Influence of the chemical composition of the catalyst on the dehydrochlorination of 1,2-dichloroethane

The experiments have been performed by a microreactor pulse method at 623 K. The activity and selectivity of the catalysts, alumina/metal chloride and silica gel/metal chloride or oxide, have been found to depend on the donor-acceptor properties of their surfaces.

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1,2-. 623 . / / , .

     

DTA analysis of the system CuCl2-KCl

Mixtures of CuCl₂ and KCl in molar ratios of Cu to K of from 0.5 to 1.0 were heated at 473 K in an air atmosphere, and then subjected to DTA analysis in the temperature range 293–773 K. A number of endothermic processes were observed, the extents of these depending on the molar ratio of Cu to K in the mixture.

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Zusammenfassung DTA-Untersuchungen haben ergeben, daß in Mischungen von CuCl₂ und KCl mit molaren Cu/K-Verhältnissen von 0,5–1,0 nach Erhitzen in Luft bei 473 K im Temperaturbereich von 293 bis 773 K eine Reihe von endothermen Prozessen verlaufen. Das Ausmaß dieser Prozesse hängt vom Cu/K-Verhältnis der Gemische ab.

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( 0,5 1,0) 293–773 , , .

     

Proton transfer to palladium during phenylacetylene hydrogenation in ethanol

Exchange processes over palladium during the liquid-phase hydrogenation of phenylacetylene have been studied by successive substitution of starting substances by deuterated products. It has been revealed that on the catalyst surface a proton transfer to unsaturated substance, gas phase and solvent takes place. Rates of the processes have been calculated.

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. , , . .

     

Specific activity of supported nickel in the hydrogenolysis of ethane

It has been found that over a wide range of dispersities (15–70 Å) the specific activity of supported nickel is independent of the metal particle size and the method of catalyst preparation. However, samples with nickel particle size 10 Å are characterized by higher specific activity, which may be related to the structural features of small nickel clusters.

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, ( 15 70 Å) . , 10 Å, , .

     

Identification of exchange-coupled V4+ and Cu2+ ions in Cu?V?Mo oxide systems

ESR studies of X(CuO)·V₂O₅·8.3 MoO₃ (X=1–2) calcined in flowing nitrogen at 250–350 °C have revealed the exchange interaction of Cu²⁺ and V⁴⁺ ions that form a paramagnetic system.

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X(CuO) V₂O₅·8,3 MoO₃, X=1–2, , 250–350°C, Cu²⁺ V⁴⁺, .

     

Samarium hydroxide as catalyst in hydrogen evolution

Hydrogen evolution on a platinum cathode taking place in Na₂SO₄ as electrolyte, is catalyzed by the formation of samarium hydroxide deposited on platinum. It is shown by voltammetric experiments that the quantity of adsorbed hydrogen is greater with samarium than without it and the H₂O reduction reaction is an irreversible process due, presumably, to a reaction between the adsorbed hydrogen and samarium hydroxide.

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Na₂SO₄, , . , , H₂O .

     

Acid-base properties of Al2O3/MgO oxides, V. Decomposition of diacetonealcohol

The activity of MgO–Al₂O₃ mixed oxides in the decomposition of diacetonealcohol was studied using a micro slurry reactor, which allowed pretreatment of the catalyst in situ. The rate constant was used to characterize the strength of the basic surface sites. A reaction order of one and a decrease of the rate constant from MgO to Al₂O₃ was observed.

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MgO–Al₂O₃ . , . . MgO Al₂O₃.

     

Kinetic investigation on alcoholysis of triethylaluminium by differential thermal analysis

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from –150 to –170 kJ mole^–1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofS _E2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

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Zusammenfassung Die Reaktion zwischen einer Lösung von Alumimumtriethyl und einer Reihe von aliphatischen oder aromatischen Alkoholen kann mittels DTA quantitativ verfolgt werden. Die negative Reaktionsenthalpie der Alkoholyse mit primären Alkoholen beträgt 150 bis 170 kJ mol^–1, sofern ein Lösungsmittelgemisch aus Tetrahydrofuran/Toluen eingesetzt wird. Die Reaktionsgeschwindigkeit in unpolaren Kohlenwasserstoffen ist grösser als in Gegenwart von Lewis-Basen. Wahrscheinlich ist der Reaktionsmechanismus vom TypS _E2, wobei die Reaktivität in der Folge primäre, sekundäre, tertiäre Alkohole fällt. Der zweite Schritt der Alkoholyse, ausgehend vom Diethylaluminiumalkoxid, ist wegen der starken Selbstassoziation weniger reaktiv. Bei Umsatz von 2 Mol Alkohol treten entsprechend der Folgereaktion zwei DTA-Peaks auf.

