Isomerization and dehydrobromination of 1-bromo-2-methylpropane on alumina modified with alkali halides

The kinetics of the dehydrobromination of 1-bromo-2-methylpropane on alumina modified with NaI and KI have been investigated. A mechanism for the isomerization reactions on alumina modified with alkali halides is proposed in order to explain the catalytic behavior of iodide ion as compared with that of chloride and bromide ions, reported in a previous paper.

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1--2- , NaJ KJ. , , , , .

     

Temperature-Programmed Desorption (TPD) of ammonia from H+-exchanged zeolites with different structures

Curves of the temperature-programmed desorption (TPD) of ammonia from zeolites were evaluated with several kinetic models. An approximately linear correlation was found between the activation energy of desorption or the heat of adsorption of H zeolites with various Si/Al ratios and the intermediate electronegativity of the zeolites, the latter representing a measure of the acid strength.This result corresponds to the change in the high-frequency infrared band of the OH groups and also to the change in the heat of adsorption, determined by microcalorimetry. Thus, the TPD of NH₃ is a useful technique for quantitative characterization of the acidic properties of several H zeolites.

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Zusammenfassung Kurven der temperaturprogrammierten Desorption (TPD) des Ammoniak von Zeolith wurden mit verschiedenen Kinetischen Modellen ausgewertet. Ein annähernd linearer Zusammenhang wurde gefunden zwischen der Aktivierungsenergie der Desorption bzw. der Adsorptionswärme von NH₃ an H-Zeolithen mit unterschiedlichem Si/Al-Verhältnis und der intermediären Elektronegativität der Zeolithe, die ein mass für die Säurestärke darstellt. Dieses Ergebnis entspricht der Verschiebung der hochfrequenten IR-Bande der OH-Gruppen und der mikrokalorimetrisch bestimmten Änderungen der Adsorptionswärme. Damit erweist sich die TPD von NH₃ als brauchbare Methode zur quantitativen Charakterisierung der sauren Eigenschaften von H-Zeolithen.

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- . - Si/Al , . , , . , - -.

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The authors wish to thank Prof. K.-H. Steinberg and Dr. M. Hunger for the zeolite samples, and R. Bauermeister for the non-linear regression programme.     

Influence of the thermal treatment of platinum alumina catalysts with exhaust gases on their activity in cyclopropane hydrogenation

The activity of platinum/alumina catalysts in cyclopropane hydrogenation has been investigated. Catalysts heated in exhaust gases are considerably less active in cyclopropane hydrogenation as compared to samples calcined in air. A relatively stable modification of the metallic surface is formed, probably as a result of coke or poison deposition.

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- . , , , , , . , , .

     

Preparation of mixed-ligand complexes of nickel via thermal decomposition

If heated to around 270° in argon, [Ni(HSal)₂] (H₂Sal=salicylic acid) gives off gaseous H₂Sal and forms [NiSal], which reacts with monoprotic ligands HL (e.g. 8-hydroxyquinoline) to form mixed-ligand complexes [NiHSalL], or with diprotic ligands H₂L' (e.g. quadratic acid) to form dinuclear complexes [HSalNiL'NiHSal].

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Zusammenfassung Die Komplexverbindung [Ni(HSal)₂] spaltet beim Erhitzen auf 270 °C in Argon Salicylsäure ab und liefert [NiSal], das mit Monoproton-Liganden HL (z. B. 8-Hydroxychinolin) zu Gemischtliganden-Komplexen [NiHSalL], mit Zweiprotonen-Liganden H₂L' (z. B. Quadratsäure) dagegen Zweikernkomplexe [HSalNiL'NiHSal] bildet.

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[Ni(HSal)₂] 270°, [NiSal], HL (., 8-) [NiHSalL] H₂L [HSalNiLNiHSal].

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The preparative and thermoanalytical part of this work was performed by C. Gribi, D. Noukakis and M. Piccand, who also drew the Figures.

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This research was supported by the Swiss National Science Fundation, grant No. 2.053-0.99.     

Contributions a l'etude cinetique des decompositions endothermiques dans des systemes solide-gaz,a l'aide des donnees thermogravimetriques

Résumé On a déterminé les paramètres cinétiques des réactions de décomposition de quelques combinaisons complexes des halogénures et pseudohalogénures de cobalt, nickel, manganèse, cuivre et cadmium, avec l'ammoniaque, la pyridine et des pyridines substituées. Pour les réactions d'ordre zéro, les valeurs des facteurs préexponentiels, calculées en considérant comme étape limitante la diffusion du composant volatil à travers la couche de la substance décomposée, concordent de façon satisfaisante avec celles déterminées expérimentalement.

