M?ssbauer spectroscopic studies of passivated layers of iron-containing catalysts for ammonia synthesis

Combined conversion electron (CEMS) and transmission -ray (MS) Mössbauer spectroscopy was used to study the structure of passivated layers of promoted and unpromoted iron-containing catalysts. In both catalysts the oxide-coated films were found to consist of small paramagnetic (at 300 K) clusters of ferric oxide.

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. , ( 300 ) .

     

Influence of carbon dioxide and carbon monoxide on the kinetics of propylene polymerization

Retardation effect of the carbon oxides on propylene polymerization, catalyzed by the TiCl₃/AlEt₂Cl system, can be described in terms of a Langmuir type equation as selective adsorption of the carbon oxides on the polymerization sites.

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, TiCl₃/AlEt₂Cl, , .

     

Kinetics of ion exchange sorption of phosphate

The kinetics of phosphate sorption on Amberlite IRA-400 has been studied as a function of temperature, nature of counterions, at two different concentrations. The film and particle diffusion coefficients and the activation parameters of the process are calculated.

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IRA-400 , . .

     

Lattice Dynamics in LaTa2-2xNb2xVO9-δ (x=0–0.1) Solid Solutions

The oxygen nonstoichiometry (x) of LaTa_2-2xNb_2xVO₉- (x = 0–0.1) solid solutions was studied using Xray phase analysis, vibrational spectroscopy, and radiospectroscopy. A correlation was found between (x) and the unit cell volume V(x) of the solid solutions. It was shown that the infrared spectra of LaTa₂VO₉- change in passing from = 0 to 0. The structural position of the oxygen vacancy in LaTa_2-2xNb_2xVO₉- is discussed.     

Effect of water on hydrogen desorption from the surface of Rh/C catalysts

An increase in the number of titration cycles results in a considerable decrease in H_T and O_T values, which in turn, brings about a decrease in the amount of desorbed hydrogen. This shows that water, being a product of titration reaction, is adsorbed on the oxidized surface of rhodium and represents a kinetic-diffusive barrier for hydrogen titration.

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, H_T O_T, , , . , , , , , - .

     

Calorimetry for thermokinetic determinations

The possibilities of using direct calorimetric measurements for the determination of kinetic parameters of processes are discussed in terms of the choice of an appropriate method of reproduction of the course of changes in the heat power generated in time, i.e. thermokinetics. Such methods are presented and it is concluded that many of these methods permit reproduction of the thermokinetics in the same way as if the experimental thermal curve were obtained in a calorimetric system characterized by a time constant 100–200 times as large as that for the thermal inertia of this calorimetric system.

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Zusammenfassung Die Möglichkeiten zur Benutzung direkter kalorimetrischer Messungen zur Bestimmung kinetischer Parameter von Prozessen werden hinsichtlich der Wahl geeigneter Methoden zur Reproduzierung des Verlaufs der Änderungen der Wärmekraft mit der Zeit, d.h. zur Reproduzierung der Thermokinetik diskutiert. Solche Methoden werden angeführt und es wird die Schlussfolgerung gezogen, dass viele dieser Methoden die Reproduzierung der Thermokinetik auf gleiche Weise wie in den Fällen erlauben, in denen die thermische Kurve mit einem kalorimetrischen System erhalten wird, dessen Zeitkonstante um 100–200mal grösser als die des diskutierten Systems ist.

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. . . , , , 100–200 .

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Presented at the 2nd Czechoslovak Conference on Calorimetry, Liblice, Czechoslovakia, 1982.     

Kinetics of the oxidation of aliphatic ketones by thallic salts in sulfuric acid medium

: - - 1–3 .

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With increasing partial pressure of molecules in atomic-molecular mixtures, the yield and intensity of radical-recombination luminescence of inorganic luminophors increase by 1–3 orders of magnitude.

     

Fischer-Tropsch synthesis on Ru/NaY catalysts: Effect of the acidity of the zeolite

A series of NaY zeolites with different Si/Al ratios were used to support the Ru catalysts. Both the activity/selectivity of Ru in F–T synthesis and the suppressing of hydrogen may be related to the acid strength of the OH groups present, which is a function of the Si/Al ratio of the zeolite.

