Structural changes of NaX zeolite during the H2S+O2 reaction

Infrared spectra in the 600, 700, and 1000 cm^–1 regions and X-ray investigations indicate that during H₂S+O₂ reaction in the temperature region of 293–473 K partial dealumination of the NaX zeolite crystal structure occurs. The dealumination increases with reaction temperature.

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- 600, 700 7000 ^–1 , H₂S+O₂ 293–473 NaX. .

     

Comparison of DSC and optical transmission measurements of polymorphic transitions

Using optical measurements on single crystals, the speed of first order transitions (K₂Cr207, KNO₃, AgNO₃) was determined and compared with the strongly smeared DSC signals. Such optical measurements are proposed to select materials which are suitable for the determination of the DSC apparatus function.

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Zusammenfassung Mit Hilfe von optischen Messungen wird die Geschwindigkeit von polymorphen Phasenumwandlungen 1. Ordnung (K₂Cr₂O₇, KNO₃, AgNO₃) bestimmt und mit entsprechenden stark verschmierten DSC-Signalen verglichen. Derartige optische Messungen erscheinen geeignet, um Substanzen zu suchen, welche für die Bestimmung der DSC-Apparatefunktion geeignet sind.

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K₂Cr₂O₇, KNO₃ AgNO₃ $ , $ . , $ .

     

Acidity modification by thermal and steam treatment in silica-alumina and its relation with methanol to hydrocarbons reaction

The physical properties as well as the acidity of an amorphous silica-alumina were modified by steam and thermal treatments and a general correlation (including samples modified by other methods) between hydrocarbon formation and surface acidity was obtained.

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, . ( , ) .

     

The investigation of thermally treated glasses of controlled porosity by means of differential thermal analysis

Some of the materials used as chromatography packings, adsorbents or catalyst supports are glasses of controlled porosity (CPGs). The chemical structure of these materials can easily be changed by heating the porous glass. Such thermal modification leads to the enrichment of the CPG surface in boron atoms. The long exposure of CPGs to thermal treatment can even cause the formation of borate crystals in the pores of the glasses. This paper considers the application of thermal analysis to the investigation of porous glasses heated for different periods of time.

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Zusammenfassung Einige der als chromatographische Säulenpackungen, Adsorbenten oder Katalysatorträger verwendeten Materialien sind Gläser mit definierter Porosität (CPGs). Die chemische Struktur dieser Materialien kann leicht durch Erhitzen verändert werden. Eine solche thermische Modifizierung führt zu einer Anreicherung von Bor in der Oberflächenschicht. Eine langdauernde Erhitzung der CPGs kann sogar zur Bildung von Boratkristallen in den Poren der Gläser führen. Im vorliegenden Artikel wird die Anwendung der thermischen Analyse zur Untersuchung von porösen Gläsern in Abhängigkeit von der Erhitzungsdauer behandelt.

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, , , . . . . , .

     

Mixed suspensions of semiconductors forming microheterojunctions. A new type of highly efficient photocatalysts: Photocatalytic production of dihydrogen from a water solution of sulfide ions in the presence of platinized ZnyCd1-y/CuxS suspension

A new method is proposed for increasing the quantum efficiency of H₂ production for the photocatalysts based on semiconductor suspensions. The method consists of the formation of suspended particles with microheterojunctions between their components--semiconductor phase.

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H₂ .

     

A rapid method for catalyst activity measurements by combination of pulse reactor, mass spectrometer and process computer

The combination of a pulse reactor attached directly (without a separation column) to a mass spectrometer/process computer system is described. To obtain a conversion/temperature diagram for the dehydration and dehydrogenation of 2-butanol less than one hour is required. Therefore, the method can be used for rapid characterization or comparison of the activities of various samples.

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, ( ) - . / 2- . .

     

Sensitivity of the solution of kinetic differential equation systems to the variations in the initial state exemplified by liquid-phase chain oxidation of hydrocarbons

The influence of the initial states on the solution of the system of differential equations for the chain mechanism of liquid phase hydrocarbon oxidation has been studied.

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, .

     

Thermal and structural properties of rare earth exchanged zeolites

A series of rare earth zeolites of types X and Y were prepared by cation exchange. Thermal analysis curves (TG/DTA) were employed to estimate the structural changes in the zeolite framework. Analogous investigations were carried out by independent methods such as XRD and IR spectroscopy. The results indicate increased thermal stability on the replacement of sodium by rare earth. Partial replacement of rare earth by ammonium/hydrogen enhances the thermal stability. The type Y zeolites are more stable than those of X type.

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Zusammenfassung Eine Reihe von Ionen der Seltenen Erdmetalle enthaltenden Zeolithen des Typs X und Y wurden durch Ionenaustausch hergestellt. Thermoanalytische Kurven (TG/DTA) wurden zur Beurteilung der strukturellen Veränderungen des Zeolithgitters herangezogen. Analoge Untersuchungen wurden mit unabhängigen Methoden (XRD und IR-Spektroskopie) ausgeführt. Es wurde festgestellt, daß ein Ersatz der Natriumionen durch Ionen der Seltenen Erdmetalle zu einer Erhöhung der thermischen Stabilität führt. Ein teilweiser Ersatz der Seltenen Erdmetallionen durch Ammonium-/Wasserstoffionen erhöht die thermische Stabilität. Zeolithe des Typs Y sind stabiler als die des X-Typs.

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X . (/) . - . . . X .

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NCL Communication No: 2186     

51V NMR studies of systems V2O5-KHSO4 and V2O5?K2SO4

Systems V₂O₅–KHSO₄ and V₂O₅–K₂SO₄ have been studied by the⁵¹V NMR method. The first system demonstrates the same states of vanadium as the previously studied V₂O₅–K₂S₂O₇, in this system a compound with an equimolar ratio of components has been found. In V₂O₅–K₂SO₄ the state of vanadium differs from the above systems and the formation of a compound with V/K=4 is observed.

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⁵¹V KHSO₄–V₂O₅ K₂SO₄–V₂O₅. , K₂S₂O₇–V₂O₅, . K₂SO₄–V₂O₅ V/K4.

     

Cyclodextrin-accelerated oxidation of iodide by oxygen in aqueous solutions containing HClO4

The oxidation of iodide to I ₃ ^– by oxygen dissolved in water containing HClO₄ has been found to be accelerated by -cyclodextrin (-CD). Among -, -, and -CDs, -CD is the most effective mediator for the oxidation reaction of iodide by oxygen. The oxidation rate of iodide is first order in the concentrations of -CD and HClO₄, whereas it is second order in the KI concentration.Part of this work was carried out at Department of Physics, Miyazaki Medical College, Miyazaki 889-16, Japan.