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Kinetic parameters were determined for the decomposition reactions of some com plexes of cobalt, nickel, manganese, copper and cadmium halides and pseudohalides with ammonia, pyridine and substituted pyridines. For the zero order reactions, the values of the pre-exponential factors calculated assuming as limiting step the diffusion of the volatile component through the layer of the decomposed substance, are in satisfactory agreement with the experimental values.

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Zusammenfassung Es wurden die kinetischen Parameter der Zersetzungsreaktionen einiger Komplexe der Halogenide und Pseudohalogenide von Kobalt, Nickel, Mangan, Kupfer und Kadmium mit Ammoniak, Pyridin und substituiertem Pyridin bestimmt. Bei den Reaktionen von Null-Ordnung zeigten die preexponentiellen Koeffizienten, berechnet, indem für die limitierende Stufe die Diffusion des flüchtigen Bestandteils durch die Schicht der zersetzten Substanz betrachtet wurde, gute Übereinstimmung mit den experimentellen Werten.

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, , , , , . . , . .

     

Role of palladium additives in CO oxidation over a complex vanadium catalyst

At small concentrations of CO, palladium initiates a radical-chain process. At high CO concentrations CO oxidation occurs only on the surface of the heterogeneous catalyst and the effect of palladium is mainly due to the specific activation of carbon monoxide on the palladium surface.

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CO . CO .

     

Study of the interaction of atomic oxygen and nitrogen with ruthenium by the bond interaction method

The heats of atomically adsorbed oxygen and nitrogen on Ru(0001) and Ru(1010) planes have been calculated by the semiempirical bond interaction method. The calculations show that oxygen is strongly adsorbed on ruthenium, while molecular nitrogen cannot be chemisorbed on ruthenium.

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- (000I) (I0I0) . , Ru , .

     

Pt(alizarine)2 complex adsorbed on titanium dioxide as a sensitizer in photocatalytic evolution of dihydrogen

Pt(alizarine)₂ complex adsorbed on the surface of titanium dioxide has been found to cause spectral sensitization of the photocatalytic activity of TiO₂. Adsorption of the complex provides simultaneously sensitization of the photoprocess and catalysis of dark steps of dihydrogen formation.

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, Pt()₂ TiO₂. , , .

     

ESR investigation of vanadium-molybdenum oxide catalysts

Upon calcination of vanadium-molybdenum catalysts in air at 500°C two ESR signals are observed. They are attributed to a solid solution of MoO₃ in V₂O₅ (a) and to the incorporation of VO²⁺ into the compound V₂MoO₈ (b).

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500°C - - , MoO₃ V₂O₅, - VO⁺² V₂ MoO₅.

     

Unimolecular decomposition of CF3OF-calculation by reduced Kassel integral in factorized form

The fall-off curves were calculated for the unimolecular decomposition of the trifluoromethyl hypofluorite at 475.8, 496.9 and 507.3 K by means of the Reduced Kassel Integral in Factorized Form.

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475,8,496,9 507,3 .

     

Effect of oxygen on reduction of NO with carbon monoxide over NiO and Cr2O3

Cr₂O₃ is found to be a less active catalyst than NiO in reduction of nitrogen oxides. Introduction of molecular oxygen into the NO–CO mixture decreases the conversion of NO_x on both catalysts. On NiO it is due to competition between O₂ and nitrogen oxides for CO. On Cr₂O₃ it is caused by the complete suppression of this reaction.

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Cr₂O₃ , NiO. NO CO NO_x ; NiO CO , Cr₂O₃- .

     

Studies of decomposition kinetics for ozone complexes with cumene and chlorobenzene

Kinetic regularities in decomposition of complexes of aromatic compounds with O₃ have been studied for ozone complexes with cumene and chlorobenzene. Oxidation effect of these complexes on both aromatic compounds and olefins has been established.

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O₃. .

     

Catalytic oxidation of cycloalkane heteroanalogs as a way to polyfunctional compounds

Liquid phase oxidation of cycloalkane diheteroanalogs catalyzed by compounds of Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺ has been studied. It has been established that these catalysts can be applied to intensify, oxidize and increase the selectivity of this process.

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: Cu², Ni²⁺, Co²⁺, Cr³⁺, Fe³⁺. .

     

Kinetics of n-propylaminolysis of some oxime ethers in 1:1 aqueous acetonitrile

Kinetic studies on the cleavage of the C–O bond of O-(2,4-dinitrophenyl)-substituted cyclohexanone, acetophenone, benzophenone and 4-bromobenzophenone oxime by n-propylamine in 11 aqueous acetonitrile has been reported. Base catalysis being absent, these second order nucleophilic substitution reactions are specific acid catalyzed. The catalytic rate coefficients are calculated and a probable mechanism proposed.

