Blocking of the silver catalyst surface in the conversion of ethylene to ethylene oxide

The conversion of ethylene oxide on silver catalysts of varying degree of oxidation has been studied. The formation of an adsorbed layer partially blocks the surface under catalytic conditions.

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, , .

     

Effect of pressure on the rate of n-heptane conversion on Pt/Al2O3 catalysts

The effect of pressure on the rates of product formation in n-heptane conversion on Pt/Al₂O₃ has been studied at 490 °C over the pressure range of 10–50 atm. It has been shown that the rate of isomerization is practically independent of pressure, and the dependence of the rates of dehydrocyclization and hydrocracking on pressure is described by simple kinetic equations. The reaction order of dehydrocyclization with respect to hydrogen tends to –2.0 at high pressures.

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- 10–50 490°C. , , . –2,0.

     

Effects of structural changes on thermal properties and pyrolysis of modified cotton fibres

The changes resulting in the supramolecular structure of cotton fibres after mercerization at different temperatures were investigated by means of X-ray diffraction, sorption measurements and determination of the degree of polymerization. For comparison, corresponding measurements were also carried out after liquid ammonia treatment. Pyrolysis of the mercerized cotton samples showed that the levoglucosan yield of NaOH-treated samples is less than that of untreated or NH₃-treated samples. Comparisons were made of the thermal stability of the modified cotton samples, as indicated by DTA and TG.A decrease in the percentage crystallinity was found to lower the onset and peak temperatures of the major decomposition reactions. An NH₃-treated sample (acetone) was less thermally stable than untreated or mercerized samples.

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Zusammenfassung Mittels Röntgendiffraktionsuntersuchungen, Sorptionsmessungen und Bestimmung deas Polymerisationsgrades wurden die Veränderungen untersucht, die durch die Merzerisierung bei verschiedenen Temperaturen in der supramolekularen Struktur von Baumwollfasern verursacht werden. Zum Vergleich wurden ähnliche Untersuchungen nach Behandlung mit flüssigem Ammoniak durchgeführt. Die Pyrolyse der merzerisierten Baumwollproben zeigt, daß die Levoglukosanausbeute bei NaOH-behandelten Proben geringer ist als bei unbehandelten oder NH₃-behandelten Proben. Auf Grundlage von DTA und TG wurden vergleichende Betrachtungen zur Wärmebeständigkeit der modifizierten Baumwollproben angestellt. Eine Abnahme de prozentualen Kristallinität senkt die Temperatur für Beginn und Peak der hauptsächlichsten Zersetzungsreaktionen. NH₃-behandelte Proben (Azeton) sind thermisch unbeständiger als unbehandelte oder merzerisierte Proben.

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, . , . , , , . . , . , , .

     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

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, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

A mathematical model of the regeneration of the catalytic solution in the liquid-phase oxidation of unsaturated hydrocarbons

The study describes the mathematical model, calculation and optimization of the technological scheme of the regeneration of the catalytic solution in the liquid-phase oxidation of hydrocarbons.

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, .

     

Le systeme eau-theophylline

The binary system water—theophylline was studied by DTA and radiocrystallography. The slow dehydration of theophylline monohydrate was observed at room temperature at relative humidities lower than 60%, without the formation of any other hydrate. The isochoric phase diagram was established. At 78 °C, a peritectic invariant occurred, owing to decomposition of the monohydrate. The existence of only one binary compound (theophylline H₂O) was confirmed by the.Tammann diagram.

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Zusammenfassung Mittels DTA und Radiokristallographie wurde das binäre System Wasser-Theophyllin untersucht. Bei einer relativen Luftfeuchtigkeit unter 60% wird bei Raumtemperatur eine langsame Dehydratation von Theophyllinemonohydrat ohne Formung anderer Hydrate beobachtet. Es wurde ein isochores Phasendiagramm entwickelt. Wegen der Zersetzung des Monohydrates tritt bei 78 °C eine peritektische Invariantheit auf. Die Existenz nur einer binären Verbindung (Theophyllin, H₂O) wird mittels eines Tammanndiagrammes bekräftigt.

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— . 60% - . . 78° , . -.

     

Studies of V?Mo?O systems with small vanadium content in acrolein oxidation

A solid solution of vanadium in MoO₃ with a solubility limit of about 3 mol.% V₂O₅ is shown to be formed. Its catalytic properties are discussed.

