Kinetic studies of Pt/Al2O3 catalyst pellets with nonuniform activity

Catalysts with nonuniform distribution of the catalytically active component (Pt) over their porous support (Al₂O₃) have been studied. A nonuniform activity distribution changes not only the reaction rate but also the kinetics can be different on these catalysts.

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(Pt) (Al₂O₃). , , .

     

Hreels studies of Hads effect on NO adsorption on Pt(111)

HREELS studies of NO molecular adsorption on clean and hydrogen covered Pt(111) have revealed that a reversible transition between bridge (₁) and on-top (₂) states of NO_ads is realized in the (NO+H₂)/Pt(111) system. In the presence of H_ads the adsorption of NO in the ₁ state is inhibited and the main state of NO_ads is ₂. Upon heating the layer (₂-NO_ads+H_ads) hydrogen desorption is accompanied by on-top to bridge state conversion.

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NO Pt(III). , (NO+H₂)/Pt(III) (₁) (₂) NO. H NO ₁ , , ₂ NO. (₂-NO+H) NO .

     

Electrochemical model of monooxygenase

The monooxygenation of aniline by hemin, with oxygen activation by direct electron transfer from a cathode to the catalytically active center and direct participation of the reduced oxygen species in the reaction has been carried out.

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.

     

The application of thermoanalytical methods in the investigation of biological substances

The equilibria and thermodynamics of a number of naturally occuring isolated compounds (e.g. proteins, amino acids, carbohydrates) have recently been studied in several laboraties in different temperature ranges, and thermoanalytical methods have been used to study structural changes of biological materials, among them human tissues.In our investigations we succeeded in appling the derivatograph for the assay of glycosaminoglycans and for the characterization of the stability of crosslinked proteins in intact human and animal tissues. By means of this method age-related and pathological changes and repair reactions were studied in various connective and vascular tissues.Other temperature-dependent techniques (DSC, polarizing microscopy) were used successfully in another series of experiments. Alterations in the characteristic order-disorder transition temperatures of human serum lipoproteins could be demonstrated in pathological conditions; the altered physical structure of lipoproteins might give an additional explanation to the assumed mechanism of different metabolic disorders.

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Zusammenfassung Die Gleichgewichte und die Thermodynamik einer Reihe von natürlich vorkommenden isolierten Verbindungen (z. B. Proteine, Aminosäuren, Kohlenhydrate) wurden in verschiedenen Laboratorien in verschiedenen Temperaturbereichen untersucht. Hierbei wurden thermoanalytische Methoden zum Studium der Strukturänderungen von biologischem Material, u. a. von menschlichem Gewebe, eingesetzt.In unseren Untersuchungen gelang es den Derivatographen zur Prüfung von Glycosaminoglycanen und zur Charakterisierung der Stabilität quervernetzter Proteine in intakten menschlichen und tierischen Geweben einzusetzen. Durch diese Methode wurden altersbedingte und pathologische Änderungen sowie Reaktionen zur Wiederherstellung in verschiedenen Binde und Vasculärgeweben studiert.Andere temperaturabhängige Techniken (DSC, Polarisationsmikroskopie) wurden in anderen Versuchsserien mit Erfolg eingesetzt.

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, . , , , , . . , . .

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Plenary lecture     

Localization phenomena of topochemical reactions

Typical localization forms of topochemical reactions taking place on the surface and inside a crystal have been compared. A kinetic model of triclinic crystal decomposition, which in contrast to known models takes into account that crystal faces react non-simultaneously, has been studied. It has been shown that depending on the value of the induction period that precedes entry of the crystal face into the reaction, and on the ratio of the linear velocities of interface advance in different directions, the decomposition may proceed without self-acceleration, or with one-fold or multi-fold self-acceleration.

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Zusammenfassung Typische Lokalisationsformen topochemischer, auf der OberflÄche und im Kristallinneren verlaufender Reaktionen werden zusammenfassend dargestellt. Das kinetische Modell der Zersetzung von triklinen Kristallen, das im Gegensatz zu bekannten Modellen die nicht gleichzeitig verlaufenden Reaktionen der einzelnen KristallflÄchen berücksichtigt, wird untersucht. Es wird gezeigt, da\ abhÄngig von der LÄnge der dem Start der Reaktion an den einzelnen KristallflÄchen vorausgehenden Induktionsperiode und von der linearen Geschwindigkeit des Fortschreitens der GrenzflÄche in verschiedene Richtungen die Zersetzung ohne oder mit einfacher oder vielfacher Selbsbeschleunigung verlaufen kann.

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, . , . , , , , .

     

Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

Novel evidence for the selective behaviour of tungsten carbide in liquid phase heterogeneous catalytic hydrogenation

Liquid (aqueous) phase catalytic hydrogenation of compounds containing two oxo-groups in -position (biacetyl, glyoxal, alloxan) was studied in the presence of tungsten carbide catalyst. It has been shown that only one of the oxo-groups is affected in the course of the process and is transformed into a >CH–OH group. Comparative studies carried out in the presence of platinum catalyst attest the selective behaviour of tungsten carbide.

