Adaption of thermal analysis for the study of water vapour adsorption isotherms

Water vapour adsorption processes and equilibria on adsorbents with polar surfaces can be well tested with an adsorption method combined with thermal analysis. The first step involves the comparison of isothermal desorption-adsorption curves and thermal curves; in the second step different equilibrium points of the adsorption isotherms are tested by means of thermal analysis.Some examples of building materials are presented to demonstrate the possibilities of the method. The types of adsorption isotherms for the samples were formally equal in all examples; only the complex method presented was able to reveal that formation of the equilibiria was induced by essentially different processes. Such processes are: physical adsorption depending on the structure of the adsorbent and the activity of the external active centres, chemisorption, chemical reaction in the solid/vapour system and chemical reaction in the water phase condensed in the capillaries.

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Zusammenfassung Prozesse und Gleichgewichte der Wasserdampfadsorption an Adsorbenten mit polarer Oberfläche können gut mit einer mit thermischer Analyse kombinierten Adsorptionsmethode getestet werden. Der erste Schritt der Methode schließt den Vergleich der Desorptions-Adsorptionsisothermen und der thermischen Kurven in sich ein, im zweiten werden Gleichgewichtspunkte der Adsorptionsisothermen durch thermische Analyse getestet.Am Beispiel von einigen Baumaterialien werden die Möglichkeiten dieser Methode demonstriert. Die Adsorptionsisothermen waren formell in allen Fällen vom gleichen Typ und nur die vorgestellte komplexe Methode ergab, daß die Ausbildung des Gleichgewichtes durch grundsätzlich verschiedene Prozesse erfolgt. Solche Prozesse sind: von der Struktur des Adsorbenten und der Aktivität der aktiven Oberflächenzentren abhängige physikalische Adsorption Chemisorption, chemische Reaktion im Festkörper/Dampf-System und in der in Kapillaren kondensierten wässrigen Phase.

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- , . — . — . . , . : , , , — , .

     

Effect of the solvent on selective hydrogenation of 6, 10-dimethylundeca-3,5,9-trien-2-one

Reaction mechanism for selective hydrogenation of pseudo-ionon on Raney-Ni in the presence of n- and iso-alcohols has been studied. From the analysis of ESR spectra, the dependence of selectivity on the solvent is concluded.

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- Ni- . .

     

Basic condensation of triphenylsilane. II. Kinetics in anhydrous isopropanol and influence of silanol

Condensation of triphenylsilane with isopropanol in presence of isopropoxide has been studied in anhydrous medium and the activation parameters have been measured. Dehydration of the medium has been obtained by means of a pre-reaction of triphenylsilane with the residual water in the solvent. In this medium the reaction is extremely slow, moreover, it is inhibited by silanol whose effect would lower the actual catalyst concentration.

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. . , .

     

A device for pulse investigation of heterogeneous catalytic reactions

In the present work a simple device is described for the pulse investigation of heterogeneous catalytic reactions and catalysts. Owing to the possibility for separate adjustment of the gas flow rate in the catalytic reactor and in the chromatographic column, it can be used for kinetic measurements too.

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- . , .

     

Infrared study of the interaction of nitric oxide with CuY zeolites

Infrared studies of the interaction of NO with CuY–A zelites have been made over the temperature range from –100°C to 400°C. Several forms of NO adsorption have been found, in particular, a stable cis-dimer at low temperatures.

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- (–100+400°C) NO CuY–A . NO, ë - .

     

Catalytic activity of the CaO?CaF2 system

Cao–CaF₂ catalysts containing 0–100%CaF₂ have been studied concerning their activity in different reactions. Maxima of activity for butene isomerization and isopropanol decomposition as well as selectivity for the alcohol dehydration were found for the sample with equimolar ratio of the components. No sample was active in cumene cracking. Suggestions are made concerning the reaction mechanisms and the active centers involved.

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CaO–CaF₂, 0–100% CaF₂, . , , . . .

     

Asymmetric hydrogenation of tryptophan precursors catalyzed by rhodium-DIOP complexes

Z-2-benzamido(acetamido)-3-(3-indolyl)-2-propenoic acids were hydrogenated with neutral and cationic rhodium(I) complexes containing the chiral diphosphine (–) or (+)–2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane [(–) or (+)–DIOP].

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Z-2- ()-3-(3-)-2- () (I), (–) (+)-2,3--2,3--1,4- ()-.

     

Kinetics of thermal decomposition of diacyl peroxides in the presence of aerosil

In the presence of aerosil the thermal decomposition of the polymeric peroxide of sebacic acid is enhanced proportionally to the filler weight fraction in the reaction system. This is attributed to the interaction of peroxide groups with acidic groups on the aerosil surface and their decomposition according to a nonradical mechanism unlike the homolytic radical decomposition in solution.

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, , . .

     

Influence of hydrogen on the aromatization of ethane over Pt/H-ZSM-5 zeolite

Hydrogen influences the activity and selectivity of a Pt/H-ZSM-5 zeolite in ethane aromatization by favoring hydrogenolysis and suppressing dehydrogenation and coking. H₂ formed during the reaction inhibits the aromatization activity.

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Pt/H-ZSM-5 , . H₂, , .

