Numerical simulation of the BZ reaction of oxalic acid with a simple four-variable model

A simple model of the bromate-cerium-oxalic acid batch oscillatory system has been constructed and examined by calculations. The model predicts a parameter range and a frequency which agree rather well with the observed values, but it does not describe the peculiar saddlenode infinite period bifurcations found experimentally in the system.

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-- . , , - .

     

Studies of V?Mo?O systems with small vanadium content in acrolein oxidation

A solid solution of vanadium in MoO₃ with a solubility limit of about 3 mol.% V₂O₅ is shown to be formed. Its catalytic properties are discussed.

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MoO₃ 3 . % V₂O₅ .

     

Influence of cobalt phthalocyanine: Deposited onto the particles of mixed Cd/CuxS suspensions on photocatalytic evolution of hydrogen from aqueous solutions of Na2S

Deposition of water-insoluble cobalt phthalocyanine CoPc onto the particles of mixed suspensions of CdS and Cu_xS can increase the rate of photoinduced evolution of H₂ from Na₂S and Na₂SO₃ solutions. At [Na₂S]=5×10^–2 M, the rate of photocatalytic reaction is almost doubled upon deposition of 6.4×10^–10 mol CoPc onto 4×10^–5 mol of CdS and of 2.9×10^–8 mol of CoPc onto 10^–5 mol of Cu_xS. At [Na₂S]=10^–1 M, which is close to the optimal concentration of Na₂S, the deposition of CoPc can provide only a 30% increase of the reaction rate.

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, CoPc CdS/Cu_xS H₂ Na₂S Na₂SO₃. Na₂S=5·10^–2 M 6.4·10^–10 CoPc 4·10^–5 CdS 2.9·10^–8 CoPc 10^–5 Cu_xS. Na₂S=10^–1 M, CoPc 30% .

     

Low-temperature oxidation of hydrogen on platinum

The interaction of oxygen adsorbed on platinum with hydrogen at low temperatures has been studied. The molecular surface oxygen is shown to be involved in the reaction with hydrogen. The steady-state rate of hydrogen oxidation has been measured at 170–350 K. The activation energy is 3 kcal/mol.

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, , , , . 170–350° , 3 /.

     

Kinetics of sulfur dioxide oxidation on a molten catalyst of nonsteady composition

In general coal ashes are less active for the No+H₂ reaction, whereas their activities for the NO+NH₃ reaction are moderately high. Pretreatment using aqueous NaOH solution increased extensively the activity of the fly ash in both the NO+H₂ and NO+NH₃ reaction.

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, NO H₂, NO NH₃ . NaOH .

     

Potentiometric titration of sorbed hydrogen on palladium carrier catalysts

A method of determination of adsorbed and absorbed hydrogen on palladium catalysts with carbon carriers is suggested and verified. The method allows H_ad and H_ab to be determined with an accuracy of about 10% using catalysts containing at least 5% Pd.

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- . . . 10% , , - , 5% Pd.

     

Promoting effect of potassium on catalytic and surface properties and phase commposition of catalysts for synthesis of alcohols

The dependence between catalytic and surface acid-base properties of Zn–Cr–K catalysts has been established. Modification by potassium and an increase in potassium concentration promotes Zn–Cr–K reduction and raises the yield of higher alcohols. The spinel structure of catalysts is preserved.

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Zn–Cr–K . Zn–Cr–K , .

     

Oxygen interaction with rhodium at low pressures I. Oxygen adsorption

Oxygen adsorption and desorption on polycrystalline Rh and Rh(100) at PO₂<10^–5 Pa and 400–1600 K have been studied using TDS and AES methods. Adsorption kinetics for both samples is described by the King model accounting for the effect on O₂ adsorption of both precursor state and lateral interaction.

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O₂ Rh(100) 10^–5 400–1600 . - , O₂ , -.

     

Investigation of isomerization of n-pentane over supported Pt catalyst modified by adsorbed Bi and Pd

-Al₂O₃-supported Bi–Pt and Pd–Pt bimetallic catalysts were prepared by electrochemical metal adsorption. Isomerization of n-pentane was studied over these catalysts in a pulse reactor. It can be concluded from the results that the properties of these catalysts differ substantially from the base Pt/-Al₂O₃ catalyst. On the modified catalysts conversion and the yield of i-pentane was found to be lower although selectivity was better. The ratio of cracking reactions was also lower than over the base catalyst.It is very probable that the adsorbed bismuth was slowly desorbing from the catalyst surface during the experiments.