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. –150 –170 ^–1 - . , . , S _E2 , , . , , . -, .

     

IR study of isopropanol adsorption on haematite

The IR study shows that isopropanol interacts with haematite at IR beam temperature both as a physisorbed form, hydrogen bonded to basic sites of the surface, and as isopropoxide groups. At 423 K a decomposition of isopropoxide groups produces enolate anions of acetone.

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, , - , . 150 °C .

     

Effect of the nature of carrier on dinitrogen fixation by supported titanium complexes

Cyclopentadienyltitanium (IV) complexes supported on Al₂O₃, SiO₂ and MgO reduced with BuLi were tested in dinitrogen fixation at room temperature under normal pressure. Only the system supported on Al₂O₃ is active in this reaction.

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- (IV), Al₂O₃, SiO₂ MgO, BuLi, . Al₂O₃.

     

Electron spectroscopic studies of copper in catalysts for methanol synthesis

The state of Cu²⁺ ions in Cu–Zn–Al catalysts for methanol synthesis has been studied by electron spectroscopy (5000–50000 cm^–1). It has been established that low-temperature ZnO stabilizes copper in a distorted octahedral coordination as cluster structures resembling (but not similar to) CuO. The presence of Al promotes the formation of these clusters and inhibits the formation of CuO.

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(5000–50000 ^–1) Cu²⁺ Cu–Zn–Al . , ZnO , ( ) CuO. , CuO.

     

Thermogravimetric investigation of the kinetics and thermodynamics of dehydration of amorphous silica

Several commercial and laboratory-synthesized specimens of silica gel have been studied, using thermogravimetry. Two forms of adsorbed water have been found: the first form, which evaporates in the temperature range 100–200°, is polymolecular water layer in open pores and loosely-bonded molecules on the surface and in the bulk of the globules; the second form, which evaporates in the temperature range 200–700°, comprises water molecules hydrogen-bonded to silanol groups, and evidently coordinated to silicon atoms. The dehydration heat of the first form, determined from the DTA curves, depends on the ratio of the two forms, and varies from 3.7±0.6 kcal/mole H₂O for coarse-grain silica gel produced at pH=7 to 12±1 kcal/mole H₂O for fine-grain silica gel of commercial chromatography grade.The activation energy of evaporation of water determined from the TG curves is about 10 kcal/mole in the temperature range 150–200°.

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Zusammenfassung Verschiedene handelsüblich und im Laboratorium synthetisierte Proben von Kieselgel wurden durch Thermogravimetrie untersucht. Zwei Formen von adsorbiertem Wasser wurden gefunden: die erste im Temperaturbereich von 100 bis 200° entweichende, ist eine polymolekulare Wasserschicht in offenen Poren und lose gebundenen Molekülen an der Oberfläche und in der Masse der kugelförmigen Teilchen; die andere Form, welche im Temperaturbereich von 200 bis 700° verflüchtigt wird, besteht aus Wassermolekülen, die durch Stickstoffbindungen an Silanolgruppen und offensichtlich koordinativ an Siliziumatome gebunden sind. Die aus den DTA-Kurven ermittelte Dehydratisierungswärme der ersten Gruppe hängt vom Verhältnis der beiden Formen ab und variiert von 3.7±0.6 kcal/Mol H₂O für grobkörniges Kieselgel, das bei pH=7 hergestellt wird, bis zu 12±1 kcal/Mol H₂O für feinkörniges Kieselgel der handelsüblichen »chromatographischen« Qualität.Die aus den TG-Kurven ermittelte Aktivierungsenergie der Verflüchtigung des Wassers beträgt im Temperaturbereich von 150 bis 200° etwa 10 kcal/Mol.

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Résumé Plusieurs échantillons de gels de silice commerciaux et synthétisés au laboratoire ont été étudiés par TG. Deux formes d'eau adsorbée ont été mises en évidence: la premiè re s'évapore entre 100 et 200° et consiste en une couche d'eau polymoléculaire dans les pores ouverts et à l'intérieur des globules; la seconde forme s'évapore entre 200 et 700° consiste en molécules d'eau liées par ponts d'hydrogène à des groupes silanol et, évidemment, par des liaisons de coordination aux atomes de silice. La chaleur de déshydratation de la première forme, déterminée à partir des courbes ATD, dépend de la proportion des deux formes et varie depuis 3.7±0.6 kcal/mole pour le gel de silice à gros grains produit à pH-7 jusqu'à 12±1 kcal/mole H₂O pour le gel de silice à grains fins de qualité commerciale «pour Chromatographie».L'énergie d'activation de l'évaporation de l'eau, calculée à partir des courbes TG, est d'environ 10 kcal/mole dans l'intervalle de température compris entre 150 et 200°.

