Influence of the crystallite size of platinum of the course of hydrogenolysis of ethane and propane over Pt/Al2O3 catalysts

The effect of the degree of platinum crystallite size on the reaction rate, selectivity and activation energy of ethane and propane hydrogenolysis has been studied in the range of platinum crystallite size of 1.7–4.0 nm. In the same range of Pt crystallite size, the activation energy of both processes shows a clear minimum. The decrease in Pt crystallite size bellow 3.0 nm brings about rapid changes in the selectivity of propane hydrogenolysis.

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( ) , -. 1,7–4,0 , .

     

Kinetic parameters of the thermal decompositions of nitritonickelates(II)

Kinetic parameters of thermal decomposition of compounds of general formulaM ₂ ^I M ^II[Ni(NO₂)₆], whereM ^I= K⁺, Rb⁺ or Cs⁺ andM ^II= Ca²⁺, Sr²⁺ or Ba²⁺, were investigated on the basis of the respective thermal curves. Calculations of the reaction order and activation energy carried out by the Coats-Redfern method and by Doyle's method (modified by Zsakó) gave similar results, The reaction order is 2 for all the compounds investigated. In the group of potassium salts the activation energy increases fromM ^II=Ca²⁺ toM ^II=Ba²⁺. In the groups of rubidium and caesium salts, the lowest activation energy is observed whenM ^II=Sr²⁺. Such behaviour of the nitritonickelates is explained in terms of structures and the principle of maximum density.

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Zusammenfassung Die kinetischen Parameter der thermischen Zersetzung von Verbindungen der allgemeinen FormelM ₂ ^I M ^II [Ni(NO₂)₆] (M ^I= K⁺, Rb⁺ oder Cs⁺ und M^II = =Ca²⁺, Sr²⁺ oder Ba²⁺) wurden auf Grund der entsprechenden thermischen Kurven untersucht. Die an Hand der Coats-Redfern Methode und der durch Zsakó modifizierten Doyleschen Methode durchgeführten Berechnungen der Reaktionsordnung und der Aktivierungsenergie ergaben ähnliche Resultate. Die Reaktionsordnung ist 2 für sämtliche untersuchten Verbindungen. In der Gruppe der Kaliumsalze steigt die Aktivierungsenergie vonM ^II=Ca²⁺ in RichtungM ^II=Ba²⁺ an. In der Gruppe der Rubidium- und Caesiumsalze wird die niedrigste Aktivierungsenergie beiM ^II=Sr²⁺ beobachtet. Dieses Verhalten der Nitritonickelate wird durch die Strukturen und das Prinzip der maximalen Dichte erklärt.

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₁ ^{2 II}[Ni(NO₂)₆], ^I= ⁺, Rb⁺Cs⁺,a ^II= ²⁺,8r²⁺²⁺. , - ( ), . 2. ^{+ 2+}. ^II=S²⁺. .

     

Differential thermal analysis study of various oxalates in oxygen and nitrogen

Differential thermal analysis (DTA) of some 25 oxalates are reported in atmospheres of oxygen and nitrogen. It is shown that in some cases in nitrogen the metal is formed, in other cases the oxide of lowest valency state is produced, while a third group give the same oxide product in nitrogen and oxygen. The production in oxygen of the oxide for the first group, and of a higher oxide in the second group is a phenomenon which in the first case involves a further reaction of the metal with the oxygen atmosphere. Another group of oxalates produce characteristic DTA curves due to the formation of carbonate as the initial decomposition product. The dehydrations of these oxalates are marked by endothermic peaks.

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Zusammenfassung Es wurden 25 verschiedene Oxalate durch DTA in Stickstoff- und Sauerstoffatmosphäre untersucht. In einigen Fällen wurde in Stickstoff das Metall gebildet, in anderen das Oxyd von niedrigster Wertigkeit. Es kommt auch vor, daß das gleiche Produkt in beiden Gasen entsteht. Beide erwähnten Produkte werden in Sauerstoff entsprechend oxydiert. Bei einigen Oxalaten erhielt man charakteristische Spitzen, die zeigten, daß das erste Zersetzungsprodukt Karbonat war. Die Dehydration dieser Oxalate zeigte sich durch endothermische Spitzen.

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Résumé On communique les résultats de l'étude de 25 oxalates par analyse thermique différentielle, dans l'oxygène et dans l'azote. On montre que pour certains d'entre eux, dans l'azote, le métal se forme, et que pour d'autres l'oxyde correspondant à la valence la plus faible apparaît; d'autres encore donnent le même oxyde dans l'azote et dans l'oxygène. Dans l'oxygène, et pour le premier groupe, il se forme l'oxyde, tandis que l'oxyde supérieur apparaît pour le second groupe; dans le premier cas, une réaction ultérieure du métal avec l'oxygène de l'atmosphère est mise en jeu. Un autre groupe d'oxalates donne des enregistrements d'ATD caractéristiques en raison de la formation de carbonate comme produit de décomposition initial. Ces oxalates se déshydratent en donnant des pics endothermiques.

