Kinetic studies on MeWO4-tungstates grown under mild hydrothermal conditions (Me=Mn2+, Fe2+, Zn2+)

The reaction mechanims and the kinetics of formation of MeWO₄-tungstates (Me=Mn²⁺, Fe²⁺, Zn²⁺) have been studied by reacting metal (II) chlorides and sodium tungstate at 493 K in a special autoclave, allowing continuous removal of the reactants.

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MeWO₄ ( Me=Mn²⁺, Fe²⁺, Zn²⁺) - (II) 493 , .

     

Mechanism of ascorbic acid oxidation by molecular oxygen in aqueous pyridine catalyzed by CO2+, Ni2+, Mn2+ and Zn2+

Data on the radical non-chain mechanism of ascorbic acid oxidation by molecular oxygen catalyzed by Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ ions are reported.

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Co²⁺, Ni²⁺, Mn²⁺ Zn²⁺.

     

Kinetics of Fe3+ and Cu2+ sorption by fibrous polyampholite

The kinetics of Fe³⁺ and Cu²⁺ sorption from sulfate salt solutions by fibrous polyampholite have been studied.

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Fe³⁺ Cu²⁺ , .

     

Mechanism of competitive oxidation and H-D exchange of cyclohexane in the PtII?PtIV?Cl??D2O?D2SO4 system

The results of kinetic studies on competitive oxidation and H-D exchange of cyclohexane in the Pt^II–Pt^IV–Cl^––D₂O–D₂SO₄ system involving variations in the concentrations of D⁺, Cl^– and Pt^II, are in agreement with two possible mechanisms involving the formation of a common intermediate alkyl-platinum complex.

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H/D Pt^II–Pt^IV–Cl^––D₂O–D₂SO₄ D⁺, Cl^–, Pt^II , - .

     

Catalytic oxidation of ascorbic acid by molecular oxygen in aqueous pyridine in the presence of Co2+, Ni2+, Mn2+ and Zn2+ ions

In aqueous pyridine solutions, Co²⁺, Ni²⁺, Mn²⁺ and Zn²⁺ effectively catalyze the oxidation of ascorbic acid by molecular oxygen. A kinetic expression consistent with the experimental data is given and a possible mechanism proposed.

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- , , . , . .

     

Kinetics of reduction of tungstovanadophosphoric heteropoly anions with VO2+ ions

The rate constants of interactions of PW_12-nV_nO₄₀ ^(3+n)– (n=1–4) heteropoly anions (HPAs) and various PW₁₀V₂O₄₀ ^–5 isomers with VO²⁺ were measured. The reactions occurred via formation of intermediate active complexes with V(IV) ions incorporated into the coordination sphere of HPA.

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VO²⁺ PW_12-nV_nO₄₀ ^–(3+n) (n=1–4) PW₁₀V₂O₄₀ ^–5. , V(IV) .

     

Interpretation of energy stability for Ti27+ and Ti26+ dimers

By using the interacting bonds method (IBM), it has been established that for the chloride Ziegler systems (TiCl₄+AlR₃) for polymerization the formation of Ti ₂ ⁷⁺ and Ti ₂ ⁶⁺ pairs is a thermodynamically favorable process.

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(TiCl₄+AlR₃) () , Ti ₂ ⁷⁺ Ti ₂ ⁶⁺ .

     

Non-empirical calculations for the probable coordinative binding of electron donor molecules by [AlO4] tetrahedra

Interaction of H₂O, NH₃ and C₅H₅N molecules with the aluminium atom of [AlO₄] tetrahedra has been calculated by the non-empirical SCF-MO LCAO method using an STO-3G basis set. The effect of Al–O bond lengths and O–Al–O angles on the calculated characteristics of chemisorbed complexes is discussed.

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, TO-3C , [AlO₄]. Al–O O–Al–O .

     

Catalysts for metathesis of olefins, prepared by anchoring of MoO2(acac)2 to Al2O3

New highly active catalysts for metathesis of olefins were obtained through the interaction of bis(acetylacetonato)dioxymolybdenum(VI) with surface OH groups of -Al₂O₃ and subsequent reduction in H₂ or CO.

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()(VI) OH -Al₂O₃ H₂ CO .

     

Hydrocarbon synthesis from methanol on erionite and mordenite catalysts synthesized in the presence of B3+, Ga3+ or Fe3+

Selectivity of erionite and mordenite type aluminosilicates synthesized in the presence of B³⁺, Ga³⁺ or Fe³⁺ has been studied in methanol conversion to hydrocarbons. The olefin to paraffin ratio in the product is proportional to the Al₂O₃ content of the zeolites.

