Effect of preparation method of nickel-zeolite catalysts on their catalytic properties

The effect of the carrier-gas (H₂, N₂, CO₂ and air) and the influence of additives (H₂S and water vapors) in the activation of Ni- and Cr-containing zeolites on their catalytic activity have been studied in toluene disproportionation.

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- (H₂, N₂, CO₂ ) (H₂S ) , Ni Cr, .

     

Crystallization kinetics of polyamide 6 containing pigments

In terms of the Avrami equation, the effects of selected organic pigments on the kinetic parameters of the isothermal crystallization of coloured polyamide 6 were examined in the temperature range 468–478 K. It was found that B Blue and BB Red are active nucleating agents, which is acribed to their crystalline structure. G Orange slightly accelerates the crystallization of PA 6 at lower temperatures and concentrations, whereas in other conditions its effect is the opposite.The isothermal data were confirmed by the results of non-isothermal crystallization. The degree of supercooling corresponding to the peak of the DSC curve was the measured feature in this case.It was found that B Blue and BB Red reduce the free energy of formation of criticalsize nuclei by 20 and 12%, respectively, which is reflected in the rates of crystallization.

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Zusammenfassung Mit Hilfe der Avrami Gleichung wurde der Einfluß einiger ausgewählter organischer Pigmente auf die kinetischen Parameter der isothermen Kristallisation gefärbter Polyamide 6 im Temperaturbereich 468–478 K untersucht. B Blue und BB Red erwiesen sich als aktive Keimbilder, was mit Hilfe ihrer kristallinen Struktur erklärt werden kann. Bei niedrigeren Temperaturen und geringeren Konzentrationen wird die Kristallisation von PA 6 durch G Orange leicht beschleunigt, unter anderen Bedingungen kann das Gegenteil beobachtet werden. Die isothermen Daten wurden durch die Ergebnisse bei nichtisothermer Kristallisation bekräftigt. In diesem Falle wurde das dem DSC Peak entsprechende Maß an Unterkühlung untersucht. Es wurde gefunden, daß B Blue und BB Red die freie Energie zur Bildung von Keimen kritischer Größe um 20 bzw. 12% herabsetzen, was sich in den Kristallisationsgeschwindigkeiten widerspiegelt.

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, -6 468–478 . , , . , . . . , , , 20 12%, .

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This work was supported by the Polish Academy of Science, goal 01.14.     

Kinetics of Co?Mo/Al2O3 catalyst reduction

According to kinetic studies on the reduction of commercial Co–Mo/Al₂O₃ and model catalysts in H₂ at 523–773 K, the kinetic curves for the reduction process have been determined. The reduction rate is shown to be higher for the commercial catalyst. Activation energies E_act for the reduction of several forms of Mo and Co in Co–Mo/Al₂O₃ catalysts are presented.

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H₂ 523–773 . , : Mo Co .

     

The thermal decomposition reactions of bis-(pyridine-2-aldoxime)-copper(II) complexes

The thermal properties of some complexes of copper(II) with pyridine-2-aldoxime (HPAO), where the ligand appears either as the ion (PAO^–) or as a neutral molecule, were determined in vacuo and in dynamic nitrogen and oxygen gas atmospheres. The study was carried out by thermoanalytical (TG, DTG. DTA), spectroscopic and spectrometric (UV-visible, IR, diffuse reflectance, mass) techniques.The initial decomposition temperature is influenced by the number of acid hydrogens in the complex; the thermal stability sequence in vacuo is: [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]The thermal decomposition reactions occur in several separate steps, the first of which gives rise to partial ligand decomposition, the reduction of copper(II) to copper(I), and the conversion of the residual pyridine-2-aldoxime into acid amide.

