Propane aromatization over Pt?Sn/ZSM-5 catalysts

Addition of Sn modifies the catalytic performance of Pt/ZSM-5. Total conversions decrease with increasing Sn/Pt ratio. Selectivity to aromatics is higher on the Pt–Sn samples. A Pt–Sn interaction has been confirmed by H₂ chemisorption and TPR experiments.

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Sn Pt/ZSM5. Sn/Pt . Pt–Sn. Pt–Sn H₂ .

     

The maximum kinetic mechanism and rate constants in the H2?O2 system

The maximum (in a combinatorial sense) kinetic mechanism of hydrogen oxidation is defined and the rate constants of all elementary steps are given. The possible error limit is given for each elementary step.

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( ) . .

     

Pyrolysis of 1-phenyl-3-pyrazolidinone

Pyrolysis of 1-phenyl-3-pyrazolidinone (phenidone) was examined in static air atmosphere by the conventional dynamic heating technique in a derivatograph. The thermal stability of 1-phenyl-3-pyrazolidinone, its melting point and the kinetic parametersE, A andn of the first partial process of the pyrolysis at different heating rates were determined. It is shown that the thermal decomposition of 1-phenyl-3-pyrazolidinone in the presence of oxygen is a rather complicated process composed of several overlapping reactions. The pyrolysis is influenced by the conditions of thermal analysis.

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Zusammenfassung Die Pyrolyse von 1-Phenyl-3-pyrazolidinon (Phenidon) wurde mit einem Derivatographen in einer statischen LuftatmosphÄre und bei konventioneller dynamischer Aufheizung untersucht. Die thermische StabilitÄt und der Schmelzpunkt von 1-Phenyl-3-pyrazolidinon sowie die kinetischen ParameterE, A undn des ersten Teilprozesses der Pyrolyse für verschiedene Aufheizgeschwindigkeiten wurden bestimmt. Es stellte sich heraus, da\ die in Gegenwert von Sauerstoff verlaufende thermische Zersetzung von 1-Phenyl-3-pyrazolidinon ein ziemlich komplizierter, aus mehreren sich überlappenden Teilschritten bestehender Proze\ ist. Die Pyrolyse wird durch die Bedingungen der thermischen Analyse beeinflu\t.

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1--3 () . , E, A n , . , 1--3- , . .

     

Solid state reactions between nickel(II) sulphide and oxides of manganese and iron

Thermogravimetry and differential thermal analysis have shown that, when nickel(II) sulphide and manganese or iron oxides are heated together, several reactions occur depending on the molar ratio of the reactants. Detailed examinations of these reactions have shown that there are a number of intermediate stages, including the formation of sulphates.

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Zusammenfassung Thermogravimetrie und Differentialthermoanalyse zeigen, daß bei gemeinsamer Erhitzen von Nickel(II)-Sulfid und Manganoder Eisenoxiden, in Abhängigkeit von dem Molarverhältnis der Reaktionspartner verschiedene Reaktionen stattfinden. Das eingehende Studium dieser Reaktionen zeigte das Auftreten einer Anzahl Zwischenstufen, darunter auch die Bildung von Sulfaten.

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Résumé On montre par thermogravimétrie et analyse thermique différentielle que plusieurs réactions peuvent se produire suivant les rapports molaires des constituants lorsque l'on chauffe du sulfure de nickel(II) avec des oxydes de manganèse ou de fer. L'étude détaillée de ces réactions a mis en évidence un certain nombre d'étapes intermédiaires, avec formation de sulfates.

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, (II) , . , , .

     

Methods for characterization and their influence on the structure of silicon-rich zeolites

H, Li, Na, Cs, NH₄, Mg and Al-ZSM 5 zeolites and H and NH₄-mordenites were studied by DTA, X-ray diffraction, TPD and adsorption measurements. The stability relating to dealumination and structure destruction depends on the nature of the cation.H and NH₄-ZSM 5 were strongly dealuminated to silicalitelike phases in the temperature range 973–1273 K during the course of the DTA measurement. NH₄-mordenite was dealuminated below 873 K in the TPD experiment on the deammonization.The thermal destruction of ZSM 5 containing Na⁺, Mg²⁺, Al³⁺ and Cs⁺ ions begins at about 1400 K. Excess sodium ions present in the original Na-ZSM 5 decreased the thermal stability. For H and NH₄-mordenites, complete amorphization was found at 1270 K.

