Characterization of Ni supported on alumina by hydrogen-oxygen titration

Hydrogen-oxygen titration was performed on Ni/-Al₂O₃ supported catalysts. Hydrogen chemisorption is used to determine the surface area. An excess in oxygen consumption was observed and related to NiO formed in the bulk. A model is proposed which takes into account the formation of an oxide in the subsurface layers of the metal.

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H₂–O₂ Ni/-Al₂O₃. H₂ . , NiO . , .

     

Unicyclic Graphs with Minimal Energy

If G is a graph and ₁,₂,..., _n are its eigenvalues, then the energy of G is defined as E(G)=|₁|+|₂|++| _n |. Let S _n ³ be the graph obtained from the star graph with n vertices by adding an edge. In this paper we prove that S _n ³ is the unique minimal energy graph among all unicyclic graphs with n vertices (n6).     

Differential thermal study of FeO and Fe3O4

Two batches of wüstite were produced from a stoichiometric mixture of Fe and Fe₂O₃ by sealing in steel tubes in vacuum and helium, respectively, and igniting the first tube at 1300° for 21 hours and the second one at 1200° for 34 hours. There were two exothermic peaks on the DTA curves of both samples at 345 and 545 to 700° due to surface oxidation of FeO to Fe₃O₄ followed by bulk oxidation of FeO to Fe₃O₄ and of Fe₃O₄ to-Fe₂O₃. The last two reactions gave rise to a dual (or twin) peak for coarse material but one peak in the case of fine material, indicating that the two reactions occurred concurrently for fine material. Similar investigations on both fine and coarse magnetites showed only two exothermic peaks which corresponded to surface and bulk oxidation, respectively. This result confirms the previous observations that coarse magnetite converts to-Fe₂O₃ by surface oxidation followed by bulk oxidation.

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Zusammenfassung Es wurden zwei Serien von Wüstit aus einem stöchiometrischen Gemisch von Fe und Fe₂O₃ in versiegelten Stahlröhren unter Vakuum bzw. Helium durch 21 stündiges Erhitzen bei 1300° bzw. 34 Stunden bei 1200° dargestellt. Die DTA-Kurve wies bei beiden Proben zwei exothermische Spitzen auf, bei 345° bzw. bei 545° bis 700° auf, die der oberflächlichen Oxydation von FeO zu Fe₃O₄ bzw. der vollständigen Oxydation von FeO zu Fe₃O₄ bzw. Fe₃O₄ zu-Fe₂O₃ entsprechen. Die beiden letzten Reaktionen verursachten eine Zwillingsspitze im Fall von grobem Material, hingegen eine einzige Spitze bei feinem Material. Diese Reaktionen verlaufen also im letzten Fall gleichzeitig. Ähnliche Versuche mit grobem und feinem Magnetit zeigten nur zwei, der oberflächlichen und massiven Oxydation entsprechenden exothermischen Spitzen. Dieses Ergebnis unterstützt die früheren Beobachtungen, daß grober Magnetit durch oberflächliche und darauffolgende vollständige Oxydation in-Fe₂O₃ überght.

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Résumé On a préparé deux séries de wüstite à partir d'un mélange stoechiometrique de Fe et Fe₂O₃ dans des tubes scellés d'acier sous vide rsp. en hélium. Un tube a été chauffé pendant 21 heures chez 1300° l'autre chez 1200° pendant 34 heures. On observe dans les courbes d'ATD des deux séries d'échantillons deux pics exothermiques chez 345° et de 545° jusqu' à 700° dûs à l'oxydation superficielle de FeO en Fe₃O₄ suivie par l'oxydation de la masse de l'échantillon de FeO en Fe₃O₄ rsp. de Fe₃O4 en-Fe₂O₃. Les deux réactions dernières donnent pour un produit à gros grains, un pic double, et pour un produit à grains fins un pic simple indiquant que dans le dernier cas deux réactions concurrentes eurent lieu. Pareilles investigations avec magnétite grossière et fine n'ont montré que deux pics exothermiques correspondant à l'oxydation superficielle et dans la masse. Ces resultats confirment les observations antérieures de la transformation de magnétite grossière en-Fe₂O₃ par oxydation superficielle suivie d'oxydation dans la masse.

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Fe Fe₂O₃ . , 1300° 21 ., — 1200° 34 . 345° 545–700°, FeO Fe₃O₄ Fe₃O₄ -Fe₂O₃. , . , . , , . , -Fe₂O₃ , .

