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.

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .

     

Comparison of the sulfurization of CoMoK/Al2O3 catalyst with H2S and CS2

Only H₂S consumption and H₂O formation was found in the sulfurization of CoMoK/Al₂O₃ water gas shift catalyst with H₂S/H₂, but CO₂ was formed first, then CH₄, H₂O and H₂S appeared in the later part of TPS with CS₂/H₂. Carbon deposition on the catalyst during the sulfurization with CS₂/H₂ caused a lower activity than the catalyst sulfurized with H₂S but could be removed in the run of WGS reaction.

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, CoMoK/Al₂O₃, H₂S/H₂ H₂S H₂O, CS₂/H₂ CO₂ CH₄, H₂O H₂S. CS₂/H₂ H₂S, , .

     

State of components in Pd/C catalysts promoted by Ho2O3

Catalysts prepared through the interaction of C₃H₅PdC₅H₅ with the surface of evacuated Ho₂O₃/C after reduction by H₂ at 573 K contain Pd and Ho₂O₃ particles whose size is 30 and 20–40 Å, respectively. XPS and TEM data indicate that Pd particles have a positive charge and their surface is partly covered by Ho oxide.

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, C₃H₅PdC₅H₅ Ho₂O₃/C, H₂ 573 Pd 30 Å Ho₂O₃ 20–40 Å. XPS TEM Pd , Ho.

     

Ammoxidation of propylene over SnO2?Sb2O4 mixed oxide catalysts doped with Ga, In or Tl

In studying the catalytic activities of SnO₂–Sb₂O₄ (SnSb=11) mixed oxides doped with Ga, In or Tl in the ammoxidation of propylene, a selectivity improvement was observed when the dopants Ga₂O₃ and Tl₂O₃ were used in low concentrations. At higher concentrations and for In₂O₃ the characteristics of the dopant prevail, disclosing that the admixed oxides are not evenly distributed in the bulk, but that the doping is rather confined to the surface layers of the catalyst.

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, Ga, In Tl 673 . , Ga₂O₃ Tl₂O₃ (0,5–2 . %). In₂O₃ . , , .

     

Kinetics and selectivity of the oxidation of alkanes in Cl2?H2O and Cl2?Hg2+?H2O solutions

Relative oxidation rate constants of several normal, iso-, cyclo-and methylcycloalkanes have been measured in Cl₂–H₂O and Cl₂–Hg²⁺–H₂O solutions at 343K. The selectivity of C–H bond dissociation in both systems is the same. HOCl is assumed to be the active species for the two systems.

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Cl₂–H₂O Cl₂–Hg²⁺–H₂O 343 , -,- ; C–H . , HOCl.

     

Kinetics of Co?Mo/Al2O3 catalyst reduction

According to kinetic studies on the reduction of commercial Co–Mo/Al₂O₃ and model catalysts in H₂ at 523–773 K, the kinetic curves for the reduction process have been determined. The reduction rate is shown to be higher for the commercial catalyst. Activation energies E_act for the reduction of several forms of Mo and Co in Co–Mo/Al₂O₃ catalysts are presented.

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H₂ 523–773 . , : Mo Co .

     

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 . ( ) .

     

Influence of CO2 and H2O on methane conversion over oxide catalysts

It has been established that the introduction of CO₂ and H₂O to the reaction mixture when using freshly prepared catalysts, increases the overall methane conversion and decreases the yield of hydrocarbons. On coked MgO their effect is insignificant.

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, CO₂ H₂O . MgO CO₂ H₂O .

     

Oxygen diffusion in Me2O?V2O5 melts

The anodic and cathodic polarization of a platinum electrode in K₂O–V₂O₅ melt have been studied. The dissolved oxygen is shown to be ionized. Diffusion coefficients of oxygen in K₂O–V₂O₅ and Na₂O–V₂O₅ melts at various temperatures and K/V ratios are presented.

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K₂O–V₂O₅. , . K₂O–V₂O₅, Na₂O–V₂O₅ K/V.

     

Acidic properties of TiO2?SiO2 catalysts

The acidic properties of a series of TiO₂–SiO₂ catalysts with different Ti/Si mole ratios have been studied. In order to determine the amount of acid centers and the acid strength distribution, the Benesi method of discontinuous titration has been used. Thermogravimetric measurements were also carried out.

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TiO₂–SiO₂ Ti/Si. , - . .