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Zusammenfassung H-, Li-, Na-, Cs-, NH₄-, Mg- und Al-Zeolithe ZSM 5 sowie H- und NH₄-Mordenit wurden durch DTA, Röntgenbeugung, temperaturprogrammierte Desorption (TPD) und Adsorptionsmessungen untersucht. Die Stabilität gegenüber Dealuminierung und Strukturzusammenbruch hängt von der Art des Kations ab. H- und NH₄-ZS_M 5 werden im Verlauf der DTA-Messungen im Bereich 973–1273 K zu Silicalit-ähnlichen Phasen dealuminiert. NH4-Mordenit wird unterhalb 873 K bei der Ammoniakabspaltung im TPD-Experiment dealuminiert. Der thermische Zusammenbruch von Na-, Mg-, Al- und Cs-ZSM 5 beginnt um 1400 K. Im ursprünglichen NaZSM 5 vorhandene überschüssige Natriumionen verringern seine thermische Stabilität. Für H- und NH4-Mordenit wird bei 1270 K vollständige Amorphisierung gefunden.

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,. H, Li, Na, Cs, NH4, Mg, Al ZSM 5 -, N4- . . , - NH4-ZSM 5 973–1273 . , NH4 873 . ZSM 5 , , , , 1400 . NaZSM 5 . /N4- 1270 .

     

Catalytic properties of sodium-containing silica gel in n-heptane decomposition

n-Heptane decomposition reactions on silica catalysts containing various amounts of sodium ions were studied. Ethylene, methane and propylene as well as unbrached -olefins were the main reaction products. The comparison of the experimental and theoretical results suggests a free-radical reaction mechanism.

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- , . , , -. - .

     

Introduction of Marinelli effective solid angles for correcting the calibration of NaI(Tl) field gamma-ray spectrometry in TL/OSL dating

A study is made of the corrections that are needed in the evaluation of the annual radiation dose, for use in TL/OSL-dating, via NaI(Tl) field gamma-ray spectrometry (monitoring of K, Th and U), calibrated via voluminous blocks that are simulating the Auger hole measuring conditions. Two cases are considered: the Heidelberg granite calibration block, which was found to be quasi-infinite, and the Oxford concrete calibration blocks, for which effective concentrations of elements are reported so as to account for their non-infiniteness. The calculations, via the software package ANGLE, are based on the concept of effective solid angles for Marinelli geometries.     

The application of ‘Z’-shaped UV cells in open-tubular capillary column liquid chromatography

Summary Z-shaped UV cells for packed capillary columns cannot be used in open-tubular capillary column liquid chromatography (OT-LC) because of their relatively large volume. With post-column solvent make-up, a commercial Z-shaped cell (volume 100 nl) was used in our OT-LC system, resulting in 9-fold sensitivity increase against on-column UV detection and with little efficiency loss. A small volume (5 nl) Z-shaped cell allows the direct coupling of the cell to high efficiency columns. For dilute samples, 9-19-fold sensitivity enhancement could be obtained. However, column efficiency decreases with increasing signal level as a result of peak deformation.     

Effect of hydrothermal treatment on the gelatinisation properties of potato starch as measured by differential scanning calorimetry

Gelatinisation temperatures as a function of moisture content were determined for potato starch. The native starch was then hydrothermally treated at a temperature 3% (Kelvin degrees) below the gelatinisation peak temperature and at moisture levels varying from 20 to 67% (by weight). Gelatinisation temperatures, temperature ranges and enthalpy values were affected for all treated samples. However, two sample populations could be distinguished: those samples treated under limited moisture conditions and other samples treated in the presence of extragranular moisture. A two-step hydrothermal treatment further increased the gelatinisation temperature, but the effect of the second step was small in comparison to that of the first.We thank the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek for research positions as aspirant (H. Jacobs) and post-doctoraal onderzoeker (R. C. Eerlingen).     

