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  • 1
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract С помощью метода ИК спектроскопии следили за образованием изоцианата из CO и NH3 на катализаторах Rh/Al2O3 и Rh/NaY. Изоцианат образуется также за счет реакции CO с координационно связанным аммиаком в виде [Rh(NH3)5Cl]2+/NaY.
    Notes: Abstract The formation of isocyanate from CO and NH3 on Rh/Al2O3 and Rh/NaY catalysts under various conditions was obtained using IR-transmission spectroscopy. Isocyanate is also formed by the reaction of CO with NH3 coordinatively bound as [Rh(NH3)5Cl]2+NaY.
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  • 2
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract CO реагирует с Rh(III), нанесенном на MgO и ZnO при повышенных температурах (〉373 К), образуя геминальные дикарбонильные частицы Rh(CO)2 на поверхности. После восстановления водородом при 743 и 473 К, соответственно, доминирующими адсорбированными формами являются линейные и мостиковосвязанные CO на больших кристаллитах Rh. Это находится в пр=qoтивоположности с Rh на других носителях, таких как Al2O3, SiO2 и т.д.
    Notes: Abstract CO reacts with Rh(III) supported on MgO and ZnO at elevated temperatures (〉373 K) to form the gem-dicarbonyl species Rh(CO)2 on the surface. After reduction with hydrogen at 743 and 473 K, respectively, the dominant adsorption forms are the linear and bridge bonded CO on larger Rh-crystallites. This is in contrast to Rh on other supports such as Al2O3, SiO2, etc.
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  • 3
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Исследовали гидрогенизацию CO на катализаторе Rh/TiO2 с большой загрузкой (25 вес.%) после восстановления последнего при 573 и 723 К. Измерением хемосорбции установлено, что Rh/TiO2 после восстановления при высокой температуре находится в состоянии сильного взаимодействия металла с носителем. В этом состоянии каталитическая активность значительно ниже, чем после восстановления при низкой температуре, а селективность гидрирования сдвигается в сторону более высоких углеводородов.
    Notes: Abstract The CO hydrogenation on a highly loaded (25 wt.%) Rh/TiO2 catalyst was investigated after reduction at 573 K and 723 K. Chemisorption measurements show that the Rt/TiO2 ratio is in the SMSI state after the high temperature reduction. The catalytic activity is significantly lower in the SMSI state than after reduction at low temperature. The selectivity of CO hydrogenation is changed in the SMSI state to higher hydrocarbons
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  • 4
    ISSN: 1573-8779
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 5
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Electronic Structure of Rh4(CO)12, a Model for Linear- and Bridge-bonded CO on Rhodium CatalystsThe electronic structure of the Rh4(CO)12 cluster containing both linear- and bridgebonded CO groups has been studied by the EHMO method and compared with that of the Ir4(CO)12 cluster with only linear-bonded CO ligands. The charge distribution shows a distinctly higher π-back donation for the bridge-bonded CO groups. This result is compared with experimental data such as bond lengths, force constants of the C—O stretching frequencies and XPS data. It allows further an interpretation of results of CO hydrogenation on supported rhodium catalysts and on rhodium model complexes.
    Notes: Die Elektronenstruktur des Clusters Rh4(CO)12, der sowohl linear als auch brückenförmig gebundene CO-Gruppen enthält, wurde im Rahmen der EHMO-Methode untersucht und mit der des Ir4(CO)12-Clusters, der nur linear gebundene Liganden aufweist, verglichen. Die ermittelte Elektronendichteverteilung weist für die brückenförmig gebundenen CO-Liganden eine deutlich höhere π-Rückbindung auf. Dieser Befund wird mit experimentellen Daten wie Bindungslängen, Kraftkonstanten der CO-Valenzschwingung und XPS-Werten verglichen. Er gestattet ferner eine Interpretation von Ergebnissen der CO-Hydrierung an Rhodiumträgerkatalysatoren sowie an Rh-Modellkomplexen.
    Additional Material: 6 Ill.
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  • 6
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a device described in a previous paper the angular dependence of the 14.7 eV energy loss of aluminum has been measured. — The dispersion coefficient and the angular dependence of the intensity of this energy loss are in good agreement with the plasma theory. The cut-off angle was found somewhat smaller than expected.
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  • 7
    ISSN: 1572-879X
    Keywords: Bimetallic Rh-Mo clusters ; Rh-Mo/SiO2 catalyst ; heteronuclear clusters ; electron microdiffraction ; EDX analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Rh-Mo/SiO2 catalysts prepared from the heteronuclear (C5H5)3RhMo2(CO)5 precursor were characterized by methods of analytical electron microscopy. The formation of bimetallic Rh-Mo crystallites with f.c.c., b.c.c. and c.p. hexagonal structures similar to those observed in bulk Rh-Mo alloys could be established and related to the outstanding properties of the catalyst.
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  • 8
    ISSN: 1572-879X
    Keywords: Solid-state ; ion exchange ; dealuminated Y zeolite ; rhodium catalysts ; infrared ; spectroscopy ; Rh dicarbonyl ; acid hydroxyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The solid-state ion exchange of Rh chloride with highly dealuminated Y zeolite has been studied by in situ FTIR spectroscopy. Thermal treatment in vacuum and calcination in oxygen up to 600°C results in an exchange limited to ca. 25% at temperatures higher than 400°C. The ion exchange can be performed much more effectively (over 50%) and at lower temperatures (100–150°C) in the presence of CO in the gas phase. A linear correlation has been found between the formation of well-defined Rh(CO) 2 + species and the simultaneous loss of acid hydroxyl groups for samples treated at different conditions. From these results a model is proposed with the formation of Rh subcarbonyls, the migration of these species to the cation positions of the zeolite and, finally, the formation of the stable well-defined Rh(CO) 2 + species at these positions as essential steps of the ion exchange in the presence of CO.
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  • 9
    ISSN: 1572-879X
    Keywords: faujasite-hosted rhodium ; in situ FTIR spectroscopy ; CO hydrogenation ; rhodium dispersion ; methanol selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol.
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  • 10
    ISSN: 1572-879X
    Keywords: Supported Mo-promoted Rh-catalysts ; heteronuclear clusters ; olefin hydroformylation ; acetaldehyde hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molybdenum promoted Rh/SiO2 catalysts have been prepared by using the heteronuclear cluster (C5H5)3RhMo2(CO)5 as well as metal salt precursors. The promoting effect of molybdenum has been studied for the hydroformylation of ethene and propene and the hydrogenation of acetaldehyde. It has been found that molybdenum, especially on the cluster-derived catalyst, increases both the hydrogenation and the hydroformylation rate of the olefins. No specific influence on the CO insertion reaction could be obtained. As an explanation, the promotion of the initial step to form intermediate surface alkyl groups has been proposed as the rate determining step for ethene hydroformylation. The promotion of the alcohol formation by bimetallic centers having Rh and Mo in close vicinity has been supported by the results of the hydrogenation of acetaldehyde.
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