Effect of hydrolysis catalyst and thermal treatment on titania synthesis via sol-gel

The effect of acidic and basic catalysts and of thermal treatment on the preparation of TiO₂ by the sol-gel method has been studied. The resultant solids were characterized by UV-Vis spectroscopy. A displacement of the band due to a fundamental transition to lower energies was observed when acid catalysts were used.

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, TiO₂ - . . .

     

Calorimetric study of the BrO3?/Ce4+/cyclohexanone and BrO3?/Ce4+/cyclopentanone oscillating systems

The heat output (Q) during the induction period of a Belousov-Zhabotinskii oscillating reaction usually evolves at a constant rate /6/; we observe in the BrO ₃ ^– /Ce⁴⁺/Cyclohexanone system a sudden change in the slope of the function Q=f(t), which corresponds to the beginning of the quasistationary phase /3/.

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(Q) - ; BrO ₃ ^– /Ce⁺⁴/ Q=f(t), .

     

Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3

The adsorption of benzene at room temperature on-Fe₂O₃ and on-Al₂O₃ powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t.Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups.

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Zusammenfassung Die Adsorption von Benzol an-Fe₂O₃- und-Al₂O₃-Pulvern bei Raumtemperatur wurde mittels Wärmefluß-Kalorimetrie und FT-IR-Spektroskopie untersucht. Beim Eisenoxid folgt auf dem Chemisorptions-Verbrennungs-Schritt ein bei Raumtemperatur reversibler, stark exothermer Adsorptionsschritt. Aluminiumoxid besitzt einige Oxydationszentren, sofern keine reduzierende Vorbehandlung erfolgt. Zwei aufeinanderfolgende reversible Adsorptionsschritte treten auf und werden der Wechselwirkung mit zwei verschiedenen Typen von Oberflächenhydroxylgruppen zugeschrieben.

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-Fe₂O₃ -l₂₃. - , . , , . , .

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This work was supported by the CNR Progetto Finalizzato Chimica Fine e Secondaria. Prof. Vincenzo Lorenzelli is gratefully thanked for the kind loan of instrumental facilities and helpful discussions.     

Observation of109Ag NMR spectra of supported silver catalysts

The first observation of¹⁰⁹Ag NMR spectra from Ag metal particles dispersed on alumina and silica, in some cases at Ag contents as low as 0.1 wt.% is reported. The Knight shifts and relaxation times are found to be typical for Ag bulk metal. The distortions of the Ag metal crystal lattice were found to contribute to¹⁰⁹Ag NMR line width. The estimation of Ag crystal size at which the metal-to-nonmetal transformation takes place was made from studies of samples with different size distribution of supported Ag particles.

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¹⁰⁹Ag , , 0,1 .%. . , ¹⁰⁹Ag . , , , -.

     

Hydrogenation of CO2 on carbon-supported nickel and cobalt

The hydrogenation of CO₂ has been studied at atmospheric pressure on Co/C and Ni/C catalysts and the results are compared with those obtained on unsupported Co and Ni. Specific activites in the form of turnover frequencies for CO₂ hydrogenation decrease with increasing metal dispersity. Carbon supported Co and Ni present a smaller selectivity for methane than bulk metals. Higher specific activities and smaller activation energies are obtained on Co catalysts, compared with those determined for Ni catalysts.

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CO₂ Co/ Ni/ Co Ni . CO₂ . Co Ni , . .

     

Complexes of O2? radical ions with palladium and platinum compounds in solutions

Coordination of O ₂ ^– radical ions with palladium and platinum compounds in solutions has been detected by the ESR technique.

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- O ₂ ^– .

     

A thermoanalytical study of treated wools

Previous studies of fibrous keratins have enabled assignments to be proposed for the endothermic processes identified in the relatively complex DTA curve. From this base, the influence of well defined chemical modifications to keratin on their observed DTA curves has been discussed. Wools are specifically treated commercially to improve shrink resistance and machine washability. To achieve these desired characteristics wools are treated, (a) by special oxidative processes, (b) with specific polymers, and (c) by combinations of (a) and (b). The DTA curves of wool samples which have been subjected to each of the three different treatments were reproducibly recorded. The significance of differences between these curves and that for the untreated fibre are discussed. Although characteristic differences in the DTA curves of wools after specific treatments can be distinguished, differential thermal analysis cannot be regarded as a general tool for such treatment characterisation. It is considered that thermogravimetry should offer a greater potential for this purpose.

