Reactivity of coordinated O2? ion-radicals in the oxidation of organic compounds

By the flow ESR method, the rates of the reaction of the radical complex Ti(IV)(O ₂ ^– ) with some aromatic compounds in aqueous solution have been measured. An elementary step of these reactions seems to be one-electron oxidation with the formation of a substrate cation-radical.

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- Ti(IV)(O ₂ ^– ) . - -.

     

Effect of vanadium content on the character of acidic sites on V2O5/Al2O3 catalysts

By IR spectroscopy and TPD the effect of vanadium content on the relative proportion of strongly acidic sites of V₂O₅/Al₂O₃ catalyst was studied.

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- - V₂O₅/Al₂O₃.

     

The role of acidity of MoO3?SiO2 and WO3?SiO2 catalysts

The acidity of various MoO₃–SiO₂ and WO₃ catalysts has been measured by means of ammonia adsorption. Whereas the acidity of silica and pure metal oxides is very low, an increase of surface acidity results from a reaction between silica support and metal oxides. A significant correlation between surface acidity and catalytic activity for aromatization of lower olefines could be found.

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MoO₃–SiO₂ WO₃ . SiO₂ . , SiO₂ . .

     

Influence of added copper on the activity of Ni/Al2O3 catalysts in the hydrogenolysis of n-butane

The influence of small Cu admixture to the Ni/Al₂O₃ system on its activity in the hydrogenolysis of n-butane was studied in the temperature range of 723–573 K. The activity was measured in a gradientless reactor. Cu added to Ni/Al₂O₃ was found to have a strong influence on the overall activity, selectivity and ratio for n-butane hydrogenolysis. A mechanism of hydrogenolysis of n-butane on the Ni–Cu/Al₂O₃ system is proposed.

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Cu Ni/Al₂O₃ - 723–573°. . Cu Bi/Al₂O₃ -. - Ni–Cu/Al₂O₃.

     

Acidic properties of TiO2?SiO2 catalysts

The acidic properties of a series of TiO₂–SiO₂ catalysts with different Ti/Si mole ratios have been studied. In order to determine the amount of acid centers and the acid strength distribution, the Benesi method of discontinuous titration has been used. Thermogravimetric measurements were also carried out.

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TiO₂–SiO₂ Ti/Si. , - . .

     

Catalytic reactions of ethanol on H3+xPMo12?xVxO40 catalysts

The catalytic decomposition of ethanol on heteropolyacids (HPA) of the series H_3+xPMo_12–xV_xO₄₀ (x=0,1,2,3) was investigated at 240°C, using a pulse method. It has been shown that besides ethyl ether, ethylene, acetaldehyde and unreacted alcohol, a certain amount of alcohol was irreversibly sorbed by HPA. The amount of the latter decreased with x, which is considered to be due to the tighter bonding of Keggin units (KU) with an increasing number of intramolecular hydrogen bonds. The yield of ethyl ether forming at the surface was almost constant but that of ethylene and acetaldehyde decreased in the series x=0,1,2, which was connected with the increasingly difficult penetration of HPA molecules into the bulk. Some differences in the behavior of the sample with x=3 were the result of partial decomposition of this thermally stable catalyst.

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H_3+xPMo_12–xV_xO₄₀ (x=0, 1, 2, 3) 240°C. , , , , . , . , , , x=0, 1, 2, . x=3 .

     

Interaction of methanol with hydrogen sulfide in the presence of K2WO4/Al2O3

Kinetic data show that in the presence of K₂WO₄/Al₂O₃, methanethiol is largely produced by the reaction of H₂S with metanol and partly with dimethyl ether. Dimethyl sulfide is formed during the interaction of methanethiol with methanol, of H₂S with dimethyl ether and as a result of methanethiol disproportionation. Methane and carbon oxides are the decomposition products of methanethiol and dimethyl sulfide and of methanol and dimethyl ether, respectively.

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, K₂WO₄/Al₂O₃ H₂S — . , H₂S . , — .

     

Reactivities of m-xylene, phenol and benzene on vanadium oxides layered on TiO2 and ZrO2

Reactivities of m=xylene, phenol and benzene over vanadium oxides layered on TiO₂ and ZrO₂ have been observed by in situ FTIR spectroscopy.

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-, , TiO₂ ZrO₂, in situ .

     

Studies on the thermal behaviour of detonating fuse and detonators

Investigations of the thermal stability of detonating fuse containing 10 g pentaerythrol tetranitrate (PETN) revealed that the cord burnt under unconfinement at 403 K. Under confinement in a steel pipe or copper tube there was a partial detonation at 403 K. In order to characterize the thermal stability of PETN and pyrotechnic composition used in fuse head of electric detonators differential thermal analysis (DTA) was used.The electric detonators of aluminium cell and copper cell were heated from ambient temperature to 373 K at an average rate of 0.4 deg/min. The rate of heating was increased gradually to 1.5 deg/min till explosion. The detonation temperature varied between 373 K and 375 K.The impact and friction sensitivity of detonating fuse was poor. There was no detonation when a 5 kg hammer was repeatedly hit over the fuse from a height of one metre. There was no detonation when the detonating fuse was rubbed by a blunt edge of steel plate till it was smashed.

