Solvent Effect on the Thermodynamics of Complex Formation with Proton Transfer from 4-Nitrophenylnitromethane to Triethylamine

In studying the thermodynamics of the formation of the 4-nitrophenylnitromethane–triethylamine ion pair in different chemical solvents within the dielectric constant interval 2.4 65, an increase in the ion pair stability with an increase in the medium polarity is revealed. Account for the effect of dielectric saturation of solvent molecules through the Blok–Walker function () gives pK= f(()) (Kis the equilibrium constant of ion pair formation), which is nearly linear. The electrostatic and nonelectrostatic components of the thermodynamic parameters of the reaction are estimated. The governing role of the covalent contribution to solvents with high polarity and of the electrostatic contribution to systems with 4–7 is established. A linear correlation between the bathochromic shift of the band in the electronic absorption spectra of solutions of the ion pair and the logarithm of the stability constant of the complex is found.     

Effect of the support on the coking of nickel catalysts in hydrocarbon steam reforming

Experiments on the coking rates of variously prepared nickel catalysts on TiO₂, Al₂O₃ and MgO in n-butane steam reforming show that changes in the relative coking rate at a rising steam excess in the gas phase depend mainly on the kind of support. The results obtained are accounted for by changes in the electron density at the site of nickel crystallite contact with the surface of various supports.

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, TiO₂, Al₂O₃ MgO, - , , , , , . .

     

Kinetic model for hydrocarbon synthesis from CO and H2 accounting for its intragroup distribution

A method to describe a multicomponent process of hydrocarbon synthesis from CO and H₂ over iron catalysts and a kinetic model to calculate the intragroup distribution of up to C₂₀ hydrocarbons, are suggested. Values for the kinetic parameters are presented.

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CO H₂ . , C₂₀, .

     

Le systeme L-citrulline-eau

Two phase diagrams of the L-citrulline-water system were obtained by using DTA on samples held in sealed glass ampoules. The first one exhibits only the anhydrous solid-liquid-vapour equilibrium, while the second one shows the peritectic decomposition reaction of L-citrulline dihydrate at 61. Tammann's curve does not reveal a maximum point for the dihydrate composition; this point is located in the water-rich part of the diagram. This must be related to the action of a non-negligible vapour pressure. A monotropic polymorphism of L-citrulline is expected. The second diagram is an isochoric (V/m=8 cm³ g^–1) section of theT-V/m-x diagram, which involves the presence of a vapour phase.

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Zusammenfassung Zwei Phasendiagramme des L-Citrullin-Wasser-Systems wurden durch DTA von in Glasampullen eingeschmolzenen Proben erhalten. Das erste bezieht sich nur auf das Gleichgewicht zwischen wasserfreiem Festkörper, Flüssigkeit und Dampf, wÄhrend das zweite die peritektische Zersetzungsreaktion von L-Citrullin-Dihydrat bei 61 wiedergibt. Die Tammann-Kurve zeigt kein Maximum bei der dem Dihydrat entsprechenden Zusammensetzung; dieser Punkt befindet sich im wasserreichen Teil des Diagramms. Dies mu\ der Wirkung eines nicht zu vernachlÄssigenden Dampfdruckes zugeschrieben werden. Ein monotroper Polymorphismus von L-Citrullin ist zu erwarten. Das zweite Diagramm ist ein isochorer (V/m=8 cm³ · g^–1) Abschnitt des eine Dampfphase involvierendenT-V/m-x-Diagramms.

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L-- , . ——, — L- 61. , , . . L-. (V/m=8 ^{3 –1}) T–V/m–x, .

     

Infrared spectra of nitric oxide adsorbed on photoreduced V/SiO2 catalyst

Studies of the IR spectra of surface species produced via NO adsorption on selectively photoreduced V/SiO₂ catalysts indicate that at low coverages NO is adsorbed on V³⁺ ions to form strongly bonded mononitrosyl species V³⁺...... NO. With increasing NO coverage, V³⁺ is oxidized to V⁴⁺, which is accompanied by the appearance of gaseous N₂O and weak adsorption of NO on V⁴⁺.

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- , NO V/SiO₂ . , V³⁺ NO V³⁺... NO. V³⁺ V⁴⁺, N₂O NO V⁴⁺.

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Structure, activity and selectivity of V2O5-TiO2 catalysts for o-xylene conversion

The formation of needle shaped crystallites of V₆O₁₃ at low V concentrations on V₂O₅-anatase coated catalysts explains the low selectivity for phthalic anhydride during o-xylene oxidation. The (010) plane of V-oxide, most active for selective oxidation of o-xylene, is not accessible and the contact of this plane with the anatase faces promotes the anatase-rutile transformation and the incorporation and blocking of V⁴⁺ ions.

