Oxygen chemisorption and activity studies on unpromoted and promoted TiO2 supported tungsten sulfide catalysts

Low temperature oxygen chemisorption (LTOC) has been applied to characterize unpromoted and promoted tungsten sulfied catalysts supported on TiO₂. LTOC, hydrodesulfurization and hydrogenation are found to correlate with the W loading.

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() - TiO₂ . , - W .

     

Selectivity of platinum-copper alloys in reactions of butanol

A short study on the title reaction confirms that at low hydrogen pressures no ether formation occurs, while when a higher hydrogen pressure suppresses the fast dehydrogenation, ethers are formed. A comparison of Pt and Pt alloys shows that ether formation is faster on large ensembles of Pt atoms, requirements of decarbonylation are less in this respect. Results of earlier studies on Ni/Cu alloys have thus been confirmed.

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, , , . Pt , , .. . , Ni/Cu.

     

A new method for preparation of Mo/Al2O3 catalysts for olefin metathesis

A new method of preparation of highly active catalysts for metathesis of -olefins through the anchoring of [Mo₂O₄(C₂O₄)₂(H₂O)₂]^2– anion to the surface of -Al₂O₃ with further thermal activation in H₂ and CO is proposed.

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- [Mo₂O₄(C₂O₄)₂(H₂O₂]^2– -Al₂O₃ H₂ CO.

     

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⁺. . , , , .

     

Thermoanalytical studies of combustion of cellulosics and activity of fire retardants

TG, DTG and simultaneous DTA were used to monitor the thermal decomposition processes of cellulose in nitrogen or in an oxidative atmosphere. Volatile products and solid residues formed during decomposition were analyzed to obtain additional information for elucidation of the thermal curves. An indication of possible flaming or smoldering combustion is discussed. The maximum weight-loss rate, the percentage amount of the residue at the final temperature, and the exothermic peak areas (DTA) could be considered as suitable criteria for the flammability of cellulosics and the activity of flame retardants. The formal kinetic parameters evaluated from the thermogravimetric measurements correspond to the limiting oxigen index (LOI) values. New observations were made using a combination of thermal analysis and LOI techniques. LOI — smoldering or LOI — flaming are mathematically determined from the plot of weight-loss rate versus oxygen concentration.

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Zusammenfassung TG, DTG und simultane DTA wurden zur Verfolgung der thermischen Zersetzungsprozesse von Zellulose in Stickstoff oder in einer oxidativen Atmosphäre eingesetzt. Während der Zersetzung entstandene flüchtige Produkte und feste Rückstände wurden analysiert um weitere Informationen zur Klärung der Kurven zu erhalten. Ein Hinweis auf mögliche flammende oder glühende Verbrennungen wird diskutiert. Die maximale Geschwindigkeit des Gewichtsverlusts, die prozentuale Menge des Rückstandes bei der End-temperatur und die exothermen Peakflächen (DTA) könnten als geeignete Kriterien für die Entflammbarkeit der Zellulosen und die Aktivität der feuerhemmenden Substanzen betrachtet werden. Die aus den thermogravimetrischen Messungen errechneten formalen kinetischen Parameter entsprechen den LOI (limiting oxygen index) Werten. Neue Beobachtungen wurden unter Einsatz einer Kombination der Thermoanalyse und der LOI-Techniken gemacht. LOI-Glut oder LOI-Entflammen werden mathematisch aus dem Zusammenhang zwischen der Geschwindigkeit des Gewichtsverlusts und der Sauerstoffkonzentration bestimmt.

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, . , , . . , , , (), - . , . . — — .

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We wish to express our thanks to Mrs. V. Michliková for her skilful assistance.     

Catalytic properties of Ni/WS2 samples in thiophene hydrogenolysis

The interaction of diallylnickel with WS₂ produces catalysts whose activity is 10–50 times higher than that of the parent sulfide. The atomic catalytic activity referred to supported nickel is independent of the catalyst type and the sulfur removed in temperature programmed reduction.

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, WS₂ , 10–50 . , , .