Characterization and thermal investigations of ammonium heptamolybdate

Thermal decomposition of ammonium heptamolybdate was studied by means of differential scanning calorimetry and thermogravimetry. DSC showed that the material decomposes in the temperature region 463–608 K in static air atmosphere, in three steps. The products of decomposition were characterized by IR spectroscopy, elemental analysis and magnetic susceptibility measurements. All the phases are paramagnetic in nature. Kinetic analysis suggested that the first two steps are controlled by a diffusion mechanism, while the third step is controlled by nuclear-growth.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie und Thermogravimetrie wurde die thermische Zersetzung von Ammoniumheptamolybdat untersucht. Laut DSC zersetzt sich die Substanz in statischer Luftatmosphäre im Temperaturbereich von 463 bis 608 K in drei Schritten. Die Produkte wurden durch IR-Spektroskopie, Elementaranalyse und Messungen der magnetischen Suszeptibilität charakterisiert. Alle Phasen sind paramagnetischer Natur. Kinetische Untersuchungen besagen für die ersten zwei Schritte einen diffusionskontrollierten, für den dritten Schritt einen wachstumskontrollierten Mechanismus.

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. , 463–608 . , . . , , — .

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The authors are grateful to the UGC, New Delhi, for financial assistance.     

The application of modulated differential scanning calorimetry to the glass transition

The modulated differential scanning calorimetry (MDSC) technique superimposes upon the conventional DSC heating rate a sinusoidally varying modulation. The result of this modulation of the heating rate is a periodically varying heat flow, which can be analysed in various ways. In particular, MDSC yields two components (reversing and non reversing) of the heat flow, and a phase angle. These each show a characteristic behaviour in the glass transition region, but their interpretation has hitherto been unclear. The present work clarifies this situation by a theoretical analysis of the technique of MDSC, which introduces a kinetic response of the glass in the transition region. This analysis is able to describe all the usual features observed by MDSC in the glass transition region. In addition, the model is also able to predict the effects of the modulation variables, and some of these are discussed briefly.Financial support has been provided by the DGICYT (Project no.PB93/1241). J.M.H. wishes to acknowledge financial assistance for a sabbatical period from the Generalitat de Catalunya.     

Thermogravimetric characterization of Quayarah heavy crude oils

Five heavy crude oil samples from the Quayarah field were thermally evaluated using two modes of thermogravimetry (TG): dynamic and programmed TG with heating and hold-up periods at 350 and 550°. The light and medium volatility fraction (L+M) appeared directly proportional to the metal content. In contrast, the heavy fraction (H) (350–550°) was inversely proportional to the metal content. This contradiction was attributed to the autocatalytic degradation of some of the heavy fraction into lighter species, which upgrades the crude with respect to the (L+M) fraction at the expense of the heavy fraction. The crudes were identical with regard to the ratio (L+M) to (H+R), whereR=residue, as a consequence of their identical API gravity and sulphur contents.The rate of degradative volatilization of the heavy fraction was measured by DTG, which indicated a direct correlation with the vanadium content as regards the onset temperatures and the DTG peak maximum.

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Zusammenfassung Fünf vom Quayarah-Feld stammende schwere Rohöle wurden mittels dynamischer und programmierter TG mit konstanten Perioden bei 350 und 550 °C charakterisiert. Der Anteil der leicht- und mittelflüchtigen Fraktion (L+M) schien proportional, der der schwerflüchtigen Fraktion (H) (350 550°) dagegen umgekehrt proportional dem Metallgehalt zu sein. Dieser Widerspruch wurde dem autokatalytischen Abbau einiger der schwerflüchtigen Komponenten zu leichteren Spezies zugeschrieben, der zu einer Erhöhung des Anteils der (L+M)-Fraktion auf Kosten der schwerflüchtigen Fraktion führt. Die Rohöle waren wegen der gleichen API-Schwere und gleicher Schwcfclgehalle hinsichtlich des Verhältnisses von (L+M) zu (H+R) identisch (R=Rückstand). Die Geschwindigkeit der degradaliven Verflüchtigung der schweren Fraktion wurde mittels DTG gemessen, wobei sich eine direkte Korrelation zwischen dem Vanadingehalt einerseits und der Einsatztemperatur bzw. dem DTG-Peakmaximum andererseits ergab.