     

On theC v toC p conversion for solid linear macromolecules

TheC _v toC _p conversion for solid linear macromolecules via the Nernst-Lindemann equationC _p -C _v =A ₀,C _p ² T/T_m is discussed on hand of data for 10 crystals and seven glasses. An average value ofA ₀=(5.11±2.41) · 10^–3 mol K J^–1 was calculated if the mole is assumed to refer to heavy atoms only. ThisA ₀ is numerically equal to the original Nernst—Lindemann constant.

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Zusammenfassung An Hand von sich auf 10 Kristalle und 7 Gläser beziehenden Daten wird die Umrechnung vonC _v -inC _p -Werte für feste lineare Makromoleküle mittels der Nernst-Lindemann-GleichungC _p -C _v =A ₀ C _p ² T/T _m diskutiert. Ein Durchschnittswert vonA ₀=(5.11±2.41) · 10^–3 mol K J^–1 wurde unter der Annahme berechnet, daß sich das Mol nur auf schwere Atome bezieht. DieserA ₀-Wert ist numerisch gleich der ursprünglichen Nerns-Lindemann-Konstanten.

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10 , - C _v C _p , —C _p –C _v = _{0 p} ² / . , , ₀ (5.11±2.41) · 10^–3 · ^–1. ₀ — .

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Support by the National Science Foundation, Polymers Program (Grant No. DMR 83-17097) is gratefully acknowledged.     

Analysis of various metal oxide/organohalide-based flame retardants

The mechanism of evaporation of various metal oxides and the formation and evaporation of metal halides in the presence of chlorine-containing compounds have been studied by complex thermal analysis including atomic absorption measurement of the evolved species. The retardation process in the case of the MoO₃+ and the ZnO + system and that for Al₂O₃ ·3H₂O has been discussed.

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Zusammenfassung Der Verdampfungsmechanismus verschiedener Metalloxide sowie Bildung und Verdampfen von Metallhalogeniden im Falle von chlorhaltigen Additiven wurde untersucht. Es wurden Messungen mittels komplexer Thermoanalyse einschließlich von Atomabsorptionsuntersuchungen der entweichenden Stoffe durchgeführt. Die Hemmungsprozesse von MoO₃ + Halogen, ZnO +Halogen und Al₂O₃ · 3H₂O werden besprochen.

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, . , - . MoO₃ + , ZnO + l₂O₃·₂.

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The authors are indebted to Prof. B. Mohai for valuable discussions and suggestions.     

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.

     

Combination and disproportionation of methyl and 2-propyl radicals with 1,1,2-trimethylallyl radicals

The combinations and disproportionations of the CH₃ and 2-propyl (iP) radicals with the 1,1,2-trimethylallyl (TMA) radical have been studied in the gas phase in the temperature interval of 389–451 K and 490–540 K, respectively. For the ratios of the terminal (t) and non-terminal (n) combinations of the CH₃ and iP radicals with the TMA radical, values of 1.9±0.1 and 2.84±±0.10 were obtained, respectively. The ratios of the tt and tn and nn to tn combinations of the TMA radical were 1.59 and 0.46, respectively. The disproportionation-combination rations were (CH₃ , TMA)=0.022±±0.012 and (iP, TMA)=0.026±0.011.

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CH ₃ 2- (iP) 1,1,2- (TMA) : 389–451 K 490–540 K. (t) (n) TMA 1,9±0,1 2,84±0,10, . tt tn nn tn TMA 1,59 0,46, . (CH ₃ , TMA)=0,022±0,012 (iP, TMA)=0,026±0,011.

     

A physico-chemical study of iron-chromium-molybdenum catalysts

In the study of the Fe_1–xCr_xMo_1·5O₆ system by X-ray, IR and Mössbauer methods the formation of solid state substitution solutions has been detected, which possess similar catalytic properties in methanol oxidation.

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, , Fe_1–xMo_1·5O₆ , .

     

Determination of the surface acidity of solid catalysts

A novel method has been developed for determining the surface acidity of white, as well as deeply colored porous solids. The method, which was tested on Al₂O₃, SiO₂–MgO–Al₂O₃ and Fe₂O₃ catalysts, is based on the adsorption of pyridine or benzylamine on acidic sites and subsequent displacement of the adsorbed bases by n-butylamine. A linear correlation was found between the concentration of acidic sites on Al₂O₃ and Fe₂O₃ catalysts and their activity in the dehydration oftert-butyl alcohol.