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Zusammenfassung Vorangegangene Untersuchungen über faserige Keratine ermöglichten Zuordnungsvorschläge für die in der verhältnismässig komplexen DTA-Kurve befindlichen endothermen Vorgänge. Auf dieser Basis wurde der Einfluss gut definierter chemischer Veränderungen in Richtung Keratin auf ihre beobachteten DTA-Kurven erörtert. Die Wollen werden im Handelsmaßstab spezifisch behandelt um ihre Widerstandsfähigkeit gegenüber dem Eingehen zu erhöhen und ihre Waschbarkeit in der Maschine zu fördern. Um diese erwünschten Charakteristika zu erreichen werden die Wollen a) durch spezielle Oxidationsvorgänge, b) mittels spezifischer Polymere und c) mit kombinierten Verfahren von a) und b) behandelt. Die DTA-Kurven von jedem dieser drei verschiedenen Behandlungen unterworfenen Wollproben wurden reproduzierbar aufgezeichnet. Die Signifikanz der Unterschiede dieser Kurven gegenüber denen der unbehandelten Fasern wird erörtert. Obwohl sich charakteristische Unterschiede in den DTA-Kurven der spezifisch behandelten Wollen beobachten lassen, kann die Differentialthermoanalyse nicht als ein allgemein anwendbares Verfahren zur Charakterisierung solcher Behandlungen betrachtet werden. Es wird angenommen, dass die Thermogravimetrie für diesen Zweck grössere Möglichkeiten bietet.

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Résumé Des études antérieures sur les kératines fibreuses ont permis de proposer des interprétations sur les effects endothermiques identifiés sur la courbe ATD relativement complexe. Sur cette base, l'influence de modifications chimiques bien définies de la kératine sur les courbes ATD observées est discutée. Les laines, à l'échelle commerciale, sont traitées spécifiquement pour augmenter leur résistance au rétrécissement ainsi que pour améliorer leur faculté de lavage en machine. Afin d'atteindre ces caractéristiques, elles sont traitées soit par des procédés oxydants spéciaux, soit par des polymères spécifiques soit par les deux. Les courbes ATD d'échantillons de laines traitées par chacune de ces méthodes ont été enregistrées de façon reproductible. Les différences observées entre les courbes obtenues avec les fibres traitées et non traitées sont discutées. Malgré des différences caractéristiques, l'analyse thermique différentielle ne peut pas être considérée comme une méthode universelle pour caractériser de tels traitements. La thermogravimétrie pourrait être potentiellement plus adaptée.

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, DTA. , DTA. , , . : ) , ) ) ) ). DTA , . . DTA , . , .

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Paper presented at the 1^st ESTA, Salford U.K.

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We wish to thank Precision Processes (Textiles) Ltd., and the International Wool Secretariat for samples and information. Their co-operation is gratefully acknowledged. One of us (WMF) wishes to record her thanks to the I.W.S. for their support of a research studentship.     

Kinetic analysis of temperature-programmed desorption of hydrogen after reduction of a NiNaY zeolite

From the kinetic analysis of TPD curves it can be calculated that hydrogen desorption after reduction at lower temperatures can be described by a rate equation of first order, while reduction at higher temperatures provides a second order equation interpreted by a change of the rate-determining step of the complex desorption process.

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, , , 2- . , .

     

Inhibition by phase transfer catalysts

While phase transfer catalysts have generally a positive effect on substitution of halides by rhodanide ion in two-phase reaction systems changing the structure of alkyl halide from primary to tert.-alkyl groups, catalysis reverses into inhibition. The assumption that this is due to the change in reaction mechanism from S_N2 to S_N1 was proved on hydrolysis of triphenylmethyl chloride in a two-phase system, where the inhibitory effect of phase transfer catalysts is even more pronounced.

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, , , , . , S_N2 S_N1, , .

