Observation of a peculiar phenomenon in the cerium-ion-catalyzed Belousov-Zhabotinskii oscillator with acetylacetone in CSTR mode

The cerium-ion-catalyzed Belousov-Zhabotinskii reaction with acetylacetonate as the organic substrate was investigated in flow reactor (CSTR) mode. Most behavior observed could be readily rationalized in terms of the Oregonator model of the Belousov-Zhabotinskii reaction. However, at high acetylacetone concentrations (>0.07 M) and rapid flow rates, the system behaved peculiarly. Large-amplitude oscillations in the response of a Ag/AgBr electrode appeared while the response of a shiny platinum electrode was flat, suggesting the absence of oscillations in redox potential. This phenomenon was reproducible and disappeared when the flowrate was decreased.

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, , - . -. , (>0,07 M) . Ag/AgBr, , -. .

     

Numerical simulation of the BZ reaction of oxalic acid with a simple four-variable model

A simple model of the bromate-cerium-oxalic acid batch oscillatory system has been constructed and examined by calculations. The model predicts a parameter range and a frequency which agree rather well with the observed values, but it does not describe the peculiar saddlenode infinite period bifurcations found experimentally in the system.

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-- . , , - .

     

Influence of cobalt phthalocyanine: Deposited onto the particles of mixed Cd/CuxS suspensions on photocatalytic evolution of hydrogen from aqueous solutions of Na2S

Deposition of water-insoluble cobalt phthalocyanine CoPc onto the particles of mixed suspensions of CdS and Cu_xS can increase the rate of photoinduced evolution of H₂ from Na₂S and Na₂SO₃ solutions. At [Na₂S]=5×10^–2 M, the rate of photocatalytic reaction is almost doubled upon deposition of 6.4×10^–10 mol CoPc onto 4×10^–5 mol of CdS and of 2.9×10^–8 mol of CoPc onto 10^–5 mol of Cu_xS. At [Na₂S]=10^–1 M, which is close to the optimal concentration of Na₂S, the deposition of CoPc can provide only a 30% increase of the reaction rate.

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, CoPc CdS/Cu_xS H₂ Na₂S Na₂SO₃. Na₂S=5·10^–2 M 6.4·10^–10 CoPc 4·10^–5 CdS 2.9·10^–8 CoPc 10^–5 Cu_xS. Na₂S=10^–1 M, CoPc 30% .

     

Catalytic properties of Cu(Acac)2 anchored to shock-compressed MgO and MgF2 supports

Catalytic properties of Cu(Acac)₂ anchored to shock-compressed MgO and MgF₂ in model reactions of hydrogenation and isomerization of heptene-1 have been studied. It is shown that by changing the defect structure of the support via shock treatment at various temperatures, the activity and selectivity of metal complex catalysts can be affected.

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Cu(Acac)₂, MgO MgF₂ -1. , , , .

     

On the mechanism of isocyanate preparation by the phosgenation reaction

A new mechanism of the transformation of amine hydrochlorides into isocyanates during the phosgenation process was proposed on the basis of radioisotope exchange between p,p'-diamino-1,2-diphenylethane dihydrochloride (³⁶Cl) and phosgene. The reaction proceeds through a transition complex of amine hydrochloride and phosgene, formed on the surface of the hydrochloride crystals.

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(³⁶Cl) ,'--1,2- . , .

     

Infrared study of the interaction between adsorbed molecules in the Co/ZnO system

The dependence of spectra on the surface coverage and data on isotope substituted CO molecules permit to reveal the resonance interaction of vibrating dipoles and the effect of induced heterogeneity, i.e. weakening of the electron-accepting properties of Zn²⁺ ions in the occupation of adjacent sites by adsorbed molecules.

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- CO , . . Zn²⁺ .

     

Kinetic analysis of thermogravimetric data. XX. Study of the thermal decomposition of some tetrathiocyanato-diamino-chromate complexes with derivatograph

The thermal decompositions of 8 complexes of the type A · H[Cr(NCS)₄(am)₂] (A=NH₃, pyridine,-picoline or aniline, andam=NH₃ or aniline) and of 14 complexes of the type M[Cr(NCS)₄(am)₂] (M=K, Ag, Tl, 1/2 Cd, 1/2 Pb or 1/3 Bi, andam=NH₃, benzylamine or aniline derivatives) were studied by means of a derivatograph. In the case of the A · H salts the formation of Cr(NCS)₃ was observed as a labile intermediate. Characteristic temperatures are discussed in terms of the polarizing effect of the outer sphere cations and of the nucleophilic character of the ligands. The results are compared with those obtained in the thermal decompositions of the analogous salts of the complex acid H₃[Cr(NCS)₆].

