

     

Catalytic synthesis of tetrahydrothiophenes

It has been established that the liquid-phase hydrogenation of thiophene and its alkyl derivatives in the presence of metallic or sulfurized palladium catalysts provides preparative yields of tetrahydrothiophene homologs at increased pressures of hydrogen and elevated temperatures.

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.

     

Modification of the catalyst surface in 1,2-dichloroethane decomposition

The strong and irreversible chemisorption of substrate or (and) reaction products (self-poisoning of catalyst surface) has been found to account for an activity decrease and changes in catalytic selectivity in the reaction. The mechanism of 1,2-dichloroethane (1,2-DCE) decomposition has been discussed.

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1,2- (1,2-), , . , — — () («» ) . 1,2-.

     

Catalytic reaction of tetrahydrofuran with H2S

The reaction of tetrahydrofuran with H₂S catalyzed by acid-base catalysts has been studied. Catalysts containing an acid-base pair, i.e. a Lewis acid center and a base center, are the most active and selective towards thiolane. Proton donor catalysts and those containing only basic centers are of low activity and selectivity.

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H₂S - . , - : - , . , , .

     

Principles of formation of nitrogen oxides in acetonitrile oxidation on copper-chromium and platinum catalysts

The dependence of the conversion of bound nitrogen to oxides on the temperature and concentrations of oxygen and acetonitrile have been determined. On copper-chromium catalysts the nitrogen of acetonitrile is oxidized predominantly to molecular nitrogen, whereas on platinum catalysts the conversion of bound nitrogen to oxides attains up to 90%.

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. , , 90%.

     

Oxygen sorption on reduced iron catalysts with different contents of promoters

Oxygen sorption has been studied in the temperature range from 78 to 773 K on molten iron catalysts for ammonia synthesis with different contents of promoters. Factors have been established that are responsible for the secondary pyrophoricity of passivated catalyst samples.

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78 773 K . , .