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V₆O₁₃ V , V₂O₅-, -. (010) , -, , - V⁺⁴.

     

A Thermal study of the precipitates formed in ammonia neutralization of acidic solutions of dissolved phlogopite

The precipitates containing mainly iron, aluminium and magnesium hydroxides, obtained from phlogopite dissolved in nitric acid by means of the neutralization procedure with ammonia, have been investigated by thermal analysis (TG, DTG and DTA). According to the present study, which is part of a larger investigation into the chemical utilization of Finnish mica minerals, the formation of solid solutions between iron and aluminium hydroxides in silt increases with an increasing neutralization temperature. Nitrogen exists mainly in the form of nitrate in silts, and magnesium forms mixed hydroxides with aluminium, which causes a separation between the iron hydroxide and magnesium aluminium hydroxide phases.

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Zusammenfassung Die von in Salpetersäure gelöstem Phlogopit durch Neutralisierung mit Ammoniak erhaltenen, hauptsächlich Eisen-, Aluminium- und Magnesiumhydroxid enthaltenden Niederschläge wurden thermoanalytisch (TG, DTG und DTA) untersucht. In der vorliegenden Arbeit, die Teil einer grossangelegten Untersuchung zur chemischen Nutzung finnischer Glimmermineralien ist, wird gezeigt, dass die Bildung fester Lösungen von Eisen- und Aluminiumhydroxiden in Schluff mit zunehmender Neutralisationstemperatur ansteigt. Stickstoff kommt in Schluff hauptsächlich in Form von Nitraten vor, und Magnesium bildet Mischhydroxide mit Aluminium, was eine Trennung der Eisenhydroxidphase von der Magnesium-Aluminium-Hydroxidphase bewirkt.

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

     

Bromide ion oxidation of various Pt surfaces

At variance with the absence of an orientation effect in the hydrogen evolution reaction, aclear difference in the electrocatalytic effect of various parts of the surface on bromide ion oxidation is observed.

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qv .

     

Influence of the gas phase on metallic reference electrodes used in work function measurements

Contact potential differences between electrodes of Pt, Au and Ta of different surface finishing were measured by the dynamic condenser method in propylene and oxygen. Propylene is irreversibly adsorbed, thus changing the work function. This renders the electrodes unsuitable as standard electrodes for work function measurements on catalysts in the atmosphere of hydrocarbons, but they may be used in adsorption studies on oxygen.

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Pt, Au Ta . , , . , .

     

Relative thermodynamic stabilities of isomeric 1,2-dialkoxyethenes

The relative thermodynamic stabilities of the geometrical isomers of a number of 1,2-dialkoxyethenes have been determined by chemical equilibration in the neat liquid and in 1,4-dioxane solution with mercuric acetate as catalyst. From the variation of the value of the equilibrium constant with temperature, the thermodynamic parameters G , H , and S of theE Z isomerization were evaluated. In all cases theZ isomer proved to be thermodynamically the more stable species, its favor increasing with the bulkiness of the alkoxy groups. The thermodynamic data obtained for theEZ isomerization of 1,2-dimethoxyethene differ significantly from those reported in the literature. An attempt to correlate the experimental thermodynamic data with MM2 calculations for the title compounds as well as for 1,2-dimethoxypropenes is presented.     

Thermal behaviour of mixed tetravalent metal salts

In contrast with the well-known zirconium and titanium phosphates, products containing these metal ions together are unknown. To investigate the thermal behaviour of such materials, samples were synthetized with various ratios of the two metal ions. The samples were identified by means of X-ray diffraction. Their thermal behaviour was investigated in the temperature interval 25–1000 °C via simultaneous TG, DTG and DTA measurements. The data obtained are presented in this paper.

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Zusammenfassung Im Gegensatz zu den wohlbekannten Zirkonium- und Titanphosphaten sind beide Metallionen gleichzeitig enthaltende Produkte unbekannt. Zur Untersuchung solcher Substanzen wurden Proben mit unterschiedlichen Mengen der beiden Metallionen gefertigt und mittels Röntgendiffraktion identifiziert. Die Proben wurden im Temperaturbereich 25–1000 °C mittels simultaner TG-, DTG- und DTA-Messungen untersucht. Die Ergebnisse werden in dieser Arbeit mitgeteilt.

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, . . - , , 25–1000°. .

