Calculation of recombination rate constants in (H2?O2) system

Rate constants of the three-body recombination for the elementary three-molecule stages in hydrogen oxydation have been calculated.

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, .

     

Kinetics of molecular exchange in CF3COOH complexes with proton acceptors

The kinetics of hydrogen bond dissociation and formation in solution has been studied by a lineshape analysis of the¹H NMR signals of the proton donor (CF₃COOH) and proton acceptor (DMF) between –100 and –170°C. It has been found that proton exchange is much slower than molecular exchange and it does not affect the lineshape. A stepwise mechanism has been confirmed.

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( ) () — –100°–170°C. , . .

     

Resonance energy transfer from Al2O3 to adsorbed N2O

Radiolysis of adsorbed N₂O is shown to occur due to both the dissociative capture of electrons and direct energy transfer from the excited states of alumina to N₂O. One excited state ensures the decomposition of three N₂O molecules.

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, N₂O , N₂O, N₂O.

     

Homogeneous decomposition of gaseous methanol induced by CO2 laser

The laser heating procedure has been used to study chain reactions under strictly homogeneous conditions. The rate constants for the initiation and overall chain decomposition of methanol have been determined.

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. - 1000–1100 °.

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .

     

Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

IR-spectroscopic studies of strength and concentration of acid centers on V2O5/Al2O3 catalysts

The strength of protonic sites and the concentration of acid centers in V₂O₅/Al₂O₃ catalysts have been estimated according to pyridine and ammonium adsorption.

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V₂O₅/Al₂O₃.

     

Reaction scheme in the non-isothermal decomposition of (C6H5NH3)4Mo8O26 · 2 H2O

The thermogravimetric decomposition of anilinum octamolybdate has been studied under non-isothermal conditions to elucidate the chemical reactions taking place in the first step of decomposition of the anhydrous compound.The decomposition products were analyzed by gas-liquid chromatography, gas chromatography-mass spectrometry (GC/MS), infrared spectroscopy and X-ray powder diffraction.The main decomposition product of aniline turned out to be indole, which is different from the major product in the isothermal decomposition at the same temperature, i.e. N-ethyl-aniline.A dehydrocyclization reaction is suggested as the rate-dependent process. This is probably due to the catalytic effect of the octamolybdate anion.

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Zusammenfassung Die thermische Zersetzung von Anilinoctamolybdat wurde unter nicht-isothermen Bedingungen thermogravimetrisch untersucht, um die im ersten Zersetzungsschritt der wasserfreien Verbindung verlaufenden chemischen Reaktionen aufzuklären. Die Zersetzungsprodukte wurden mittels Gas-Flüssigkeits-Chromatographie, Gaschromatographie-Massenspektrometrie (GC/MS), Infrarotspektroskopie und Röntgendiffraktometrie analysiert. Als Hauptprodukt der Zersetzung von Anilin wurde Indol gefunden, während bei isothermer Zersetzung bei gleicher Temperatur vorwiegend N-Äthylanilin entsteht. Es wird angenommen, daß beim nicht-isothermen Prozeß eine wahrscheinlich durch das Octamolybdat katalysierte Dehydrocyclisierungsreaktion verläuft.

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, . - , -- , . , -N- . , , -.

     

Influence of thermal treatment and rehydration of Al2O3 on the amount of Al3+ ions migrating into HCl solution

The amount of Al³⁺ ions migrating into HCl solution from unit surface of Al₂O₃ grows with increasing oxide calcination temperature up to 1123 K, remains unchanged up to 1373 K and then, after the formation of -Al₂O₃, rises sharply. Preliminary rehydration of the surface - and -Al₂O₃ relatively decreases their amount.

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Al³⁺, Al₂O₃, 1123 1373 , -Al₂O₃ . - -Al₂O₃ , .

     

Catalytic and physico-chemical properties of Al2O3?H3PO4 system, II. Donor-acceptor properties

Donor-acceptor properties of catalysts containing different quantities of orthophosphoric acid on -alumina were studied. The decrease in N₂O decomposition rate was found to be parallel with that of one-electron donor sites. Catalysts containing more than 0.4 mmol H₃PO₄/g Al₂O₃ exhibit individual surface properties due to the formation of an aluminium phosphate phase in the surface layer.

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- , -Al₂O₃. , N₂O . , 0,4 H₃PO₄/ Al₂O₃ .

     

Ligand exchange between bis-acetylacetonato cobalt (II) and organotin compounds SnR2Cl2 (R=Ph, Et), I. NMR identification of exchange products in the Co(AA)2?SnPh2Cl2 system

NMR studies of the interaction between bis-acetylacetonato Co(II) and organotin compound SnPh₂Cl₂ (Ph=C₆H₅ ^–) in chloroform solutions with pyridine additive have revealed ligand exchange between the initial components to form Co(II) and Sn(IV) complexes with different numbers of ligands.

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Co(II) SnPh₂Cl₂ (Ph=C₆H₅ ^–). , Co(II) Sn(IV) .

