Interaction of styrene with triphenylphosphinecobalt complexes

The interaction of the cobalt phosphine complexes Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ and H₃Co(PPh₃)₃ with styrene yields mono and dinuclear complexes identified by the ESR method. A paramagnetic complex, Co(PPh₃) (styrene)₂, is one of the intermediates in the catalytic hydrogenation of styrene.

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Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ H₃Co(PPh₃)₃ . , Co(PPh₃) ()₂.

     

Relations between the probability of heterogeneous-homogeneous radical-chain mechnism and oxygen bond energy in oxide catalysts

Transition metal oxides increase the first ignition limit for 2 H₂+O₂ mixture (P₁) due to their reduction by H atoms, which leads to chain termination. The dependence of P₁ on the metal-oxygen bond energy and also on the heterogeneous catalytic activity of oxides has been established.

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(P₁) -, . P₁ -, P₁ - .

     

Effect of vanadium content on the character of acidic sites on V2O5/Al2O3 catalysts

By IR spectroscopy and TPD the effect of vanadium content on the relative proportion of strongly acidic sites of V₂O₅/Al₂O₃ catalyst was studied.

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- - V₂O₅/Al₂O₃.

     

Propos sur l'interpretation de l'energie d'activation experimentale

Résumé Les résultats de divers travaux montrent que la valeurE _e de l'énergie activation expérimentale tirée des diagrammes d'Arrhénius varie avec la pression, dans le cas de réactions de décompositions endothermiques.L'analyse de divers modèles permet d'expliquer cette constatation en montrant que la grandeurE _e n'a pas le sens d'une énergie d'activation mais est une fonction de nombreux paramètres. Deux d'entre eux ont été retenus dans le cadre de cette étude: le terme d'écart à l'équilibre et le terme de gradient thermique, provoqué par l'endothermicité du phénomène.Cette analyse permet d'établir une prévision de la fonctionE _e (P) conforme aux résultats expérimentaux.

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The results from various investigations show that the experimental activation energy valueE _e derived from the Arrhenius diagrams varies with pressure for endothermic decomposition reactions.The analysis of various models allows this fact to be accounted for by showing thatE _e should be regarded not in its fundamental formulation, but as being a function of numerous parameters. Two of these were taken into account in the present study, i.e. deviation from equilibrium and a thermal gradient due to the fact that the phenomenon is endothermic.FunctionE _e (P) fitting the experimental results may be predicted by such an analysis.

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Zusammenfassung Die Ergebnisse verschiedener Untersuchungen zeigen, dass die aus den Arrhenius-Diagrammen abgeleiteten experimentellen Werte der AktivierungsenergieE _e bei endothermen Zersetzungsreaktionen mit dem Druck variieren.Die Analyse verschiedener Modelle ermöglicht eine Erklärung dieser Tatsache, indem gezeigt wird, dassE _e nicht in ihrer grundliegenden Formulierung betrachtet werden darf, sondern als Funktion einer Anzahl von Parametern. Zwei dieser Parameter wurden in der vorliegenden Untersuchung berücksichtigt d.h. die Abweichung von dem Gleichgewicht und der thermische Gradient, welcher infolge der endothermen Beschaffenheit der Erscheinung auftritt.Eine den Versuchsergebnissen entsprechende FunktionE _e (P) kann mittels einer solchen Analyse vorausgesagt werden.

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, _e, , . , _ee , . , : , , . _e (), , .

     

Temperature programmed desorption of NH3 and H2O from NH4NaX and CoNH4NaX zeolites

A study has been made of temperature programmed desorption (TPD) of NH₃ and H₂O from samples of NH₄X and CoNH₄X zeolites of various degree of exchange. NH₃ TPD peaks could be explained by interaction of NH₃ with different Brönsted and Lewis acidic centers. Moreover a water peak at high temperatures allowed interpretations of the dehydroxylation, and by reason of the characteristic desorption temperatures a particular state of the Co²⁺ ions in the CoNH₄X zeolites is postulated.

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- () NH₃ H₂O NH₄X CoNH₄X . NH₃ NH₃ =qs . . Co²⁺ CoNH₄X.

     

Thermal analysis studies on electrochemically oxidized carbon fibers

The results are presented of studies on the effect of electrochemical oxidation of carbon fibers (CFs) in 1 mol·dm^–3 H₂SO₄ on their thermal decomposition in air.The resistance to oxidation of the as-received fibers increases with increasing ordering of their internal structure, characterized by the interlayer spacing¯d ₀₀₂ of the graphite crystallites.After anodic oxidation, the resistance to oxidation of CFs in air is markedly decreased. It is shown that in the course of anodic polarization of CFs with a current density of more than 5 A·m^–2, the regions of the material with highest ordering convert to graphite oxide, which is hydrophilic and thermally unstable.

