Structure of Pt/ZnAl2O4 catalysts

The effect of the support preparation technique (solgel and coprecipitation) on the final Pt/ZnAl₂O₄ catalyst is presented. The structural properties of the solids obtained are correlated to the selectivity and activity for isobutane dehydrogenation in H₂ and He reaction media. If a highly dispersed catalyst is suitable, the support has to be prepared by the sol-gel method.

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( — ) Pt/ZnAl₂O₄. H₂ He. , — .

     

Effect of 3d transition metal 2,4-pentanedionates on the photolysis of 1,2,3,4-tetrahydro-1-naphthylhydroperoxide

The photoinitiated decomposition of 1,2,3,4-tetrahydro-naphthylhydroperoxide (THP) is accelerated by the addition of 2,4-pentanedionates of some transition metals. The composition of the reaction products varies according to the type of metal complex present.

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1, 2, 3, 4--1-- () 2,4- . .

     

Promoting effect of potassium on catalytic and surface properties and phase commposition of catalysts for synthesis of alcohols

The dependence between catalytic and surface acid-base properties of Zn–Cr–K catalysts has been established. Modification by potassium and an increase in potassium concentration promotes Zn–Cr–K reduction and raises the yield of higher alcohols. The spinel structure of catalysts is preserved.

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Zn–Cr–K . Zn–Cr–K , .

     

Investigation of isomerization of n-pentane over supported Pt catalyst modified by adsorbed Bi and Pd

-Al₂O₃-supported Bi–Pt and Pd–Pt bimetallic catalysts were prepared by electrochemical metal adsorption. Isomerization of n-pentane was studied over these catalysts in a pulse reactor. It can be concluded from the results that the properties of these catalysts differ substantially from the base Pt/-Al₂O₃ catalyst. On the modified catalysts conversion and the yield of i-pentane was found to be lower although selectivity was better. The ratio of cracking reactions was also lower than over the base catalyst.It is very probable that the adsorbed bismuth was slowly desorbing from the catalyst surface during the experiments.

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Bi–Pt Pd–Pt -Al₂O₃. -, . , Pt/Al₂O₃. , - , . , . , .

     

Highly active photoadsorbed oxygen species on zinc oxide

Photoadsorbed oxygen is the intermediate for the photo-isotope exchange of molecular oxygen with the ZnO surface. Its most active species are those having a maximum intensity in thermal desorption spectra at 390–430 K.

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ZnO. , 390–430 , .

     

Hydrogenation of ethylene on gadolinium X, Y and L-type zeolites

It is shown that Gd-zeolites have a catalytic activity towards ethylene hydrogenation at 1 atm. This activity decreases with an increase in the SiO₂/Al₂O₃ ratio from 2.2 to 6.1 and 4.1, i.e. upon going from an X type zeolite to Y and L. For these types of zeolite the activity grows with an increase in Gd³⁺ content from 50 to 80%. Oxygen addition to the reaction mixture stabilizes the catalytic activity of zeolites.

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, qv 1 . , SiO₂/Al₂O₃ 2,2 6,1 4,1, .. X Y L. , 50 80%. .

     

“In situ” EPR studies of interaction between benzene and ZSM-5 zeolites

The effect of the state of adsorbed layers on the formation of monomeric and dimeric benzene cation-radicals (CR) on ZSM-5 zeolites has been studied. Removal of benzene is shown to be accompanied by disappearance of CR, which is reversible and takes place with preservation of the sites for their stabilization.

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- (KP) ZSM-5. , KP, .

     

Thermal behaviour of copolymers of methyl methacrylate and iso-octyl/iso-decyl methacrylate

Thermal behaviour of copolymers of methyl methacrylate (MMA) with iso-octyliso-decyl methacrylate was investigated using dynamic thermogravimetry, mass spectroscopy and pyrolysis gas chromatography. The copolymer samples were stable upto 250 °C. Total loss in weight was observed around 400 °C. The degradation in homopolymers as well as copolymers proceeded by predominans loss of monomer.