     

Mechanism of RuIV-catalyzed oxidation of alkanes in aqueous solutions

The Ru^IV-catalyzed oxidation of alkanes in aqueous solutions includes activation of the oxidant Ox (Cr^VI, HNO₃, HClO₄, etc.) via Ox–Ru^IV complex formation and is accompanied by H atom abstraction from the alkane by the activated oxidant.

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Ru^IV - Ox (Cr^IV, HNO₃, HClO₄ .) Ox–Ru^IV - .

     

Thermal study of some sulphosuccinates

The thermal properties of some sulphosuccinates and their intermediates were studied by using combined dynamic thermal analysis and mass spectrometry. The temperature ranges were similar in the two methods, and a scheme of thermal decomposition of the compounds investigated was suggested. In the first temperature range of thermal decomposition of the sulphosuccinate a-rupture of the molecular ion occurs. In the second temperature range, the fragmentation proceeds in two directions: either-rupture of the ethoxylated nonylphenol, or-rupture of the acid residue of the sulphosuccinates.

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Zusammenfassung Mittels einer Kombination von dynamischer Thermoanalyse und Massenspektroskopie wurden die thermischen Eigenschaften einiger Sulfosukzinate und deren Zwischenprodukte untersucht. Im ersten Temperaturbereich der thermischen Zersetzung des Sulfosukzinates findet eine-Spaltung des Molekülions statt. Im zweiten Temperaturbereich tritt auch ein alternativer Fragmentierungsweg auf: eine-Spaltung des Säurerestes des Sulfosukzinates.

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- . . - -. : - - .

     

Toluene disproportionation on ultrastable Pd-and Cr-containing Y zeolites

Studies of the disproportionation of toluene on ultrastable Y zeolites have revealed that the incorporation of Pd into Cr containing zeolite at 400°C increases its catalytic activity and stability.

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. , Pd Cr- 400 C .

     

Kinetic investigation on alcoholysis of triethylaluminium by differential thermal analysis

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from –150 to –170 kJ mole^–1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofS _E2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

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Zusammenfassung Die Reaktion zwischen einer Lösung von Alumimumtriethyl und einer Reihe von aliphatischen oder aromatischen Alkoholen kann mittels DTA quantitativ verfolgt werden. Die negative Reaktionsenthalpie der Alkoholyse mit primären Alkoholen beträgt 150 bis 170 kJ mol^–1, sofern ein Lösungsmittelgemisch aus Tetrahydrofuran/Toluen eingesetzt wird. Die Reaktionsgeschwindigkeit in unpolaren Kohlenwasserstoffen ist grösser als in Gegenwart von Lewis-Basen. Wahrscheinlich ist der Reaktionsmechanismus vom TypS _E2, wobei die Reaktivität in der Folge primäre, sekundäre, tertiäre Alkohole fällt. Der zweite Schritt der Alkoholyse, ausgehend vom Diethylaluminiumalkoxid, ist wegen der starken Selbstassoziation weniger reaktiv. Bei Umsatz von 2 Mol Alkohol treten entsprechend der Folgereaktion zwei DTA-Peaks auf.

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. –150 –170 ^–1 - . , . , S _E2 , , . , , . -, .

     

Hydrodenitrogenation activity of sulfided catalysts

Activities of hydrodenitrogenation catalysts were compared using a batch mode autoclave reactor. The hydrodenitrogenation of carbazole, a model coal nitrogen compound, was the reaction studied. The highest activity and the highest rate constant for carbazole and total nitrogen removal were found in the case of NiMo/Al₂O₃ catalyst.

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. , . , NiMo/Al₂O₃.

     

ESR studies of the generation of adsorbed oxygen radicals under irradiation of CaO in the range of surface absorption

Anion-radicals of oxygen O ₂ ^– and complexes of molecular oxygen with hole centers [X·O₂] (g₁=2.002, g₂=2.009, g ₃ ¹ =2–015, g ₃ ² =2.016) and [Y·O₂] (g=2.004, g=2.012) have been found to form under CaO irradiation in the range of surface absorption (h4 eV). ESR spectra of X and Y centers have not been observed. They are suggested to be anion-radicals O _st ^– in various coordinations: (O _3C ^– )_st and (O _4C ^– )_st, respectively.