     

Apport de l'analyse thermique differentielle quantitative a l'etude du polymorphisme du nitrate de potassium a la pression atmospherique

Résumé Application de l'ATD quantitative à l'étude des transformations structurales du nitrate de potassium. Les échantillons (1 à 8 mg) sont chauffés et refroidis dans l'azote sec, à la pression atmosphérique. Au refroidissement, on observe toujours les transitions successives I III II. Le pic exothermique correspondant à I III apparaît dans un intervalle de température très reproductible (118 – 120°). Les mesures de surface confirment la parfaite réversibilité de I III déjà signalée par C. Mazières. Les transitions III I et II I ont lieu pratiquement à la même température (127–130°) mais l'aire du pic endothermique correspondant à III I est plus faible et représente 51.5 % de la valeur observée pour II I. En prenantH=13.2 cal/g comme valeur de référence pour la transition II I, on trouveH=6.8± 0.2 cal/g pour III I. La transformation III II suit un processus en deux étapes, fortement influencé par le traitement thermique antérieur de la phase I.

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The changes in the structure of potassium nitrate have been studied by differential thermal analysis. The samples were heated and cooled in a stream of dry nitrogen, at atmospheric pressure. On cooling, the following transformations have been observed: I III II. The exothermic peak corresponding to the I III transformation appeared at 118–120° with good reproducibility. Surface area measurements show the complete reversibility already observed by Mazières for the I III transformation. The III I and the II I processes take place at the same temperature (127–130°), but the peak corresponding to the III I change is of lower intensity, representing only 51.5% of that of the peak belonging to the II I transition. If the enthalpy change belonging to process II I,H=13.2 cal/g, that belonging to transition III I,H=6.8±0.2 cal/g. Transformation III II proceeds in two steps and is greatly influenced by the preceding heat treatment of phase I.

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Zusammenfassung Quantitative Differentialthermoanalyse wurde zur Untersuchung der strukturellen Umwandlungen von Kaliumnitrat herangezogen. Die Proben (1–8 mg) wurden in trockenem Stickstoff bei atmosphärischem Druck erhitzt und abgekühlt. Beim Abkühlen lassen sich immer die sukzessiven Umwandlungen I III II beobachten. Die dem Übergang I III entsprechende exothermische Spitze erscheint sehr reproduzierbar bei 118–120°. Die Oberflächenmessungen bezeugen die vollständige Reversibilität von I III, schon früher angegeben von Mazières. Die Übergänge III I und II I erfolgen praktisch bei gleicher Temperatur (127–130°), doch die endothermische Spitze von III I ist schwächer und entspricht nur 51.5% des für II I beobachteten Wertes.H=13.2 cal/g als Referenzwert für Übergang II I genommen, ergibt sichH=6.8±0.2 cal/g für III I. III II Übergang verläuft in zwei Schritten, die durch das thermische Vorleben der Phase I stark beeinflußt sind.

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. . I III II. , I III, 118–120°. , I III. III I II I (127–130°), , III I 51,5% III. II I H=13,2 /. III I 6,8 ± 0,2 /. III II I.

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Mémoire présenté en l'honneur du 70^e anniversaire du Professeur Clément Duval.     

A desk computer program for the calculation of rate constants

A desk computer program has been written in BASIC programming language to optimize the values of rate constants determined from kinetic measurements of time and concentration data. The program is capable of the simultaneous refinement of a maximum of 5 rate constants. A FORTRAN version using the Gear method is also available.

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, BASIC , . 5 . FORTRAN .

     

High temperature thermal decomposition of propane

The thermal decomposition of propane has been studied by pulse chromatographic method within the temperature range of 975–1083 K. The kinetic parameters of the reaction have been determined.

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- 975–1083 . .

     

On theC v toC p conversion for solid linear macromolecules

TheC _v toC _p conversion for solid linear macromolecules via the Nernst-Lindemann equationC _p -C _v =A ₀,C _p ² T/T_m is discussed on hand of data for 10 crystals and seven glasses. An average value ofA ₀=(5.11±2.41) · 10^–3 mol K J^–1 was calculated if the mole is assumed to refer to heavy atoms only. ThisA ₀ is numerically equal to the original Nernst—Lindemann constant.

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Zusammenfassung An Hand von sich auf 10 Kristalle und 7 Gläser beziehenden Daten wird die Umrechnung vonC _v -inC _p -Werte für feste lineare Makromoleküle mittels der Nernst-Lindemann-GleichungC _p -C _v =A ₀ C _p ² T/T _m diskutiert. Ein Durchschnittswert vonA ₀=(5.11±2.41) · 10^–3 mol K J^–1 wurde unter der Annahme berechnet, daß sich das Mol nur auf schwere Atome bezieht. DieserA ₀-Wert ist numerisch gleich der ursprünglichen Nerns-Lindemann-Konstanten.