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, . , Al₂O₃, SiO₂–MgO–Al₂O₃ Fe₂O₃, -. Al₂O₃ Fe₂O₃ - .

     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

Effect of substituents at silicon on the oxidative addition of trisubstituted silanes to [RhCl(cod)PPh3]

Summary Trisubstituted silanes, HSiR_3–n X _n (R = Me, Et, Pr or Bu; X = Cl, OEt or Ph; and n = 0–3) readily undergo oxidative addition to complex [RhCl(cod)PPh₃] (where cod = cycloocta-1,5-diene).The quantitative correlation between rate constants, k ₁, of the reaction, followed spectrophotometrically at 20 °C in benzene solutions, and the structure of tri-substituted silanes represented by stereoelectronic parameters , and E of the substituents, was established: logk ₁ = a + b + c + dE. The reaction rate is accelerated by electron-withdrawing substituents at silicon and retarded by the bulk and pd donation of nonalkyl substituents.Author to whom all correspondence should be directed.     

X-ray spectral investigation by synchrotron radiation of supported Re/SiO2 and (Re+Pt)/SiO2 catalysts prepared via triethoxyrhenium

Using synchrotron radiation L_III absorption spectra of rhenium in Re/SiO₂ and (Re+Pt)/SiO₂ catalysts prepared via triethoxyrhenium have been studied. The conclusion has been drawn that reduced catalysts contain lowvalent rhenium ions and their composition is more uniform than that of the previously examined catalysts Re/Al₂O₃ and (Re+Pt)/Al₂O₃ prepared by a conventional impregnation technique.

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L_III- Re/SiO₂ (Re+Pt)/SiO₂, . , , Re/Al₂O₃ (Re+Pt)/Al₂O₃, .

     

Trends in the high-temperature heat capacities of ternary chalcopyrite semiconductors

The anharmonic contribution to the heat capacity of any chalcopyrite semiconductor A^IB^IIIC ₂ ^VI or A^IIB^IVC ₂ ^V is evaluated. It is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds, and there is no essential difference in the degree of lattice anharmonicity of the two groups of compounds. Except for CdGeAs₂, the trend in the Grüneisen constants is the same.

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Zusammenfassung Der anharmonische Beitrag zur Wärmekapazität verschiedener Halbleiterverbindungen A^IB^IIIC ₂ ^VI und A^IIB^IVC ₂ ^V vom Chalkopyrit-Typ wird bestimmt. Es wird gezeigt, dass die Gitteranharmonizität mit steigender relativer Atommasse der Bestandteile der Verbindungen abnimmt und dass keine wesentlichen Unterschiede in der Gitteranharmonizität beider Gruppen von Verbindungen bestehen. Der Trend der Grüneisen-Konstanten ist der gleiche, ausgenommen bei CdGeAs₂.

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^IIII ₂ ^{VI IIIV} ₂ ^V . , , , . , CdGeAs₂.

     

Electronic state of the active site of A V?P?O/SiO2 catalyst in oxidation of chlorine-containing hydrocarbons

V⁴⁺ ions in slightly associated states are supposed to play the role of V–P–O/SiO₂ active sites. V⁴⁺ ions are reduced to V³⁺ during deactivation of the V–P–O/SiO₂ catalyst.

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V–P–O/SiO₂ V⁴⁺ . V–P–O/SiO₂ V⁴⁺ V³⁺.

     

Die Bestimmung der Bildungsenthalpien von in thermischen Zersetzungsreaktionen auftretenden Verbindungen durch Einwurfkalorimetrie — Bildungsenthalpie AlCl3 · 6 H2O,amorph-Al2O3, γ-Al2O3, Al2O3 · 2 H2O · 2 HCl

Zusammenfassung Die Bestimmung der Bildungsenthalpien von Verbindungen, die als stabile Produkte an thermischen Zersetzungsreaktionen beteiligt sind, erfolgte durch Messung der Reaktionsenthalpien. Die kalorimetrischen Experimente wurden in einem Einwurfkalorimeter ausgeführt, welches auf der Grundlage des WÄrmeflu\prinzips arbeitet. An Hand der Bestimmung der Standardbildungsenthalpie des Calciumcarbonates wurde die Me\methodik überprüft. Die Reproduzierbarkeit der kalorimetrischen Messungen betrÄgt im untersuchten Temperaturbereich von 298 K bis 1600 K gleich ±2%. Die Bildungsenthalpien unter Standardbedingungen _BH ₂₉₈ in kJ/mol für AlCl₃ · 6H₂O, amorph-Al₂O₃, –Al₂O₃,Al₂O₃ · 2 H₂O · · 2 HCl betragen –2667 ± 8, –1625 ± 39, –1654 ± 39, –2626 ± 4.

