On the thermal decomposition of Zn(NO3)2·6H2O and its deuterated analogue

The thermal dehydration and decomposition of Zn(NO₃)₂·6H₂O (I) were studied via DTA, TG and DSC, quantitative analysis and IR spectroscopy, and compared with those of Zn(NO₃)₂·6D₂O (II). The following phase transitions were observed: melting of the salts; partial dehydration to tetrahydrate; formation of basic nitrate-hydrate; and formation of ZnO.The sum of the enthalpies of dehydration and thermal decomposition for I was 286 kJ/mol, while that for II was 299 kJ/mol (data from DSC). The probable mechanisms were determined from the TG curves and the formal kinetic parameters were calculated for the two stages of thermal decomposition. Calculations with an equation of the accelerating-type exponential law gave for the formation of basic zinc nitrate-hydrateE ^*=59 kJ/mol for I andE ^*=64 kJ/mol for II. For the decomposition of the basic salt, the equation for bidimentional diffusion yieldedE ^*=127 kJ/mol for I andE ^*=138 kJ/mol for II.

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Zusammenfassung Mittels DTA, TG, DSC, Elementaranalyse und IR-Spektroskopie wurde die thermische Dehydratation und Zersetzung von Zn(NO₃)₂ · 6H₂O (I) untersucht und mit der von Zn(NO₃)₂· 6D₂O (II) verglichen. Folgende Phasenumwandlungen konnten beobachtet werden: Schmelzen des Salzes; teilweise Dehydratation zu Tetrahydrat; Bildung von basischem Nitrathydrat; und Bildung von ZnO. Die Summe der Enthalpien für Dehydratation und Zersetzung betrug für I 286 kJ/mol und für II 299 kJ/mol (berechnet aus DSC). Die wahrscheinlichen Mechanismen wurden auf Grundlage der TG-Kurven festgelegt und die formalen kinetischen Parameter für die zwei Schritte der thermischen Zersetzung berechnet. Berechnungen ergaben für die Bildung des basischen ZinknitrathydratesE _m ^* =59 kJ/mol bei I undE ^*=64 kJ/mol für II. Für die Zersetzung des basischen Salzes lieferte eine Gleichung für zweidimensionale DiffusionE ^*=127 kJ/mol für I undE ^*=138 kJ/mol für II.

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, , , (I). (II). ; , , - . , I 286 · ^–1, II 299 · ^–1. , . , , ^* I - 59 · ^–1, II- 64 · ^–1. ^* , , I II, , 127 138 · ^–1.

     

Influence of HCl on butene isomerization catalyzed by ethanolic rhodium trichloride II. Calculation and interpretation of the rate constants of the triangle scheme

The values of the rate constants of the triangle scheme, calculated by means of a non-linear least-squares method, depend systematically on the HCl concentration. The alteration of the cis-trans selectivity expressed by the ratio k_1c/k_1t might indicate a change in the mechanism of isomerization with the HCl concentration.

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, , . - , k_1c/k_1t, .

     

Application of emissionless infrared diffuse reflectance spectrometry for following reactions of adsorbed alcohols on an alumina catalyst

IR spectra of adsorbed alcohols on alumina were measured under the reaction conditions at elevated temperatures. The transient response of IR absorption intensity indicates that alkoxides are reactive adsorbed species but carboxylates are not. The rate constants of surface reactions were calculated from the transient response.

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, . , , , —, .

     

Thermal behaviour of transition metal complexes of dithiocarbazic esters. II

A thermal study (simultaneous TG and DTA measurements) was carried out on the dithiocarbazic ester complexes M[N³CH₂R₁N²C¹(S)SCH₃]₂, where M=Ni, Pt; R₁=C₆H₅. The following disproportionation reaction occurs in the solid state: II is formed through deprotonation of the CH₂ group bound to N³, whereas III is formed through protonation of N³.The influence of inductive and/or steric effects on the mechanism of this reaction is discussed, taking into account the electrochemical and X-ray data on the complexes Pt[NRNC(S)SR']₂ with differentR substituents: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃; R=CH₃, CH₂Ph.These results accord with the behaviour of the same complexes in solution.

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Zusammenfassung Dithiokarbamidsäureesterkomplexe M[N³CH₂R₁N²C¹(S)SCH₃]₂ mit M=Ni, Pt und R₁=C₆H₅ wurden thermisch untersucht. Im festen Zustand spielt sich folgende Disproportionierungsreaktion ab: II wird durch Deprotonierung der an N³ gebundenen CH₂ Gruppe und III durch Protonierung des Atoms N² gebildet. Unter Zuhilfenahme der elektrochemischen und Röntgendaten der Komplexe Pt[NRNC(S)SR']₂ mit verschiedenen Substituenten R: R=H, Ph, CH₂Ph, CH₂C₅H₁₁, CH(CH₃)₂, C(CH₃)₃ und R=CH₃ bzw. CH₂Ph wurde der Einfluß von induktiven und/or sterischen Effekten auf den Reaktionsmechanismus diskutiert. Diese Ergebnisse stehen in Übereinstimmung mit dem Verhalten der Komplexe in Lösung.