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Zusammenfassung Die thermische Zersetzung von 8 Komplexverbindungen des Typs A ·H[Cr(NCS)₄(am)₂] (A=NH₃, Pyridin, -Picolin, Anilin und am=NH₃ und Anilin) und von 14 Komplexen des Typs M[Cr(NCS)₄(am)₂] (M=K, Ag, Tl, 1/2 Cd, 1/2 Pb, 1/3 Bi und am=NH₃, Anilin und Anilinderivate) wurde mit dem Derivatographen untersucht. Im Falle der A. H Salze wird die Bildung von Cr(NCS)₃ als labiles Zwischenprodukt beobachtet. Die charakteristischen Temperaturen und kinetischen Parameter werden abgeleitet und auf der Basis der molekularen Struktur erörtert. Im Falle der M Salze werden die DTAPeaks aufgrund des Polarisationseffektes der Kationen der äußeren Sphäre und des nukleophilen Charakters der Liganden diskutiert. Die Ergebnisse werden mit jenen der thermischen Zersetzung der analogen Salze des H₃[Cr(NCS)₆] Komplexes verglichen.

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A. H[Cr(NCS)₄ ()₂], — , , - , «» . M[Cr(NCS)₄ ()₂], -, Ag, Tl, 1/2 Cd, 1/2Pb 1/3 Bi, « » — , . . Cr(NCS)₃, . , . , - . H₃[Cr(NCS)₆].

     

Some kinetic problems of inorganic topochemistry

Some problems of the kinetics and mechanisms of reactions of inorganic solids have been considered: the subject of inorganic topochemistry and its interrelation with adjacent disciplines; localization forms and typical forms of kinetic curves of topochemical reactions; the choice of single-meaning characteristics of the stability of solid compounds; and the employment of rational methods of investigation of decomposition kinetics.

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Zusammenfassung Es werden einige Probleme hinsichtlich der Kinetik und des Mechanismus der Reaktionen von Feststoffen betrachtet: Gegenstand der anorganischen Topochemie und dessen Beziehung zu angrenzenden Wissenschaftszweigen; Lokalisations- und typische Formen der kinetischen Kurven topochemischer Reaktionen; Auswahl eindeutiger Charakteristika für die Stabilität feststoffiger Verbindungen und Entwicklung zweckmäßiger Methoden zur Untersuchung der Kinetik von Zersetzungsvorgängen.

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, : , , .

     

Damped concentration oscillations in the oxidation of the reduced forms of heteropolyacids

Concentration oscillations of reduced forms of phosphorus-molybdenum, silicon-molybdenum, and silicon-tungsten heteropolyacids of the 12th row have been induced by the pulse radiolysis of their 5×10^–2M aqueous solutions. Appearance of these oscillations seems to be related to the reaction of reduced forms of heteropolyacids with hydrogen peroxide which is also produced during water radiolysis.

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-, 12- , 5·10^–2M . , -, - , .

     

Kinetics of sulfur dioxide oxidation on a molten catalyst of nonsteady composition

In general coal ashes are less active for the No+H₂ reaction, whereas their activities for the NO+NH₃ reaction are moderately high. Pretreatment using aqueous NaOH solution increased extensively the activity of the fly ash in both the NO+H₂ and NO+NH₃ reaction.

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, NO H₂, NO NH₃ . NaOH .

     

Evidence for a weak metal-support interaction in alumina-supported nickel catalysts

The reduction of Ni/Al₂O₃ at high temperatures does not result in a decrease of the H₂ uptake and catalytic activity towards C₂H₆ hydrogenolysis per metal surface atoms. This is typical of a weak metal-support interaction. Moreover, no Ni–Al alloy formation has been detected by magnetism. This behavior, at variance with that of Ni/SiO₂, confirms that the occurrence of the strong metal-support interaction is probably related to support reduction with alloy formation.

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Ni/Al₂O₃ H₂ C₂H₆, . - . , Ni–SiO₂, , , , .

     

Polymorphic modifications of barium metagermanate

Polymorphic transformations of BaGeO₃ were investigated by DTA and X-ray diffraction methods and the data obtained were compared with those previously published. BaGeO₃ undergoes a reversible phase transformation at 1100° from a low-temperature hexagonal polymorph to a medium-temperature polymorph having an unknown crystal structure, which undergoes a further reversible transformation at 1200° to a high-temperature orthorhombic polymorph found to be stable up to the melting temperature of 1287°. On cooling from the melt, the high-temperature form can be retained metastably at room temperature, but transforms to the low-temperature form at 900°.