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The heats of formation of stable compounds produced during thermal decomposition reactions were determined by measurements of enthalpies of reactions. The investigations were performed by using a heat-flow dropping calorimeter. The validity of the method was confirmed by measurement of the heat of formation of calcium carbonate. All calorimetric results had an accuracy of ± 2 %. The heats of formation under standard conditions, _bH ₂₉₈ kJ mol^–1, for AlCl₃ · 6 H₂O, amorphous Al₂O₃, -Al₂O₃ and Al₂O₃ · 2 H₂O · 2 Hcl are –2667±8, –1625±39, –1654±39, and –2626 ± 4, respectively.

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Résumé On a déterminé à partir des mesures des enthalpies de réaction la chaleur de formation des composés stables qui participent aux processus de dégradation thermique. Les expériences calorimétriques ont été effectuées dans un calorimètre à chute à flux de chaleur. On a vérifié la méthode de mesure en déterminant l'enthalpie de formation standard du carbonate de calcium. La reproductibilité des mesures calorimétriques est de 2% entre 298 K et 1600 K. Les enthalpies de formation _BH ₂₉₈ ^– en kJ/mole, dans les conditions standards de AlCl₃ · · 6 H₂O, Al₂O₃ amorphe, -Al₂O₃, Al₂O₃ · 2 H₂O · 2 HCl s'élèvent respectivement à –2667 ± 8, –1625± 39, –1654±39, –2626±4.

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, . . . ±2%. _B H ₂₉₈ (.^–1) AlCl₃ 6H₂O, ,-Al₂O₃ Al₂O₃. 2H₂O. 2HCl , , –2667 ± 8, –1625 ± 39, –1654 ± 39 –2626 ± 4.

     

X-ray and thermal studies on uranyl acetates of zinc,magnesium and nickel

Thermal decomposition of metal uranyl acetates is one of the best ways of preparation of uranates in crystalline form at low temperatures. Acetates of the type M(UO₂)₂(OAc)₆·7H₂O (M=Zn(II), Mg(II) and Ni(II) were prepared and characterised. Their X-ray powder diffraction analysis showed that they all belong to the orthorhombic crystal class.The thermal decomposition of acetates in air goes through the reduction of uranium(VI) to uranium(IV) during acetate decomposition followed by reoxidation by oxygen. Zinc uranylacetate gave on thermal decomposition ZnU₃O₁₀, the nickel salt gave NiU₃O₁₀ and the magnesium salt gave a mixture of MgUO₄ and MgU₃O₁₀. The thermal decomposition of acetates in helium led to reduction of uranium(VI) to uranium(IV) with the formation of UO₂. No lower valent uranates could be identified.

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Zusammenfassung Thermische Zersetzung von Metalluranylazetaten ist eine der geeignetsten Methoden zur Darstellung kristalliner Uranate bei niedrigen Temperaturen. Azetate des Types M(UO₂)₂(OAc)₆·7H₂O mitM=Zn(II), Mg(II) und Ni(II) wurden hergestellt und beschrieben. Eine Pulverdiffraktionsanalyse zeigte, daß alle der orthorhombischen Kristallklasse angehören. Der thermische Zerfall der Azetate in Luft vollzieht sich während des Azetatzerfalls über die Reduktion von Uran(VI) zu Uran(IV) bis zu einer anschließenden Reoxydation durch Sauerstoff. Bei der thermischen Zersetzung liefert Zinkuranylazetat ZnU₃O₁₀, das Nickelsalz liefert NiU₃O₁₀ und das Magnesiumsalz ein Gemisch aus MgUO₄ und MgU₃O₁₀. Der thermische Zerfall der Azetate in Helium führt zur Reduktion von Uran(VI) zu Uran(IV) unter Bildung von UO₃. Uranate mit niedrigerer Wertigkeit konnten nicht identifiziert werden.

