Determination of the surface acidity of solid catalysts

A novel method has been developed for determining the surface acidity of white, as well as deeply colored porous solids. The method, which was tested on Al₂O₃, SiO₂–MgO–Al₂O₃ and Fe₂O₃ catalysts, is based on the adsorption of pyridine or benzylamine on acidic sites and subsequent displacement of the adsorbed bases by n-butylamine. A linear correlation was found between the concentration of acidic sites on Al₂O₃ and Fe₂O₃ catalysts and their activity in the dehydration oftert-butyl alcohol.

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, . , Al₂O₃, SiO₂–MgO–Al₂O₃ Fe₂O₃, -. Al₂O₃ Fe₂O₃ - .

     

Selective hydrogenation of fatty oils on alloyed Ni?Al catalyst. I. Kinetic model

On the basis of literature data concerning the reaction mechanism, a kinetic model for the selective hydrogenation of cotton-seed oil on the S-3 commercial alloyed Ni–Al catalyst is suggested. Its parameters have been identified according to the experimental data obtained in an agitated slurry reactor at T=140–200°C and P=0.2–0.8 MPa.

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, C-3. , , t=140–120°C, P=0.2–0.8 .

     

Effect of the state of vanadium cations on the IR spectra of adsorbed carbon monoxide

ESR and IR-spectrosocpic studies of the effect of the state of vanadium ions on the IR-spectra of adsorbed CO have revealed complex formation of CO with V⁴⁺ (vCO at 2192 and 2205 cm^–1) and V³⁺ (vCO at 2178 and 2185 cm^–1) ions.

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-- - CO. CO V⁴⁺ (vCO 2192, 2205 cm^–1) V³⁺ (vCO 2178, 2185 cm^–1).

     

Catalytic epoxidation of propylene with tert-butyl peroxide in presence of molybdenum complexes on polymer carriers

A polymer catalyst has been synthesized on the basis of Amberlite IRA-45 anion-exchange resin modified with molybdenum hexacarbonyl. Its catalytic activity in the epoxidation of propylene with tert-butyl hydroperoxide is similar to the activity of Mo(CO)₆ used under homogeneous conditions.

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, - Amberlite IRA-45, . - Mo(CO)₆, .

     

Thermogravimetry of copper and copper oxides (Cu2O-CuO)

The thermogravimetry of mixtures of metallic copper and copper oxides was studied. The experiments were performed by heating the samples in air to 700–800° to transform all the components to copper(II) oxide, and continuing the heating in nitrogen to 1050–1100° when the dissociation of copper(II) oxide to copper(I) oxide is complete. The identification of the components and their quantitative determination were carried out by determining the shape, size, and ratio of the segments of the curves obtained during the heating. The method can be used for quantitative analysis of mixtures of copper and/or copper oxides.

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Zusammenfassung Gemische von metallischem Kupfer und Kupferoxiden wurden thermogravimetrisch untersucht. Zur Überführung aller Komponenten in Kupfer(II)-oxid erhitzte man sie in Luft auf 700–800°, um daraufhin bis zur vollständigen Dissoziation des Kupfer-(II)-oxids zu Kupfer(I)-oxid unter Stickstoff die Temperatur bis auf 1050–1100° zu steigern. Die Identifizierung der Komponenten und ihre quantitative Bestimmung erfolgten durch die Form, Größe und die Verhältnisse der verschiedenen Abschnitte der erhaltenen Kurven. Diese Methode ist zur quantitativen Bestimmung von Gemischen aus Kupfer und Kupferoxid sowie von Kupferoxiden geeignet.

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Résumé Étude thermogravimétrique de mélanges du cuivre métallique et d'oxydes de cuivre. Les échantillons sont d'abord chauffés dans l'air jusqu'à 700–800° jusqu'à ce que tous les constituants soient transformés en oxyde de cuivre(II); le chauffage est ensuite poursuivi dans l'azote jusqu'à 1010–1100°, où la dissociation de l'oxyde de cuivre(II) en oxyde de cuivre(I) est complète. Les constituants ont été identifiés et dosés en utilisant la forme, la dimension et les proportions des différentes parties des courbes pendant le chauffage. La méthode peut être utilisée pour l'analyse quantitative de mélanges de cuivre et ou d'oxydes de cuivre.