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10 , - C _v C _p , —C _p –C _v = _{0 p} ² / . , , ₀ (5.11±2.41) · 10^–3 · ^–1. ₀ — .

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Support by the National Science Foundation, Polymers Program (Grant No. DMR 83-17097) is gratefully acknowledged.     

Thermal stability and phase transformations in a commercial vanadia-molybdena alkali-promoted catalyst

Temperature-programmed decomposition, thermal analysis, thermogravimetry and high-temperature X-ray analysis have been used to investigate a commercial catalyst for the selective oxidation of benzene into maleic anhydride. It was shown that phase transformations took place in the vanadia-molybdena alkali-promoted catalyst. The transformations were caused either by high-temperature treatment or by catalytic work in an industrial plant. As a result, the-bronze phase was formed. In the high-temperature region a reversible transformation of the bronze phase was observed. This was interpreted as the phase transformation.

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Zusammenfassung Temperaturprogrammierte Zersetzung, Thermoanalyse, Thermogravimetrie und Hochtemperatur-Röntgenanalyse wurden zur Untersuchung eines kommerziellen Katalysators für die selektive Oxydation von Benzol zu Maleinsäure herangezogen. Es wird gezeigt, daß in dem einen Alkalipromotor enthaltenden Vanadinoxid-Molybdänoxid-Katalysator Phasenübergänge vor sich gehen. Die Phasenübergänge, als deren Ergebnis eine-Bronzephase gebildet wird, wurden entweder durch Hochtemperaturbehandlung oder durch sich in einer industriellen Anlage während des Betriebes abspielenden Vorgänge verursacht. Im Bereich hoher Temperaturen wurde eine reversible Umwandlung der Bronzephase beobachtet, die als Phasenübergang interpretiert wurde.

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- , , . , - , , . , , -. .

     

Infrared spectroscopic study of the adsoprtion of methacrylates on aerosil

The type and ratio of the attached groups was measured by FT-IR spectroscopy for the adsorption of three methacrylates. The adsorption enthalpies can be determined from a correlation with infrared frequency shifts.

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--. -.

     

Synthesis of high-silicon zeolites in bialkaline systems

Rubidium and cesium zeolites (SiO₂Al₂O₃=4–9.2) of the faujasite, chabazite, erionite, offretite, phillipsite and pollucite type, L-zeolites as well as ZKF-2, ZKF-8 and ZKF-18 of unknown structure have been obtained. Their pore size is 4–10 Å and their thermostability is 1073–1223 K, which permits to use these zeolites as catalyst components.

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, , , , , , L, -2 -8 (SiO₂Al₂O₃=4–9,2). 4–10 Å 1073–1223 K, .

     

A mechanistic study of cycloaddition of carbon dioxide to propyne over supported Rh4 and Fex Rhy carbonyl cluster derived catalysts

CO₂ undergoes cycloaddition to propyne on a cationic rhodium site with the assistance of O^2–/OH^– of support or iron oxide over Rh₄ and Fex Rhy carbonyl clusterderived catalysts.¹³CO₁₂ labeling and FTIR studies suggest that monodentate carbonate formed on the catalyst surface is most likely a key species to offer an active CO₂ to be converted into a carbonyl intermediate prior to the product 4,6-dimethyl-2-pyrone.

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CO₂ O^2–/OH Rh₄ Fex Rhy. ¹³CO₂ , CO₂ , 4,6--2-.

     

Reactivity of benzoic acid esters towards cumylperoxy radicals

The alkoxy groups of aromatic carboxylic acid esters are attacked by cumylperoxy radicals. The rate constants for the abstraction of a hydrogen atom by cumylperoxy radicals are: for methyl benzoate k₂=(4.28±0.8)×10¹⁰ exp (–20.5±1.5/RT) and for ethyl benzoate k₂=(9.41±0.8)×10¹⁰ exp(–18.5±1.5/RT) l/mol sec. The strengths of the primary and the secondary C–H bonds of these compounds have been estimated.

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, . k₂=(4,28±0,8)·10¹⁰ exp (–20,5±1,5/RT) k₂=(9,41±0,8)·10¹⁰ exp (–18,5±1,5/RT) /·. C–H .

