Characterization of the redox-reactivity of transition metal oxides by temperature-programmed limited thermal decomposition (TPLTD)

The concept of labile lattice oxygen (LLO) as a consequence of the Mars-Van Krevellen model was reminded, and contrasted with the surface oxygen species. Methods of characterizing of the Me-O bond strength were reviewed emphasizing the temperature-programmed limited thermal decomposition (TPLTD). A series of Ag_xV₂Mo_yO_z was characterized by TPLTD. Two forms of LLO were distinguished. The weaker form is independent on Ag-doping, in contrast to the stronger one. Activation energy of TPLTD of the stronger bound LLO was a linear function of the anion vacancy concentration.

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Zusammenfassung Aus dem Konzept des labilen Gittersauerstoffs (LLO) als Konsequenz des Mars-Van Krevellen-Modells wird die Rolle der Oberflächen-Sauerstoff-Spezies hervorgehoben. Ein Überblick über die Methoden zur Charakterisierung der Me-O-Bindung wird unter besonderer Betonung der temperaturprogrammierten begrenzten thermischen Zersetzung (TPLTD) gegeben.Eine Reihe Ag _x V₂Mo _y O₂ wurde mittels TPLTD charakterisiert, dabei konnten zwei Arten von LLO unterschieden werden. Die schwächere Form ist im Gegensatz zu der stärkeren unabhängig vom Silbergehalt. Die Aktivierungsenergie der TPLTD der stärker gebundenen LLO hängt linear von der Konzentration der Anionenfehlstellen ab.

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, - , . Me- . Ag_xV₂Mo_yO_z, . , , . n.

     

Investigation of antiradical activity of pyrazolo-[3,4-b]pyranes in ethylbenzene oxidation

Kinetic parameters of the antiradical activity of pyrazolo [3,4-b]pyranes in the initiated low-temperature oxidation of ethylbenzene determined by the chemiluminescence method indicate that these pyranes have considerable antiradical properties like the known effective inhibitors.

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[3,4-b] qp . , [3,4-b] .

     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

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, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

Methode calorimetrique de mesure des enthalpies de formation des alliages liquides a forte tension de vapeur

The heat effects corresponding to the dissolution of solid PbSe in liquid Pb-Se alloys starting from pure Pb were measured with a direct reaction calorimeter. The partial enthalpy of formation of PbSe in the melt and the integral enthalpy of formation of the Pb-PbSe system in the liquid state referred the liquid Pb and PbSe were deduced. Then, from a very simple change of reference state, and in the knowledge of the enthalpy of PbSe, the integral enthalpy of formation of Pb-Se liquid alloys with reference to pure liquid components could be derived. The results agreed very well with those obtained previously on the dissolution of Se in Pb. The method used can be applied whenever the component to be added to the bath has a high vapor pressure.

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Zusammenfassung Die bei der Überführung von festem PbSe in flüssige Pb-Se-Legierungen auftretenden Wärmeeffekte wurden mittels direkter Reaktionskalorimetrie bestimmt. Die auf flüssiges Pb und PbSe bezogene partielle Bildungsenthalpie des Pb-PbSe-Systems im flüssigen Zustand wurde ermittelt. Durch eine geringfügige Veränderung des Referenzzustandes konnte bei Kenntnis der Enthalpie von PbSe die integrale Bildungsenthalpie von flüssigen Pb-Se-Legierungen in Bezug auf die reinen Komponenten abgeleitet werden. Die Ergebnisse stimmen gut mit denen überein, die früher für die Auflösung von Se in Pb erhalten wurden. Die Methode ist anwendbar, wenn dem Bade zuzugebende Komponenten einen hohen Dampfdruck haben.

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Pb-Se Pb-Se, . Pb-Se Pb-PbSe Pb Pb-Se. PbSe, Pb-Se . , . , .

     

Kinetics and mechanism of elimination of methoxyphenethyl chlorides in the gas phase

The kinetics for the gas phase elimination of o-and m-methoxy-2-phenylethyl chlorides have been investigated over the temperature range of 390-464°C and pressure range of 38–119 Torr. The reactions in seasoned vessels and in the presence of the free radical inhibitor propene, are homogeneous and unimolecular and follow a first-order rate law. The o-anisyl and p-anisyl substituents at the -position of ethyl chloride assist anchimerically the elimination processes. The formation of a cyclic product, benzodihydrofuran, from o-methoxy-2-phenylethyl chloride suggests an intimate ion pair mechanism operating in this reaction.

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- --2- 390–464°C 38–119 . - , , , . - - - . , , --2- , .