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- O ₂ ^– [XO₂] (g₁=2.002, g₂=2.009, g ₃ ¹ =2.015, g ₃ ² =2.016) (g=2.004, g=2.012) CaO (h4 ). X Y . , - O _st ^– , : (O _3C ^– )_st (O _4C ^– )_st, .

     

Contribution to the phase diagram of the system PbCl2-AgCI

The side parts of the phase diagram of the binary system PbCl₂-AgCl were studied by using DTA. The only miscibility was found on the silver chloride side up to a concentration of 1.5±0.5 mole% PbCl₂. No solid solution of AgCl in PbCl₂ was observed on the lead chloride side.

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Zusammenfassung Mittels DTA wurden die Randzonen des Phasendiagrammes des binären Systemes PbCl₂-AgCl untersucht. Mischbarkeit konnte lediglich auf der Silberchloridseite bis zu einer Konzentration von 1.5±0.5 mol% mol% PbCl₂ festgestellt werden. Auf der Bleichloridseite konnten keinerlei Mischkristalle zwischen AgCl und PbCl₂ beobachtet werden.

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PbCl₂-AgCl. 1,5±0,5 %. .

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We are very grateful to our colleagues Dr E. Krová and Dr Z. Pokorná for the preparation of the single-crystals and for the chemical analysis.     

Simplest model of self-oscillations in association reactions

The simplest scheme of association reactions is suggested, whose mathematical model permits the existence of self-oscillations.

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, .

     

The thermal decomposition of ammonium metavanadate,I

The stoichiometry of the various stages involved in the thermal decomposition of ammonium metavanadate has been shown to correspond to a stepwise decrease in the ratio of ammonia and water to V₂O₅, with V₂O₅ being the final product in vacuum, in air and in argon. In ammonia, VO₂ is formed. The actual stages and intermediates are dependent upon the prevailing atmosphere. Chemical analyses, together with infrared absorption spectra and X-ray powder data, have enabled the intermediates and products to be characterized and the structural changes involved in the decomposition to be discussed.

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Zusammenfassung Es wurde gezeigt, daß die verschiedenen Stufen in der thermischen Zersetzung von Ammoniummetavanadat dem stufenweisen stöchiometrischen Verlust von Ammonia und Wasser entsprechen. In Vakuum, Sauerstoff und Argon ist V₂O₅, in Ammoniak VO₂ das Endprodukt. Die Zwischenprodukte der einzelnen Stufen sind von der umgebenden Gasatmosphäre abhängig. Durch chemische, infrarot- und röntgenspektroskopische Analyse gelang es, diese zu charakterisieren und so die durch die Zersetzung hervorgerufenen strukturellen Umlagerungen zu deuten.

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Résumé On montre que les différentes étapes de la décomposition thermique du métavanadate d'ammonium correspondent à la diminution progressive de l'eau et de l'ammoniac par rapport à V₂O₅; cet oxyde constitue le produit final dans le vide, dans l'air et dans l'argon. Dans l'ammoniac, c'est VO₂ qui se forme. Les étapes respectives et les intermédiaires dépendent de l'atmosphère qui prévaut. A l'aide de l'analyse chimique, des spectres d'absorption infrarouge et des données de rayons X sur poudre, on a pu caractériser les intermédiaires et les produits formés, ainsi que les changements structuraux provoqués par la décomposition.

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, V₂O₅. , V₂O₅. . , , .

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We wish to acknowledge helpful comments from Prof. L. Glasser and Dr. N. H. Agnew and financial support from the National Institute for Metallurgy, Johannesburg, South Africa.     

Aromatization of propene on ZSM-5 zeolites

Cu-ZSM-5, CuZn-ZSM-5 and H-ZSM-5 have been studied for propene aromatization at comparable conditions. It was established that all samples are active for aromatization (yields 50%) and demonstrate high selectivity for benzene, toluene and xylenes formation ( 90%). The role of acid centers in all stage of the aromatization is discussed.

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Cu-ZSM-5, CuZn-ZSM-5 H-ZSM-5 . ( 50%) , ( 90%). .