     

Propagation of vibrational excitation in an adsorbed layer

Using a crystal model with an adsorbed layer, the propagation of vibrational excitation induced by an adsorbed particle is considered. The relaxation times of excitation have been estimated. The role of excitation transfer processes in adsorption-desorption phenomena is discussed.

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, . . - .

     

Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of (basic) beryllium carbonate

Iron(II) sulphate heptahydrate undergoes decomposition in the presence of basic beryllium carbonate without any interaction with the carbonate. The components of the mixture decompose individually. Iron(II) sulphate decomposes with the formation of tetrahydrate, monohydrate, anhydrous salt, oxysulphate and ferric sulphate as intermediate phases. The basic beryllium carbonate decomposes to the oxide with BeO·BeCO₃ as the intermediate compound.

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Zusammenfassung In Gegenwart von basischem Berylliumcarbonat zersetzt sich Eisen(II)-sulfat-Heptahydrat, ohne mit dem Carbonat in Wechselwirkung zu treten. Die Komponenten des Gemisches zersetzen sich individuell. Die Zersetzung des Eisen(II)-sulfats verläuft über die Zwischenphasen Tetrahydrat, Monohydrat, wasserfreies Salz, Oxysulfat und Eisen(III)-sulfat. Das basische Berylliumcarbonat wird über die intermediäre Verbindung BeO·BeCO₃ in das Oxid überführt.

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, . . , , , . .₃.

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The authors are grateful to Dr. B. R. Sant for his keen interest and useful suggestions throughout this work. They also express their sincere thanks to Prof. P. K. Jena, Director, for his kind permission to publish the results. One of us (MSRS) thanks the Director for a Senior Fellowship.     

Kinetics and mechanism of thermal decomposition of cadmium(II) complexes with substituted thioureas

From the thermal decomposition curves of cadmium(II) complexes with substituted thioureas (methyl-, dimethyl-, ethyl-, diethyl-, butyl-, dibutyl-, phenyl-, diphenyl-, acetyl- and benzoylphenylthiourea), the kinetic parameters of the thermal decompositions of these complexes were determined and a decomposition mechanism was suggested. The following thermal stability sequence is given for the Cd(II) complexes: complexes with alkylthioureas < complexes with phenylthioureas < complexes with acylthioureas.

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Zusammenfassung Die kinetischen Parameter der thermischen Zersetzung von Verbindungen der Formeln Cd(MeTM)₄(ClO₄)₂, Cd(DMeTM)₄(ClO₄)₂, Cd(EtTM)₄(ClO₄)₂, Cd(DEtTM)₄(ClO₄)₂, Cd(BuTM)₄(CtO₄)₂, Cd(DBuTM)₄(ClO₄)₂, Cd(AcTM)₃(ClO₄)₄, Cd(FTM)₄(ClO₄)₂ und Cd(DFTM)₄(ClO₄)₂ wurden mittels TG and DTG untersucht. Die Reaktionsordnung (n) und die Aktivierungsenergie (E _a) wurden nach der graphischen Methode ermittelt.

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(- , - , - , - , - -l- ), . : < < .

     

Conversion of dehydrolinalyl acetate in catalytic hydrogenation on metals

Low selectivity of dehydrolinalyl acetate (DeHLA) hydrogenation into linalyl acetate and ester group detachment are predicted in accordance with quantum-chemical data obtained for its homologue dimethyl ethynyl carbinol acetate. Experimental data are confirmed by theoretical calculations. DeHLA hydrogenation produces a variety of products.

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, - . . .

     

DSC and vapour pressure investigation of some β-diketonates

DSC and vapour pressure measurements are presented on some Be, Al and Cr complexes with 2,4-pentanedione tetramethyl-3,5-heptanedione, 1,1,1-trifluoro-2,4-pentanedione and hexafluoro-2,4-pentanedione. Thermodynamic functions are given for the sublimation, vaporization and melting processes of the substances.

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Zusammenfassung Die Ergebnisse von DSC- und Dampfdruckmessungen einiger Komplexe von Beryllium, Aluminium und Chrom mit 2,4-Pentandion (HAA), Tetramethyl-3,5-heptandion (HTHD), 1,1,1-Trifluoro-2,4-pentandion (HATA) und Hexafluoro-2,4-pentandion (HHFA) werden beschrieben. Die berechneten thermodynamischen Funktionen für Sublimation, Verdampfung und Schmelzen der Komplexverbindungen sind tabelliert.

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, 2,4- , 1,1,1-- -2,4- -3,5- . , .