Investigation of ethylene interaction with some oxidants in the presence of Pd2+ in acetic acid

The composition of products from the interaction of ethylene with some o oxidants, catalyzed by palladium acetate in acetic acid has been studied, An assumption is made on the possible reason for the influence of such oxidants on the selectivity of formation of ethylene glycol ethers.

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, , . .

     

Temperature-Programmed Desorption (TPD) of ammonia from H+-exchanged zeolites with different structures

Curves of the temperature-programmed desorption (TPD) of ammonia from zeolites were evaluated with several kinetic models. An approximately linear correlation was found between the activation energy of desorption or the heat of adsorption of H zeolites with various Si/Al ratios and the intermediate electronegativity of the zeolites, the latter representing a measure of the acid strength.This result corresponds to the change in the high-frequency infrared band of the OH groups and also to the change in the heat of adsorption, determined by microcalorimetry. Thus, the TPD of NH₃ is a useful technique for quantitative characterization of the acidic properties of several H zeolites.

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Zusammenfassung Kurven der temperaturprogrammierten Desorption (TPD) des Ammoniak von Zeolith wurden mit verschiedenen Kinetischen Modellen ausgewertet. Ein annähernd linearer Zusammenhang wurde gefunden zwischen der Aktivierungsenergie der Desorption bzw. der Adsorptionswärme von NH₃ an H-Zeolithen mit unterschiedlichem Si/Al-Verhältnis und der intermediären Elektronegativität der Zeolithe, die ein mass für die Säurestärke darstellt. Dieses Ergebnis entspricht der Verschiebung der hochfrequenten IR-Bande der OH-Gruppen und der mikrokalorimetrisch bestimmten Änderungen der Adsorptionswärme. Damit erweist sich die TPD von NH₃ als brauchbare Methode zur quantitativen Charakterisierung der sauren Eigenschaften von H-Zeolithen.

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- . - Si/Al , . , , . , - -.

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The authors wish to thank Prof. K.-H. Steinberg and Dr. M. Hunger for the zeolite samples, and R. Bauermeister for the non-linear regression programme.     

Hydrogen-oxygen titration and carbon monoxide chemisorption for the measurement of supported palladium surface areas

Hydrogen-oxygen titration and carbon monoxide chemisorption of silica supported palladium have been investigated, using the pulse chromatographic technique. An excellent agreement between metal surface areas derived from both methods was observed.

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H₂–O₂ . , .

     

Mechanism of alkyl iodide reduction to alkanes in aqueous solutions of Na2PtCl4?NaI?HClO4

Platinum(II) catalyzes the reduction of alkyl iodides to alkanes according to a mechanism involving oxidative addition of RI to Pt(II), reduction of the product complex RPt(IV) to RPt(II) by iodide ions and protolysis of the latter particle.

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(II) , RI Pt^II, - RPt^IV RPt^II .

     

Influence of the thermal treatment of platinum alumina catalysts with exhaust gases on their activity in cyclopropane hydrogenation

The activity of platinum/alumina catalysts in cyclopropane hydrogenation has been investigated. Catalysts heated in exhaust gases are considerably less active in cyclopropane hydrogenation as compared to samples calcined in air. A relatively stable modification of the metallic surface is formed, probably as a result of coke or poison deposition.

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- . , , , , , . , , .

     

Preparation of mixed-ligand complexes of nickel via thermal decomposition

If heated to around 270° in argon, [Ni(HSal)₂] (H₂Sal=salicylic acid) gives off gaseous H₂Sal and forms [NiSal], which reacts with monoprotic ligands HL (e.g. 8-hydroxyquinoline) to form mixed-ligand complexes [NiHSalL], or with diprotic ligands H₂L' (e.g. quadratic acid) to form dinuclear complexes [HSalNiL'NiHSal].

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Zusammenfassung Die Komplexverbindung [Ni(HSal)₂] spaltet beim Erhitzen auf 270 °C in Argon Salicylsäure ab und liefert [NiSal], das mit Monoproton-Liganden HL (z. B. 8-Hydroxychinolin) zu Gemischtliganden-Komplexen [NiHSalL], mit Zweiprotonen-Liganden H₂L' (z. B. Quadratsäure) dagegen Zweikernkomplexe [HSalNiL'NiHSal] bildet.