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. 700–800: ( (), 1050–1100° [ () (I)]. , , . / .

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The author wishes to acknowledge the financial assistance provided by the Technion — Israel Institute of Technology.The author wishes also to thank Dr. R. F. Tylecote (University of Newcastle Upon Tyne, England) for very helpful comments and useful discussions of this investigation and to Mrs. N. Leder for chemical analyses.     

IR and thermal studies on lanthanum zirconyl oxalate

Lanthanum zirconyl oxalate hydrate (LaZO) was prepared and characterized by chemical analysis and i.r. spectral studies. Its thermal decomposition was investigated by using DTA, TG, X-ray diffraction and i.r. spectral studies. On the basis of the TG and`isothermal results, a tentative decomposition scheme was proposed. In the first step the dehydration of LaZO takes place in two steps between room temperature and 498 K, to give the anhydrous compound. The anhydrous oxalate decomposes in a series of steps (498–548 K, 548–673 K and 673–773 K). Finally the decomposition of the carbonate takes place (773–1073 K) to give lanthanum zirconate (La₂Zr₂O₇).

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Zusammenfassung Lanthanzirkonyloxalathydrat (LaZO) wurde hergestellt und durch chemische Analyse sowie durch Infrarotspektroskopie charakterisiert. Seine thermische Zersetzung wurde unter Einsatz von DTA, TG, Röntgendiffraktion und Infrarotspektroskopie untersucht. Aufgrund der TG und isothermen Ergebnisse wurde ein Zersetzungsschema vorgeschlagen. In der ersten Stufe erfolgt die Dehydratisierung von LaZO in zwei Schritten zwischen (RT-498 K) um die Anhydroverbindung zu ergeben. Das wasserfreie Oxalat wird in einer Serie von Stufen zersetzt und verschiedene Zwischenprodukte enthalten sowohl Oxalat als auch Carbonat (498–548 K, 548–673 K und 673–773 K). Abschließend findet die Zersetzung des Carbonats statt (773–1073 K) unter Bildung von Lanthazirkonat (La₂Zr₂O₇).

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Résumé L'oxalate hydraté de lanthane-zirconyle (LaZO) a été préparé et caractérisé par analyse chimique et spectrométrie infrarouge. La décomposition thermique de ce composé a été examinée par ATD, TG, diffraction des rayons X et spectrométrie infrarouge. Un mécanisme de décomposition est proposé, d'après les résultats TG, obtenus en régimes dynamique et isotherme. Dans un premier temps la déshydratation de LaZO a lieu en deux étapes (température ambiante —498 K) pour fournir le composé anhydre. L'oxalate anhydre se décompose en plusieurs étapes et plusieurs composés intermédiaires contenant l'oxalate ainsi que du carbonate (498–548 K, 548–673 K, 673–773 K). Finalement, la décomposition du carbonate (773–1073 K) fournit du zirconate de lanthane (La₂Zr₂O₇).

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, . , , . , . , 498 . , , 498–548 , 548–673 673– 773 . 773–1073 -La₂Zr₂O₇.

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The authors are grateful to Dr. W. U. Malik, Prof. & Head of Chemistry Department, Roorkee University, for providing the research facilities. V. B. R. is also grateful to the CSIR (India) for the award of a senior research fellowship.     

X-ray and thermal studies of ferroelectric Dy2(MoO4)3

Dysprosium molybdate, Dy₂(MoO₄)₃, displays a ferroelectric phase transition at 145 °C. The X-ray and thermal (DTA, TG and DSC) properties of this compound have been studied. The X-ray study confirmed the ferroelectric phase in the orthorhombic space group Pba2. Thermal analysis demonstrated the existence of a ferroelectric and another phase transition in this compound.