     

Carbon content and H2 chemisorption of a regenerated Pt catalyst

The effect of the cracking of¹⁴C-labelled cyclohexene on the chemisorption (thermodesorption) of hydrogen on a thermally treated Pt powder catalyst has been studied. It has been established that (i) under the usual conditions of regeneration (calcination of the catalyst at 500°C for 1–2 hrs in a stream of air) the products of cracking cannot be completely removed from the catalyst, and (ii) as compared with the pure catalyst, the carbon deposit content of the catalyst not only increases the amount of chemisorbed hydrogen but also leads to new desorption peaks on the thermodesorption curve.

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, C¹⁴, () . (1) ( 500°C 1–2 ) (2) - - , : .

     

IR spectroscopic studies of H2S adsorption on acid and base catalysts

IR spectra of H₂S adsorbed on various types of catalysts have been studied by monitoring changes in the properties of their surfaces from the spectra of probe molecules. It is shown that H₂S is adsorbed only dissociatively on basic centers (BC); on proton centers (PC) it forms H-complexes, while with the participation of strong Lewis acid centers (LAC), it is adsorbed both associatively and dissociatively.

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- H₂S , -. , H₂S (), () -, ()- , .

     

Methane synthesis from CO/H2O mixture on supported nickel catalysts, II. Surface species in CO?H2 and CO?D2O interaction by IR spectroscopy

The species resulting in CO, CO+H₂ or CO+D₂O adsorption on supported Ni catalysts were followed by IR spectroscopy and their role in methane synthesis mechanism is discussed.

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- , CO, CO+H₂ CO+D₂O . .

     

Role of tin in a PtSb alloy and a Pt-Sn/Al2O3 reforming catalyst

The conversion of n-hexane was studied on a Pt-Sn/Al₂O₃ catalyst, a PtSn alloy and on the corresponding Pt catalysts. The results indicate the same catalytic effect of tin in supported and unsupported catalysts. It is concluded that the role of tin is connected with alloy formation.

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- Pt-Sn/Al₂O₃, PtSn Pt-. . , .

     

Modification of the catalytic and chemisorptive properties of Pt/SiO2 catalysts by high temperature reduction and restoration by O2?H2 treatments

The reduction of Pt/SiO₂ at 1100 K results in a decrease of the quantity of absorbed hydrogen and of the catalytic activity in benzene hydrogenation, ethane hydrogenolysis and neopentane isomerization, which cannot be accounted for by metal sintering. O₂ treatment followed by reduction at moderate temperature restores the usual properties of the catalyst. This behavior is similar to that observed on Pt/TiO₂ catalysts, the difference lying in the temperature at which the phenomenon appears.

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Pt/SiO₂ 1100 , , . O₂ , . Pt/TiO₂ , .

     

Kinetics and mechanism of oxidation of D-altrose by aqua-cerium(IV) in perchloric acid medium

Kinetics of the oxidation of D-altrose by Ce(IV) perchlorate has been studied in perchloric acid medium. At equivalent concentrations the overall order of the reaction is two, being unity in each reactant. The reaction is characterized by a primary positive kinetic salt effect. Perchloric acid has been found to enhance the rate, while the addition of the reaction products retards the rate. No evidence for initial complexation has been obtained. Thermodynamic parameters have been determined and a mechanism consistent with the observed results is proposed.

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D- Ce(IV) . , . . , . . , .

     

Acidity and oxidation activity of MoO3?UO3/SiO2 catalysts

The effect of UO₃ on the acidity of MoO₃–UO₃/SiO₂ catalysts has been studied by means of infrared spectroscopy of adsorbed pyridine. The surface acidity exhibited a maximum for the same U/(U+Mo) atomic ratio (=0.11) that yielded a maximum in total conversion for isobutene oxidation. The catalytic properties for oxidation are discussed in terms of the acidic properties of the samples.

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UO₃ MoO₃–UO₃/SiO₂ . U/(U+Mo)=0,11, . , .

     

Kinetics of Cr(VI) and V(V) oxidation of trans-stilbene and indene

Title reactions are acid catalyzed and strongly dependent on the permittivity of the medium. With Cr(VI) indene reacts faster than trans-stilbene, but with V(V), trans-stilbene reacts faster than indene. The mechanism is discussed.

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. Cr(VI) , -, V(V) - , . , .

     

IR spectroscopic studies of Ru3(CO)12 interaction with disperse metallic palladium supported on SiO2

IR spectroscopic studies of the interaction of Ru₃(CO)₁₂ with reduced Pd/SiO₂ have revealed that at 298 K Ru₃(CO)₁₂ chemisorbs on the surface of metallic palladium and is partly oxidized by OH-groups of SiO₂. Subsequent reduction by hydrogen leads to the formation of bimetallic clusters possessing nonadditive chemisorption properties.

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- Ru₃(CO)₁₂ Pd/SiO₂. 298 Ru₃(CO)₁₂ , OH- SiO₂. , .