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. M(UO₂)₂(OAc)₆ · 7H₂O, M = , . , . , . ZnU₃O₁₀, — NiU₃O₁₀, MgUO₄ MgU₃O₁₀. . .

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The authors thank Dr. D. D. Sood, Head, Fuel Chemistry Division, for his encouragement during the course of this work.     

Characterization of chiral building blocks for vitamin D metabolites by DSC

The enantiometric purity of a vitamin D₃ metabolite was determined more exactly by means of DSC than by¹ H-NMR. The melting curve was analysed by the partial area method based on the Schröder-van Laar equation. In order to find a suitable method for separation(R)-2,3-dihydroxy-3-methylbutylp-toluenesulfonate from the racemate, the phase diagram of the enantiomers was evaluated from DSC results. The occurrence of a racemic compound was confirmed by an X-ray diffraction investigation of the racemate and the enantiomers. The conclusions are discussed in comparison with the results of previous investigations.

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Zusammenfassung Die Enantiomeren-Reinheit des Vitamin D3-Metaboliten (R)-2,3-Dihydroxy-3-methylbutyl-p-toluensulfonat (R-I) lässt sich durch DSC genauer als mittels¹ H-NMR ermitteln. Dazu wird die Schmelzkurve nach der Partialflächenmethode ausgewertet, die auf der Schröder-van Laar'schen Gleichung beruht.Zum Auffinden einer geeigneten Methode für die Abtrennung des R-Enantiomeren aus dem Racemat wurde das Phasendiagramm der Enantiomeren aus DSC-Messungen konstruiert. Das Vorliegen einer racemischen Verbindung wurde durch Röntgenbeugungsuntersuchungen von Racemat und reinen Enantiomeren bestätigt. Die Ergebnisse werden mit denen früherer Untersuchungen verglichen.

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D₃ , . , -. (R) -2,3--- -- , . . .

     

Reduction of benzylideneaniline over supported Pd catalysts

In this work we have carried out a study on the liquid phase hydrogenation of benzylideneaniline, using dihydrogen over various supported Pd catalysts. Benzyl-ideneaniline reduction can be classified as insensitive to the catalyst structure. On the other hand, no compensating effect has been observed in performing the reaction over different supported Pd catalysts.

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Pd , . . Pd , .

     

Kinetic isotope effect in trans-alkylation with ethylbenezene

Kinetic isotope effect (KIE) measurements in the trans-alkylation of toluene and benzene with ethylbenzene in hexane in the presence of AlBr₃ at 313 K indicate that deuterium in the toluene methyl group causes a small inverse KIE characteristic for a -complex transiton state. The small direct KIE found for the reaction with C₂D₅C₆H₅ does not agree with a mechanism involving alkyl-and -phenylalkyl cations.

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() - AlBr₃ 313 . , , - C₂D₅C₆H₅ , - -.

     

Thermal Behaviour of some dioxane adducts ofM(C6F5)2 (M=Pd,Pt)

The thermal treatment of the pentafluorophenyl derivativesM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) or Pt (n=2); Dx=dioxane] leads to the formation of the new dioxane adducts M(C₆F₅)₂Dx (M=Pd, Pt) and Pt(C₆F₅)₂Dx_1.5. Calculations of the order of reaction and the activation energy of some of the decomposition reactions are described. The values were determined by the Coats-Redfern and Freeman-Carroll methods. Structural data on the isolated intermediates were obtained by infrared spectroscopy and magnetic susceptibility measurements.

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Zusammenfassung Die thermische Behandlung der PentafluorphenylderivateM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) oder Pt (n=2); Dx=Dioxan] führt zu der Bildung der neuen DioxanaddukteM(C₆F₅)₂Dx (M=Pd, Pt) und Pt(C₆F₅)₂Dx_1.5. Die Berechnungen der Reaktionsordnung und der Aktivierungsenergie einiger Zersetzungsreaktionen werden beschrieben. Die Werte wurden durch die Methoden von Coats-Redfern und Freeman-Carroll bestimmt. Die Strukturangaben der isolierten Zwischenprodukte wurden durch Infrarotspektroskopie und Messung der magnetischen Suszeptibilität erhalten.

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(₆F₅)₂, M=Pd n=2, 3 Pt _n=2, - , -M(C₆F₅)₂ (=Pd, Pt) (₆F₅)_21,5. , — —. .