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NaY Si/Al Ru. / Ru -, OH-, Si/Al .

     

IR spectroscopic studies of H2S adsorption on acid and base catalysts

IR spectra of H₂S adsorbed on various types of catalysts have been studied by monitoring changes in the properties of their surfaces from the spectra of probe molecules. It is shown that H₂S is adsorbed only dissociatively on basic centers (BC); on proton centers (PC) it forms H-complexes, while with the participation of strong Lewis acid centers (LAC), it is adsorbed both associatively and dissociatively.

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- H₂S , -. , H₂S (), () -, ()- , .

     

Kinetic measurements on polymers — Applications and limits

A modern kinetic evaluation method for nonisothermal reactions measured with TG or DSC is presented. The obtained kinetic data are the basis for computation of a reaction process under any condition, e.g. isothermal or adiabatic. The measurements were performed on a Mettler TA3OOO system with built-in evaluation software. Mainly the following reactions are discussed: polyaddition of an epoxy premix and pyrolysis of polystyrene. To judge the reliability of the results, 4 check procedures are recommended.

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Zusammenfassung Es wird eine moderne kinetische Auswertungsmethode für durch TG oder DSC verfolgte nichtisotherme Reaktionen vorgestellt. Die erhaltenen kinetischen Daten stellen die Basis der Berechnung der Reaktionsprozesse unter jeder, z.B. isothermer oder isobarer Bedienung dar. Die Messungen wurden mit dem Mettler-System TA3000 mit Auswertungs-software ausgeführt. In erster Linie werden die folgenden Reaktionen diskutiert: Polyaddition eines Epoxy-Vorgemisches, Pyrolyse von Polystyrol. Zur Beurteilung der Zuverlässigkeit der Ergebnisse werden 4 Testverfahren empfohlen.

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, . - , , . TA 3000 . - . .

     

Dispersity of oxidized and reduced palladium on Al2O3

The amount of PdO not dissolving in dilute HCl as a function of its content in palladium catalysts calcined in air has been determined. Mean size of Pd particles in the same samples has been evaluated from oxygen chemisorption. A comparison of these data indicates their correlation, which permits to determine Pd dispersity variations according to the solubility of supported PdO before reduction.

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. . , .

     

A systematic theory of one-cell differential thermal analysis

The mathematical theory is developed for heat transfer in the cells of DTA instruments with no temperature gradient. Equations are derived for the various portions of the differential curve. The concepts of real and hypothetical base lines are introduced and rules are formulated for plotting them. Three methods are proposed for processing the curves, with and without the introduction of base lines. The physical meanings of the geometrical elements of the thermal curves and their relationship with the experimentally determined thermal quantities are elucidated. Equations in differential and integral forms are derived for the base line of the cell and the base line of the reaction.

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Zusammenfassung Eine mathematische Theorie für den Wärmeübergang in Zellen von DTA-Geräten ohne Temperaturgradient wird entwickelt. Für die einzelnen Abschnitte der differentiellen Kurve werden Gleichungen abgeleitet. Das Konzept der reellen und hypothetischen Grundlinien wird eingeführt und Regeln für deren Konstruktion werden aufgestellt. Drei Methoden zur Darstellung der Kurven mit und ohne Einführung der Grundlinien werden vorgeschlagen. Die physikalische Bedeutung der geometrischen Elemente der thermischen Kurven und deren Beziehung zu den experimentell bestimmten thermischen Größen werden klargestellt. Für die Grundlinie der Zelle und für die der Reaktion werden Gleichungen in differentieller und integraler Form abgeleitet.

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, . . . — . . .

     

IR study of interaction of propylene at CoO-MgO and CoO-MoO3-MgO surfaces

IR spectra of propylene adsorbed in CoO-MgO and CoO-MgO-MoO₃ solid solutions show that a surface -complex with Co²⁺ ions is formed, strongly bonded in the former case and weakly in the latter. Thus, introduction of Mo strongly modifies the catalytic properties of Co²⁺ active centers. In the presence of oxygen, allylic species, aldehyde and carboxylate complexes appear.

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, CoO-MgO CoO-MgO-MoO₃ - Co²⁺, . , Mo Co²⁺. - .

