X-ray studies of ZSM-5 zeolites with framework cations of various sizes

From a comparison of the X-ray difractograms for various ZSM-5 zeolites the isomorphous substitution of framework Si⁴⁺ by large cations (Al³⁺, Ga³⁺, Fe³⁺) is suggested to be ordered as contrasted to the statistical substitution by small ones (B³⁺).

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ZSM-5 , Si⁴⁺ (Al³⁺, Ga³⁺, Fe³⁺) , (B³⁺).

     

Hydrogenolysis of ethane over Ni/Al2O3 catalysts of high nickel dispersity

The effect of nickel dispersity on the rate of ethane hydrogenolysis and the number of B₅ centers has been studied. A maximum in the rate of ethane hydrogenolysis is observed in the range of nickel dispersity of 2–3.5 nm. There is a minimum of the apparent activation energy of ethane hydrogenolysis in this range of metal crystallite size.

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₅. 2–3,5 . .

     

Catalytic properties of phosphorus and sodium promoted VMo catalysts in acrolein oxidation

The change in the ratio of stepwise and concerted routes of acrolein conversion to complete oxidation products upon promotion of a V-Mo catalyst by phosphorus and sodium dopants is ascribed to modification of surface acid-base properties.

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V-Mo - .

     

Fractal analysis of co hydrogenation over rhodium catalysts

A fractal scaling law has been applied to products of carbon monoxide hydrogenation over silica supported rhodium catalysts. The results indicate structure sensitivity and that the type of structural sensitivity is product dependent.

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, . , , .

     

Catalytic preparation of mesityl oxide from acetone

In the process of the aldol condensation of acetone the preparation of mesityl oxide has been studied with respect to the temperature and the nature of catalyst. Strong basic ion exchangers Ionenaustauscher III (Merck III) and Lewatit MP 500 were used in the temperature range from 0 to 50°C. Better results are achieved with Merck III, as is evident from DAA/MO yields, rate constants and energy activation values. Empirical expressions for DAA/MO production are given.

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(). Ionenaustauscher III (Merck III) Lewatit MP 500 0 50°C. / (= ), , Merck III. - /.

     

Kinetics and mechanism of substitution reactions of complexes,XX

Thermal decomposition of 21 complexes of the type [Co(DH)₂(amine)₂]NCS has been studied under the conditions of thermogravimetric analysis, by using different heating rates. From the thermogravimetric curves apparent kinetic parameters of the pyrolysis reaction have been derived by means of the modified Doyle method. Apparent reaction order increases and apparent activation energy decreases with increasing heating rate. Thus, the obtained kinetic parameters do not characterize the purely chemical reaction, but the complex heterogeneous process as a whole. The explanation of the observed effect is discussed. Results are compared with those obtained with other analogous complexes.

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Zusammenfassung Die thermische Zersetzung von 21 Komplexen des Typs [Co(DH)₂(Amin)₂]NCS wurde thermogravimetrisch bei verschiedenen Aufheizungsgeschwindigkeiten untersucht. Aus den TG-Kurven wurden die scheinbaren kinetischen Parameter der Reaktion mit Hilfe der Doyleschen Methode ermittelt. Bei zunehmender Aufheizungsgeschwindigkeit wächst die scheinbare Reaktionsordnung während die scheinbare Aktivierungsenergie abnimmt. Die erhaltenen chemischen Parameter kennzeichnen nicht die eigentliche chemische Reaktion, sondern den ganzen komplexen heterogenen Vorgang. Die beobachteten Effekte wurden diskutiert und die Ergebnisse verglichen mit Resultaten von Untersuchungen anderer analoger Komplexe.

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Résumé On a étudié par thermogravimétrie, avec différentes vitesses d'échauffement, la décomposition thermique de 21 complexes du type [Co(DH)₂(amine)₂SCN. On a calculé suivant la méthode deDoyle les paramètres cinétiques apparents déduits des courbes d'ATG. L'ordre apparent de la réaction augmente si la vitesse d'échauffement croît, alors que l'énergie d'activation apparente décroît. Les paramètres cinétiques obtenus ne caractérisent que le processus hétérogène complexe et non la réaction chimique proprement dite. Les effets observés ont été discutés et comparés avec les résultats obtenus avec d'autres complexes analogues.

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21 [(D)₂()₂]NS , . . . , , . . , .

     

Poisoning effect of carbon monoxide on the desorption process of hydrogen from palladium

The desorption of H₂ from clean and CO-poisoned Pd wires was studied by a temperature programmed desorption technique. Poisoning effect of CO on H₂ desorption process can be accounted for in terms of blockage of the surface sites for the recombination of H atoms.