     

Thermal studies on some complexes of Pd(II)

The formulae suggested for a series of complexes of Pd(II) with various amino acids have been verified by thermal methods using a derivatograph. A correlation of the obtained kinetic parameters with the structures suggested by electronic and IR spectra of the substances has been attempted.

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Zusammenfassung Es wurden Formeln für eine Serie von Komplexverbindungen des Pd(II) mit verschiedenen Aminosäuren vorgeschlagen und thermogravimetrisch bewiesen. Die Übereinstimmung zwischen den erhaltenen kinetischen Parametern und den durch ERS und Infrarotspektroskopie angedeuteten Strukturen wurde geprüft.

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Résumé On a vérifié par thermogravimétrie des formules brutes proposées pour les combinaisons complexes du Pd(II) avec divers acides aminés. On a examiné la correlation entre les paramètres cynétiques obtenus et les structures déduites des spectres IR et electroniques.

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ë , Pd(II) . , , .

     

Acetylene adsorption on a clean iridium surface

The interaction of C₂H₂ with a polycrystalline iridium surface at 140 KT500 K has been studied by AES, XPS and UPS. A model of the bonding between C₂H₂ and Ir by the 1 orbitals of the hydrocarbon is proposed. The more pronounced energy splitting between the orbitals of acetylene during adsorption compared to that in the gas phase is ascribed to deformation of the acetylene molecule.

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C₂H₂ . 140 KT500 K AES, XPS UPS. C₂H₂ Ir 1- . - , , .

     

A thermogravimetric study of the solid-state reaction between alumina and strontium carbonate

The kinetics of the solid-state reaction between alumina and strontium carbonate were studied by thermogravimetry. The effects of the structure ( or) and/or doping (with Li⁺ or Cd²⁺) of the alumina on the kinetics of the reaction were examined. The results obtained were correlated with the phase composition and structural changes, followed by a number of physicochemical analyses (DTA, XRA and IRA) throughout the course of the reaction.

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Zusammenfassung Die Kinetik der Festkörperreaktion zwischen Aluminiumoxid und Strontium-carbonat wurde thermogravimetrisch untersucht. Die Effekte der Struktur ( und) und/oder des Dopens des Aluminiumoxids (mit Li⁺ oder Cd²⁺) auf die Kinetik der Reaktion wurde untersucht. Die erhaltenen Ergebnisse wurden mit der Phasenzusammensetzung und mit durch physikalisch-chemische Analysenverfahren (DTA, XRA und IRA) während des Reaktionsverlaufs verfolgten strukturellen Veränderungen in Beziehung gebracht.

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. ( ) Li⁺ Cd²⁺ . , , - .

     

Isomerization, dehydrogenation and cracking of methylcyclohexane over HNaY zeolites

On HNaY zeolites the fractions of acid sites which are active for cracking, isomerization and dehydrogenation of methylcyclohexane do not increase linearly with increasing degree of exchange. Isomerization and dehydrogenation seem to involve a similar activated complex, while cracking proceeds through a different one and requires stronger acid sites. Activation energies are independent of exchange degree.

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HNaY, , . , . .

     

Hydrocondensation of CO: Catalytic activity of modified iron-alumina catalysts

The activity of modified Fe/Al₂O₃ catalysts in the hydrocondensation of CO has been studied in terms of the selectivity for light olefins and of repartition of the hydrocarbon products.

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Fe/Al₂O₃ CO, .

     

Influence of anchored cerium ions on the dispersity and activity of Pd/SiO2 catalysts

(Pd+Ce)/SiO₂ catalysts prepared by decomposition of organometallic complexes of Ce and Pd have higher activity, dispersity and selectivity in methanol synthesis than Pd/SiO₂ catalysts.

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, (Pd+Ce)/SiO₂ , Ce Pd, Pd/SiO₂.

     

Shape selectivity and maximum molecular size in methanol to hydrocarbons transformation

The maximum product size obtained during methanol to hydrocarbons transformation on medium and large pore zeolites and amorphous silica-aluminas is not governed by shape selectivity but it is a consequence of operational conditions and other process characteristics such as the occurrence of cracking reactions.

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, , , .

     

Reactivity of coordinated O2?, ion-radicals towards one-electron reductants

Using the flow ESR method, the rates of the reaction between the radical complex Ti(IV)(O ₂ ^– ) and one-electron reductants in aqueous solution have been measured. The redox potential for the Ti(IV) (O ₂ ^– )/Ti(IV) (O ₂ ^2– ) couple is about 1.7 V.

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Ti(IV)(O ₂ ^– ) . - Ti(IV)(O ₂ ^– )/Ti(IV)(O ₂ ^2– ) 1,7 .

     

Gas-phase hydroformylation of propylene on Ru/SiO2 catalysts

Ru/SiO₂ catalysts prepared by reduction of supported RuCl₃·xH₂O are active in gas-phase hydroformylation of propylene at low pressure (ca. 0.3 MPa) of H₂+CO+C₃H₆ mixtured and show unexpectedly high selectivity towards unbranched oxo-products. Data concerning the effect of electronic state and dispersity of Ru on their catalytic behavior have been obtained.

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Ru/SiO₂, RuCl₃·xH₂O, (0,3 ) - . .