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- - (, , ). , >C=O >CH–OH, . .

     

Thermal properties of thio-and selenocyanatocopper(II) complexes with bipyridine and phenanthroline

The paper deals with the thermal properties of complex compounds of the general formula CuL₂(NCX)₂ (whereL=bipy or phen,X=S or Se). The phenanthroline complexes exhibit a higher thermal stability than those with bipyridine. For the latter complexes thermal decomposition begins with the release of bipyridine molecules, while for the phenanthroline complexes redox reactions of pseudohalogenide ligands with Cu(II) take place. The redox reactions start at a lower temperature for the selenocyanate complexes than for the thiocyanate complexes.

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Zusammenfassung Vorliegende Arbeit behandelt die thermischen Eigenschaften von Komplexverbindungen der allgemeinen Formel CuL₂(NCX)₂ (mitL=Bipyridin oder Phenanthrolin undX=S oder Se). Die Phenanthrolinkomplexe zeigen eine grössere thermische Stabilität als die Bipyridinkomplexe. Die thermiscne Zersetzung letzterer beginnt mit der Abgabe von Bipyridinmolekülen, während bei den Phenanthrolinkomplexen Redoxreaktionen von Pseudohalogenidliganden·mit Cu(II) stattfinden. Diese Redoxreaktionen beginnen bei den Selenozyanatkomplexen bei niedrigeren Temperaturen als bei den Thiozyanatkomplexen.

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CuL₂(NCX)₂, L= , X= . . , — . - , .

     

Ab initio investigation of the electron structure in bis-Cu+ acetylene and vinylidene complexes

[Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺ and [Cu(-C₂H₂) (-CCH₂]⁺ complexes have been studied by the ab initio double-zeta basis set method. It has been established that all calculated compounds are stable to decomposition into two C₂H₂ molecules and Cu⁺ cation and into one C₂H₂ molecules and the respective monocomplex. Calculation results suggest the possibility of intramolecular acetylene-vinylidene rearrangement in the coordination sphere of Cu⁺.

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ab initio : [Cu(-C₂H₂)₂]⁺, [Cu(-CCH₂)₂]⁺, [Cu(-C₂H₂) (-CCH₂)]⁺. C₂H₂ Cu⁺ C₂H₂ . - Cu⁺.

     

Silylation of porous glass supported platinum catalysts

Effect of silylation with hexamethyldisilazane on adsorption and catalytic properties of porous glass-supported platinum catalysts has been studied. Catalytic activity decreases markedly with an increase in surface coverage by trimethylsilyl groups for all the following reactions examined: hydrogenation of benzene, dehydrogenation of cyclohexane and dehydrocyclization of n-hexane.

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Analysis of lattice thermal conductivity of GaAs at high temperatures

The lattice thermal conductivity of GaAs has been analysed in the entire temperature range 100–800 K in the frame of the Sharma-Dubey-Verma (SDV) model of phonon conductivity, and very good agreement has been found between the calculated and experimental values of the lattice thermal conductivity in the entire temperature range of study. The temperature exponentm(T) for the three-phonon scattering relaxation rate for GaAs has also been calculated in the above temperature range. The separate percentage contributions due to transverse and longitudinal phonons have also been studied.

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Zusammenfassung Die Gitter-Warmeleitfähigkeit von GaAs wurde im Temperaturbereich zwischen 100 und 800 K im Rahmen des Modells der Phononen-Leitfähigkeit von Sharma-Dubey-Verma (SDV) untersucht und eine sehr gute übereinstimmung zwischen den berechneten und Versuchswerten der Gitter-Wärmeleitfähigkeit im ganzen untersuchten Temperaturbereich gefunden. Der Temperaturexponentm=m(T) für die Drei-Phonenen-Streuungs-Relaxationsgeschwindigkeit bei GaAs wurde im obengenannten Temperaturbereich ebenfalls berechnet. Die durch transversale und longitudinale Phonone verursachten einzelnen prozentualen Beiträge wurden ebenfalls untersucht.

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Résumé La conductibilité thermique du réseau de GaAs a été analysée dans tout l'intervalle de température allant de 100 à 800 K, dans le cadre du modÊle de conductibilité de phonons de Sharma-Dubey-Verma (SDV). Une trÊs bonne concordance a été observée entre les valeurs calculées et expérimentales de la conductibilité thermique du réseau dans l'intervalle de température étudié. L'exposant de températurem(T) a également été calculé dans ce domaine de température pour la vitesse de relaxation de la diffusion de trois phonons. Les pourcentages individuels des contributions des phonons transversaux et longitudinaux ont également été étudiés.

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100–800 CaAs -- . . m() CaAs. , .

     

Investigation of the self-heating phenomenon in the bulk polymerization of acrylonitrile

The temperature of the polymerizing system was measured with a thermistor during the bulk polymerization of acrylonitrile initiated by azoisobutyronitrile. The temperature of self-heating suddenly rises at a conversion of about 2%. This jump of temperature is presumably caused by the formation of a gel structure and, consequently, the outfall of thermal convection within the system.