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Zusammenfassung Dysprosiummolybdat, Dy₂(MoO₄)₃ (Abk.: DMO), ein Vertreter der Seltener-denmolybdatreihe zeigt bei 145 °C einen ferroelektrischen Phasenübergang. Röntgendiffraktion und thermische Eigenschaften (DTA, TG, DSC) der genannten Verbindung wurden untersucht. Auf Grund der Röntgendiffraktionsuntersuchung gehört die ferroelektrische Phase in die orthorhombische Raumgruppe Pba2. Mittels Thermoanalyse konnte bei dieser Verbindung die Existenz ferroelektrischer und anderer Phasenübergänge nachgewiesen werden.

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145 °C. (, ) . , Pba2. .

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The authors wish to thank Prof. A. Paul and Mr. R. Bhatnagar for their kind help in some of the experimental work. One of us (MR) gratefully acknowledges a Fellowship from DST, Government of India.     

Kinetics and mechanism of isothermal dehydration of LiKC4H4O6 · H2O single-crystals

The kinetics of isothermal dehydration of LiKC₄H₄O₆.H₂O single-crystals was investigated in the [001] crystallographic direction under a dynamic vacuum of 6.7×10^–5 Pa with a quartz crystal microbalance. The removal of H₂O molecules may be described by a diffusion equation for a semi-infinite medium. The diffusion coefficients vary from 2.13×10^–11 cm² s^–1 at 391.7 K to 9.9×10^–9 cm² s^–1 at 453.2 K. The scanning electron microscope data provide some evidence that the dehydration is not a topochemical reaction. From the experimental data it is concluded that the anhydrous product is in the state of premelting. This explains the anomalous diffusion energyE _D=37±1 kcal mol^–1 and preexponential factorD ₀=5×10⁹ cm² s^–1.

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Zusammenfassung Die Kinetik der Entwässerung von LiKC₄H₄O₆.H₂O in [001] — Richtung unter dynamischem Vakuum wurde mit einer Quarzkristall-Mikrowaage verfolgt. Die Abgabe von Wasser kann mit einer Diffusionsgleichung für ein halb-unendliches Medium beschrieben werden, die Diffusionskoeffizienten variieren von 2, 13 · 10^–11 cm²s^–1 bei 391,7 K bis 9,9 · 10^–9 cm² s^–1 bei 453,2 K. Rasterelektronenmikroskopische Aufnahmen zeigen, daß die Entwässerung nicht topochemisch abläuft. Nach dem experimentellen Ergebnis befindet sich das entwässerte Produkt in einem Vorschmelz-Stadium. Daraus erklären sich die anomalen Werte für die DiffusionsenergieE _D=(37±1) kcal mol–1 und den präexponentiellen FaktorD ₀=5 · 10⁹ cm² s^–1.

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6,7 · 10. LiKC₄H₄O₆.H₂O [001]. . 2,13·10^{–11 2 –1} 391,7 9,9·10^{–9 2 –1} 453,2 . , . , «», E =37±1 ·^{– 1} ₀=5·10⁹²·^–1.

     

Pt catalyst for the liquid-phase epoxidation of cyclohexene with an O2/H2 mixture

Conditions are found for the preparation of Pt catalysts providing the formation of epoxy-derivative in the reaction of cyclohexene with an O₂/H₂ mixture.

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Pt .

     

A study of thermal preparation OF c-Mn2P4O12

With the application of thermogravimetry under quasi-isothermal-isobaric conditions, the reaction course of the calcination of Mn(H₂PO₄ · H₂O to give dimanganese cyclotetraphosphate has been studied. Isothermal calcination was also carried out in an electric furnace at various temperatures (200 min). The reaction products were analyzed by chromatography, IR and NMR spectrocopy, and X-ray diffraction analysis. The compositions of the calcinates were determined through extraction with various inorganic and organic solvents.

