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, . . . .

     

Catalytic and physico-chemical properties of Al2O3?H3PO4 system, II. Donor-acceptor properties

Donor-acceptor properties of catalysts containing different quantities of orthophosphoric acid on -alumina were studied. The decrease in N₂O decomposition rate was found to be parallel with that of one-electron donor sites. Catalysts containing more than 0.4 mmol H₃PO₄/g Al₂O₃ exhibit individual surface properties due to the formation of an aluminium phosphate phase in the surface layer.

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- , -Al₂O₃. , N₂O . , 0,4 H₃PO₄/ Al₂O₃ .

     

Hydrogenation of CO2

The hydrogenation of CO₂ has been studied on three different series of catalysts: Fe/MgO, Ni/Ti, Cr/Zn doped with potassium. Reaction was carried out in a conventional flow microreactor system at 15 bar at 250–350°C. Three independent competing reactions: Reverse gas-water shift (RGWS), Fischer-Tropsch (FT) and methanol synthesis were observed.

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CO₂ : Fe/MgO, Ni/Ti, Cr/Zn . 15 250–350°C. : RGWS, F.T. .

     

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. , - . .

     

Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

Catalysts for metathesis of olefins obtained through [Mo3O4(C2O4)3 (H2O)3]2? coordinated to γ-Al2O3

New highly active catalysts for the metathesis of olefins have been obtained through the interaction of [Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– anion with Al₂O₃ surface and further activation in H₂ or CO atmosphere.

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[Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– Al₂O₃ H₂ CO .

     

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 .

     

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, , .

     

Influence of the chlorine content of Al2O3 on its catalytic activity and coke formation

The catalytic activities of aluminas with different chlorine contents for cumene cracking, o-xylene isomerization, n-hexane isomerization and cracking and methylcyclopentane cracking were studied. The catalytic activity and the acidity increase continuously when the chlorine content increases. Coke formation is only noticiable with methylcyclopentane, increasing with the chlorine content of the alumina.

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, -, - . . - , - .

     

Triterpene glycosides of Gleditschia triacanthos IV. The structure of triacanthosides A1 and G

Summary The pericarps ofGleditschia triacanthos L. have yielded a new triterpene glycoside — triacanthoside A₁ — and it has been shown that it has the structure of echynocystic acid 3-O-[-D-xylopyranosyl-(14)--L-arabopyranosyl-(13)--D-glucopyranoside].It has been shown that the O-glycosidic moiety of triacanthoside G coincides in structure with triacanthoside A₁. The O-acyloside moiety of triacanthoside G contains the trisaccharide D-glucopyranosyl-(13)-O-L-arabopyranosyl-(14)-O-L-rhamnopyranose.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 314–316, May–June, 1973.     

The preparation, characterization, and thermal behaviour of some lithium aluminum oxides: Li3AlO3 and Li5AlO4

The purpose of this research was to study the best conditions for the synthesis of the double oxides Li₅AlO₄ and Li₃AlO₃ in the solid state starting from the simple oxides, and to determine their heats of formation.Li₅AlO₄ was obtained from Li₂O₂ or Li₂O and -Al₂O₃ in a Li/Al molar ratio of 51, and was characterized by X-ray methods. Lithium orthoaluminate, Li₃AlO₃, was obtained from Li₂O₂ and -Al₂O₃ in a molar ratio 31. The postulated formula, Li₃AlO₃, was confirmed by chemical analysis.The temperature ranges in which the compounds are stable were established by the DTA method, and were found to be very limited for Li₃AlO₃ (400–430°) but greater for Li₅AlO₄ (440 — more than 600°).The heats of formation of Li₅AlO₄ and Li₃A10₃, also determined by means of the DTA method, were found to be –552.3 ± 0.8 kcal/mole and –416.8 ± 2 kcal/mole, respectively.

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Zusammenfassung Es wurden die Bildungsverhältnisse der doppelten Oxide Li₅AlO₄ und Li₃AlO₃ in fester Phase ausgehend von den einfachen Oxyden geprüft und ihre Bildungswärmen bestimmt. Li₅AlO₄ wurde aus Li₂O₂ oder Li₂O und -Al₂O₃ beim Molverhältnis von Li/Al 5 1 erhalten und röntgenographisch identifiziert. Das Orthoaluminat Li₃AlO₃ erhielt man beim Molverhältnis 3 1 von Li₂O₂ und -Al₂O₃. Die Zusammensetzung von Li₃AlO₃ wurde durch chemische Analyse nachgewiesen. Die DTA-Prüfung zeigte, daß Li₃AlO₃ nur im sehr kleinen Temperaturgebiet (400–430°), Li₅AlO₄ hingegen im weiteren Bereich zwischen 440–600° stabil ist. Die Bildungswärmen betrugen für Li₅AlO₄ –552.3±0.8, für Li₃AlO₃ –416.8±2 kcal/Mol.