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Zusammenfassung Es werden die Ergebnisse einer Untersuchung über den Einfluß der elektrochemischen Oxydation von Kohlefiber (CF) in 1 molarer H₂SO₄ auf dessen thermische Zersetzung in Luft dargelegt. Ihre Oxydationsbeständigkeit wächst mit steigender innerer Strukturordnung, charakterisiert durch den Zwischenschichtabstand¯d ₀₀₂ zwischen den Graphitkristalliten. Nach anodischer Oxydation ist die Oxydationsbeständigkeit von CF in Luft deutlich niedriger. Es wurde gezeigt, daß sich die Materialregionen mit der geordnetsten Struktur im Verlauf der anodischen Polarisation von CF mit einer Stromdichte von mehr als 5 A·m^–2 in hydrophiles und thermisch instabiles Graphitoxid umwandeln.

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1 M . , d ₀₀₂ . . , 5 · ^–2, , .

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The author is indebted to Miss Lucyna Hrynczyszyn for experimental assistance during the derivatographic measurements. This study was carried out with support from Government Research Programme 01. 15.     

Study of selective dissociation in C6F5H?C6F5D mixtures induced by intense CO2 laser pulses

Irradiation of a C₆F₅H–C₆F₅D mixture at 1 Torr by a tunable CO₂ pulse laser brings about chiefly dissociation of one component depending on the frequency of emission absorbed by the proper molecules. The addition of radical acceptors increases the selectivity by suppressing secondary reactions.

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C₆F₅H C₆F₅D 1 CO₂-, , . .

     

Sorption of H2, O2 and CO on bimetallic catalysts Pd?Ag/Al2O3 over a wide temperature range

Adsorption of hydrogen, oxygen and carbon monoxide on Pd–Ag/Al₂O₃ catalysts of different compositions within the temperature range from 293 to 773 K has been investigated. Adsorption measurements have been carried out by the pulse chromatographic method. The results obtained reflect interactions of the above adsorbates with the alloy surface, strongly enriched in silver atoms, as a result of surface segregation processes.

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, Pd–Ag/Al₂O₃ 293–773 K. . , , .

     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields

The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation to-Fe₂O₃ was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe₃O₄ and FeO at the expense of Fe₂O₃ is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

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Zusammenfassung Der Einfluß eines elektrischen Feldes auf die thermische Dehydratisierung des amorphen hydratisierten Eisen(III)oxids in oxidierenden, inerten und reduzierenden Atmosphären wurde durch Röntgendiffraktometrie untersucht. In oxidierenden und inerten Atmosphären wurde die Umwandlung zu -Fe₂O₃ durch elektrische Felder gefördert, besonders an der negativen Elektrode. Die Form der Kristallite des Produkts war ebenfalls an der negativen Elektrode am größten. Beide Ergebnisse werden durch die Proteinwanderung zur negativen Elektrode erklärt, wo diese Wasser bilden, das für die kristalline Phase als Keimbildner fungiert. In reduzierenden Atmosphären wird die Bildung von Fe₃O₄ und FeO auf Kosten von Fe₂O₃ durch elektrische Felder besonders an der negativen Elektrode erleichtert. Mögliche Reaktionsmechanismen werden erörtert und die Rolle der Protonen bei der Stabilisierung defekt-spineller Zwischenstufen und Produkte besprochen.

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Résumé L'effet d'un champ électrique sur la déshydratation thermique de l'oxyde de fer(III) hydraté amorphe a été étudié par diffractométrie des rayons X, dans des atmosphères oxydante, inerte et réductrice. En atmosphères oxydante et inerte, le champ électrique facilite la transformation en -Fe₂O₃, en particulier à l'électrode négative. La taille des cristaux formés est également plus élevée à l'électrode négative où il se forme de l'eau qui agit comme agent de nucléation de la phase cristalline. En atmosphère réductrice, le champ électrique facilite la formation de Fe₃O₄ et FeO, aux dépens de Fe₂O₃, en particulier à l'électrode négative. On considère les mécanismes de réaction possibles et on discute le rôle des protons sur la stabilisation des produits et des intermédiaires défauts-spinelles.

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- (III) , . -Fe₂O₃ , , . , , . Fe₃O₄ FeO Fe₂O₃ . , .

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The author is indebted to P. J. Melling for assistance with the measurements in H₂/N₂ atmospheres.     

Thermogravimetric study of some disperse dyestuffs

Two disperse dyestuffs, though exhibiting similar behaviour upon TG-DTG-DTA, have different dyeing properties. Thermoanalytical investigations are not sufficient to predict dyeing characteristics and fastness.

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Zusammenfassung Zwei Dispersionsfarbstoffe, die sich bei der TG-DTG-DTA ähnlich verhalten, zeigen unterschiedliche Färbeeigenschaften. Thermoanalytische Untersuchungen sind nicht ausreichend, um Färbeeigenschaften und die Farbechteheit vorherzusagen.

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, , , . .

     

Kinetic model for methanol conversion over Mg-ZSM-5 zeolite

The catalytic conversion of methanol to olefins over ZSM-5 zeolite modified by ion exchange with Mg exhibits an autocatalytic character. On this basis an overall kinetic model of the reaction was proposed which allowed the determination of rate constants and apparent activation energy.

