Nature of propene chemisorption centers on molybdenum trioxide

As shown by temperature-programmed desorption (TPD), the quantity of reversibly chemisorbed propane on MoO₃ passes through a maximum depending on the degree of surface reduction. Using the ESR method, it is shown that the centers of propene chemisorption do not contain Mo⁵⁺ ions but presumably isolated Mo⁴⁺ ions.

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, MoO₃ . , Mo⁺⁵. , Mo⁺⁴.

     

Some peculiarities in ESR spectra of titanium complexes in catalysts for isoprene polymerization in excess A1R3

It has been established that at low temperatures of TiCl₄+AOC catalyst preparation in solution (with Ti/Al1/15), ESR spectra exhibit rhombic anisotropy of the g-factor. Experiments with the sample having 61 % concentration of⁴⁷Ti isotopes suggest the formation of associates of Ti³⁺ with magnetic ordering, apparently due to the Jahn-Teller cooperative effect.

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TiCl₄+ AOC ( Ti/Al1/15) g-. ⁴⁷Ti (61%) Ti³⁺ , , -.

     

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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.

     

Heterogeneous-homogeneous decomposition of HNO3

In contrast to ZSM zeolites impregnated with V⁵⁺ salts, catalysts prepared by adding V³⁺ salts during zeolite synthesis exhibited (even when transformed into cristobalite by oxidative activation) higher selectivity to furane in the oxidation of butadiene. Non-oxidative activation preserved the zeolitic structure and increased both the total activity and the selectivity to furane.

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ZSM, V⁵⁺, V³⁺ ( ) . , , .

     

Catalytic activity of high-silicon TsVK and Y type zeolites

Conversion of paraffins on TsVK and Y zeolites follow a similar mechanism yielding the same intermediates. Low selectivity of Y zeolites with respect to aromatic hydrocarbons is attributed to the strong adsorption of these hydrocarbons on zeolites. It is assumed that the centers of strong adsorption are Al³⁺ ions in cationic positions in zeolite.

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, . . , Al³⁺ .

     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

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Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

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Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

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

     

On the catalytic system MgO?Na

Acid-base and radical properties of two sets of MgO–Na catalysts have been studied. The catalysts were prepared (I) by impregnation of MgO with NaOH in aqueous solution, and (II) by evaporation of metallic sodium onto a MgO surface. The catalyst prepared by the second method was much more basic than pure MgO (H_o=35) and showed a high activity in olefin isomerization.

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- MgO–Na. 1) MgO (NaOH) 2) MgO. , , , MgO(H₀=35), .

     

A new method to obtain supported oriented oxides: MoO3 graphite catalyst in propylene oxidation to acrolein

Oriented MoO₃-graphite catalysts were prepared by oxyhydrolysis of a MoCl₅-graphite intercalation compound and used in catalytic oxidation of propylene. Results show a correlation between the building of specific crystal faces of MoO₃ and a selectivity towards acrolein formation.

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MoO₃- -MoCl₅- - . MoO, - .

     

Use of Pd/Sepiolite systems as hydrogenation catalysts I. Hydrogenolysis of N-blocked amino acids and dipeptides with molecular hydrogen

In this work we have assessed the use of sepiolites from Vallecas (Madrid, Spain) as supports of Pd catalysts applicable to the liquid-phase unblocking of amino acids and dipeptides protected by a benzyloxycarbonyl group (Z) with gaseous hydrogen. The sepiolites used have been compared with other supports employed by our team. We have also discussed the influence of the type of amino acid or dipeptide, the catalytic support and the precursor Pd salt on the unblocking rate.

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(, ) Pd , , (Z), . , . , Pd .

     

Structure effects of palladium complexes with phosphinated polystyrene on their catalytic properties in phenylacetylene hydrogenation

The structure of palladium acetate complexes with phosphinated polystyrene has been studied by IR and UV spectroscopy. The results indicate that on polystyrene both mono- and dinuclear palladium complexes are formed. The comparison of the catalytic properties of palladium complexes on phosphinated polystyrene with those of mono- and dinuclear complexes supported on silica confirmed the formation of dinuclear palladium complexes on polystyrene surface.

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- - . , . - , , .