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Zusammenfassung Die thermischen Eigenschaften einiger Komplexe von Kupfer(II) mit Pyridin-2-aldoxim (HPAO), in denen der Ligand entweder als Ion (PAO^–) oder als neutrales Molekül vorliegt, wurden im Vakuum und in dynamischer N₂- und O₂-Atmosphäre ermittelt. Zur Untersuchung wurden thermoanalytische (TG, DTG, DTA) und spektrometrische (UV-sichtbar, IR, diffuse Reflektionsspektrophotometrie, Massenspektrometrie) Techniken herangezogen. Die Temperatur, bei der die Zersetzung beginnt, wird durch die Zahl der sauren Wasserstoffatome im Komplex beeinflußt; für die thermische Stabilität im Vakuum gilt die Reihenfolge [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]. Die thermischen Zersetzurigsreaktionen verlaufen in mehreren diskreten Schritten, wobei der erste von diesen eine partielle Zersetzung des Liganden, die Reduktion von Kupfer(II) zu Kupfer(I) und die Konversion des verbleibenden Pyridin-2-aldoxims in das Säureamid in sich einschließt.

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-2- ( ), (-), . (, , ) , - , , - . , [Cu(PAO)₂H]CI > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂] , , -2- .

     

Thermal decomposition of calcium sulphate in carbon monoxide

Simultaneous TG and DTA studies were performed on analytical grade calcium sulfate and on samples of natural gypsum and phosphogypsum in carbon monoxide atmosphere. The decomposition temperatures and mechanism are influenced by the mineral impurities of the sample and the heating rate as well as the CO content of the gas atmosphere.

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Zusammenfassung Simultane TG- und DTA-Untersuchungen von analytisch reinem Calciumsulfat und Proben von natürlichem Gips und Phosphogips wurden in Kohlenmonoxidatmosphäre ausgeführt. Temperatur und Mechanismus der Zersetzung werden durch mineralische Verunreinigungen der Probe, durch die Aufheizgeschwindigkeit und durch den CO-Gehalt der Gasatmosphäre beeinflußt.

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. - , , .

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The authors are indebted to Professor M. Veiderma for fruitful discussions and continuous support. The scholarship from Finnish Government to one of us (R. K.) is gratefully acknowledged.     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

Catalytic conversion of dimethylsulfide to methylmercaptan

The effect of reaction conditions on the methylmercaptan formation from dimethylsulfide in H₂S catalyzed by -Al₂O₃ has been studied. The reaction is first order with respect to dimethylsulfide. It has been revealed that the maximum activity in this reaction is observed for the catalysts whose surface contains a large number of aprotonic acid centers and moderate-strength basic sites.

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-Al₂O₃. , . . , , .

     

Oxidative dehydrogenation (OXD) of n-butane I. Activity of natural quartz II. Kinetic and catalytic activity of nickel oxides

The oxidative dehydrogenation of n-butane on nickel oxide catalysts and on natural quartz, used as catalysts diluent, were studied. It is assumed that oxygen ions from the oxide lattice participate in the initial step of the reaction.

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- , . , .

     

Mössbauer study of the thermal decompositions of alkaline earth tris(oxalato)ferrates(III)

The thermal decompositions of alkaline earth tris(oxalato)ferrates(III) (Mg, Ca, Sr and Ba) have been studied by Mössbauer spectroscopy and other techniques. During the thermal decomposition, dehydration occurs first, followed by reduction to iron(II) species, and oxides and ferrites (MFe^IIIO₄) are then formed at higher temperature. In the case of strontium tris(oxalato)ferrate(III), strontium ferrite (SrFe^IVO₄) is formed at 700°.

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Zusammenfassung Die thermische Zersetzung von Tris(oxalato)ferraten(III) der Erdalkalimetalle (Mg, Ca, Sr, Ba) wurde durch Mössbauer-Spektroskopie und andere Techniken untersucht. Im Verlaufe der thermischen Zersetzung verläuft zunächst die Dehydratisierung, gefolgt von der Reduktion zu Eisen(II)-Species. Oxide und Ferrite (MFe^IIIO₄) werden danach bei höheren Temperaturen gebildet. Strontium-tris(oxalato)-ferrat(III) geht bei 700 °C in Strontiumferrit (SrFe^IVO₄) über.

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() () , , ë . , , MFe^IIIO₄. 700° SrFe^IVO₄.

     

Determination of hydroxyl groups and/or water on the surface of oxide catalysts by a pulse chromatographic method

A pulse chromatographic method based on the reaction of gaseous dimethylzinc tetrahydrofura nate was developed for the determination of surface hydroxyl groups and/or adsorbed water in solid porous materials. The procedure is rapid and gives results comparable to other methods. Some heterogeneous catalysts and supports have been analyzed.