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C–O O-(2,4-)- , , 4- - - (11). . .

     

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 .

     

Investigation of surface phenomena on solid catalysts by thermogravimetry

Thermogravimetry was applied to the investigation of the phenomena of adsorption, chemisorption, desorption and surface reactions on solid catalysts. The measurements were carried out with 13 NaX and NaY type zeolites and with silica gels treated with sodium hydroxide, in the presence of cumene and methanol. On the basis of the quantitative results it is possible to give an interpretation of surface phenomena and to establish the existence of various active centres on the surface of the catalysts.

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Zusammenfassung Adsorptions-, Chemisorptions- und Desorptionserscheinungen, sowie Oberflächenreaktionen an festen Katalysatoren wurden thermogravimetrisch untersucht. Die Messungen wurden an Zeoliten der Typen 13 NaX und NaY und an mit Natriumhydroxid behandelten Silikagelen in Gegenwart von Cumol und Methanol durchgeführt. Aufgrund der quantitativen Ergebnisse war es möglich, die Oberflächenerscheinungen zu deuten und das Vorhandensein von verschiedenen aktiven Zentren an der Katalysatoroberfläche nachzuweisen.

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Résumé On a appliqué la méthode thermogravimétrique à l'étude des phénomènes d'adsorption, de chemisorption et de désorption ainsi qu'aux réactions de surface sur des catalyseurs solides. Les mesures ont été effectuées sur zéolites de type 13 NaX et NaY et sur des silicagels traités par la soude en présence de cumène et de méthanol. Des résultats quantitatifs permettent de donner une interprétation des phénomènes de surface et d'établir l'existence de divers centres actifs à la surface des catalyseurs.

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, , , . , , , , . 13 NaX NaY , . .

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The authors express their gratitude to Prof. S. Malinowski for help and discussion and to Mr. W. Dziklinski for his technical help.     

Marcelin-de Donder kinetics near equilibrium

A linear approximation for the Marcelin-de Donder kinetics (MC) near the point of detailed equilibrium (p.d.e./is studied. In particular it is shown that in the invariant plane the p.d.e. is stable knot.

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- (MD) (...). , , ... — .

     

Efficiency of sensitization of titanium dioxide by adsorbed acridine yellow in photocatalytic hydrogen evolution

Quantum efficiency of the photocatalytic hydrogen evolution upon illumination in the self-and dyesensitized absorption bands of suspended titanium dioxide has been determined. The photocatalytic activity observed upon illumination in the sensitization band is shown to be due to absorption of light quanta by adsorbed molecules of the dye.

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. , .

     

Catalytic properties of palladium oxide systems in the hydrogenation of crotonaldehyde

Catalytic properties of Pd black-oxide systems have been studied in hydrogenation of crotonaldehyde. It has been revealed that the additions of basic and amphoteric oxides (MgO, Fe₂O₃ and ZnO) increase the hydrogenation rate of the ethylenic bond in crotonaldehyde.

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Pd-- . , (MgO, Fe₂O₃, ZnO) .

     

Chiral recognition of enantiomeric peptides in water at 25° by calorimetry

The heats of dilution in water of binary and ternary solutions of the two enantiomeric forms ofN-acetylalanineamide have been measured at 25°. The excess enthalpies, expressed as virial expansion series, permit evaluation of the pairwise self and cross enthalpic coefficients. As for the chiral forms of some monosaccharides, the cross coefficient for the interaction between theD andL forms ofN-acetylalanineamide is slightly but significantly different from the corresponding self coefficient. A weak, water-mediated chiral recognition can be assumed to exist between pairs of amide molecules.

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Zusammenfassung Die Verdünnungswärmen von binären und ternären wässrigen Lösungen der zwei enantiomeren Formen von N-Acetylalaninamid wurden bei 25 °C gemessen. Die in einer Virialexpansionsreihe entwickelten Überschußenthalpien ermöglichen die Berechnung der self und cross Enthalpiekoeffizientenpaare. Was die optisch aktiven Formen einiger Monosaccharide anbetrifft, so ist der cross Koeffizient für die Wechselwirkung zwischen der D- und L-Form von N-Acetylalaninamid etwas, aber signifikant verschieden von dem entsprechenden self Koeffizienten. Es kann angenommen werden, daß Paare von Amidmolekülen eine schwache, durch Wasser vermittelte Unterscheidungsfähigkeit hinsichtlich der optischen Aktivität zeigen.

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25° - N-. . L- N- , , , . .

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This work was carried out with the financial support from the italian C. N. R. (Rome) and from the Ministry of Public Education.