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H₂ , CO, - . CO H₂ , , , .

     

Acio-Base properties and actvity of complex oxide catalysts for m-xylene ammoxidation

Introduction of small quantities of alkaline and alkalineearth metal oxides into supported Sb–Bi–V oxide catalysts increasses the concentration of surface basic centers and increases significantly its activity in m-xylene ammoxidation. Promoting effect is suggested to be due to the heterolytic type of the primary activation of hydrocarbon.

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- -. .

     

Chemical oscillatory reaction in a hydrodynamic oscillator

The periodic mixing of the reactants (bromate-thiocyanate or bromate-hydroxylamine) by the hydrodynamic oscillator gives rise to both periodic and aperiodic chemical oscillations.

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(- -) , .

     

Structural peculiarities of orthorhombic MoO3 prepared at low temperatures

Upon drying the solution prepared via the ion exchange of sodium molybdate on KU-2-8 cationite, MoO₃ is formed with water molecules in the interlayer space.

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, KU-2-8, , .

     

Action des molecules organiques sur les composes d'insertion de metaux alcalins dans le graphite

Resume Les bases de Lewis (Tétrahydrofuranne, Diméthyl-2,5 tétrahydrofuranne, Diméthoxyéthane, Diméthyl éther du triéthylène glycol, Dioxanne, Triéthylamine, N,N,N,N tétraméthyl éthylène diamine) pénètrent dans les composés d'insertion de métaux alcalins dans le graphite (LiC₁₂, KC₃₆).Des changements de stades et de nouvelles distances interplanaires sont observées par diffraction des rayons X. En général, les nouveaux composés lamellaires obtenus comportent plusieurs phases, et sont comparables aux composés ternaires obtenus par synthèse directe.Ces solvates peuvent contenir jusqu'à deux molécules de solvant par cation, leurs stabilités thermiques peuvent donner des informations sur les pouvoirs complexants des solvants basiques.

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Lewis bases (tetrahydrofuran, 2,5-dimethyltetrahydrofuran, dimethoxyethane, triethyleneglycol dimethyl ether, dioxane, triethylamine, N,N,N,N-tetramethylethylenediamine) penetrate into graphite inclusion compounds of alkali metals (LiC₁₂, KC₃₆).Stage changes and new interlayer distances are inferred from the X-ray diffraction data. Generally these lamellar compounds have several phases. They are similar to those made by direct synthesis.These solvates can contain up to two solvent molecules for one cation and the complexing powers of the solvents can be inferred from their thermal stabilities.

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Zusammenfassung Die Lewis-schen Basen (Tetrahydrofuran, Dimethyl-2,5-Tetrahydrofuran, Dimethoxyäthan, Triäthylenglykol Dimethyläther, Dioxan, Triäthylamin, N,N,N,,N-Tetramethyl-Á thylendiamin) dringen in die Insertionsverbindungen der Alkalimetalle des Graphits ein (LiC₁₂, KC₃₆).Phasenveränderungen und neue interplanare Entfernungen wurden mittels Röntgendiffraktion beobachtet. Im allgemeinen bestehen die erhaltenen neuen lamellaren Verbindungen aus verschiedenen Phasen und können mit den durch direkte Synthese erhaltenen Ternärverbindungen verglichen werden.Diese Solvate können je Kation bis zu zwei Molekülen Lösungsmittel enthalten, ihre Thermostabilitäten können Informationen über das Komplexierungsvermögen der basischen Lösungsmittel geben.

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( , 2,5- , , , , , N,N,N,N ) - (LiC₁₂, KC₃₆). - . , , . . .

     

Effect of bond energies of a catalyst with reacting atoms on the selectivity of CO hydrogenation over metals

In hydrogenation over metals (M)_j carbon monoxide is adsorbed as a molecule. C–O bond rupture in partially hydrogenated complex, MCHOH, leads to MO and MCH₂ and then to hydrocarbons, while transformation of MCHOH into MCH₂OH gives alcohols and other oxygen-containing compounds. Selectivity towards hydrocarbons increases with increasing energy of M–O bonds.

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(M) . C–O MCHOH MO MCH₂ — ; MCHOH MCH₂OH . M–O.

     

After-effect of light in the photocatalytic oxidation of isobutene on immobilized vanadium oxide catalysts

A photocatalytic after-effect of visible and UV light in isobutene oxidation to acetone on immobilized vanadium oxide catalysts has been established. It is ascribed to the formation of labile active sites from coordinatively unsaturated V(V) compounds upon irradiation.

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. - - .

