ESCA study of (Mo+Pt)/SiO2, (W+Pt)/SiO2 and (Re+Pt)/SiO2 catalysts

Supported catalysts obtained from organometallic compounds have been studied by ESCA. The data obtained indicate a decrease in electron density on the Pt atoms as a result of interaction with Mo, W and Re ions bound to silica.

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, . , Mo, W, Re, .

     

Conversion of hydrocarbons on supported catalysts prepared via decomposition of surface complexes. Preparation and properties of (Ga+Pt)/SiO2 and (Ga+Pt)/Al2O3 catalysts

The addition of gallium is shown to increase Pt dispersity and its stability to deactivation in n-hexane dehydrocyclization, to decrease the rate of n-hexane hydrogenolysis and to increase the selectivity to benzene, apparently, due to the interaction of Pt clusters with surface Ga ions.

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, -, - . .

     

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, . . . .

     

Mo(V)/SiO2 supported catalysts for the epoxidation of allyl chloride

New Mo(V)/SiO₂ supported catalysts as the products of settlement of MoO(OH)₃ on silica were obtained and ESR examined. Catalytic activity in epoxidation of allyl chloride with cumene hydroperoxide was found.

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MoO(V)/SiO₂, MoO(OH)₃ S O₂. .

     

Transformation of n-hexane on Al2O3and SiO2supported Pt, Pt+Ga and Ir+Pt+Ga catalysts prepared by anchoring methods

Summary Transformation of n-hexane over Al₂O₃and SiO₂supported Pt, Pt+Ga and Ir+Pt+Ga catalysts was studied in a continuous-flow reactor operated under slug-pulse mode at 520°C. Bimetallic catalysts were prepared by introducing first Ga(OEt)₃and then diallylplatinum as precursor compounds. Iridium was then introduced viadecomposition of Ir₄(CO)₁₂adsorbed onto Pt+Ga catalysts. The addition of Ga to Pt/SiO₂catalyst decreased hydrogenation, aromatization and hydrogenolysis selectivity. Over Pt/Al₂O₃catalyst Ga increased hydrogenolysis selectivity and decreased isomerization and C₅-cyclization. The main effect of Ir was to increase hydrogenolysis selectivity and the stability of catalysts.</o:p>     

Infrared spectroscopic study of CO adsorption on supported bimetallic Pt?Pb/SiO2 catalysts

With increasing Pb content, the IR band of linearly adsorbed CO is significantly shifted to lower frequencies. The greatest influence of lead is observed up to 15% Pb. An X-ray diffraction study indicates the formation of Pt_5–7–Pb and Pt–Pb alloys for bimetallic catalysts with a Pt/Pt+Pb ratio equal to 30%.

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Pb CO . 15% Pb. 30% , , Pt–Pb Pt_5–7–Pb.

     

The H2S decomposition activity of supported MoS2 catalysts prepared via PFHS method

Silica-supported MoS₂ catalysts prepared via precipitation from homogeneous solution (PFHS) exhibited high surface areas (180–190 m² g^–1 and activities which were about twice those of the unsupported specimens. An 8% Mo catalyst showed optimum activity. The superior activity of the supported specimen was attributed to the higher population of active sites occasioned by the good dispersion during PFHS. TEM examination also confirmed the existence of small MoS₂ crystallites on the silica support.     

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 . , .

     

Investigation of supported nickel catalysts by X-ray absorption spectrometry and X-ray diffraction using synchrotron radiation

In a previous paper a study of the supported nickel catalysts based on extended X-ray absorption fine structure spectroscopy was presented for analysis of the first coordination shell. The present study evidenced a strong deformation of the local structure of the metal due to its interaction with oxide support. The average particle size, microstrains and probability of faults, the particle size distribution function of supported Ni catalysts were determined by X-ray diffraction method. The method is based on Fourier analysis of experimental X-ray line profile (1 1 1), (2 0 0) and (2 2 0). The global structure is obtained with a fitting method based on the generalized Fermi function facilities for approximation. A chemisorption model was elaborated by correlation of the local and global structure connected with the specific surface areas. The results obtained on supported Ni catalysts which are used in H/D isotopic exchange reactions are reported. Both types of measurements were performed on the Beijing synchrotron radiation facilities.     

Acidity of SiO2, SiO2?Al2O3 and γ-Al2O3 supports and supported molybdena catalysts

Acidity of SiO₂, -Al₂O₃ and SiO₂–Al₂O₃ supports and supported Mo-catalysts in oxidized and reduced state are characterized by IR-spectroscopic and gravimetric pyridine (py) adsorption measurements. Differences in surface acidities are interpreted as results of differences in chemical compositions, molybdena-support interactions and molybdena dispersities.