     

Zur Kenntnis des Systems Palladium-Kadmium

Zusammenfassung Mit Hilfe mikroskopischer, röntgenoraphischer und magnetischer Untersuchungen konnten die Gleichgewichtsverhältnisse in dem System Palladium—Kadmium weitgehend aufgeklärt werden. Palladium löst bis maximal 26 At.-% Cd bei 750° C. Mit steigendem Kadmiumgehalt konnten folgende intermediäre Phasen festgestellt werden: Eine tetragonale Phase mit einem homogenen Bereich von 34 bis 49 At.-% Cd bei 750° C, die im L l₀-Typ kristallisiert. Bei ungefähr 60 At.-% Cd wurde eine kubisch-raumzentrierte Struktur festgestellt, die unter 325°C in + zerfällt. Die schon bekannteHume-Rothery--Phase liegt in dem Bereich von 80 bis 82 At.-% Cd. Außerdem existieren noch zwei weitere -ähnliche Strukturen, ₁ und , die sich an der Palladiumseite an anschließen. Es liegen Anzeichen dafür vor, daß bei höherer Temperatur zwischen und noch eine -Phase auftritt, die sowohl zur - wie auch zur -Struktur verwandt zu sein scheint.Die Gitterkonstanten der kristallographisch eindeutigen Strukturen und ihr Verlauf mit der Konzentration werden angegeben. Die magnetischen Messungen bestätigen den anomalen Diamagnetismus bei der -Phase. Die Legierungen der -Phase sind schwach diamagnetisch, während die - und -Phase paramagnetisches Verhalten zeigen.Mit 8 Abbildungen     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

An index of electrotopological state for atoms in molecules

A new method for molecular structure quantitation is described, in which both electronic and topological attributes are united. The method uses the hydrogen-suppressed skeleton to represent the structure and leads to a graph invariant index for the individual atoms and hydride groups of the molecular skeleton. An intrinsic atom value is calculated for each atom asI = ( + 1)/, in which and are the counts of valence and sigma electrons of atoms in the molecular skeleton, that is, exclusive of bonds to hydrogen atoms. The electrotopological state valueS _i for an atomi is defined asS _i =I _i + I _i, where the influence of atom j on atom i, I _i, is given as (I _i-j _j)/r ²;r is the graph separation between atoms i and j, counted as number of atoms, includingi andj. The information in the electrotopological state values is revealed by examples of various types of organic structures, including chain branching and heteroatom variation. The relation of the E-state value to NMR chemical shift is demonstrated for a series of carbonyl compounds.     

Calorimetric studies of aluminosilicate catalysts heats and entropies of cumene adsorption on cation substituted metakaolinite

Differential heats of cumene adsorption at 293 K on Ca-, Sr- and Ba-substituted metakaolinites at surface coverages up to 0.1 have been measured on a Calvet microcalorimeter. The presence of two energetically different adsorption centers are shown to be determined by the nature of the exchanged cation; the adsorption heats decrease in the sequence Ba, Sr, Ca, Mg.

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293 Ca-, Sr, Ba- 0.1. . , Ba, Sr, Ca, Mg.

     

Thermal stability of epoxy compounds cured with boron trifluoride complexes

The thermal resistances of epoxy resins cured with complexes of boron trifluoride with benzylamine, 2-benzylaminoethanol and 2-anilinoethanol were examined. Thermal analysis data were used to compare the thermal resistances of epoxy compusitions cured with polyamines (aliphatic and aromatic), acid anhydrides and complexes of boron trifluoride with the above amines.

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Zusammenfassung Der WÄrmewiderstand von mit Komplexen von Bortrifluorid mit Benzylamin, 2-Benzylamino-Äthanol und 2-Anilino-Äthanol gehÄrteten Epoxyharzen wurde untersucht. Anhand thermoanalytischer Daten wurden die WÄrmewiderstandswerte von mit (aliphatischen und aromatischen) Polyaminen, SÄureanhydriden und Komplexen von Bortrifluorid mit den oben angeführten Aminen gehÄrteten Epoxy-Kompositionen miteinander verglichen.

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, , 2- 2-. , ( ) .