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Zusammenfassung Der Verlauf der Dimangan-cyclotetraphosphat ergebenden Kalzinierung von Mn(H₂PO₄)₂ · H₂O wurde thermogravimetrisch unter quasi-isothermen-isobaren Bedingungen untersucht. Isotherme Kalzinierung wurde auch im elektrischen Ofen (200 min) bei verschiedenen Temperaturen ausgeführt. Die Reaktionsprodukte wurden chromatographisch, IR- und NMR-spektroskopisch sowie röntgendiffraktometrisch analysiert. Die Zusammensetzung der kalzinierten Produkte wurde via Extraktion mit verschiedenen anorganischen und organischen Lösungsmitteln bestimmt.

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Mn(H₂PO₄ · H₂O. . . - , - - . .

     

On the applicability of the first-order equation for the reactions of solids

It is suggested that besides its traditional application to describe random nucleation, the first-order equation F1 can be used for the diffusion kinetics of gas-solid small particles reactions.

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, F1 - - .

     

Preparation of catalysts by spray decomposition

Spray decomposition of solutions is an uncommon but very promising technique for the preparation of multicomponent solid systems with welldefined structure. The experimental arrangement is described and a summary of the systems prepared until now is given. These are MgO–ZnO, CaO, CdO, Al₂O₃. Fe₂O₃ solid solutions and CdO. CdSO₄ and Al₂O₃. Al₂(SO₄)₃ systems.

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, , . : MgO·ZnO, CaO·CdO,. Al₂O₃·Fe₂O₃ CdO·CdSO₄ Al₂O₃·Al₂ (SO₄)₃.

     

Studies on catalytically active surface compounds, VIII. On the reaction of VCl4 with aerosil

The preparation and hydrolysis of silica supported vanadium catalysts have been investigated using VCl₄ as a paramagnetic probe. Chemical analysis shows the possibility of the VCl₄ molecule to react one, two, or three hydroxy groups of the surface. The type of reaction is influenced by the temperature of pretreatment of aerosil (TPA). ESR measurements show distortions of the tetrahedral coordination of the (SiO)_nVCl_4–n surface complex, which is strongest for the threefold attachment (n=3) of VCl₄ to the surface. Hydrolysis is accompanied by an increase of the coordination number and leads to highly mobile vanadium species.

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, VCl₄ . , VCl₄ , . . (SiO)_nVCl_4–n, VCl₄ (n=3). .

     

IR-spectroscopic studies of the interaction of pyridine bases with vanadium and molybdenum oxides supported on magnesia

As shown by IR-spectroscopic studies, pyridine bases interacting with V₂O₅ and MoO₃ supported on MgO form hydrogen bonds with surface hydroxyls and coordinate bonds with V and Mo ions. The interaction of 2,6-dimethylpyridine adsorbed on the surface with oxygen leads to the formation of 6-methylpyridine-2-carboxaldehyde, whose formyl group interacts with surface hydroxyls.

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, V₂O₅ MoO₃, MgO, V Mo. 2,6- 6--2-, OH-.

     

Hydrogenation of carbon monoxide catalysts prepared by pyrolysis of Co2(CO)8 on various oxide supports

Catalysts prepared by pyrolysis of Co₂(CO)₈ on oxide supports have been studied in the hydrogenation of CO. It is shown that MgO and -Al₂O₃-based catalysts are less active than those supported on SiO₂, TiO₂ and ZrO₂. The application of -Al₂O₃ as a support increases the relative yield of light hydrocarbons.

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, Co₂(CO)₈ , CO. , MgO -Al₂O₃ SiO₂, TiO₂ ZrO₂. -Al₂O₃ .