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Zusammenfassung Untersuchungen der thermischen Stabilität von Sprengschnuren mit 10 gm^–1 PETN zeigten, daß die Schnur frei bei 403 K verbrennt. Unter Abschluß in einem Stahloder Kupferrohr tritt bei 403 K eine partielle Detonation auf. Zur Charakterisierung der thermischen Stabilität von PETN und von pyrotechnischen Mischungen, die in Zünderköpfen von elektrischen Sprengkapseln verwendet werden, wurde Differentialthermoanalyse (DTA) angewendet. Die elektrischen Sprengkapseln von Aluminium- und Kupferzellen wurden mit einer durchschnittlichen Aufheizgeschwindigkeit von 0.4 Grad/min von Raumtemperatur auf 373 K erhitzt. Die Aufheizgeschwindigkeit wurde bis zur Explosion allmählich auf 1,5 Grad/min erhöht. Die einzelnen Detonationen erfolgten bei einer Temperatur zwischen 373 und 375 K. Die Stoß- und Reibempfindlichkeit der Sprengschnur war gering. Bei einem mehrmaligen Einwirken eines 5 kg-Hammers aus einer Höhe von 1 m erfolgte keine Detonation. Bei Reiben mit der unscharfen Kante einer Stahlplatte bis zur Zerstörung erfolgte keine Detonation.

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, 10 ^–1 PETN, , 403 , 403 . PETN , , . 373 0,4°/. 1,5°/ . 373 375 . . 5 1 . , .

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The authors are indebted to the Director, Central Mining Research Station for giving permission to publish this paper. The views expressed in the paper are those of the authors and not necessarily of the institute which they belong to.     

Effect of the activation conditions on the catalytic properties of Pt/Al2O3 catalysts

The effect of the activation conditions of Pt/Al₂O₃ catalysts has been investigated in the hydrogenation of benzene and in the hydrogenolysis of ethane. Whatever the conditions of calcination or reduction, specific activities of all catalysts for benzene hydrogenation remain constant. On the other hand, for identical dispersities, the cacination in a wet argon flow increases the specific activity of platinum for hydrogenolysis of ethane, pointing out the role of wet pretreatment on defect building or on the faceting of supported metallic catalysts.

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Pt/Al₂O₃ . , . , , . .

     

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, .

     

Rate of14N2 desorption from the surfaces of nitrides in the presence and absence of15N2 in the gas phase

The rates of¹⁴N₂ desorption from the surfaces of nitrides have been measured in the presence and absence of¹⁵N₂ in the gas phase. Whatever the adsorption heat and the form of surface species, the adsorption of¹⁵N₂ molecules does not affect the rate of¹⁴N₂ desorption.

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¹⁴N₂ ¹⁵N₂ . , ¹⁵N₂ ¹⁴N₂.

     

Effect of Sn addition on the catalytic properties of the metallic phase in Pt?Sn/Al2O3 catalysts

Platinum-tin/alumina supported catalysts have been studied. The TPR results show an assisted reduction of tin by platinum. The effect of alloying in cyclohexane dehydrogenation, o-xylene hydrogenation and cyclopentane hydrogenolysis is discussed.

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- , . . , - .

     

Hydrogenation of carbon monoxide catalysts prepared by pyrolysis of Co2(CO)8 on various oxide supports

Catalysts prepared by pyrolysis of Co₂(CO)₈ on oxide supports have been studied in the hydrogenation of CO. It is shown that MgO and -Al₂O₃-based catalysts are less active than those supported on SiO₂, TiO₂ and ZrO₂. The application of -Al₂O₃ as a support increases the relative yield of light hydrocarbons.

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, Co₂(CO)₈ , CO. , MgO -Al₂O₃ SiO₂, TiO₂ ZrO₂. -Al₂O₃ .

     

51V-,29Si- and27Al-NMR studies of the interaction of active component of vanadium catalysts for SO2 oxidation with supports

NMR studies have revealed that silicas and aluminosilicates interact with the active components of vanadium catalysts, in the former case merely yielding surface compounds.

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, , .

     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Studies on catalytically active surface compounds, IX. Formation of O2? radicals on VCl4/SiO2 catalysts

The conditions for the formation of O ₂ ^– on VCl₄/SiO₂ catalysts have been investigated. It is shown that thermal vacuum treatment (TVT) of unhydrolyzed catalysts leads to partial hydrolysis of the surface vanadium complex caused by the silanol groups of the support. The ability of the catalysts to generate O ₂ ^– radicals was found to depend on the degree of hydrolysis caused by thermal vacuum treatment.

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O ₂ ^– VCl₄/SiO₂. , , . , O ₂ ^– , .

     

Experimental study of the initial stage of Li2SO4·H2O single crystal dehydration in vacuum

The initial stage of the Li₂SO₄·H₂O single crystal isothermal dehydration has been studied by means of quartz crystal microbalance. As found, weight loss in the initial process may be considered as H₂O molecule diffusion from a semiinfinite medium. The numerical values of the H₂O molecule diffusion in Li₂SO₄·H₂O have been calculated from the results obtained.

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. - - - -. - Li₂SO₄·H₂O.

     

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 . .

     

Nature of the activity and the kinetics of cyclohexene hydrogenation by the catalytic system (C5H5)2 TiCl2?LiC4H9

The reaction of tributylphosphine with the catalytic system (C₅H₅)₂ TiCl₂–LiC₄H₉ prepared in an atmosphere of H₂ has been investigated in toluene solution. By using the ESR technique, a hydride complex Cp₂Ti(H) (PBu₃) has been detected. The proportionality between the rate of cyclohexene hydrogenation and the complex concentration has been established. The kinetics of cyclohexene hydrogenation has been investigated and a reaction mechanism is proposed.

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Cp₂TiCl₂–LiC₄H₉ (Cp–C₅H₅), H₂, Cp₂Ti(H) (PBu₃). Ti (III). .