Toluene disproportionation and coke formation over fluorided alumina and hydrogen-mordenite

Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.

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(0,8, 12 ) (12 ). -, . , , , . , - . .

     

Precipitation of iron catalysts for the Fischer-Tropsch synthesis

The batch Fischer-Tropsch wise precipitation of iron catalysts for the synthesis in the pH range of 4.60 to 7.91 is described in detail. Each step of the precipitation has been controlled by measurements of the relevant parameters to produce definite catalysts. Factors influencing the reproducibility are shortly discussed.

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- pH=4,60–7,91. . , .

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Effect of stirring on the Belousov-Zhabotinskii reaction: A problem of interpretation

It is probable that different phenomena attributed to mechanical stirring during the Belousov-Zhabotinskii (BZ) reaction are caused by atmospheric oxygen and, as far as our experiments show, they have nothing to do with dissipative structures or with the turbulence of the reacting mixture.

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, , , -, .

     

Ru(III) catalyzed oxidation of some aliphatic alcohols by N-bromosuccinimide (NBS). A kinetic study

Kinetics of Ru(III) catalyzed oxidation of methanol, ethanol, n-propanol, n-butanol, isopropanol and iso-butanol by N-bromosuccinimide (NBS) in the presence of Hg(II) acetate have been studied in acid medium. The oxidation exhibits a fractional order in [alcohol] and first order in [NBS]. The applicability of Taft's equation was tested. The probable mechanism is discussed.

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, , -, -, - () Hg(II), Ru(III), . . . .

     

Formation of nitrogen oxides during the oxidation of nitromethane on copper-chromium catalyst

Principles of the oxidation of nitromethane on a 30% CuCr₂O₄/-Al₂O₃ catalyst over the temperature range from 210 to 485 °C have been studied. The conversion of bound nitrogen to oxides depends on initial concentrations of nitromethane and oxygen in the range corresponding to the complete conversion of nitromethane (350–485 °C). The composition of oxidation products is determined by the oxygen to nitromethane ratio.

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30% CuCr₂O₄/-Al₂O₃ 210–485°C. (350–485°C) . , .

     

Chemical,dehydration, differential thermal and X-ray analysis of Salal bauxite deposits

Chemical, dehydration, differential thermal and X-ray analysis data on four samples of mineral deposits from the Salal region (J & K) have been determined to assess their mineral compositions. All the samples appear to be kaolinitic in character, though in association with other mineral impurities, such as boehmite, diaspore and dickite, in varying proportions.

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Zusammenfassung Vier Proben von Minerallagerstätten der Salal-Region (J & K) wurden chemisch sowie mittels DTA und röntgenographischer Analyse untersucht, um ihre Mineralzusammensetzung zu ermitteln. Alle Proben sind dem Charakter nach kaolinitisch, allerdings in unterschiedlichen Verhältnissen mit anderem mineralischem Material wie Boehmit, Diaspor und Dickit verunreinigt.

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, , , . , - , .

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The authors are grateful to the Head of the Department of Physics, Jammu University, for his interest in the research programme.     

The lability of carbon monoxide adsorbed on rhodium

Carbon monoxide which is retained by a rhodium surface after heating to 573 K exchanges with gas phase carbon monoxide at 293 K. The retained species is postulated as *–C=O–*.

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, 573 , 293 . *–C=O–*.

     

Oxygen adsorption on silver-gold alloy

Oxygen adsorption on Ag/Au alloys has been studied by field-emission microscopy (FEM). A decrease in the silver concentration of alloy is accompanied by a drastic fall in its ability to absorb oxygen. Using the interacting bonds method (IBM), the adsorption heat of atomic oxygen on the (100) plane of the silver-gold alloy has been calculated.

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. , . (100) .

     

Quantum-chemical study of the optical properties of MgO surface hydroxy groups

Cluster models of MgO surface OH groups have been studied by the semi-empirical CNDO method. The calculated stretching vibration frequencies of OH bonds and localized electron excitation energies on the OH-groups are shown to depend on the oxygen atom coordination.