     

Thermoanalytical investigation of sodium acetate trihydrate for application as a latent heat thermal energy storage material

The thermal behaviour of sodium acetate trihydrate (NaAc · 3H₂O) was investigated by DTA, Q-TG and measurements of the solubility properties. The nucleation efficiency of Na₄P₂O₇ · 10H₂O for the crystallization of NaAc · 3H₂O melts is not stable over long periods. Stratification can be ascribed to the formation of anhydrous sodium acetate in the supercooled melts. Under static heat storage conditions, NaAc · 3H₂O and Na₄P₂O₇ · 10H₂O do not exhibit stable behaviour.

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Zusammenfassung Das thermische Verhalten von Natriumacetat-trihydrat (NaAc · 3H₂O) wurde durch DTA, Q-TG und Löslichkeitsmessungen untersucht. Der Keimbildungseffekt von Na₄P₂O₇ · 10H₂O gegenüber NaAc · 3H₂O ist über längere Zeit nicht stabil. Die Schichtbildung kann zurückgeführt werden auf die Bildung von wasserfreiem NaAc in unterkühlten Schmelzen. Unter statischen Bedingungen der Wärmespeicherung zeigen NaAc·₃H₂O und Na₄P₂O₇ · 10H₂O kein stabiles Verhalten.

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, Q- . Na4P2O7 · 102, . . .

     

O2 and CO adsorption on Ru(001) plane

Activity and selectivity data obtained in n-hexane dehydrocyclization over Pt/Al₂O₃ and Pd–Pt/Al₂O₃ catalysts exposed to different thermal treatment processes are compared. The ageing phenomena were most pronounced on catalysts treated in hydrogen at higher temperatures. The Pd–Pt/Al₂O₃ catalyst possessed lower cracking activity with a parallel increase of the selectivity for benzene and iso-hexanes.

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, - Pt/Al₂O₃ Pd–Pt/Al₂O₃, . , . Pd–Pt/Al₂O₃ .

     

Hydrogenation of CO2 on carbon-supported nickel and cobalt

The hydrogenation of CO₂ has been studied at atmospheric pressure on Co/C and Ni/C catalysts and the results are compared with those obtained on unsupported Co and Ni. Specific activites in the form of turnover frequencies for CO₂ hydrogenation decrease with increasing metal dispersity. Carbon supported Co and Ni present a smaller selectivity for methane than bulk metals. Higher specific activities and smaller activation energies are obtained on Co catalysts, compared with those determined for Ni catalysts.

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CO₂ Co/ Ni/ Co Ni . CO₂ . Co Ni , . .

     

Thermal and calorimetric investigations on crystalline hydrates of barium hydroxide and their deuterated analogues

The thermal decompositions of Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O and Ba(OH)₂ · D₂O were studied and the phase transitions were identified by DSC and DTA methods. The corresponding enthalpy changes were determined and compared with those calculated from the thermodynamic data. A decrease of the thermal stability was demonstrated for the deuterated crystal hydrates in comparison with the normal ones.

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Zusammenfassung Die thermische Zersetzung von Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O und Ba(OH)₂ · D₂O wurde untersucht. Phasenübergänge wurden mittels DSC und DTA ermittelt. Die entsprechenden Enthalpieveränderungen wurden bestimmt und mit den aus thermodynamischen Daten berechneten Werten verglichen. Die deuterierten Kristallhydrate sind thermisch weniger stabil als die leichtes Kristallwasser enthaltenden Verbindungen.

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()₂ · 8₂, ()₂ · 8D₂O, Ba(OH)₂·H₂O Ba(OH)₂·D₂O. , . .

     

Change of selectivity of butadiene oxidation due to zeolitic support for phosphorus-vanadium catalyst

The effect of the OH groups of the zeolites HY, HZSM-5 and HZSM-11 on the selective behavior of the supported active component P–V–O (P/V=1) in the oxidation of butadiene is characterized in detail and discussed. It was shown that the change in the selectivity was caused by the interaction of the pure component with the protondonor centres of zeolite: on this type of catalysts with the supported active component only furan and not maleic anhydride is formed as a product.

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OH- HY, HZSM-5 HZSM-11 P–V–O (P/V=1) . , - : , .