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, B³⁺, Ga³⁺ Fe³⁺. , / Al₂O₃ .

     

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.

     

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 .

     

Calorimetric study of the BrO3?/Ce4+/cyclohexanone and BrO3?/Ce4+/cyclopentanone oscillating systems

The heat output (Q) during the induction period of a Belousov-Zhabotinskii oscillating reaction usually evolves at a constant rate /6/; we observe in the BrO ₃ ^– /Ce⁴⁺/Cyclohexanone system a sudden change in the slope of the function Q=f(t), which corresponds to the beginning of the quasistationary phase /3/.

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(Q) - ; BrO ₃ ^– /Ce⁺⁴/ Q=f(t), .

     

H2O? radicals trapped in Y-type zeolites

The results of CHDO/SP calculations do not support the detection of H₂O^– ions in MgY and CaY zeolites.

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CNDO/SP H₂O^– MgY CaY.

     

Cyclohexene isomerization activity of aluminas with low Na+ contamination

Although the contamination of aluminate aluminas with 0.005–0.01% Na⁺ does not change the qualitative acid strength distribution as compared with high purity alumina, it has a very strong influence upon cyclohexane isomerization activity which increases after introducing Cl^–.

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Na⁺ 0,005–0.014%, , , , Cl^–.

     

Observation conditions and thermal stability of O2? on SnO2

A sharp change in the relaxational characteristics of O ₂ ^– anion radicals on SnO₂ is observed under physical adsorption of O₂ molecules in an amount less than 10¹⁶ m^–3. The thermal stability of sites for O ₂ ^– stabilization on SnO₂ is analyzed. Molecular oxygen, forming O₂, is shown to desorb with increasing temperature without participating in reoxidation of the oxide.

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O ₂ ^– SnO₂ O₂ 10¹⁶ M^–2. O ₂ ^– SnO₂. , O₂, O ₂ ^– , .

     

ESR spectra of O2? on SnO2. effect of adsorbed CO on the conditions of stabilization of O2?

The physical adsorption of CO molecules on SnO₂ is shown to be accompanied by a reversible change in the ESR parameters of CO ₂ ^– anion radicals. The effect of CO is different for SnO₂ samples with different life histories.

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, CO SnO₂ - O ₂ ^– , CO SnO₂ .

     

IR spectra of NO and NO+CO mixtures adsorbed on Fe2O3

The interaction of NO and NO+CO mixtures with Fe₂O₃ has been studied by IR spectroscopy. The conclusion has been made that adsorption bands in the region of 1200–1700 cm^–1 belong to nitrite-nitrate structures, the band at 1810 cm^–1 characterizes catalytically active particles of NO adsorbed on reduced surface sites, Fe²⁺, the bands at 2210 and 2240 cm^–1 are due to vibrations of gaseous N₂O.

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- NO NO+CO Fe₂O₃. , 1200–1700 ^–1 - ; 1810 ^–1 NO, , Fe²⁺; 2210 2240 ^–1 N₂O.

     

On the mechanism of propene oxidation on Bi3Mo2FeO12 and Bi2Mo2Fe2O12 catalysts

Oxidation of propene on Bi₃Mo₂FeO₁₂ and Bi₂Mo₂Fe₂O₁₂ and Bi₂(MoO₄)₃ has been compared with the interaction of allyl iodide and diallyl oxalate with these compounds. Bi₂Mo₂Fe₂O₁₂ was found to be the most active and the least selective in propene oxidation. The three compounds show at the same time the same activity in acrolein formation from allyl iodide and oxalate. The results are interpreted in terms of the two-center mechanism of propene oxidation [9, 10]. The role of iron in elementary steps of propene oxidation on Bi–Mo–Fe–O catalysts is also discussed.

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Bi₃Mo₂FeO₁₂, Bi₂Mo₂Fe₂O₁₂ Bi₂(MoO₄)₃ . Bi₂Mo₂Fe₂O₁₂ . . , . Bi–Mo–Fe–O.

     

Studies on catalytically active surface compounds, IX. Formation of O2? radicals on VCl4/SiO2 catalysts

The conditions for the formation of O ₂ ^– on VCl₄/SiO₂ catalysts have been investigated. It is shown that thermal vacuum treatment (TVT) of unhydrolyzed catalysts leads to partial hydrolysis of the surface vanadium complex caused by the silanol groups of the support. The ability of the catalysts to generate O ₂ ^– radicals was found to depend on the degree of hydrolysis caused by thermal vacuum treatment.

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O ₂ ^– VCl₄/SiO₂. , , . , O ₂ ^– , .