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  • 1
    Electronic Resource
    Electronic Resource
    In situ FTIR spectroscopy on rhodium-exchanged NaX zeolite with different metal dispersion during syngas reaction (1994)
    Springer
    Catalysis letters 27 (1994), S. 119-130 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806985
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  • 2
    Electronic Resource
    Electronic Resource
    Metal dispersion dependent selectivities for syngas conversion on faujasite X hosted rhodium (1992)
    Springer
    Catalysis letters 13 (1992), S. 247-259 
    Details
    ISSN: 1572-879X
    Keywords: Faujasite X hosted rhodium ; rhodium particle size ; IR-spectroscopy ; TEM ; CO hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different metal dispersions of Na-faujasite X hosted rhodium were generated and characterized by transmission electron microscopy (TEM) and IR-spectroscopy. CO hydrogenation has been studied over these Rh/NaX-zeolite catalysts. The finer rhodium dispersion with a mean particle size of 1–2 nm shows a higher selectivity towards oxygenates (methanol, ethanol and dimethyl ether) as compared to the coarser dispersion (4–5 nm), where nearly exclusively methane and higher hydrocarbons are formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00770997
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  • 3
    Electronic Resource
    Electronic Resource
    Amination of dimethyl ether on zeolite catalysts. 2. Acidic properties of the used T-zeolites and their influence on the catalytic reaction (1992)
    Springer
    Catalysis letters 14 (1992), S. 359-371 
    Details
    ISSN: 1572-879X
    Keywords: Dimethylether amination ; methylamines ; zeolite T ; acidic properties ; TPDA ; IR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Freshly prepared and used H/Na, K-T-zeolite catalysts for the conversion of dimethyl ether and ammonia to the three methylamines have been characterized by temperature-programmed desorption of ammonia and IR spectroscopy. Activity and selectivity depend on the nature and number of the acid sites. With time on-stream, deep alterations in the catalyst behaviour have been observed. The activity of the catalyst is decreased by blocking of active sites ≈ 5–10 h: furthermore, during an initial period hydrocarbons were formed almost exclusively on strong-acid sites. A second period is characterized by an increased “shape selectivity” observed in the distribution of the methylamines. The amination will proceed probably on left weak-acid sites and on the outer surface in a third period, however, without “shape selectivity” due to the progressive blocking of the inner catalyst surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769674
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