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Zusammenfassung Mittels dynamischer Thermogravimetrie, Massenspektroskopie und Pyrolysengaschromatographie wurde das thermische Verhalten von Kopolymeren aus Methylmethacrylat (MMA) und Isooktyl/Isodecyl-methacrylat untersucht. Die Kopolymerproben waren bis 250 °C stabil. Ein vollständiger Gewichtsverlust wurde bei 400 °C beobachtet. Der Abbau sowohl der Homopolymere als auch der Kopolymere erfolgt durch eine überwiegende Abgabe von Monomeren.

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, - /- . /- . 250°. 400°. , .

     

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 .

     

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 .

     

Applications of thermoelectrometry to metal-ion modified polyimide films

As part of a research program to decrease the electrical resistivity of polyimide films with ionic additives a variable temperature three probe electrical resistivity measurement system has been designed and constructed. Sample temperature, electrification time, atmosphere, and measurement mode are computer controlled. As a data interpretation aid, temperature cycled analysis can be routinely performed. Surface resistivities in the range 10³–10¹⁵ ohm and volume resistivities in the range 10⁵–10¹⁸ ohm-cm are theoretically measurable under well controlled experimental conditions from room temperature to 250°. The electrical resistivity measurement system is useful for the evaluation of polymer films or films in general. Application of the system for analysis of cobalt, lithium and tin ion-modified polyimide films and some experimental considerations are presented. Correlation of the electrical measurements with differential scanning calorimetry, thermomechanical analysis, and thermogravimetric analysis is demonstrated.

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Zusammenfassung Als Teil eines Forschungsprogramms zur Herabsetzung des elektrischen Widerstandes von Polyimidfilmen mit ionischen Additiven wurde ein 3-Proben-Meßsystem zur Ermittlung des elektrischen Widerstandes in Abhängigkeit von der Temperatur entworfen und konstruiert. Probentemperatur, Elektrisierungszeit, Atmosphäre und Meßmethoden waren computergesteuert. Als Dateninterpretationshilfe kann eine hinsichtlich der Temperatur zyklische Analyse routinemäßig ausgeführt werden. Die Oberflächenwiderstände sind im Bereich von 10³–10¹⁵ Ohm und die Volumenwiderstände im Bereich von 10⁵–10¹⁸ Ohm-cm unter gut kontrollierten experimentellen Bedingungen von Raumtemperatur bis 250° theoretisch meßbar. Das elektrische Widerstandmeßsystem ist nützlich für die Bewertung von Polymerfilmen oder Filmen im allgemeinen. Die Anwendung des Systems zur Analyse von mit Co-, Li- und Sn-Ionen modifizierten Polyimidfilmen und einige experimentelle Hinweise werden angegeben. Es wird gezeigt, daß die mit dem beschriebenen System erhaltenen Resultate mit durch DSC, thermomechanische Analyse und TG erhaltenen Werten korrelieren.

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, , . , , . . 10³–10¹⁵ , 10⁵–10¹⁸ 250°. , . , , , . , .

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The financial support of the National Aeronautics and Space Administration is gratefully appreciated. The assistance of John Swartzentruber in performing many of the measurements is recognized.     

Kinetics of the oxidation of some polycyclic aromatic hydrocarbons by lead tetraacetate in aqueous acetic acid and perchloric acid medium

The state of metal cations in CuCr₂O₄/-Al₂O₃ catalysts under its operation in catalytic heat generators has been examined. IR spectra of adsorbed CO indicate copper ion reduction in the catalyst to Cu⁺, whose surface concentration was determined. Diffuse reflectance spectra have revealed that the initial catalyst contains Cr(VI), disappearing after reaction.

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CuCr₂O₄/-Al₂O₃ (). - CO , Cu⁺. Cu⁺. , Cr(VI), .

     

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, .

     

Co(salen) catalyzed oxidation of oximes with t-butyl hydroperoxide

Co(salen) catalyzed the oxidation of oximes with t-butyl hydroperoxide to give the parent carbonyl compounds, providing a new convenient route to deoximation reaction. A plausible mechanism involves a substrate radical intermediate.

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Co() -, . . .

     

Catalytic properties of V?Sb?O systems in acrolein oxidation

Catalytic properties of V-Sb-O systems in acrolein oxidation have been studied. It has been established that the changes in the activity and selectivity of the catalysts are due to the phase and chemical properties of the system.

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