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[Ni(HSal)₂] 270°, [NiSal], HL (., 8-) [NiHSalL] H₂L [HSalNiLNiHSal].

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The preparative and thermoanalytical part of this work was performed by C. Gribi, D. Noukakis and M. Piccand, who also drew the Figures.

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This research was supported by the Swiss National Science Fundation, grant No. 2.053-0.99.     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

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Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

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Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

ESR investigation of vanadium-molybdenum oxide catalysts

Upon calcination of vanadium-molybdenum catalysts in air at 500°C two ESR signals are observed. They are attributed to a solid solution of MoO₃ in V₂O₅ (a) and to the incorporation of VO²⁺ into the compound V₂MoO₈ (b).

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500°C - - , MoO₃ V₂O₅, - VO⁺² V₂ MoO₅.

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

Studies of the structure of multicomponent Raney nickel catalysts

Genesis and structure of Raney nickel catalysts modified by Mo, Fe and Ca have been studied by XPS, SIMS and Auger and electron microprobe methods. It has been established that these catalysts are inhomogeneous and their structure can be described by models accounting for the interaction and localization character of metal components, their oxides and hydroxides.

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, - Ni-, Mo, Fe Ca. , , , .

     

TPD studies of hydrogen adsorption on group VIII metals

Hydrogen desorption proceeds in several temperature regions and differs by its order of magnitude and activation energy. Differential curves of adsorbed hydrogen distribution with respect to the desorption activation energy, dN/dE (E), show a considerable inhomogeneity of adsorbed atomic species and the energetic homogeneity of molecular species.

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. dN/dE (E) .

     

The activity of Ni/AlPO4, Ni/AlPO4?Al2O3 and Ni/AlPO4?SiO2 catalysts in the hydrogenation of e-cinnamaldehyde

Liquid-phase catalytic hydrogenatio of E-cinnamaldehyde was carried out by using new supported nickel catalysts (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ and Ni/AlPO₄–SiO₂) in methanol as solvent under low hydrogen pressure (4.1 bar) and 298 K. The kinetic orders are zero in H₂ and aldehyde. The selectivity to the hydrogenaton of the C=C double bond is very high (>99%)

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- (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ Ni/AlPO₄–SiO₂) (4,1 ) 298 . H₂ . C–C (>90%).

     

Hydrogenation of nitric oxide on platinum black in acidic solution

By comparison of the catalytic hydrogenation and electrochemical reduction of NO on platinum black catalysts it has been shown that the hydrogenation of NO to ammonia and to hydroxylamine occurs in the diffusion controlled region only.

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NO , NO .

     

Transient response study of the participation of adsorbed forms of ammonia in propene ammoxidation

On the basis of transient response studies, it is suggested that ammonia on the surface of a Mo–Si–Bi–P oxide catalyst forms a compound that is stable at the reaction temperature and whose reaction with propene yields acrylonitrile.

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, Mo–Si–Bi–P , .

     

IR characterization of surface hydroxy groups on haematite

The OH stretching absorptions (3670, 3640 and 3460 cm^–1) detected on haematite samples obtained by thermal decomposition of goethite, are assigned to monocoordinated and bridged free surface OH's and to hydrogen bonded OH's in surface micropores, respectively, on the basis of their behavior to successive adsorption of methanol, pyridine and D₂O and surface structural models.

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OH (3670, 3640 3460 ^–1) , . OH, OH, , , , D₂O, .

     

Alkylation of toluene with methanol on zeolites: Evidence for Rideal type mechanism

Alkylation of toluene with methanol on zeolites H, Na–Y, FAU and H-ZSM-5 has been carried out. The results are consistent with the Rideal type mechanism.

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H, Na–Y, FAU H-ZSM-5. .

     

Nature of propene chemisorption centers on molybdenum trioxide

As shown by temperature-programmed desorption (TPD), the quantity of reversibly chemisorbed propane on MoO₃ passes through a maximum depending on the degree of surface reduction. Using the ESR method, it is shown that the centers of propene chemisorption do not contain Mo⁵⁺ ions but presumably isolated Mo⁴⁺ ions.

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, MoO₃ . , Mo⁺⁵. , Mo⁺⁴.