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, -- . , - . - , .

     

Oxidative dehydrogenation of ethylbenzene over a charcoal catalyst

The oxidative dehydrogenation of ethylbenzene over a charcoal catalyst has been studied by the pulse technique. The styrene yields for the oxidation of ethylbenzene by gaseous oxygen and upon the interaction of ethylbenzene with oxygen adsorbed on charcoal are shown to be the same.

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. , , , .

     

Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

Estimation of nonlinear relaxation of catalytic reactions

Nonlinear relaxation time has been considered as a differential characteristic determined by the reciprocal value of the relative decrease in the deviation rate of the current concentration vector of intermediates from that of their steady-state concentrations. This characteristic is used for the analysis of some model reactions.

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, , .

     

Structural studies of nickel-based Raney catalysts

Electron microscopy and Mössbauer spectroscopy studies of nickel-based Raney catalysts have revealed that the catalysts are formed through the successive aggregation of their structural elements. Catalyst particles are covered by a thin layer of nickel oxide.

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Differential thermal analysis of poly(vinylidene chloride) crystals

The melting behavior of poly(vinylidene chloride) (PVDC) was studied using differential thermal analysis (DTA). Crystals were grown isothermally from 0.1% and 0.02% dilute solutions of the polymer in 1.2-dibromoethane and monobromobenzene. Both solid and oil samples were used for the DTA experiments. Solid samples are defined as dried down crystals and oil samples are crystals which have been suspension exchanged in silicone oil without letting them dry out. Thermal curves of solid samples are similar to those obtained previously with as-polymerized crystals, that is they show two endotherms. The lower temperature peak corresponds to the melting of lamellae as formed. The upper peak at around 200°C, may be due to the melting of crystals which have reorganized during heating. Thermal curves of oil samples show two extra small peaks in addition to those of the solid samples. From the results of annealing and degradation experiments, these two peaks may correspond to a small portion of the crystals which have been partially degraded to form double bonds and thus possess lower melting points. An alternative explanation is that there is an as yet unreported second crystal form of PVDC.

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Zusammenfassung Das Schmelzverhalten von Poly/vinylidenchlorid (PVDC) wurde unter Einsatz der Differentialthermoanalyse (DTA) untersucht. Die Kristalle wurden unter isothermen Bedingungen aus 0.1 % und 0.02% verdünnten Lösungen des Polymeren in 1.2-Dibromäthan und Monobrombenzol gezüchtet. Sowohl »feste« als auch »ölige« Proben wurden für die DTA-Versuche eingesetzt. Als »feste« Proben wurden getrocknete Kristalle definiert und »ölige« als solche, bei welchen die Suspension im Siliconöl verblieb, ohne sie austrocknen zu lassen. Die thermische Kurven der »festen« Proben sind den bereits früher mit polymerisierten Kristallen erhaltenen ähnlich, d. h. sie zeigen zwei Endotherme. Der Peak bei der niedrigeren Temperatur entspricht den Schmelzen der gebildeten Lamellen. Der obere Peak bei etwa 200° kann dem Schmelzen von während der Aufheizung reorganisierten Kristallen zugeschrieben werden. Die thermische Kurven der »öligen« Proben zeigen zwei zusätzliche kleine Peaks außer denen an »festen« Proben. Aus den Ergebnissen der Temper- und Zersetzungsversuche dürften diese beiden Peaks einen kleinen Anteil der teilweise unter Bildung von Doppelbindungen zersetzten Kristalle entsprechen, welche auf diese Weise niedrigere Schemlzpunkte haben. Eine alternative Erklärung ist, daß es eine bisher nicht beschriebene zweite Kristallform von PVDC gibt.

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() . ( 0.1% 0.02%) 1.2- . «» « » . « » , — , , . - «» . . 200° , . « » , , . , , , . . , .

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The authors wish to thank the NSF Materials Division for support of this work under grants DMR 72-03292 A01 and A02.     

Parent and mixed ligand complexes in the copper(II)-ethylene glycol-sulphate system

Eleven copper(II)-ethylene glycol-sulphate complexes of different compositions were prepared, one of them-CuGl₂(H₂O)₂SO₄-in single-crystal form. A thermoanalytical study of these complexes revealed three types of thermal decomposition pattern. The X-ray structure of the single-crystal demonstrated the presence of ethylene glycol bridges resulting in endless chains in the crystal.

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Zusammenfassung Elf Kupfer(II)-äthylenglykol-sulfat-Komplexe unterschiedlicher Zusammensetzung wurden dargestellt, einer davon — CuGl₂(H₂O)₂SO₄ — in Form von Einkristallen. Die thermoanalytische Untersuchung dieser Komplexe ergab drei Typen der thermischen Zersetzung. Die röntgendiffraktometrische Bestimmung der Struktur des in Form von Einkristallen erhaltenen Komplexes zeigte, daß den Kristall endlose Ketten von Äthylenglykolbrücken durchziehen.

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() — , — CuGl₂(H₂O)₂SO₄ — . . , , .