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SiO₂, -Al₂O₃ SiO₂–Al₂O₃, Mo -- . , .

     

Ring opening of methylcyclopentane over Al2O3 and SiO2 supported Rh catalysts

Hydrogenolytic ring opening of methylcyclopentane (MCP) was investigated on Rh/Al₂O₃ and Rh/SiO₂ catalysts, prepared by the incipient wetness method. Strong dependence can be seen in the yield and distribution of ring opening products as a function of temperature and hydrogen pressure. They depended also on the support used. The ring opening reaction required high hydrogen coverage, and was not random (hindered in the vicinity of the methyl group), thus, mainly 2-methylpentane (2MP) and 3-methylpentane (3MP) were formed. The fragments consisted of C₁–C₅ alkanes, with methane andi-pentane as main fragments. This means the possibility of breaking two C−C bonds during one sojourn of the reactant on the catalyst, both taking place far from the substituent. The loose positive correlation between the ratios ofi-pentane/n-pentane and 3MP/n-hexane seems to support this conclusion. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

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 , .

     

Influence of Pr ions on the properties of Pd/SiO2 and Pt/SiO2 catalysts in oxidation of n-butane

It has been established that (M_VIII+Pr)/SiO₂ catalysts (M_VIII=Pd or Pt) obtained from organometallic precursors, have increased the dispersity of Pt, but their TN in deep oxidation of n-butane is by 3–6 times lower than that of unmodified M_VIII/SiO₂.

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(M_VIII+Pr)/SiO₂ ( M_VIII=Pd, Pt), , Pt, 3–6 - M_VIII/SiO₂.

     

Dispersity of (Ru+Pd)/SiO2 catalysts and their properties in CO hydrogenation and ethane hydrogenolysis

The decreased activity of bimetallic catalysts obtained by the interaction of Ru₃(CO)₁₂ with Pd/SiO₂ in the synthesis of hydrocarbons from CO and H₂ and in ethane hydrogenolysis compared with Ru/SiO₂ is due to the dilution, of ruthenium by less active palladium atoms.

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, Ru₃(CO)₁₂ Pd/SiO₂, CO Ru/SiO₂ .

     

Synthesis and studies of catalysts prepared by supporting Hf(CH2Ph)4 on SiO2 and Al2O3

Catalysts prepared by supporting Hf(CH₂Ph)₄ on silica and alumina were studied. Their catalytic activity in ethylene polymerization was shown to increase considerably upon heating in hydrogen. IR spectroscopic studies of catalysts heated in hydrogen show the formation of surface Hf hydrides.

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, Hf (CH₂Ph)₄ . , . .

     

Sulfuration of Pt/Al2O3, Pt?Re/Al2O3 and Pt?Ir/Al2O3 catalysts

Three reforming catalysts Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃ have been sulfurated by H₂S and tested by their activities in benzene hydrogenation. By treatment at 500°C under hydrogen flow only a part of the initial activity of the non-sulfurated catalyst is retained. So only a part of the adsorbed sulfur is easily removed in these conditions. The remaining sulfur for each of the catalysts (Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃) gives the same atomic ratio of 0.5 sulfur atom per accessible metallic atom.

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Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃ . 500°C H₂ . . ., . (Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃) 0,5.

     

The consistency of repeated H2?O2 titration cycles on supported Pt catalysts

H₂ and O₂ uptakes at 296 K on a Pt/Al₂O₃ catalyst remained constant during repeated H₂–O₂ titration cycles conducted in a high vacuum adsorption system. Previously reported variations in these uptakes are attributed to adsorption of contaminants during desorption conditions. Also, it was found that nearly 40% of the H₂ adsorbed could be removed by degassing at 296 K for 1 hr.

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H₂ O₂ 296 Pt/Al/₂O₃ H₂–O₂, . . , 40% H₂ 1 296 .

     

Pt LIII-edge XANES and EXAFS studies on γ-Al2O3 supported Pt catalysts

Pt L_III-edge XANES and EXAFS were employed to investigate the nature of Pt/γ-Al₂O₃, Pt−Sn/γ-Al₂O₃ and Pt−Fe/γ-Al₂O₃ catalysts. The results indicated that Pt species on these catalysts were all in the oxidized states before reduction, and in the metallic states after reduction. The dispersity of the Pt species on the catalysts was very high after reduction. The electronic properties of the highly dispersed Pt species were different from that of the bulk Pt in large crystallites. An interaction between Pt and the metal-oxide modified γ-Al₂O₃ support is proposed. The interaction improved the dispersity of the Pt species on the catalysts and is thought to be the reason for the enhanced activity and selectivity for dehydrogenation reactions over these catalysts.     

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. , - . .