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() 25 . , , , . , , , , , , . , , . .

     

Adsorption-desorption hysteresis in porous networks

As a result of computer experiments with model porous networks, the factors (other than pore shape and size distribution) determining the form of the adsorption-desorption hysteresis loop have been elucidated.

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, - - .

     

An alternative model for partly diffusion controlled cage recombination

We proposed a simple kinetc model in which a diffusional physical process and a chemical process of reaction in a cage occur simultaneously. Good agreement between experimental results and the kinetic model are found.

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, . .

     

Effect of Rh/Al2O3 on the reduction of ZnO in a mechanical mixture of these components

The effect of reoxidation temperature on TPR of 5% Rh/Al₂O₃ catalyst and its mechanical mixture with ZnO has been investigated. The results suggest bimodal character of supported rhodium and surprisingly high effect of this metal on ZnO reduction in the mixture.

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5% Rh/Al₂O₃ ZnO. , ZnO .

     

Spectral and thermal studies of copper(II) complexes of 3- and 4-pyridinealdoxime

Copper(II) complexes of 3- and 4-pyridinealdoxime have been prepared and analyzed by spectroscopic (ir and diffuse reflectance) and thermoanalytical (TG, DTG and DTA) techniques. For both these systems, only species with metal: organic ligand: chloride ratio of 122 were found, and the organic ligand appears as a neutral molecule. The spectral data suggest a polymeric structure where the copper(II) ions are in a distorted octahedral environment.The thermal decompositions occur through the reduction of copper(II) to copper(I) and the conversion of the residual organic ligand into acid amide, as found for dihydrogenbis(pyridine-2-aldoxime) copper(II) chloride, but the initial decomposition temperatures are slightly increased, giving rise to the thermal stability sequence:

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Zusammenfassung Kupfer(II)-Komplexe von 3- und 4-Pyridinaldoxim wurden hergestellt und spektroskopisch (IR und diffuse Reflexion) sowie thermoanalytisch (TG, DTG und DTA) analysiert. Für beide Systeme wurden nur Species mit einem Metall:Ligand:Chlorid-Verhältnis von 122 gefunden. Der organische Ligand liegt als neutrales Molekül vor. Die Spektren deuten auf eine polymère Struktur hin, in der die Kupfer(II)-Ionen in einer verzerrten oktaedrischen Koordination vorliegen. Die thermischen Zersetzungen verlaufen über die Reduktion von Cu(II) zu Cu(I) und die Umwandlung des verbleibenden organischen Liganden in Säureamid, wie für Dihydrogen-bis(pyridin-2-aldoxim)-kupfer(II)-chlorid gefunden wurde, aber die Temperaturen des Beginns der Zersetzung und damit die thermische Stabilität steigen in der Reihenfolge [Cu(Py₄-CHNOH)₂Cl₂][Cu(Py₃-CHNOH)₂Cl₂]>[Cu(Py₂-CHNOH)₂]Cl₂ etwas an.

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(, ) ( ) 3- 4- . 122, . , . -( -2-)- . , , , : Cu(4-Py-CHNOH)₂Cl₂Cu(3-Py-CHNOH)₂Cl₂>Cu(2-Py-CHNOH)₂Cl₂.

     

Le systeme binaire fluorure de rubidium-fluorure d'hydrogene

Résumé Le diagramme des équilibres liquide-solide du système fluorure de rubidium-fluorure d'hydrogène a été tracé dans sa totalité. Six espèces stables se manifestent RbF · nHF (avecn=7, 4, 3, 2, 3/2, 1). Un septième composé dont la composition probable est 2RbF · 5HF se manifeste à l'état métastable.

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Liquid-solid equilibria are studied in the complete binary system RbF-HF. Several compounds are observed: RbF ·nHF withn=7, 4, 3, 2, 3/2 and 1. A seventh compound, 2RbF · 5HF, is detected as an unstable form.

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Zusammenfassung Flüssig-fest Gleichgewichte des Binärsystems RbF-HF wurden umfassend untersucht. Sechs stabile Verbindungen wurden beobachtet: RbF ·n HF (n=7, 4, 3, 2, 3/2 und 1). Eine siebente Verbindung, 2 RbF · 5 HF ist metastabil.

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- RbF-HF. RbF·nHF =7,4,3,2, 3/2 1. — 2RbF·5HF — .