     

Sorption of H2, O2 and CO on bimetallic catalysts Pd?Ag/Al2O3 over a wide temperature range

Adsorption of hydrogen, oxygen and carbon monoxide on Pd–Ag/Al₂O₃ catalysts of different compositions within the temperature range from 293 to 773 K has been investigated. Adsorption measurements have been carried out by the pulse chromatographic method. The results obtained reflect interactions of the above adsorbates with the alloy surface, strongly enriched in silver atoms, as a result of surface segregation processes.

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, Pd–Ag/Al₂O₃ 293–773 K. . , , .

     

Structure of Pt/ZnAl2O4 catalysts

The effect of the support preparation technique (solgel and coprecipitation) on the final Pt/ZnAl₂O₄ catalyst is presented. The structural properties of the solids obtained are correlated to the selectivity and activity for isobutane dehydrogenation in H₂ and He reaction media. If a highly dispersed catalyst is suitable, the support has to be prepared by the sol-gel method.

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( — ) Pt/ZnAl₂O₄. H₂ He. , — .

     

Characterization of MoS2/SiO2 by ESR and NO adsorption

Six MoS₂/SiO₂ samples were characterized by XRD, BET surface area, ESR and NO adsorption measurements. Correlation was found between the amount of Mo⁵⁺, sulfur radicals and adsorption capacity for oxygen and NO.

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MoS₂/SiO₂ , , , NO. Mo⁵⁺, NO.

     

Vapor phase oxidation of 2-methylpyridine on V2O5/TiO2 (anatase) catalysts

The influence of catalyst composition and reaction parameters on the yield of pyridine-2-carboxaldehyde has been studied for the title process. It has been established that monolayer vanadia on TiO₂ (anatase) is a highly selective catalyst for the partial oxidaton of 2-methylpyridine to pyridine-2-carboxaldehyde.

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-2-. , TiO₂ () 2- -2-.

     

Oxidizing supported reagents, III. Oxidation of alcohols by new supported K2Cr2O7 reagents

Several new supported K₂Cr₂O₇ reagents are used in the oxidation of secondary alcohols. The influence of the number of active sites and the nature of solid support on the yield is discussed. The influence of the structure of alcohol on the yield of ketone is analyzed.

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K₂Cr₂O₇ . . .

     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

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, 423 743 CH₄/O₂ 1 9, . . .

     

Reduction kinetics of Mo/Al2O3 catalysts

Studies of the reduction kinetics of MoO₃ and Al₂O₃–MoO₃ catalysts in H₂ at 523–823 K indicate that molybdenum is present in Al₂O₃/MoO₃ in three forms: as Mo⁶⁺ in the Al₂O₃ lattice and as MoO₃ and Al₂(MoO₄)₃ phases. Activation energies of reduction E_act determined according to the Avrahmy-Erofeev equation, are reported.

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MoO₃ Al₂O₃–MoO₃ H₂ 523–823 . Al₂O₃–MoO₃ : Mo⁶⁺ Al₂O₃ MoO₃ Al₂(MoO₄)₃, . -.

     

Stereoselectivity observed in cross metathesis of cis- and trans-2-butene with 1-butene over Re2O7/Al2O3 catalyst

Cross metathesis of cis- and trans-2-butene with 1-butene was studied over Re₂O₇/Al₂O₃ catalyst in a recirculation system at 313 K. Formation of ethylene and hexenes was inhibited by 2-butenes; formation of propene and pentene proceeded without induction from trans- and with induction from cis-2-butene and 1-butene. Selective formation of trans-2-pentene was observed from trans-2-butene, but no such selectivity was characteristic for cis-isomers.

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- -2- 1- Re₂O₇/Al₂O₃ 313 . 2-; - -2- 1-. -2 -2-, , - .

     

Effect of iron on the behavior of Fe2O3?MoO3/SiO2 ammoxidation catalysts

Catalytic ammoxidation of propylene was studied using Fe₂O₃–MoO₃/SiO₂ catalysts, which have been prepared following a special method. Interaction of ammonia with the catalysts was studied by means of IR spectroscopy and gravimetrically using a McBain balance. Introduction of iron into MoO₃/SiO₂ catalysts modifies acidic as well as redox properties.

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Fe₂O₃–MoO₃/SiO₂ . . - . MoO₃/SiO₂ , .