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Zusammenfassung Polymorphe Umwandlungen von BaGeO₃ wurden unter Anwendung der DTA- und Röntgendiffraktionsmethoden untersucht und die erhaltenen Angaben mit den früher veröffentlichten verglichen. Bei 1100° vollzieht sich eine reversible Phasentransformation der BaGeO₃ von der hexagonalen Struktur bei niedrigen Temperaturen in eine Verbindung unbekannter Kristallstruktur bei mittleren Temperaturen, welche wiederum bei 1200° eine weitere reversible Umwandlung in eine orthorhombische Struktur erfuhr und sich bis zur Schmelztemperatur von 1287° als stabil erwies. Beim Abkühlen der Schmelze kann die Form bei hohen Temperaturen bei Zimmertemperatur in metastabilem Zustand erhalten bleiben, wird jedoch bei 900° in die Form bei niedrigen Temperaturen umgewandelt.

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Résumé On a étudié les transformations polymorphiques de BaGeO₃ par ATD et diffraction des rayons X et comparé les résultats avec ceux obtenus antérieurement. A 1100° C BaGeO₃ subit une transformation de phase réversible de la forme hexagonale stable à basse température à la forme stable à moyenne température, de structure cristalline inconnue, qui se transforme réversiblement à 1200° C en une phase orthorhombique qui reste stable jusqu'à 1287° C. Au refroidissement, la forme stable à haute température peut être maintenue à l'état métastable à la température ambiante, mais elle se transforme à 900° C en la forme stable à basse température.

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BaGeO₃ . BaGeO₃ 1100° - - 1200° , 1287°. - , - 900°.

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This investigation was supported by the Boris Kidri Foundation for Scientific Research     

Influence of the nonmetallic component in binary chromium compounds on their catalytic activity in carbon monoxide oxidation

Oxidation kinetics of carbon monoxide on chromium carbide, nitride and boride has been studied. The activity of chromium compounds was compared with the electronic state of the chromium atom according to XPS data. A reaction mechanism is proposed and an assumption is made on the predominant effect of the nonmetallic component on the character of change in the catalytic activity of chromium compounds.

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, . . .

     

Thermal and electrical properties of dilute CR-NI base alloys

The ferro-paramagnetic phase transition in dilute Cr-Ni base alloys was investigated through a qualitative study of their thermal conductivity as a function of temperature in the near vicinity of the transition. A single apparatus [I] was used for measurements of the thermal and electrical conductivities and specific heats of three thin rod samples having Cr concentrations of 0.12, 0.51 and 1.13 at%.A voltagevs. temperature (V vs 0) relation was applied [2] to measure the ratio between the thermal and electrical conductivities. The thermal conductivity data were then evaluated by using the electrical resistivity results obtained from the measured currentvs. voltage (I vs. V) characteristic curves. A model describing the effect of Cr concentration on the (I vs. V) curve wasproposed and tested. The effect of Cr concentration on specific heat is presented.

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Zusammenfassung Die ferromagnetische Phasenumwandlung von Cr-Ni Legierungen wurde über die Temperaturabhängigkeit der Wärmeleitfähigkeit dieser Proben in der Nähe der Phasenumwandlung untersucht. Mit einem einzigen Instrument [1] konnten für die drei Stäbchenproben mit einem Cr-Gehalt von 0,12, 0,51 und 1,13% die elektrische als auch die Wärmeleitfähigkeit bestimmt werden. Zur Bestimmung des Verhältnisses von Wärme- und elektrischer Leitfähigkeit wurde eine Spannungs-Temperatur-Beziehung [2] angewendet. Unter Hinzunahme des aus den charakteristischen Stromstärke-Spannungsdiagrammen (I-U) ermittelten specizifischen elektrischen Widerstandes konnten dann die Leitfähigkeitangaben ermittelt werden. Es wurde ein Modell zur Interpretation des Effektes der Cr-Konzentration auf die I-U Diagramme entwickelt und getestet. Außerdem wurde der Effekt der Cr-Konzentration auf die specifische Wärme dargestellt.

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, Cr-Ni, . , 0,12; 0,51 1,13 . '- . , , - . , - . .