     

Kinetics of dehydration and thermal decomposition of Sr(NO3)2.4H2O and its deuterated analogue with a view to obtaining SrO

The kinetics and mechanism of thermal dehydration of Sr(NO₃)₂.4H₂O and its deuterated analogue were studied by means of DTA, TG and DSC. The temperatures, enthalpies and weight losses of phase transitions were measured. The dehydration occurs in a stepwise manner, and the composition of the intermediate depends on the rate of thermal decomposition. The kinetic parameters (E ^* andZ) for the two steps of dehydration at a heating rate of 5 deg min^–1 were calculated. A correlation was found between the dispersity of the end-product of the thermal decomposition (SrO) and the conditions of its preparation.

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Zusammenfassung Kinetik und Mechanismus der thermischen Entwässerung von Sr(NO₃)₂.4H₂O und der deuterierten Verbindung Sr(NO₃)₂.4D₂O wurden mittels TG-DTA und DSC untersucht. Temperaturen, Enthalpien und Gewichtsverluste der Phasenumwandlungen wurden gemessen. Der Prozess verläuft stufenweise, die Zusammensetzung des Zwischenprodukts hängt von der Zersetzungsgeschwindigkeit ab. Die kinetischen ParameterE ^* undZ der beiden Entwässerungsstufen bei einer Aufheizgeschwindigkeit von 5 Grad min^–1 wurden berechnet. Zwischen der Dispersität des Endproduktes SrO und seinen Bildungsbedingungen wurde eine Korrelation gefunden.

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, . . , . , 5 /, E Z. .

     

Kinetics and mechanism of elimination of methoxyphenethyl chlorides in the gas phase

The kinetics for the gas phase elimination of o-and m-methoxy-2-phenylethyl chlorides have been investigated over the temperature range of 390-464°C and pressure range of 38–119 Torr. The reactions in seasoned vessels and in the presence of the free radical inhibitor propene, are homogeneous and unimolecular and follow a first-order rate law. The o-anisyl and p-anisyl substituents at the -position of ethyl chloride assist anchimerically the elimination processes. The formation of a cyclic product, benzodihydrofuran, from o-methoxy-2-phenylethyl chloride suggests an intimate ion pair mechanism operating in this reaction.

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- --2- 390–464°C 38–119 . - , , , . - - - . , , --2- , .

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

The height of DSC phase transition peaks application to liquid crystals

A new method for differentiating first- and second-order transition in liquid crystalline systems is proposed. It is based on the use of the ratioN=h/h ₀, whereh ₀ is the height of the transition peak recorded by DSC at a heating rateT _p with a massm, andh is the height of the corresponding peak when the heating rate or the mass is doubled. The application of this new concept to phase transitions in octylcyanobiphenyl (8CB) is mentioned.

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Zusammenfassung Eine neue Methode zur Unterscheidung von Umwandlungen erster und zweiter Art in flüssigen Kristallen wird vorgeschlagen, die auf Anwendung des VerhältnissesN=h/h₀ basiert, wobeih ₀ die Höhe des durch DSC bei einer AufheizgeschwindigkeitT _p und für die Massem registrierten Umwandlungspeaks undh die Höhe des entsprechenden Peaks bei Verdoppelung der Aufheizgeschwindigkeit oder der Masse bedeuten. Auf die Anwendung dieses neuen Konzepts auf Phasenübergänge in Octylcyanobiphenyl (8CB) wird eingegangen.

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. N=h/h ₀, h ₀- , T _p m, h- . -.

     

Studies of the structure of multicomponent Raney nickel catalysts

Genesis and structure of Raney nickel catalysts modified by Mo, Fe and Ca have been studied by XPS, SIMS and Auger and electron microprobe methods. It has been established that these catalysts are inhomogeneous and their structure can be described by models accounting for the interaction and localization character of metal components, their oxides and hydroxides.

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, - Ni-, Mo, Fe Ca. , , , .

     

A mechanistic explanation for the SO2 oxidation rate data of a Cs/V catalyst at high pressures and conversions

A preliminary attempt to modify a molybdena-silica for ethylene homologation was performed by adding copper. Ethylene homologation (3C₂H₄2C₃H₆) was enhanced 2.5 times on copper doped catalyst. Contrary to this, ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) was suppressed in the presence of copper. The selectivity of the homologation to metathesis was increased 7.5 times.

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- , (3C₂H₄2C₃H₆), . 2,5 , (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . 7,5 .

     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

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Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

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