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MoO₃ 3 . % V₂O₅ .

     

Mutual effect of benzene and maleic acid anhydride in their adsorption on V2O5?MoO3 catalysts

TPD studies have revealed that benzene and maleic anhydride are adsorbed on different active sites of the V₂O₅–MoO₃ catalyst.

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, - .

     

Peculiarities of propylene metathesis over catalysts prepared by anchoring of Mo(V) oxalate to γ-Al2O3

Propylene metathesis over catalysts prepared by coordination of Mo(V) oxalate to -Al₂O₃ has been studied.

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, (V) -Al₂O₃.

     

Hydrogenolysis reactions during propane aromatization over Pt/ZSM-5

Propane aromatization has been investigated over Pt/ZSM-5 in the temperature range of 400–500°C. Hydrogenolysis of propane to methane occurs mainly on the platinum sites and becomes an important route in propane transformation when reactions leading to aromatics tend to reach thermodynamic equilibrium.

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Pt/ZSM-5 400–500°C. , .

     

Correlations between photosorption and photocatalytic activities of alkali metal halides

An analysis of the correlation suggests that the common stages in photosorption, photooxidation and photodecomposition of some simple molecules on alkali metal halides are connected with catalyst photoexcitation.

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, , , .

     

Effect of vibrational excitation on the reactivity of methyl fluoride with bromine atoms

The influence of non-equilibrium vibrational excitation of CH₃F molecules on the rate of their reaction with bromine atoms has been investigated. A three-fold increace in the reaction rate has been registered at CH₃F and Br₂ pressures of 0.07 Torr and at 100°C. The increase is shown not to be associated with equilibrium thermal heating.

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CH₃F . CH₃F Br₂ 0,07 100°C. , .

     

Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

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.

     

Selective electroreduction of dinitrogen on a rotating copper amalgam electrode

On an amalgamated rotating copper disk electrode in an alkaline methanol solution in the presence of mixed Ti(OH)₃–Mo(III) hydroxide, dinitrogen is shown to be selectively electroreduced to hydrazine in the potential range –1.6 to –1.9 V (with respect to the saturated calomel electrode).

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, Ti(OH)₃–Mo(III) –1,6+ –1,9 ( ) .

     

Methanol conversion to lower hydrocarbons over proton exchanged NaY zeolite catalysts

Various NaY zeolites protonated with an aqueous NH₄Cl solution were effective catalysts for methanol conversion to lower hydrocarbons. Even NaY zeolite protonated up to the degree of 4% showed a high catalytic activity at relatively low reaction temperatures.

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NaY, NH₄Cl, . 4%- NaY .

     

Combinations of alkyl radicals with alkyl and substituted allyl radicals

In contrast with expectations based upon simple collision theory, reactions of alkyl radicals with substituted allyl radicals yield cross-combination ratios of =2. Reactions of CH ₃ ^\ with some C₅ radicals give >2, in accordance with theory.

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, =2. CH₃ ^\ C₅ >2, .

     

Kinetics of SO2 oxidation on K2S2O7?V2O5 catalyst in non-steady conditions

Studies of SO₂ oxidation on a molten component of vanadium catalysts in non-steadystate conditions indicates that the kinetics agree fairly well with an oxidation-reduction mechanism. In the low temperature range (<790 K) tetravalent vanadium can be partially crystallized.

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. , - . ( 790 ) .

     

Oxidation of propylene over tellurium oxides and Cd?Te?Mo?O and Mn?Te?Mo?O systems

The catalytic behavior of the Cd–Te–Mo–O and Mn–Te–Mo–O systems in the selective oxidation of propylene to acrolein has been related to the MTeMoO₆ phases in the region rich in Te and to the MMoO₄ phases with Te as dopant in the region poor in Te. In view of the possible relevance of Te⁴⁺ and Te⁶⁺ ions to catalysis, the behavior of the different forms of tellurium oxide is also discussed.

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Cd–Te–Mo–O Mn–Te–Mo–O MTeMoO₆ Te MMoO₄ Te Te. Te⁺⁴ Te⁺⁶ .

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This work was supported by the Italian C.N.R. (Roma)     

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber have revealed that for the catalysts obtained by the reduction of preactivated samples, no complete reduction of platinum takes place.

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, , , .