Thermal decomposition of homo- and copolymers of isobutylene

The thermal properties of polyisobutylene and isobutylene-isoprene copolymers were studied. Thermal curves were interpreted with regard to supplementary data. It was found that the degradation of both homo- and copolymers proceeds to a much higher extent in air than in argon. It follows from the results that peroxide formation plays a significant role in the degradation of this group of polymers.This finding correlates well with the influence of dicumyl peroxide and phenyl--naphthylamine on the thermal properties of the isobutylene polymers investigated in this work.

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Zusammenfassung Die thermischen Eigenschaften von Polyisobutylen- und Isobutylen-Isopren-Kopolymeren wurden untersucht. Die thermischen Kurven wurden unter Berücksichtigung ergänzender Angaben gedeutet. Es wurde festgestellt, dass die Zersetzung sowohl von Homoals auch von Kopolymeren in Luft in einem viel grösseren Ausmass verläuft, als in Argon. Aus den Ergebnissen folgt, dass die Peroxidbildung bei der Zersetzung dieser Gruppe von Polymeren eine bedeutende Rolle spielt.Diese Aussage ist in guter Übereinstimmung mit dem Einfluss von Dicumylperoxid und Phenyl- naphthylamin auf die thermischen Eigenschaften der untersuchten Isobutylenpolymere.

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Résumé On a étudié les propriétés thermiques des copolymères polyisobutylène et isobutylèneisoprène. On a interprété les courbes thermiques en considérant des données supplémentaires. On a établi que la dégradation tant des homoque des copolymères s'effectue d'une manière beaucoup plus importante dans l'air que dans l'argon. Nos résultats montrent que la formation du peroxyde joue un rôle important sur la dégradation de ce groupe de polymères.Cette conclusion est en bon accord avec l'influence du peroxyde de dicumyle et de la phényl-naphtylamine sur les propriétés thermiques des polymères d'isobutylène étudiés dans notre travail.

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- . . , , . , . -- .

     

V2O5/TiO2 oxidation catalysts, IV. Adsorption of acrolein on sodium-containing systems

Adsorption of acrolein on vanadia/titania catalysts fits a polymerization kinetics if Na–V compounds are not present or the vanadium content is lower than that corresponding to formation of a monolayer of vanadia on the titania support.

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, Na–V .

     

Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

Kinetic studies of Pt/Al2O3 catalyst pellets with nonuniform activity

Catalysts with nonuniform distribution of the catalytically active component (Pt) over their porous support (Al₂O₃) have been studied. A nonuniform activity distribution changes not only the reaction rate but also the kinetics can be different on these catalysts.

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(Pt) (Al₂O₃). , , .

     

Liquid-phase hydrogenation on new AlPO4?SiO2 supported rhodium catalysts

The liquid-phase catalytic hydrogenation of various organic compounds was carried out using new rhodium catalysts supported on AlPO₄–SiO₂ (2080 wt. %) system, in methanol as solvent, under low hydrogen pressure (0.55 MPa) and at 293 K. Neither alkene isomerization nor hydrogenolysis products were detected in any of the cases.

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AlPO₄–SiO₂ (2080 . %), , , (0,55 MPa) 293 . , .

     

Hydrogen pressure dependence of the reaction of neopentane with hydrogen over Pd/SiO2 and Pt/SiO2 catalysts

H₂ pressure influences in different ways the reaction rates of neopentane conversion over Pd/SiO₂ and Pt/SiO₂ catalysts. It seems that on Pt/SiO₂ both isomerization and hydrogenolysis involve a common surface intermediate (probably an adalkyl), whereas on Pd/SiO₂ the hydrogenolysis goes via more dehydrogenated species than those involved in isomerization.

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H₂ Pt/SiO₂ Pd/SiO₂. , Pt/SiO₂ (, ), Pd/SiO₂ , .

     

Investigation of toluene formation on Pt/Al2O3 catalyst in n-hexane dehydrocyclization

Formation of toluene, a chain lengthening product, has been observed on Pt/Al₂O₃ catalyst in n-hexane dehydrocyclization. Toluene formation is influenced by the catalyst pretreatment processes and the reaction temperature. A correlation has been found between the ageing phenomena and toluene formation.