     

Interaction of a Single State with a Known Infinite System Containing One-Parameter Eigenvalue Band

Interaction of a quantum system S ₁ ^a containing a single state |> with a known infinite-dimensional quantum system S ^b containing an eigenvalue band [ _a , _b ] is considered. A new approach for the treatment of the combined system S =S ₁ ^a S ^b is developed. This system contains embedded eigenstates |()> with continuous eigenvalues [ _a , _b ], and, in addition, it may contain isolated eigenstates | _I > with discrete eigenvalues _I [ _a , _b ]. Exact expressions for the solution of the combined system are derived. In particular, due to the interaction with the system S ^b , eigenvalue E of the state |> shifts and, in addition, if E[ _a , _b ] this shifted eigenvalue broadens. Exact expressions for the eigenvalue shift and for the eigenvalue distribution of the state |> are derived. In the case of the weak coupling this eigenvalue distribution reduces to the standard resonance curve. Also, exact expressions for the time evolution of the state |(t)> that is initially prepared in the state |(0)>|> are obtained. Here again in the case of the weak coupling this time evolution reduces to the familiar exponential decay. The suggested method is exact and it applies to each coupling of the system S ₁ ^a with the system S ^b , however strong. It also presents a relatively good approximation for the interaction of a nondegenerate eigenstate | _s > of an arbitrary system S ^a with an infinite system S ^b containing a single eigenvalue band, provided this eigenstate is relatively well separated from other eigenstates of S ^a and provided the interaction between the systems S ^a and S ^b is not excessively strong.     

A new symmetrical micro-thermobalance

A new symmetrical micro-thermogravimetric analyzer has been developed. The symmetrical design of this instrument allows determination of very small mass changes over a wide range of temperatures. The utility of the instrument was demonstrated by studying the decomposition characteristics of CaC₂O₄·H₂O and the curing and decomposition kinetics of a glass filled polymer composite.

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Zusammenfassung Ein neuer symmetrische mikrothermogravimetrischer Analyser wurde entwickelt. Die symmetrische Gestaltung dieses Instruments ermöglicht die Bestimmung sehr geringer, sich über weite Temperaturbereiche hinziehender Massenveränderungen. Die Brauchbarkeit des Instruments wird demonstriert, in dem die Zersetzungscharakteristik von CaC₂O₄.H₂O und die Kinetik der Härtung und Zersetzung von glassverstärkten Polymerverbundstoffen untersucht wird.

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- . . ₂₄.₂, .

     

Study of the thermal dissociation of processes of nickel(II) and cobalt(II) β-diketonate adducts

Thermal dissociation processes of-diketonate adducts with the composition ML₂ · 2B (L = acetylacetone and its substituted derivatives;M = Ni, Co;B = H₂O, BuNH₂CH₃OH, Py, NH₃) were investigated. Kinetics of dissociation were studied in a flow reactor. For dehydration processes a compensation relationship is observed (lgA=E+b), demonstrating analogous mechanisms.A semi-quantitative series of the thermodynamic stabilities of the dihydrates is obtained from experimental data at quasi-equilibrium conditions (Q-derivatograph).

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Zusammenfassung Es wurden die thermischen Dissoziationsprozesse von-Diketonataddukten der Zusammensetzung ML₂ · 2B (L=Azetylazeton und dessen substituierte Abkömmlinge;M=Ni, Co;B=H₂O, BuNH₂, CH₃OH, Py, NH₃) untersucht. Die Kinetik der Dissoziation wurde in einem Flowreaktor untersucht. Als Beweis für die Ähnlichkeit der Mechanismen der Dehydrierungsprozesse konnte eine lgA=aE+b Beziehung festgestellt werden. Von unter Quasi-Gleichgewichtsbedingungen gewonnenen Daten konnte eine semiquantitative Serie der thermodynamischen Stabilitäten der Dihydrate abgeleitet werden (Q-Derivatograph).

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- ML₂·2B (L = ;M= Ni, Co;B=H₂O, BuNH₂, CH₃OH, Py, NH₃). ; (lgA=aEs+b) . (Q- ).

     

Kinetics of phase transformations in Cu-Al and Cu-Zn-Al alloys

The non-isothermal kinetics of the solid-state reactions taking place in Cu-Al and Cu-Zn-Al alloys were studied by DTA and X-ray measurements. It was found that the degree of conversion, which represents the change in the reacting system, is a function of the area increase in the DTA peak. The kinetic analysis shows that DTA is a useful method for the study of formal kinetic laws. From thef() functions, conclusions on the mechanism of the phase transformations can be drawn.

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Zusammenfassung Die nicht-isotherme Kinetik von in Cu-Al und Cu-Zn-Al-Legierungen verlaufenden Festkörperreaktionen wurden mittels DTA und Röntgenmessungen untersucht. Es wurde festgestellt, daß die Zunahme der Fläche des DTA-Peaks abhängig von dem die Veränderungen im Reaktionssystem repräsentierenden Konversionsgrad ist. Die kinetische Analyse zeigt, daß die DTA eine nützliche Methode zur Untersuchung der formalen kinetischen Gesetzmäßigkeiten ist. Aus den Functionenf() können Schlußfolgerungen hinsichtlich des Mechanismus der Phasenübergänge gezogen werden.