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

     

“In situ” EPR studies of interaction between benzene and ZSM-5 zeolites

The effect of the state of adsorbed layers on the formation of monomeric and dimeric benzene cation-radicals (CR) on ZSM-5 zeolites has been studied. Removal of benzene is shown to be accompanied by disappearance of CR, which is reversible and takes place with preservation of the sites for their stabilization.

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- (KP) ZSM-5. , KP, .

     

XPS studies of the surface of Sn?Sb?O catalysts

Electronic state of the cations of Sn–Sb catalysts has been investigated by the XPS method. The established change in the charge of tin and antimony ions is ascribed to the interaction between catalyst components during its formation. It has been found that the surface of Sn–Sb–O catalysts accumulates antimony, which accounts for their high selectivity in partial oxidation of olefin.

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-- - . , . Sn–Sb–O - , .

     

On the mechanism of isocyanate preparation by the phosgenation reaction

A new mechanism of the transformation of amine hydrochlorides into isocyanates during the phosgenation process was proposed on the basis of radioisotope exchange between p,p'-diamino-1,2-diphenylethane dihydrochloride (³⁶Cl) and phosgene. The reaction proceeds through a transition complex of amine hydrochloride and phosgene, formed on the surface of the hydrochloride crystals.

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(³⁶Cl) ,'--1,2- . , .

     

Study of copper chromite catalysts, III. Structure and catalytic activity of copper chromite catalyst in reductive alkylation reaction

The catalytic activity of copper chromite catalysts prepared by thermal decomposition reaction of basic copper(II) ammonium chromate, CuCrO₄[Cu(OH)₂]_0.17–(NH₄OH)_0.78, and copper(II) chromate CuCrO₄, has been studied. The catalysts with highly disordered structure, prepared from basic copper(II) ammonium chromate at 270–320 °C, show the highest catalytic activity in reductive alkylation reaction. The activity of recrystallized catalysts, prepared from basic copper(II) ammonium chromate or CuCrO₄ at higher decomposition temperature, is significantly lower.

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, Cu(II), CuCrO₄[Cu(OH)₂]_0,17(NH₄OH)_0,78, Cu(II), CuCrO₄. , Cu(II) 270–320°C, . , Cu(II) CuCrO₄ , .

     

Evidence for a weak metal-support interaction in alumina-supported nickel catalysts

The reduction of Ni/Al₂O₃ at high temperatures does not result in a decrease of the H₂ uptake and catalytic activity towards C₂H₆ hydrogenolysis per metal surface atoms. This is typical of a weak metal-support interaction. Moreover, no Ni–Al alloy formation has been detected by magnetism. This behavior, at variance with that of Ni/SiO₂, confirms that the occurrence of the strong metal-support interaction is probably related to support reduction with alloy formation.

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Ni/Al₂O₃ H₂ C₂H₆, . - . , Ni–SiO₂, , , , .

     

Preparation and study of Mn-containing silicates of zeolite structure

The Cu–SiO₂ catalyst prepared by ion exchange method shows a longer life for the dehydrogenation of methanol, as compared with those of Cu catalysts prepared by other methods. This suggests that the highly dispersed Cu particles on the support cannot be easily aggregated during the reaction.

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Cu–SiO₂, , , , . , .

     

Hydrocondensation of CO2 (CO) over supported iron catalysts

Hydrogenation of CO₂ was investigated on iron-copper supported catalysts. Hydrocarbons, except methane, were formed through the CO intermediate, which is formed first in the water gas-shift reaction.

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CO₂ - . CO, , , .

     

Nature of the adsorption centers of oxide catalysts and the direction of propylene conversion

According to the analysis of spectral data on adsorbed propylene forms, an attempt has been made to establish a relationship between the nature of olefin adsorption center, the adsorbed form during precatalysis and the direction of conversion.

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, .

     

Observations on the acetone-malonic acid mixed substrate hydrogen peroxide-iodate-manganese(II) oscillating system

The acetone-malonic acid mixed substrate hydrogen peroxide-iodate-manganese(II) oscillating system has been examined under fixed conditions where two oscillatory phases are separated by a lengthy iodine production and consumption period. The intermediate period is considered to result from oxidation of malonic acid-iodomalonic acid.

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- — — (II) , . - .