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OH- MgO. , OH- , OH-, .

     

Catalytic reduction of nitric oxide with hydrogen over a cobalt-alumina catalyst. The effect of potassium additives

Catalytic reduction of NO with hydrogen has been studied using a differential reactor operated at atmospheric pressure. The process was carried out over a Co/Al catalyst containing potassium oxide as an additive. The presence of potassium generally produces a decrease in activity of the Co/Al catalyst except for very low concentrations of potassium atoms.

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NO , . Co/Al, . Co/Al, , .

     

Heats of adsorption of CO2 and NH3 on natural mordenites

The heats of adsorption of CO₂ and NH₃ were studied for sodium, lithium, calcium and decationized forms of natural mordenites. The exchange of Na⁺ for Ca²⁺ leads to increasing adsorption heats at low coverages. For CO₂ the region of elevated heats corresponds to the formation of Ca²⁺ ... CO₂ adsorption complexes. Two molecules of NH₃ probably interact with each Ca²⁺ ion (or with the Li⁺ ions in Li-mordenite). The heats of adsorption of NH₃ on decationized mordenite are much higher than those on calcium mordenite.

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Zusammenfassung Adsorptionswärmen von CO₂ und NH₃ an der Na-, Li-, Ca- und dekationisierten Form von natürlichem Mordenit wurden bestimmt. Der Austausch von Na⁺ gegen Ca²⁺ führt zu einer Erhöhung der Adsorptionswärmen bei geringen Bedeckungen. Bei CO₂ erfolgt im Bereich hoher Adsorptionswärmen die Bildung des Adsorptionskomplexes Ca²⁺ ...CO₂. Mit jedem Ca²⁺-Ion (bzw. Li⁺-Ion im Li-Mordenit) treten wahrscheinlich zwei NH₃-Moleküle in Wechselwirkung. An dekationisiertem Mordenit sind die Adsorptionswärmen von NH₃ höher als an Ca-Mordenit.

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, , . . Ca²⁺ ... CO₂. B , , ( -). , -.

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The authors would like to thank Dr. I. A. Belitsky for supplying the sample of natural mordenite. They also thank Professor S. P. Zhdanov for his interest and encouragement of this work.     

Studies on the catalytic oxidation of propylene on ferric molybdate

Ferric molybdate is less selective in the partial oxidation of propylene than bismuth molybdate. Its catalytic behavior is similar to that observed on other transition metal molybdates. The intrafacial nature of the reaction is established through kinetic and adsorption measurements.

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, . . .

     

Gas phase photoreaction of SO2 with n-pentane in the presence of NO

The spectrum of an intermediate, ascribed to nitrosopentane, has been detected in the photolysis of SO₂-pentane-NO mixtures. This may be explained by a radical photolysis mechanism involving an initial H-atom abstraction from the pentane molecule by SO₂.

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SO₂--NO , . , H .

     

Continuous recording of the X-ray diffraction pattern during catalysis: Methanol on molybdenum trioxide

Using a modified Guinier-Lenne camera, the X-ray diffraction pattern of a solid catalyst at work was continuously recorded on a photographic film. During methanol catalysis on a high area orthorhombic MoO₃ sample, no phase change is observed in the presence of oxygen at 200 °C (30 h); under the same conditons, but without oxygen, MoO₃ is converted within 2 h to the bronze H_xMoO₃ (x=0.6).

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-, - . MoO₃ - 200 °C (30 ); , MoO₃ H_xMoO₃(x=0,6) 2 .

     

Influence of lead on propane aromatization over Pt/ZSM5 catalysts

Aromatization of propane has been investigated over Pt-Pb/ZSM5. Addition of Pb decreases propane conversion with a corresponding increase in the aromatic selectivity. Hydrogenolysis reactions are inhibited by the presence of lead.

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Pt–Pb/ZSM-5. Pb . .

     

Energy dissipation and selectivity in the catalytic oxidation of ammonia

A qualitative interpretation of selectivity changes in ammonia oxidation, based on considerations of energy dissipation processes is presented.

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, .