     

The possible formation of surface ethylidyne on platinum black and its effect on some catalytic properties

Secondary Ion Mass Spectra of Pt-black exposed to ethylene at 633 K contain a PtC₂H₃ cluster identified tentatively with adsorbed ethylidyne like that reported for single crystal surfaces. The catalytic properties of Pt pretreated by ethylene are, to some respect, superior in hydrocarbon transformations to those containing other, less defined carbonaceous overlayers.

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- Pt-, 633 , PtC₂H₃, , . Pt, , , , , .

     

Unusual selectivity in photooxygenation of alkanes by air in CH3CN solutions catalyzed by CrCl3?C6H5CH2N(C2H5)3Cl

A new system CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN for photooxygenation of alkanes is suggested. Unlike metal chlorides and oxocomplexes, it oxidizes alkanes to produce ketones and small amounts of alcohol. Adding of benzene, methylene chloride or ethanol to the cyclohexane solution rises the oxygenation rate and changes the ketone/alcohol ratio. With small amounts of hydroquinone the formation rate of cyclohexanone (but not of cyclohexanol) sharply decreases. Kinetic isotope effect in the oxidation of C₆H₁₂ and C₆D₁₂ is 1 for cyclohexanol and 2.9 for cyclohexanone. Cyclohexanol formation is assumed to follow a mechanism that does not involve free radicals. Free radicals can participate in the route toward ketone.

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CrCl₃–C₆H₅CH₂N(C₂H₅)₃Cl–CH₃CN . , . , /. ( ) . C₆H₁₂ C₆D₁₂ 1 2,9 . , , . , .

     

Kinetics of oxidation of adonitol by manganese(III) pyrophosphate

Adonitol is oxidized to ribose by Mn(III) pyrophosphate under the conditions [adonitol] [Mn(III)]. The oxidation rate is first order with respect to both oxidatn and substrate and decreases inversly with [pyrophosphate]_free. Thermodynamic parameters are reported and a suitable mechanism involving free radicals is proposed.

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(III) [] [Mn(III)]. , - []. - .

     

A simple cell for IR or UV/VIS investigations of solids

A new low-cost, simple cell for transmission IR or UV/VIS measurements on solid catalysts is described. The cell may be easily adapted to various applications by simple replacing of some its elements by others.

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, . , .

     

ESR spectra of47Ti-enriched titanium catalysts for polymerization

For the first time ESR spectra of⁴⁷Ti-enriched Ziegler system Ti-TIBA in toluene have been studied. For the ratio Ti/Al1, more accurate h. f. s. constants have been found. For Ti/Al1/15 no h. f. s. have been observed, which is ascribed to ordering due to the cooperative Jahn-Teller effect.

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TiCl₄+ ⁴⁷Ti. Ti/Al1 . Ti/Al1/15 , -.

     

Thermal modification of silica gels with temperature programing

A derivatograph was used for the thermal modification of the surface properties of different silica gels. Analogous investigations were carried out with an isothermal method. The possibility of using the thermal method of temperature programming to modify adsorbents is discussed.

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Zusammenfassung Ein Derivatograph wurde zur thermischen Modifizierung der Oberflächeneigenschaften von verschiedenen Kieselgelen benutzt. Analoge Untersuchungen wurden unter isothermen Bedingungen ausgeführt. Möglichkeiten zur Modifizierung von Adsorbentien mit der temperaturprogrammierten thermischen Methode wurden diskutiert.

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. . , .

     

Effect of solvent on photochemically induced olefin metathesis by tungstenhexacarbonyl

Effect of solvents on photochemically induced metathesis of pentene-2 by W(CO)₆ has been investigated. Structure of the catalyst and a reaction mechanism are proposed.

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-2 W(CO)₆. .

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO₄·1/2H₂O(VO)₂P₂O₇+2 H₂O for VOHPO₄·1/2H₂O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different PV atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different PV ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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Zusammenfassung Der Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO₄.1/2H₂O(VO)₂P₂O₇+2H₂O für auf verschiedene Weise dargestelltes VOHPO₄.1/2H₂O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.

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- . , VOHPO₄ · 1/2H₂O, VOHPO₄ · 1/2H₂O(VO)₂P₂O₇ + 2H₂O, - PV 0,91,3. - 1-.

     

Use of ozonized oxygen in heterogeneous catalysis. Effect on the apparent activation energy

The catalytic oxidation of lower olefins has been studied. The effect of ozonized oxygen has been examined. The results show that the apparent activation energy decreases. The industrial importance of the phenomenon is pointed out.

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. , . . .

     

Influence of water vapor on propylene oxidation on VMo catalyst

The dependence of reaction rates for acetone and acetic acid formation on the concentration of water vapor is determined on the basis of the participation of surface hydroxy groups and Brönsted acid centers of the catalyst.

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