     

Thermal and structural relationships within the Cd-picoline-chloride family including the α, β and γ-types

Thermal and structural properties of complexes of CdCl₂ with picolines were studies. The structures of tetra-- and tetra--picoline as well as di-- and di--picoline complexes were found to be identical and their thermal decomposition paths were analogous. New polynuclear complexes which could not be obtained from solution have been prepared through thermal decomposition. Their symmetry and cell dimensions were determined.

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Zusammenfassung Es wurden die thermischen und strukturellen Eigenschaften von CdCl₂-Komplexen mit Pikolinen untersucht Die Strukturen der tetra-- und tetra--, sowohl der di-- und di--Pikolinkomplexe wurden als gleich befunden, der Verlauf ihrer thermischen Zersetzung war ähnlich. Auf dem Wege der thermischen Zersetzung konnten neue polynukleare Polymerkomplexe hergestellt werden, was in Lösung nicht gelang. Es wurden deren Symmetrie und Zellabmaße ermittelt.

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

     

Complexes formed between nickel(II), copper(II), zinc(II) and aspirin

Complexes of nickel(II), copper(II) and zinc(II) with aspirin have been prepared. Examination of the complexes of nickel(II) and zinc(II) indicates that they are salicylato complexes in which the aspirin has been de-ethanoylated.Chemical, spectral and magnetic properties show that the nickel(II) and copper(II) complexes have dimeric, octahedral structures while the zinc(II) complex has a tetrahedral structure. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis. Thermal decomposition products were obtained for the nickel(II) and zinc(II) complexes. Their structures are octahedral with the exception ofbis-salicyclic acid-zinc(II) which is tetrahedral.

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Zusammenfassung Komplexe von Nickel (II), Kupfer (II) und Zink (II) mit Aspirin wurden hergestellt. Die Untersuchung der Koordinationsverbindungen von Nickel (II) und Zink (II) zeigt, daß dies Salycylatkomplexe sind, in welchen das Aspirin de-äthanoliert wurde.Die chemischen, spektralen- und magnetischen Eigenschaften zeigen, daß die Nickel (II)- und Kupfer (II)-Komplexe dimere Oktaederstrukturen besitzen, während der Zink (II)-Komplex eine Tetraederstruktur besitzt. Die Zersetzung der Komplexe wurde durch Thermogravimetrie und Differentialthermoanalyse untersucht. Thermische Zersetzungsprodukte der Nickel (II)- und Zink (II)-Komplexe wurden erhalten. Ihre Strukturen sind oktaedrich, mit Ausnahme vonBis-Salicyclosäure-Zink (II), dessen Struktur tetraedrisch ist.

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(II), (II) (II) . (II) (II) , , , . . . , , , , . . . , - , .

     

Product selectivity and qualitative reaction scheme for the dehydrogenation and hydrogenolysis of n-butane over supported ruthenium at high temperature

The dehydrogenation and hydrogenolysis of n-butane (n-C₄) over a Ru–Al₂O₃ catalyst (0.849 w/w% Ru) have been studied at 490°C at different time factors. Some runs have also been made on pure -Al₂O₃ at 490°C and on Ru-black at temperatures between 100 and 490°C, feeding n-butane and hydrogen. The analysis of the selectivity vs. time factor allows to prove that the initial reactions taking place are n-C₄ dehydrogenation to 1-butene and 2-butenes and skeletal isomerization to isobutane. The initial molar selectivity to the n-butenes reaches about 70%. A qualitative reaction scheme is proposed.

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- (-C₄) Ru–Al₂O₃ (0,849 .% Ru) 490°C . -Al₂O₃ 490°C Ru- 100–490°C - . , -C₄ 1- 2- . - 80%. .

     

Infrared study of photooxidation of nitrogen oxides and ammonia adsorbed on alumina

Changes in the IR spectra of nitrogen oxides and ammonia adsorbed on Al₂O₃ caused by UV irradiation indicate that in the presence of gaseous or liquid (–196°C) O₂ photooxidation takes place, resulting mostly in the formation of surface NO ₃ ^– ions.

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- - , Al₂O₃, , (–196°C) NO ₃ ^– .

     

Ammonia decomposition on Ir and Pt wires

The rates of ammonia decomposition on polycrystalline Ir and Pd wires were measured at temperatures between 900 and 2000 K and at pressures between 50 and 770 Torr. Rates on Ir were fitted with a Langmuir-Hinshelwood unimolecular reaction rate expression. Rates on Pd could not be fitted with a rate expression, although activation energies were obtained.

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Ir Pd 900–2000 50–770 . Ir --. Pd . .