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- Pt/Al₂O₃ — . . .

     

Steady state kinetic equation for SO2 oxidation on vanadium catalysts

From the analysis of the detailed reaction mechanism and taking into account vanadium complex formation processes, a steady state kinetic equation has been derived to describe experimental data in a wide range of reaction conditions.

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, .

     

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 ^– , .

     

Studies on the catalytic decomposition of N2O over the solid solution La2CuxZn1?xO4 (0

U. Kameswari  J. Christopher  C. S. Swamy 《Reaction Kinetics and Catalysis Letters》1990,41(2):381-388

Temperature programmed reduction and oxidation of Ir/Al2O3 catalysts

3 % Ir/Al₂O₃ catalysts have been studied by means of temperature programmed reduction and oxidation. With growing degree of metal oxidation (higher T_ox) reducibility of the catalysts at low temperatures decreases.

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3% Ir/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), .

     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. II. Sulfur resistance of Pt?Re/Al2O3 modified with ZSM-5

The sulfur resistance of Pt–Re/Al₂O₃-ZSM-5 catalyst has been investigated for normal heptane reforming. It was found that while sulfur acts as a poison for Pt–Re/Al₂O₃, it can play an important role in activity maintenance and aromatics production when ZSM-5 zeolite is present.

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Pt–Re/Al₂O₃-ZSM-5 -. , , Pt–Re/Al₂O₃, ZSM-5.

     

V2O5/TiO2 oxidation catalysts, III. Oxidation of CO on pure and sodium-doped systems

The activity of vanadia/titania catalysts in CO oxidation has been tested and found to be of the same order as that observed for unsupported vanadia; the simultaneous presence of vanadium-sodium compounds cancels the activity, probably because of the elimination of labile V=0 species at surface defects.

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V₂O₅/TiO₂ CO, V₂O₅; - , , V=0 .

     

Thermal desorption of hydrogen and carbon monoxide from Pd?Pb/Al2O3 catalysts

Thermal desorption of CO and H₂ from the surface of Pd/Al₂O₃ and Pd–Pb/Al₂O₃ catalysts has been investigated. No significant effects of adding lead to palladium catalysts on the activation energy of desorption process have been observed.

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CO H₂ Pd/Al₂O₃ Pd–Pb/Al₂O₃. - .

     

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.

     

Potassium addition to Fe/MgO, Ni/MgO and Ni/SiO2: Reducibility, dispersity and stabilization of the promoter by the support

The influence of potassium addition on the morphological properties of Fe/MgO and Ni/MgO has been investigated: KNO₃ addition to precursors results in a decrease of the reducibility and in a smaller dispersity of the metallic phase. A loss of potassium is observed at reduction temperatures in excess of 773 K. Silica-supported Ni behaves differently: silica inhibits the potassium volatilization and nickel reducibility is enhanced. This illustrates how promoter effects can be influenced by the nature of support.

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Fe/MgO Ni/MgO: KNO₃ . , 773 K. , : . .

     

Chemisorption of H2, O2 and CO on bimetallic catalysts Rh?Ag/Al2O3

Comparison of adsorptive properties of Rh–Al₂O₃ catalysts in relation to H₂, O₂ and CO as adsorbates points to different surface interactions between the adsorbates and metallic surface of the catalysts. The differences may result from the changing composition of bimetal surface in relation to the catalyst composition and/or from the changing stoichiometry of surface interactions of the adsorbates.

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H₂, O₂ CO Rh–Ag/Al₂O₃ . , , () .

     

Catalytic reaction of tetrahydrofuran with H2S

The reaction of tetrahydrofuran with H₂S catalyzed by acid-base catalysts has been studied. Catalysts containing an acid-base pair, i.e. a Lewis acid center and a base center, are the most active and selective towards thiolane. Proton donor catalysts and those containing only basic centers are of low activity and selectivity.

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H₂S - . , - : - , . , , .

     

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-. . , .