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M[N³CH₂R₁N²C¹(S)SCH₃]₂, M= Ni, Pt,R ₁=C₆H₅. : II CH₂ , N³, III N². () , Pt[NRNC(S)SR]₂, R= , aR= . .

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We thank prof. A. La Ginestra for many helpful discussions on the various aspects of this work.     

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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, , / , . , . .

     

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.     

Determination de la purete des substances chimiques par analyse calorimetrique differentielle (A. C. D.)

Purity determination by DSC is possible if the impurity concentration lies within the limits 0.01 to 20 mole%. The thermodynamic equation of Schröder-Van Laar was used.This equation takes into account the effect of the departure of solutions from ideality, and the difference between the heat capacities in the solid and molten states.

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Zusammenfassung Eine Reinheitbestimmung mittels DSC ist möglich, wenn die Konzentration der Verunreinigung zwischen 0.01 und 20 Mol-% liegt. Es wurde die thermodynamicshe Gleichung von Schröder-Van Laar angewandt. Diese Gleichung berücksichtigt den durch die Abweichung der Lösungen vom idealen Zustand bedingten Effekt und den Unterschied der Wärmekapazität im festen Zustand und in der Schmelze.

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, 0.01–20 %. --, .

     

AlPO4?ZrO2 catalysts, IV. Cyclohexene skeletal isomerization activity of systems obtained in ethylene oxide

The use of AlPO₄–ZrO₂ (weight ratio AlPO₄/ZrO₂=3) as catalyst systems obtained with ethylene oxide and subjected to different stages of heat treatments has been studied through their catalytic activity in the skeletal isomerization of cyclohexene to 1- and 3-methylcyclopentenes (1- and 3MCP). The apparent rate constants and selectivity to 1-MCP are used for an evaluation of the presence and amount of strong acid sites, the only ones capable of giving rise to skeletal isomerization. The decrease in catalytic activity as calcination increases is consistent with not only the decrease in the amount of acid sites measured vs. weaker organic bases but also with the decrease in Brönsted acidity, as shown by the decrease in O–H band intensity.

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AlPO₄–ZrO₂ ( AlPO₄/ZrO₂=3), , 1- 3- (1- 3-). 1- , . , , , O–H.

     

Ammonia decomposition on polycrystalline Pt at pressures between 1.3 and 93 kPa

The kinetics of ammonia decomposition on polycrystalline Pt at temperatures between 600 and 1700 K and at pressures between 1.3 and 93 kPa were measured and correlated with a Langmuir-Hinshelwood unimolecular reaction rate expression. This rate expression had previously been shown to fit data in the same temperature range for pressures between 2 and 1400 Pa.

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Pt 600–1700 1,3 93 , - . , , , 2 1400 .

     

Effect of bond energies of a catalyst with reacting atoms on the selectivity of CO hydrogenation over metals

In hydrogenation over metals (M)_j carbon monoxide is adsorbed as a molecule. C–O bond rupture in partially hydrogenated complex, MCHOH, leads to MO and MCH₂ and then to hydrocarbons, while transformation of MCHOH into MCH₂OH gives alcohols and other oxygen-containing compounds. Selectivity towards hydrocarbons increases with increasing energy of M–O bonds.

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(M) . C–O MCHOH MO MCH₂ — ; MCHOH MCH₂OH . M–O.

     

Influence of pore diffusion on the rate of n-heptane conversion on a Pt/Al2O3 catalyst under reforming conditions

Under reforming conditions, the rate of n-heptane conversion on a large Pt/Al₂O₃ catalyst grain, in contrast to that in the kinetic region, depends on the hydrogen to hydrocarbon mole ratio. The rate equation for the reaction on a large grain agrees well with the experimental results obtained by a gradientless method under pressure.

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- , , : . , .

     

Studies of the structure of multicomponent Raney nickel catalysts

Genesis and structure of Raney nickel catalysts modified by Mo, Fe and Ca have been studied by XPS, SIMS and Auger and electron microprobe methods. It has been established that these catalysts are inhomogeneous and their structure can be described by models accounting for the interaction and localization character of metal components, their oxides and hydroxides.

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, - Ni-, Mo, Fe Ca. , , , .

     

Solid-state decomposition studies on fluoroperoxo species of transition metals part II

The kinetics of isothermal decomposition of solid K₂Zr₂(O₂)₂F₆·2H₂O have been studied in the temperature range 100–226° under vacuum. The fractional decomposition has been determined by measuring the pressure of evolved oxygen during pyrolysis with the help of a McLeod gauge. The values ranged from 0.05 to 0.62. The vs. t data showed that the kinetics are deceleratory throughout the course of the reaction. The initial part of the decomposition reaction could be best described by a unimolecular decay law, while the later stages obey contracting volume kinetics. The activation energies have been determined and the respective values for the above stages are 13.6 and 6.9 kcal·mole^–1.