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, Cu-Al Cu-Zn-Al. , , , . . f() .

     

Establishment of chemical equilibrium: A mathematical characteristic

The time derivative of mean value of the state position indicator and the probability density of the first passage times for the state of exact equilibrium, both in the form of a function approximating the -distribution, characterize the establishment of macroscopic chemical equilibrium. The time parameter of this function has the meaning of the time required for chemical equilibrium to be established.

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, , -, . , .

     

Thermochemistry of hydrated rare earth orthophosphates

The hydrated rare earth orthophosphates LnPO₄ ·xH₂O (Ln=La-Dy) contain zeolitic water in the structural channels, which is released reversibly up to 300°. The thermal stabilities of the hydrates depend upon the nature of the Ln atom. The dehydration temperature decreases with decreasing ionic radiusr of Ln³⁺, according to the general equation=(r–a)/b (where is the DSC and/or DTG dehydration peak temperature, anda andb are empirical constants depending on the experimental conditions).The contracting-area rate equation was valid for linearization of the isothermal vs. time plots in the range 0; 0.65. Kinetic values ofE, A, H ⁺ and S⁺ were calculated and the kinetic stabilities of the hydrates are discussed.

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Zusammenfassung Die hydratisierten Seltenerdiphosphate LnPO₄·xH₂O (Ln=La bis Dy) enthalten in Kanälen ihrer Struktur zeolithisches Wasser, das reversibel bis 300 °C abgegeben wird. Die thermische Stabilität der Hydrate hängt von der Natur des Ln ab. Die Entwässerungstemperatur sinkt mit abnehmendem Ionenradiusr der Ln3+-Ionen gemäss:=(r–a)/b (a undb sind empirische Konstanten, die von den experimentellen Bedingungen abhängen). Die isotherme Entwässerung lässt sich im Umsatzbereich 0 0,65 mit der Gleichung für kontrahierende Fläche (zweidimensionale Phasengrenzreaktion) beschreiben. Die kinetischen Grössen AktivierungsenergieE, -enthalpieH ^*, und -entropieS ^* wurden berechnet und die kinetische Stabilität der Hydrate wird diskutiert.

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LnPO4·xH2O (Ln=La-Dy) , 300°. . r =(r-)/b, 9 — , a b — , . — <0; 0,65>. , , ^* S ^* .

     

Changes in the surface characteristics of residues from the thermal decomposition of nickel oxysalts

The changes in surface area and density which occur during the decomposition of eight nickel oxysalts have been reported. Surface area peaks were observed in the temperature range 473 K to 673 K. An equation relating to the number of product particles (n) produced from a single particle of original material has been derived. Logn was shown to vary linearly with temperature, wheren is the number of product particles formed from one original reactant particle.

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Zusammenfassung Es wird über die Veränderungen der Oberfläche und Dichte berichtet, welche bei der Zersetzung von acht Nickeloxysalzen auftreten. Oberflächenpeaks wurden im Temperaturbereich von 473 K bis 673 K beobachtet. Eine Gleichung wurde abgeleitet, welche sich auf die Zahl (n) der sich aus einem einzigen Partikel der Ausgangssubstanz bildenden Produktpartikel bezieht. Es wurde bewiesen, daß sich logn linear zur Temperatur ändert, wobein die Zahl der sich aus einem reagierenden Ausgangspartikel bildenden Produktpartikel ist.

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Résumé Etude des changements de surface spécifique et de densité pendant la décomposition de huits oxysels du nickel entre 473 K à 673 K. En désignant parn le nombre de particules issues d'une particule unique du matériau initial, on montre que logn varie linéairement avec la température.

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8 - , . , , 473–673 . , (), . logn .

     

Comparison between ESR spectra and activities of bismuth tungstate catalysts

Electron spin resonance absorptions have been studied in bismuth tungstate catalysts with Bi/W ratios of 2/3, 1/1, 2/1 and 6/1. The first three systems exhibit a mean g value of 2.07±0.04 while the last one does not show any ESR signal. All the systems are diamagnetic. The signals at g=2.03–2.11 are attributed to oxygen ion-radicals chemisorbed (O ₂ ^– ) on W⁶⁺. An attempt has been made to correlate these whith the catalytic activities of the bismuth tungstates in the oxidation of propylene and 1-butene.

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Bi/W=2/3, 1/1, 2/1 6/1. g=2,07±0,04, . . g=2,03 2,11 - (O₂ ^–), W⁺⁶. 1-.