Steric substituent effect on the resin catalyzed hydrolysis of alkyl acetate esters

The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, E_s. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, S^x, values increase in the order: n-octyl-

, , 70%- . , , E_S. . , . , S^*, : --<-<, .

     

Physicochemical properties and hds activity of CoMo?P?Al2O3 catalysts

Porous structure, acidity and hds activity of the CoMo–P–Al₂O₃ catalysts have been studied. Phosphorus was introduced jointly with molybdenum. This method of phosphorus incorporation gave substantial diminution of surface area, moderate changes of acidity and decrease in hds activity for the catalysts with P₂O₅ content higher than 5 wt.%.

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, CoMo–P–Al₂O₃. . , P₂O₅ 5 .%.

     

On the reduction of NiO forms in magnesia supported catalysts

Reducibility of Ni/MgO catalysts has been studied by the temperature-programmed reduction (TPR) technique in the temperature range of 373–1273 K. The profile of reduction reveals the presence of various forms of NiO. The effects of nickel loading and treatment temperature on catalyst reducibility have been evaluated. The formation of NiO–MgO solid solution controls the whole reduction of Ni/MgO system.

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Ni/MgO 373–1273 . NiO. . Ni/MgO NiO–MgO.

     

Thermal decompositions of kaolinite intercalation compounds

Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.Decomposition of the potassium acetate intercalation compound proceeds simultaneously with the dehydroxylation of kaolinite at an extrapolated onset temperature of 360 °C. The high-temperature reactions (dehydroxylation and transformation) of kaolinite obtained through the decomposition of intercalation compounds with volatile intercalation agents depend on the conditions applied during decomposition.

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Zusammenfassung Mittels Röntgenbeugung und thermischer Analyse (simultane TG-DTG-DTA und quasi-isotherme-quasi-isobare TG) konnte gezeigt werden, daß das molare Verhältnis Einlagerungsmedium/Kaolinit in allen Einlagerungsverbindungen etwa 1 ist. In gesättigter Atmosphäre des jeweiligen Einlagerungsmediums ist die Einlagerungsverbindung stabil bis über 150 °C. Die Zersetzung der Kaliumacetat-Einlagerungsverbindung läuft zusammen mit der Dehydroxylation des Kaolinits bei einer extrapolierten onset-Temperatur von 360 °C ab. Die Hochtemperaturreaktionen (Dehydroxylation, Phasenneubildung) von Kaolinit, der aus der Zersetzung von Einlagerungsverbindungen mit flüchtigen Einlagerungsmedien erhalten würde, werden von den Zersetzungsbedingungen beeinflußt.

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- ( , , ) , - 1. , , 150°. — ** 360°, ** . , , .

     

Error analysis of surface area determinations by the chromatographic technique

The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.

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.

     

Cobalt complex with immobilized porphyrin in hydrazine oxidation

Porphyrin immobilized on silica and its complex with cobalt have been prepared and identified. Oxidation kinetics is described by the Michaelis-Menten equation.

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- . - --.

     

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) . , . . , . . , .

     

Methanol conversion on silica-aluminas. Production of light olefins

The catalytic behavior on both low and high alumina silica-aluminas in converting methanol into hydrocarbons under various experimental conditions is reported, special attention being given to C₂–C₄ olefin production. Olefin production increases with contact time W/F in the range of 0–4.65 h and decreases when temperatures are higher than 360–400°C. Selectivity to light olefins can be as high as 65%.

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, , , , C₂–C₄. 0–4,65 360–400°C. 65%.

     

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 . .

     

A study of the surface heterogeneity and catalytic activity of catalysts by means of reaction thermodesorption

Reaction thermodesorption is studied. A generalized wiew is offered regarding the routes along which the transformations take place under the conditions of temperature-programmed desorption.

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. , .

     

Decomposition of n-pentadecyl hydroperoxides in the presence of nickel and cerium stearates

Overall and radical decompositions of n-pentadecyl hydroperoxides by nickel and cerium stearates have been studied. Reaction orders, effective activation energies, rate constants for the overall decompostion and radical formation have been calculated.

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- n- . , , - .

     

Effect of homogeneous initiator on heterogeneous-homogeneous oxidation of methane

A kinetic method of freezing out free radicals combined with recording ESR spectra was used to study the HCl effect on the partial oxidation of methane over SiO₂. This effect is ascribed to the surface modification of catalyst.

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HCl SiO₂. .

     

Kinetics and mechanism of redox reactions of U(III) ions with 2-chloro and 2-bromopropanoic acids

The kinetics and mechanism of redox reactions of U³⁺ ions with 2-chloro and 2-bromopropanoic acids were studied. The influence of pH led to the determination of the rate constants corresponding to two parallel steps. The influence of binary mixtures on the reaction rate was followed. The kinetic results for halogen-substituted carboxylic acids forming an isokinetic series have been compared.

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U⁺³ 2-- 2- . pH . . , .

     

Effect of Rh/Al2O3 on the reduction of ZnO in a mechanical mixture of these components

The effect of reoxidation temperature on TPR of 5% Rh/Al₂O₃ catalyst and its mechanical mixture with ZnO has been investigated. The results suggest bimodal character of supported rhodium and surprisingly high effect of this metal on ZnO reduction in the mixture.

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5% Rh/Al₂O₃ ZnO. , ZnO .

     

UV-VIS spectroscopic study of interaction and transformation of allyl alcohol on zeolites HZSM-5

Formation of alkenylcarbenium ions has been proved during transformation of allyl alcohol on zeolite HZSM-5.

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HZSM-5.

     

Evidence for different types of sites on alumina surface

PASCA has been used to search for evidence on different types of sites existing on alumina surfaces. The results indicate that PtCl ₆ ^2– interacts with different surface sites, forming MSI complexes PtO_xCl_y–S_k, PtO_xCl_y–S_s and PtO_xCl_y–St. Surface sites in different aluminas may be different in chemical and electronic properties.

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. PtCl₆ ^2– , PtO_xCl_y–S_k, PtO_xCl_y–S_S PtO_xCl_y–S_t. .

     

Oscillatory behavior in the oxidation of hematoxylin with bromate and sulfuric acid

Uncatalyzed and catalyzed oscillatory behavior in the redox potential in the oxidation of hematoxylin with acidic (H₂SO₄) bromate is reported.

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- (H₂SO₄) .

     

Activity of Ni?Mo hydrodesulfurization catalysts supported on mixed alumina-zirconia

The hydrodesulfurization (HDS) of thiophene by nickel-molybdenum catalysts supported on alumina-zirconia has been investigated. The effect of varying the ratios of oxides in the support is to produce a minimum in the activity for HDS, and the coimpregnated catalysts are shown to be more active than the analogous co-precipitated catalysts.

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(HDS) -, . HDS. , .