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Résumé On a recherché les meilleures conditions pour réaliser la synthèse à l'état solide des oxydes doubles Li₅AlO₃ et Li₃AlO₃ en partant des oxydes individuels et pour déterminer leur chaleur de formation. Li₅AlO₄ a été obtenu en partant de Li₂O₂ (ou Li₂O) et de -Al₂O₃ dans le rapport molaire Li/Al=5/1; il a été caractérisé par étude aux rayons X. L'orthoaluminate de lithium, Li₃AlO₃, a été obtenu en partant de Li₂O₂ et de -Al₂O₃ mélangés dans le rapport 3/1. L'analyse chimique a confirmé la formule présumée Li₃AlO₃. L'ATD a permis de déterminer le domaine de stabilité thermique de ces composés: très restreint pour Li₃AlO₃ (400–430°), plus grand pour Li₅AlO₄ (440-plus de 600°), ainsi que leurs chaleurs de formation: –416.8±2 kcal/mole et –552.3±0.8 kcal/mole, respectivement.

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— Li₅AlO₄ Li₃AlO₃ . Li₅AlO₄ Li₂O₂ Li₂O -l₂₃ Li/Al 51, . , Li₃AlO₃, Li₂O₂ -l₂₃ 31. . , , , Li₃AlO₃ (400—430 °?) Li₅AlO₄ (440- 600 °?). Li₅AlO₄ Li₃AlO₃ 552.3 ± 0.8 416.8 ± 2 /, .

     

Surface redox properties of Rh/AlPO4 and Rh/AlPO4?SiO2 catalysts

Electron donor and acceptor properties of AlPO₄ and AlPO₄–SiO₂ (2080 wt. %) supported rhodium catalysts have been studied. It was observed that the effect of metal deposition on both electron acceptor and donor properties depend on the support and precipitation agent. AlPO₄ supported rhodium showed better acoeptor than donor properties, while for Rh/AlPO₄–SiO₂, the acceptor properties were superior. However, the effect of metal on the redox properties is slight.

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AlPO₄ QlPO₄ SiO₂ (2080 .%). ]ye . AlPO₄ , , Rh/AlPO₄–SiO₂ . , - .

     

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 .

     

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 . .

     

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.

     

A mechanistic study of cycloaddition of carbon dioxide to propyne over supported Rh4 and Fex Rhy carbonyl cluster derived catalysts

CO₂ undergoes cycloaddition to propyne on a cationic rhodium site with the assistance of O^2–/OH^– of support or iron oxide over Rh₄ and Fex Rhy carbonyl clusterderived catalysts.¹³CO₁₂ labeling and FTIR studies suggest that monodentate carbonate formed on the catalyst surface is most likely a key species to offer an active CO₂ to be converted into a carbonyl intermediate prior to the product 4,6-dimethyl-2-pyrone.

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CO₂ O^2–/OH Rh₄ Fex Rhy. ¹³CO₂ , CO₂ , 4,6--2-.

     

Studies of the reactions of Br(2P3/2) and Br(2P1/2) with SiH4

Photobromination of SiH₄ under uv-irradiation at various wavelengths has been studied. Rate constants for the elementary reactions Br(²P_3/2)+SiH₄HBr+SiH₃ (k=3.2×10^–11 exp(–21.8±2.5)/RT, cm³/s) and Br^* (²P_1/2)+SiH₄HBr+SiH₃ (k^*=(3±1)×10^–13 cm³/s) have been determined in the temperature range from 300 to 415 K.

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- . Br(²P_3/2)+SiH₄HBr+SiH₃, k=3,2×10^–11 exp (–21,8±2,5)/RT ³/ Br^*(²P_1/2)+SiH₄HBr+SiH₃, k^*=(3±1)×10^{–13 3}/ 300–415 K.

     

Temperature programmed desorption of NH3 and H2O from NH4NaX and CoNH4NaX zeolites

A study has been made of temperature programmed desorption (TPD) of NH₃ and H₂O from samples of NH₄X and CoNH₄X zeolites of various degree of exchange. NH₃ TPD peaks could be explained by interaction of NH₃ with different Brönsted and Lewis acidic centers. Moreover a water peak at high temperatures allowed interpretations of the dehydroxylation, and by reason of the characteristic desorption temperatures a particular state of the Co²⁺ ions in the CoNH₄X zeolites is postulated.

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- () NH₃ H₂O NH₄X CoNH₄X . NH₃ NH₃ =qs . . Co²⁺ CoNH₄X.

     

Preparation of active platinum hydrogenolysis catalyst supported on TiO2 phase dispersed on SiO2

Platinum catalysts supported on a TiO₂ phase well-dispersed on SiO₂ (TiO₂/SiO₂) exhibited a high activity for butane hydrogenolysis; activity was 12 orders of magnitude higher than those of platinum catalysts supported on SiO₂ and TiO₂.

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Pt, TiO₂, SiO₂ (TiO₂/SiO₂), ; 12 , SiO₂ TiO₂.

     

HCN synthesis from NH3 and CH4 on Rh and Ir

The synthesis of hydrocyanic acid from methane and ammonia on Rh and Ir wires was studied at temperatures varying between 1200 and 1500 K at one atmosphere. Activation energies and preexponential factors are reported.

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1200–1500K . .