     

Influence of physical state of high-temperature, superconductor YBa2Cu3O7?δ on its catalytic properties in low-temperature ortho-para hydrogen conversion

The transformation of a dispersed high-temperature superconductor from its normal to superconducting state was found to result in the loss of its catalytic properties in orhto-para-hydrogen conversion.

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, -- .

     

Quality control of the cure process of thermosetting resins by means of differential scanning calorimetry

Calorimetric and rheological characterizations of thermosetting resin formulations containing a novalac epoxy resin hardened with 60 to 120 parts per hundred of methylated maleic acid adduct anhydride are described. The calorimetrically determined epoxy conversion has been related to the gelation limits theoretically calculated from Flory's non-linear copolymerization theory and experimentally verified in rheological tests.

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Zusammenfassung Die kalorimetrische und rheologische Charakterisierung der Ansätze von hitzhärtbarem Harz wird beschrieben. Die Ansätze enthalten ein mit 60–120% methyliertem Maleinsäure-Adduktanhydrid gehärtetes Novolackepoxidharz. Die kalorimetrisch bestimmte Epoxid-konversion wurde auf die theoretisch aus der nicht-linearen Flory'schen Kopolymerisationstheorie berechneten und experimentell durch rheologische Tests bestätigten Erstarrungsgrenzen bezogen.

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, - . -, , , .

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Financial and scientific support by the CNR Progetto Chimica Fine e Secondaria and the Societa Italiana Resine (SIR) is gratefully acknowledged.     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

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Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

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, , , . . , . , , . , .

     

Mechanism of the liquid-phase oxidation of diethyl sulfide catalyzed by heteropoly acids

It has been established that in the oxidation of diethyl sulfide by¹⁸O₂ in CH₃C¹⁶O₂H–H₂ ¹⁶O solution at 369 K catalyzed by heteropoly acids, sulfoxide and sulfone with 44–54%¹⁸O enrichment are formed. The process is accompanied by isotope exchange of molecular oxygen.

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, ¹⁸O₂ CH₃C¹⁶O₂H–H₂ ¹⁶O 369 ¹⁸O 44–54%, .

     

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. , , , , .

     

Formulation of apparent reaction order and its application

The apparent reaction order _j with respect to component i was shown to be described as _i = lnR/lnp_i where R and p_i are the reaction rate and the partial pressure of component i, respectively. This equation makes it possible to compare the parameters in the power functional rate equation and those in the fractional rate equation with each other. An application was illustrated on a steady-state two-step kinetics.

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_i і _i = lnR/lnp_i, R p_i і, . , , . .

     

TPD studies of hydrogen adsorption on group VIII metals

Hydrogen desorption proceeds in several temperature regions and differs by its order of magnitude and activation energy. Differential curves of adsorbed hydrogen distribution with respect to the desorption activation energy, dN/dE (E), show a considerable inhomogeneity of adsorbed atomic species and the energetic homogeneity of molecular species.

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. dN/dE (E) .

     

Hydrogenation of nitric oxide on platinum black in acidic solution

By comparison of the catalytic hydrogenation and electrochemical reduction of NO on platinum black catalysts it has been shown that the hydrogenation of NO to ammonia and to hydroxylamine occurs in the diffusion controlled region only.

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NO , NO .

     

Study of the preparation process of perovskite oxides SmMnO3 by XRD and TPR technique

Perovskite oxides SmMnO₃ have been prepared by citric acid complexing, carbonate coprecipitation, nitrate direct decomposition and ceramic method. The effects of preparation methods and the calcination temperature on the formation of perovskite structure were studied by XRD and TPR technique, and the key steps in formation of SmMnO₃ are discussed.

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SmMnO₃ , , . . SmMnO₃.

     

Zum Thermischen Verhalten von Alkylammonium- und Kalium-N-Alkylthiocarbamaten

Zusammenfassung Es wurde das thermische Verhalten von Alkylammonium- und Kalium-N-alkylthiocarbamaten der Zusammensetzung (RNH₃) (RHNCXY) mit X=Y=S oder X= S und Y= 0; R=n-C₃H₇,i-C₃H₇,n-C₄H₉,i-C₄H₉,c-C₆H₁₁ bzw. K(RHNCOS) mit R= CH₃ C₂H₅,n-C₃H₇,i-C₃H₇,n-C₄H₉,i-C₄H₉,c-C₆H₁₁ untersucht. Die Zersetzungsmechanismen zeigen bei allen untersuchten Verbindungen einen ähnlichen Charakter. Im Verlaufe der Thermolyse entstehen symmetrische Dialkylharn- bzw. -thioharnstoffe sowie Aminé, CS₂ (bzw. COS) und H₂S. Während sich die Alkylammoniumthiocarbamate ohne Rückstand zersetzen, verbleibt bei den Kaliummonothiocarbamaten Kaliumsulfat als Rückstand. Für den Prozeß der Harn- bzw. Thioharnstoffbildung während der ersten Abbaustufe der Alkylammoniumthiocarbamate wurden die Aktivierungsenergien berechnet.

