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  • 1
    Electronic Resource
    Electronic Resource
    The role of alkali cations in zeolite synthesis from silicate solutions containing N,N,N-trimethyl-1-adamantammonium cations (1996)
    Springer
    Catalysis letters 38 (1996), S. 1-9 
    Details
    ISSN: 1572-879X
    Keywords: zeolite synthesis ; SSZ-24 ; SSZ-31 ; alkali cations ; N,N,N-1-adamantammonium cation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Zeolite synthesis from aqueous N,N,N-trimethyl-1-adamantammonium (TMAA+)-alkali (Na+, K+, Rb+, and Cs+) silicate mixtures is studied using X-ray diffraction, elemental analysis, scanning electron microscopy, and29Si magic angle spinning (MAS),1H-13C cross-polarization (CP) MAS and1H-29Si CP MAS NMR spectroscopies. SSZ-24 forms in the presence of potassium cations, and SSZ-31 crystallizes in the presence of sodium cations. This is the first report of SSZ-31 synthesis from Na-TMAA silicate mixtures. Unknown silicates form in the presence of rubidium and cesium cations, whereas no crystalline material is observed in synthesis mixtures devoid of alkali cations. The alkali cations do not appear to serve as templates or void fillers during zeolite crystallization, nor do they stabilize soluble silicate anions which serve as building blocks during zeolite crystallization. Rather, the alkali cations appear to regulate the transformation of the amorphous synthesis gel into either crystalline zeolite or other silicate phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806891
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  • 2
    Electronic Resource
    Electronic Resource
    Lewis acidity as an explanation for oxide promotion of metals: implications of its importance and limits for catalytic reactions (1994)
    Springer
    Catalysis letters 27 (1994), S. 243-249 
    Details
    ISSN: 1572-879X
    Keywords: oxide promotion ; acidity ; CO and CO2 hydrogenation ; Rh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sub-monolayer quantities of metal oxides are found to influence CO hydrogenation, CO2 hydrogenation, acetone hydrogenation, ethylene hydroformylation, ethylene hydrogenation, and ethane hydrogenolysis over Rh foils. The metal oxides investigated include AlOx, TiOx, VOx, FeOx, ZrOx, NbOx, TaOx, and WOx. Only those reactions involving the hydrogenation of C-O bonds are enhanced by the oxide overlayers. The coverage at which maximum rate enhancement occurs is approximately 0.5 ML for each oxide promoter. Titanium, niobium, and tantalum oxides are the most effective promoters. XPS measurements after reaction show that of the oxides studied titanium, niobium, and tantalum oxide overlayers are stable in the highest oxidation states. The trend in promotion effectiveness is attributed to the direct relationship between oxidation state and Lewis acidity. For the oxide promoters, bonding at the metal oxide/metal interface between the O-end of adsorbed CO and the Lewis acidic oxide is postulated to facilitate C-O bond dissociation and subsequent hydrogenation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813909
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    Paper (German National Licenses)
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