     

Nonisothermal kinetics of independent reactions

A general approach to the solution of peak seperation problem applicable not only in nonisothermal kinetics, but also in chromatographic, spectroscopic and polarographic studies of catalysts is suggested.

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, , , , , .

     

Structural and substructural parameters of carbon supports sibunit and altunit

Two carbon material — sibunit and altunit have been studied using X-ray phase analysis methods. Coherent scattering region of Sibunit is a globule with a diameter of 35 Å, which preserves a stratified structure of graphite with the azimutal disorientation of graphite networks. Altunit has a diamond structure and consists of small particles with the average size of 20 Å, having no microstrains and characterized by a narrow size distribution of particles.

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— . , 35 Å, . , 20 Å, .

     

Kinetics of the formation of whewellite and weddelite by displacement reactions

The nucleation and crystallization of whewellite and weddelite during displacement reactions has been investigated by means of thermomicroscopy, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Gypsum cleavage plates were immersed at different temperatures in solutions of oxalic acid and alkali oxalates. The reaction product (whewellite and/or weddelite) formed on the gypsum crystal surface. Depending on the concentration of the solution and on the time and temperature, different degrees of reaction, which means varying amounts and crystal forms or Ca-oxalate were found. An evaluation of the growth rate was possible by means of thermogravimetry. Conditions for the preparation of pure weddelite by precipitation from solutions have been established.

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Zusammenfassung Keimbildung und Kristallisation von Whewellit und Weddelit bei Verdrängungsreaktionen wurden durch Thermomikroskopie, Thermogravimetrie, Röntgenbeugung und Rasterelektronenmikroskopie untersucht. Gipsspaltplättchen wurden bei verschiedenen Temperaturen in Oxalsäure- und Natriumoxalatlösungen eingetaucht. Das Reaktionsprodukt (Whewellit oder Weddelit) bildete sich auf der Oberfläche des Gipskristalls. In Abhängigkeit von der Konzentration der Lösung, der Zeit und der Temperatur wurden verschiedene Umsetzungen, d. h. verschiedene Menge und Kristallformen von Calciumoxalat gefunden. Die Wachstumsgeschwindigkeit ließ sich aus thermogravimetrischen Messungen ermitteln. Die Bedingungen zur Herstellung reinen Weddelits durch Fällung aus der Lösung wurden ermittelt.

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

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We are grateful to Mr. R. Wessicken, Laboratorium für Festkörperphysik, ETH Zürich, Zürich-Hönggerberg, for taking the SEM-Photographs. Also, the kind help of Dr. A. Reller, Institute of Inorganic Chemisty, University of Zürich, for running the X-ray heating photographs is acknowledged.     

Oxidative polymerization of durene and diphenyl oxide in the presence of palladium(II) and heteropolyacids

The possibility of obtaining tetramers from durene or diphenyl oxide in the presence of H₅PMo₁₀V₂O₄₀, a reversible oxidant, and palladium acetate as catalyst is demonstrated.

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— H₅PMo₁₀V₂O₄₀ .

     

Oxidation of CO on Ag-based composite oxides

Thermal stability of the oxidized state of silver was increased in the Cr, Mn, Fe and Co oxides. However, Ni and Cu oxides did not stabilize Ag, leading to its aggregation to form metallic Ag at 400°C. The Ag in the former group exhibited high catalytic activity in the oxidation of CO due to the formation of composite oxides with these transition metals.

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Cr, Mn, Fe Co. , Ni Cu Ag, 400°C. Ag CO, .

     

Extension of the diffusional kinetics models involving changes in activation energy

On the basis of previous modifications of the Zhuravlev and Ginstling-Brounshtein models, a generalization of kinetic diffusional models is proposed. With the assumption that the rate of the activation energy change during the reaction is inversely proportional to the reaction time, it has been shown that all diffusional kinetic equations in heterogeneous systems take the formF()=KT ⁿ , whereF() is a function of the degree of conversion andK andn are constants related to the rate constant.

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Zusammenfassung Auf Grund vorangegangener Modifikationen der Modelle von Zhuravlev und Ginstling-Brounshtein wird eine Verallgemeinerung der kinetischen Diffusionsmodelle vorgeschlagen. Mit der Annahme, daß die Geschwindigkeit der Änderung der Aktivierungsenergie während der Reaktion umgekehrt proportional der Reaktionszeit ist, wird gezeigt, daß alle kinetischen Diffusionsgleichungen für heterogene Systeme die FormF()=KT ⁿ haben, woF() eine Funktion des Konversionsgrades undK undn mit der Geschwindigkeitskonstante in Beziehung stehende Konstanten sind.

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- . , , , F()=KT ⁿ , F() — , K n — .