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, , / , . , . .

     

Potassium addition to Fe/MgO, Ni/MgO and Ni/SiO2: Reducibility, dispersity and stabilization of the promoter by the support

The influence of potassium addition on the morphological properties of Fe/MgO and Ni/MgO has been investigated: KNO₃ addition to precursors results in a decrease of the reducibility and in a smaller dispersity of the metallic phase. A loss of potassium is observed at reduction temperatures in excess of 773 K. Silica-supported Ni behaves differently: silica inhibits the potassium volatilization and nickel reducibility is enhanced. This illustrates how promoter effects can be influenced by the nature of support.

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Fe/MgO Ni/MgO: KNO₃ . , 773 K. , : . .

     

IR study of 1-hexene isomerization on HZSM-5 zeolites

In the IR spectra of 1-hexene adsorbed on HZSM-5 zeolites with different Si/Al ratios, a new band at 1510 cm^–1 has been observed. The cis/trans-2-hexene and trans-2-hexene/1-hexene ratios were determined.

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1-, HZSM-5 Si/Al, 1510 cm^–1. /-2- -2-/1-.

     

Promotion of nickel catalysts for the steam reforming of methane

The influence of additives (Cu, Fe and Al₂O₃) on the textural and catalytic properties of nickel in steam reforming of methane is described. The effects of structural promoting by Al₂O₃ and of electronic promoting by copper are reported. The rate of steam reforming of methane was measured in a gradientless reactor at atmospheric pressure.

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(Cu, Fe Al₂O₃) . Al₂O₃ . .

     

Preparation and study of Mn-containing silicates of zeolite structure

The Cu–SiO₂ catalyst prepared by ion exchange method shows a longer life for the dehydrogenation of methanol, as compared with those of Cu catalysts prepared by other methods. This suggests that the highly dispersed Cu particles on the support cannot be easily aggregated during the reaction.

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Cu–SiO₂, , , , . , .

     

Intermediate oxygen-containing compounds in oxidative condensation of methane over sodium-manganese catalysts

CH₂O conversion over sodium-manganese oxide and oxychloride catalysts in methane dehydrodimerization have been studied under unsteady-state conditions at high temperatures (600–750 °C). It has been established that formaldehyde conversions produce deep oxidation (CO, CO₂), condensation (C₂H₄, C₂H₆) and methanation products through CH₃O^– formation and decomposition.

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(600–750°C) CH₂O - . , (CO, CO₂) (C₂H₄, C₂H₆), , CH₃O^–.

     

Radical addition of methyldichlorosilane to vinyl acetate

The GC-MS method was used to identify the addition products of methyldichlorosilane to vinyl acetate. Radiation-induced addition of methyldichlorosilane to vinyl acetate produces 2-methyldichlorosilylethyl ethyl ether. The reaction follows a radical-chain mechanism. The ratio of the rate constants of methyldichlorosilyl radical addition to C=C and C=O to vinyl acetate amounts to 0.4±0.1 (303 K).

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- . , - 2- . , C=C C=O 0,4±0,1.

     

A bifunctional stopcock-winch device in cells for infrared investigations of solids

A simple glass device is described acting as stopcock and winch at the same time. The device is especially suitable for the dislocation of solid sample holders in IR cells.

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, . .

     

Influence of carbon dioxide on the position of oxygen adsorption equilibrium on silver

Due to interaction with carbon dioxide, when some adsorbed oxygen atoms on silver surfaces are converted into carbonate groups, the binding energy diminishes and the volatility of adsorbed oxygen rises.

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, , .

     

Ru(III) catalyzed oxidation of acetanilide and substituted acetanilides by potassium iodate in aqueous acetic acid medium at constant ionic strength

The order with respect to [Ru(III)] is unity while zero order with respect to [IO₃ ^–] and complex dependence on [substrate] have been observed. The variation of [HClO₄] and solvent composition have no pronounced effect on the rate. A plausible mechanism is suggested.

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[Ru(III)], [IO₃ ^–] . CClO₄ . .