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The thermal behaviours of alkylammonium and potassium N-alkylthiocarbamates of general formula (RNH₃) (RHNCXY) (where X= Y= S or X= S and Y= 0; R=n-C₃H₃,i-C₃H₃,n-C₄H₉,i-C₄H₉ orc-C₆H₁₁) and K(RHNCOS) (where R=CH₃, C₂H₅,n-C₃H₇,i-C₃H₇,n-C₄H₉,i-C₄H₉ orc-C₆H₁₁) were investigated. The decomposition mechanisms exhibit a similar character for all studied compounds. In the course of thermolysis symmetric dialkylureas and dialkylthioureas, as well as amines, CS₂ (or COS) and H₂S are formed. The alkylammonium thiocarbamates decompose without any residue, whereas with potassium monothiocarbamates potassium sulfate is left as a residue. For the process of urea and thiourea formation during the first step of decomposition, the activation energies were computed for some compounds.

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Résumé On a étudié le comportement thermique des N-alcoyl-thiocarbamates d'ammonium et de potassium de composition (RNH₃) (RHNCXY), avec X=Y=S ou X=S et Y=O; R=n-C₃H₇,i-C₃H₇,n-C₄H₉,i-C₄H₉,c-C₆H₁₁ ainsi que des composés K(RHNCOS) avec R=CH₃, C₂H₅,n-C₃H₇,i-C₃H₇,n-C₄H₉,i-C₄H₉,c-C₆H₁₁. Les mécanismes de décomposition montrent un caractère similaire pour tous les composés. Au cours de la thermolyse il se forme des dialcoylcarbamides symétriques ou des thiocarbamides ainsi que des amines, CS₂ (ou COS) et H₂S. Alors que les alcoylthiocarbamates d'ammonium se décomposent sans résidu, les monothiocarbamates de potassium donnent du sulfate de potassium comme résidu. On a calculé les énergies d'activation pour la réaction de formation de la carbamide ou de la thiocarbamide pendant la première étape de la décomposition des alcoylthiocarbamates d'ammonium.

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N- (RNH₃) ((RHNCXY), X=.Y=S X=S Y=; R=-₃₇, -₃₇, -C₄H₉, -₄₉, -₆₁₁ K(RHNCOS) c R=₃, ₂₅, -₃₇, -C₃H₇, -₄₉, o-C₄H₉ -₆₁₁. . : , CS₂ ( COS) H₂S. , . , .

     

Iron-chromium catalysts in the conversion of methanol with water vapor

The catalytic properties of iron-chromium catalysts in methanol conversion with water vapor were studied. The activity of the catalysts is shown to depend on the method of preparation and their Cr₂O₃ content. The Cr₂O₃ admixture is found to play the role of a stabilizer of the active surface.

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. Cr₂O₃. Cr₂O₃ .

     

Transient response study of the participation of adsorbed forms of ammonia in propene ammoxidation

On the basis of transient response studies, it is suggested that ammonia on the surface of a Mo–Si–Bi–P oxide catalyst forms a compound that is stable at the reaction temperature and whose reaction with propene yields acrylonitrile.

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, Mo–Si–Bi–P , .

     

Co-adsorption studies of ethene with isotopically labelled water and hydrogen on copper/silica

The coadsorption of ethene with isotopically labelled water and hydrogen has been studied at temperatures between 423 and 623 K in a flow system. Ethene exchange has been shown to be independent of hydrogenation. When water is presnet, hydrogenation is poisoned but exchange can occur.

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423–623 . . , .

     

The possible formation of surface ethylidyne on platinum black and its effect on some catalytic properties

Secondary Ion Mass Spectra of Pt-black exposed to ethylene at 633 K contain a PtC₂H₃ cluster identified tentatively with adsorbed ethylidyne like that reported for single crystal surfaces. The catalytic properties of Pt pretreated by ethylene are, to some respect, superior in hydrocarbon transformations to those containing other, less defined carbonaceous overlayers.

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- Pt-, 633 , PtC₂H₃, , . Pt, , , , , .