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350 550°. (+ ) , () (350–550°) — . , . + +, — , . . , , .

     

Periodic precipitation of mercury sulphide

Summary In the gelatin medium Revert types of rings of mercuric sulphide are obtained. A system containing both Revert types of rings and Direct types of rings in the same test tube is obtained in the agar agar and starch gels.

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Zusammenfassung In Gelatine als Medium erhält man Ringe von Quecksilbersulfid vom Revert-Typus. Ein System, das beiderlei Ringe, Revert-Typus und Direkt-Typus im gleichen Proberohr aufweist, wird in Agar-Agar- und Stärke-Gelen erhalten.

     

ESR studies on stabilized cool flame of propylene

In the oxidation of propylene a sharp change in the concentration of radicals, observed when passing from the slow reaction region to cool flames, indicates the chain character of the cool flame. Unlike propane and butane, the temperature dependence of the radical concentration and the maximum self-heating are practically unchanged within 603–663 K.

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. , . , 603–663 , .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Glycosides of marine invertebrates. X. The structure of stichoposides A and B from the holothurianStichopus cloronotus

The structures of two triterpene oligosides from the holothurianStichopus cloronotus (Brandt) have been established; they are: 23-acetoxy-3-[O--D-quinovopyranosyl-(12)--D-xylopyranosyloxy]holost-7(8)-ene and 23-acetoxy-3-[O--D-glucopyranosyl-(12)--D-xylopyranosyloxy]holost-7(8)-ene.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 181–184, March–April, 1981.     

A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5

The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16相似文献   

Alkylation of toluene with methanol on zeolites: Evidence for Rideal type mechanism

Alkylation of toluene with methanol on zeolites H, Na–Y, FAU and H-ZSM-5 has been carried out. The results are consistent with the Rideal type mechanism.

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H, Na–Y, FAU H-ZSM-5. .

     

Recent progress in numerical methods for the determination of thermokinetics

The results of a multinational concerted programme on the determination of thermokinetics are presented. The purpose of the programme was to compare different numerical methods which have been independently proposed for the determination of thermokinetics from experimental calorimetric data. To achieve this end, the same experimental data, obtained from two heat-flow calorimeters, were distributed and successively analyzed by the different methods. Numerical methods based on the state function theory, on Fourier transform analysis, on dynamic optimization and on a simple differentiation of the data were thus critically tested.

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Zusammenfassung Es wurden die Ergebnisse der gemeinsamen Arbeiten über die Bestimmung der Thermokinetik mit 4 numerischen Methoden (dynamische Optimalisierung, Methode der Zustandfunktionen, harmonische Analyse und umgekehrte Korrektion) vorgestellt. Die experimentellen Daten wurden mit Hilfe von 2 Kalorimetern mit einer konstanten Temperatur des Isoliermantels ermittelt. Die Durchführung der Versuche ermöglichte ein Vergleich der angewandten Methoden.

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Résumé Les résultats d'un programme de recherches concerté multinational sur la détermination des données thermocinétiques sont présentés. Le but du programme était de comparer différentes méthodes numériques proposées indépendamment pour la détermination des données thermocinétiques à partir des mesures calorimétriques expérimentales. Pour celà, les mêmes données expérimentales fournies par deux calorimètres à flux de chaleur ont été distribué es et analysées successivement par 4 méthodes: utilisation des variables d'état, analyse de la transformée de Fourier, optimalisation dynamique et simple différentiation des données.

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. , . , , . , , , .

     

Arsido iron carbonyl clusters

Summary The XAsFe₄(CO)₁₄ (X = Cl, Br) clusters have been prepared and characterised and a new synthesis under mild conditions has been found for As₂Fe₃(CO)₉. The latter complex has at least two isomeric structures in solution.A preliminary account of this work was given in a lecture.The terms pnicogen and pnictide have been introduced as group names for the group Va family of elements analogous to the use of chalcogen and chalcogenid as group names for the group VIa elements.