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Zusammenfassung Die Kinetik der isothermen Zersetzung von festen K₂Zr₂(O₂)₂F₆·2H₂O wurde im Temperaturbereich von 100–226° im Vakuum untersucht. Die fraktionierte Zersetzung wurde durch Messung des Druckes des während der Pyrolyse entwickelten Sauerstoffs mit einem McLeod-Manometer bestimmt. Die -Werte variierten von 0.05 bis 0.62. Die -t Daten zeigen, daß die Kinetik im Verlauf der Reaktion herabgesetzt wird. Der erste Teil der Zersetzungsreaktion konnte am besten durch ein unimolekulares Zerfallgesetzt beschrieben werden, während die späteren Phasen der Kinetik der Volumenkontraktion gehorchten. Die Aktivierungsenergien wurden berechnet und die entsprechenden Werte für obige Reaktionen ergaben sich 13.6 bzw. 6.9 Kcal mol^–1.

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K₂Zr₂(O₂)₂F₆·2₂ 100–226°. «» , , . «» 0.05 0.62. –t , . , — . , , , 13.6 6.9 .^–1.

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One of the authors (SMK) is grateful to I.I.T. Delhi for a research scholarship.     

Fractal analysis of co hydrogenation over rhodium catalysts

A fractal scaling law has been applied to products of carbon monoxide hydrogenation over silica supported rhodium catalysts. The results indicate structure sensitivity and that the type of structural sensitivity is product dependent.

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, . , , .

     

n-Butane oxidation over a vanadium-phosphorus catalyst

The activity of vanadium-phosphorus oxide catalysts with respect to maleic anhydride formation in n-butane oxidation has been found to correlate with the concentration of V⁴⁺ ions in the catalysts. The steady catalytic activitv of the samples examined is achieved more rapidly upon prereduction.

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, - - . , .

     

PMR study of the lifetime of complexes with a strong hydrogen bond at low temperatures

The kinetics of formation and cleavage of hydrogen bonds in complexes of carboxylic acids with proton acceptors have been studied by PMR spectroscopy over the range –100 to 150°C. The activation parameters of the processes have been measured.

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¹H –100° ÷–155°C . .

     

Construction of a thermoanalyzer for DTA-TD-TMAG-T measurements on metals up to 1100 °C

A thermoanalyzer is described for the simultaneous testing of metals and alloys by three methods: differential thermal analysis (DTA), thermal dilatometry (TD) and thermomagnetometry (TMAG). One reference specimen is used as a standard for each of the above kinds of analysis. Measurements can be performed in vacuum or in a static or dynamic atmosphere of gases at any pressure between normal and 5× 10^–5 Torr. The temperature of the sample can be changed linearly in the range 20–1100 °C. DTA and TD are performed classically, whereas TMAG is based on the temperature and magnetic field-dependences of the reversible magnetic susceptibility of the sample. Some analysis results are presented.

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Zusammenfassung Es wird ein Thermoanalysator zur simultanen Untersuchung von Metallen und Legierungen durch drei Methoden beschrieben: Differentialthermoanalyse (DTA), Thermodilatometrie (TD) und Thermomagnetometrie (TMAG). Für alle drei Verfahren wurde die gleiche Referenzsubstanz als Standard benutzt. Messungen können im Vakuum oder is statischer bzw. bewegter Atmosphäre von Gasen beliebigen Druckes zwischen Normaldruck und 5·10^–5 Torr durchgeführt werden. Die Temperatur der Probe kann zwischen 20 und 1100 °C linear variiert werden. Während DTA und TG die herkömmlichen Verfahren zu Grunde liegen, basiert TMAG auf der Temperatur- und Magnetfeldabhängigkeit der reversiblen magnetischen Suszeptibilität der Probe. Einige Analysenergebnisse wurden dargestellt.

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: (), () (). . , 5·10^–5 . 20–1100°. , . .

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Presented at the 4th European Symposium on Thermal Analysis and Calorimetry, Jena, GDR, August 1987.     

Adsorption characteristics of some zeolites

Attempts have been made to correlate the Si/Al atom ratio, the degree of crystallinity, crystallite dimensions and the mean diameter of crystalline particles with the relative adsorption affinity index (RAI). Differences in molecular sieving effect and in some diffusional aspects between traditional zeolites and the new shape-selective ZSM are revealed by the adsorption characteristics of cyclohexane, benzene, toluene, neopentane and xylenes.

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Si/Al , , , (RAI). - ZSM , , , .

     

Heterogenized rhodium complexes as hydrogen transfer catalysts

Cationic rhodium(I) norbornadiene complexes with polystyrene-immobilized imidazole, tetramethylbiimidazole or phosphine ligands in the presence of potassium hydroxide catalyze hydrogen transfer from isopropanol to acetophenone and 1-hexene. [Rh(NBD) (poly-PPh₂)₂] ClO₄ complexes are particularly efficient for the reduction of acetophenone, but slow decomposition to rhodium metal is observed.

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(I) , , , 1-. [Rh(NBD) (-PPh₂)₂]ClO₄ , .