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ZSM-5, Mg, . , .

     

State of components in Pd/C catalysts promoted by Ho2O3

Catalysts prepared through the interaction of C₃H₅PdC₅H₅ with the surface of evacuated Ho₂O₃/C after reduction by H₂ at 573 K contain Pd and Ho₂O₃ particles whose size is 30 and 20–40 Å, respectively. XPS and TEM data indicate that Pd particles have a positive charge and their surface is partly covered by Ho oxide.

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, C₃H₅PdC₅H₅ Ho₂O₃/C, H₂ 573 Pd 30 Å Ho₂O₃ 20–40 Å. XPS TEM Pd , Ho.

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .

     

Melting memory effect of the β-modification of polypropylene

The pure-modification of polypropylene has been prepared. It has been found that the nature of the melting of the-modification strongly depends on the thermal history of the sample (melting memory effect). The melting of samples cooled to room temperature after crystallization is a complex process consisting of three partially overlapping processes (-melting recrystallization in the-modification (-recrystallization) -melting). If heating starts at the temperature of crystallization, the-modification melts separately, without-recrystallization. Under melting conditions free from the interference caused by-recrystallization, the-modification exhibits the melting characteristics of thermodynamically stable modifications. The thermodynamic equilibrium melting point of the-modification has been determined to beT _m ⁰ ()=456 K.

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Zusammenfassung Die-Modifikation von Polypropylen wurde rein dargestellt. Es wurde festgestellt, daß die Natur des Schmelzens der-Modifikation stark von der thermischen Vorgeschichte der Probe (Schmelzerinnerungseffekt) abhängt. Das Schmelzen von nach der Kristallisation auf Zimmertemperatur abgekühlter Proben ist ein komplexer, aus drei sich teilweise überlappenden Prozessen (-Schmelzen Rekristallisation in der-Modifikation, die sog.-Rekristallisation -Schmelzen) bestehender Vorgang. Wenn das Aufheizen bei der Kristallisationstemperatur beginnt, so schmilzt die-Modifikation, ohne daß -Rekristallisation eintritt. Unter Schmelzbedingungen frei von störenden Einflüssen der -Rekristallisation zeigt die-Modifikation die Schmelzcharakteristiken von thermodynamisch stabilen Modifikationen. Der thermodynamische Gleichgewichtsschmelzpunkt der-ModifikationT _m ⁰ () liegt bei 456 K.

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- . , ( ). , , , : - -, - . , - - . , -,- . - T _m ⁰ ()=456 .

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The author is indebted to Attila Ille for his help in the experimental work.     

Mechanism of carbon monoxide oxidation on nickel oxide and its solid solutions

On the basis of studying the isotope exchange of oxygen and the position of the Fermi level in the system MiO–Li_xNi_1–xO, an explanation is proposed for the compensation effect in the reaction of CO oxidation on nickel oxide and its solid solutions.

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NiO–Li_xNi_1–xO CO .

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

A rapid method for catalyst activity measurements by combination of pulse reactor, mass spectrometer and process computer

The combination of a pulse reactor attached directly (without a separation column) to a mass spectrometer/process computer system is described. To obtain a conversion/temperature diagram for the dehydration and dehydrogenation of 2-butanol less than one hour is required. Therefore, the method can be used for rapid characterization or comparison of the activities of various samples.

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, ( ) - . / 2- . .

     

Structure of amorphous Fe(III) hydroxides and their ageing products

X-ray analysis has revealed that at pH=7.5–12.0 similar amorphous Fe(III) hydroxides are formed. Their structural peruliarity is the presence of local regions with ordered arrangement of atoms typical for -FeOOH in the volume of primary particles. Ageing at pH=7.5 and 353 K leads to structure rearrangement to -Fe₂O₃.

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pH 7,5–12,0 Fe(III). , -FeOOH. pH 7,5 353 -Fe₂O₃.

     

Thermal decomposition of crystalline molecular sieve (C3H7)3N-AlPO4-5

The thermal decomposition of (C₃H₇)₃N-AlPO₄-5 in inert and oxidizing gas atmospheres has been studied by TG, DTG and DTA in the temperature range 303–1273 K. The removal of tripropylamine occluded in the channels of the aluminophosphate occurs in a number of steps and is strongly influenced by the gas atmosphere.

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Zusammenfassung Die thermische Zersetzung von (C₃H₇)₃N-AlPO₄-5 wurde in inerter und oxydierender Gasatmosphäre mittels TG, DTG und DTA im Temperaturbereich von 303–1273 K untersucht. Der Austritt des in den Kanälen des Aluminiumphosphats okkludierten Tripropylamins erfolgt über eine Anzahl von Stufen und wird stark von der Gasatmosphäre beeinflußt.

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, (C₃H₇)₃N-AlPO₄-5 303–1273 . , , .

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We are grateful to Dr. V. G. Gunjikar, Mr. J. S. Gujaral and Dr. (Mrs) A. Mitra of the Special Instrument Group of our Laboratory for their co-operation in the work.