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, . , 100–200° . , 200–700°, , , , - . , , 3.7 + 0.6 / H₂O , pH=7 12±1 / ₂ , . , , 10 / 150–200°.

     

Role of oxygen diffusion in catalysts for selective oxidation

The effective coefficients of oxygen diffusion for the series of oxide catalysts for the selective oxidation of organic compound (V–Mo–O, Bi–Mo–O, Ga–Sb–O, Mg–O) have been measured. Diffusion coefficients in different catalysts defined at optimal operation temperatures for these catalysts were found to be close. The possibility of using oxide systems as catalysts for selective oxidation is determined by their ability to achieve sufficiently large oxygen diffusion coefficients at the reaction temperature.

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(V–Mo–O., Bi–Mo–O., Ga–Sb–O, Mg–O). , , . , .

     

Effect of the dielectric constant on the reactivity of alkyl and polychloroalkyl radicals in addition and substitution reactions

Generalized data for the effect of reaction medium on the elementary steps of radical homo-and cotelomerization of olefins with carbon tetrachloride are generalized.

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.

     

Tunnel recombination of surface and bulk radiation defects in finely dispersed CaO at 4.2 and 77 K

Recombination of radiation defects in CaO is shown to occur through electron tunneling from surface F_s ⁺ to V^–-center stabilized in the bulk.

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, CaO F_s ⁺- V^–-, .

     

A poor man's calorimeter (PMC) for small animals

A simple calorimeter is described which consists of a cooling/warming box as used for picnic equipment. The volume of this calorimeter is 8 dm³, the sensitivity is 19.2 mV/W, and the time constant is 580 s. As such an instrument is designed for animals weighing some 100 g, a signal of 10 to 50 mV can be expected, which can easily be monitored with the usual laboratory recorders. The long-time baseline drift is sufficiently small when the calorimeter is placed in a wooden box with Styropore insulation. Experiments were run for 1 to 15 h with various animals, among them chinese hamsters, hedgehogs, turtles and rats. The price of the box is appr. $ 100.

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Zusammenfassung Es wird ein einfaches Kalorimeter beschrieben, das aus einer Kühl/Wärme-Box für Campingausrüstungen besteht. Das Volumen dieses Kalorimeters beträgt 81, die Empfindlichkeit 19,2 mV/Watt und die Zeitkonstante 580 Sekunden. Da solch ein Instrument für Tiere mit einigen 100 g Lebendgewicht bestimmt ist, kann ein Signal von 10–50 mV erwartet und von den in Laboratorien allgemein verwendeten Schreibern aufgezeichnet werden. Die Langzeitdrift der Grundlinie ist genügend klein, wenn das Kalorimeter in einer Holzkiste mit Styropor-Isolierung untergebracht ist. Experimente wurden über Zeiträume von 1–15 Stunden mit verschiedenen Tieren ausgeführt, darunter Goldhamster, Igel, und Ratten. Der Preis der Box beträgt etwa 100 $.

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, -. 8 , 19,2 / — 580 . , 100 , 10–50 . , . 1 15 , , , . 100 .

     

Effect of organic nitrate additives on the combustion rate of hexane flame

Studies of the effect of cyclohexyl- and isopropyl nitrate additives on the combustion rate of fuel-rich and-poor hexane-air mixtures indicate that both substances can be either a promotor or an inhibitor of combustion depending on the concentration. A mechanism is suggested to account for this phenomenon.

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- . , . , .

     

Oscillatory kinetics of the permanganate oxidation of oxalic acid?

The oxidation of oxalic acid by permanganate satisfies the mechanistic criteria of the oscillatory kinetics. However, the oscillatory changes in the absorbancy eventually found are due to formation of colloidal and coagulated MnO₂ and not to the chemical events.

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. , , MnO₂, .

     

INDO study of the interaction of methanol with molybdates

The energy of interaction between a methanol molecule and an MoO ₄ ^2– group of the Fe₂(MoO₄)₃ and Ga₂(MoO₄)₃ lattice, and the force constant of the C–H bond calculated by the INDO method show that the deformation of MoO ₄ ^2– tetrahedra leading to the displacement of Mo⁶⁺ to the edge attacked, increase the stabilizing contribution to the energy and decrease the C–H force constant. This effect is maximal at 1_Mo–O2 Å.

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INDO MoO ₄ ^2– , - Fe(MoO₄)₃ Ga₂(MoO₄)₃ C–H, , MoO ₄ ^2– , Mo⁶⁺ , C–H. 1_Mo–O2 Å.