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  • 1
    Electronic Resource
    Electronic Resource
    Probing acid sites in MAPO-36 by solid state NMR (1996)
    Springer
    Catalysis letters 39 (1996), S. 141-146 
    Details
    ISSN: 1572-879X
    Keywords: metal-AlPO4 ; NMR spectroscopy ; acid site ; acetone conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An ordering of magnesium is observed in the as-synthesized MAPO-36 molecular sieve. Upon calcination, part of the magnesium is removed from the sample and part occupies extraframework positions thus rendering a random distribution of magnesium in the lattice. The shoulder observed in the31P spectrum of the calcined sample is assigned to P(3Al, 1Mg) sites in conflict with the earlier assignment to P-OH groups. The bridging hydroxyl groups located at these sites are detected in the1H MAS spectrum at 3.6 ppm. Further, MAPO-36 catalyzed acetone conversion to mesityloxide that cracked at elevated temperature to yield acetic acid and aliphatics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00805573
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  • 2
    Electronic Resource
    Electronic Resource
    In situ NMR of heterogeneous catalysis: new methods and opportunities (1999)
    Springer
    Topics in catalysis 8 (1999), S. 81-86 
    Details
    ISSN: 1572-9028
    Keywords: NMR ; zeolite ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ NMR has been extensively applied in the past decade to obtain basic mechanistic information about reactions in heterogeneous catalysis. Most studies in the literature have employed either sealed glass ampoules of catalyst and adsorbate that are heated outside of the NMR probe or variable temperature studies of samples sealed in magic‐angle spinning (MAS) rotors. In situ NMR studies of sealed samples fail to duplicate the conditions of temperature, reagent introduction and product removal found in bench‐top microreactor studies of catalysis. Previous attempts to more closely duplicate the conditions in flow reactors have motivated NMR studies using temperature jumps and the development of MAS probes with reagent flow. These methods have not yet achieved the time scales of several seconds or tenths of seconds that are typical of catalytic reactions. The pulse‐quench catalytic reactor has been developed to permit NMR studies of catalyst samples that have been prepared under actual reaction conditions. Pulse‐quench studies have provided evidence in support of a carbon‐pool mechanism for methanol‐to‐gasoline chemistry on HZSM‐5 and led to the identification of a pentamethylbenzenium cation formed in a zeolite by the alkylation of benzene with excess methanol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019140506645
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