Počet záznamů: 1  

Structure of framework aluminum Lewis sites and perturbed aluminum atoms in zeolites as determined by 27Al{1H} REDOR (3Q) MAS NMR spectroscopy and DFT/molecular mechanics

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    0439638 - ÚMCH 2015 RIV DE eng J - Článek v odborném periodiku
    Brus, Jiří - Kobera, Libor - Schoefberger, W. - Urbanová, Martina - Klein, Petr - Sazama, Petr - Tabor, Edyta - Sklenák, Štěpán - Fishchuk, A. V. - Dědeček, Jiří
    Structure of framework aluminum Lewis sites and perturbed aluminum atoms in zeolites as determined by 27Al{1H} REDOR (3Q) MAS NMR spectroscopy and DFT/molecular mechanics.
    Angewandte Chemie - International Edition. Roč. 54, č. 2 (2015), s. 541-545. ISSN 1433-7851. E-ISSN 1521-3773
    Grant CEP: GA ČR(CZ) GA14-10251S; GA ČR(CZ) GA13-24155S
    Institucionální podpora: RVO:61389013 ; RVO:61388955
    Klíčová slova: aluminum * density functional calculations * Lewis acids
    Kód oboru RIV: JN - Stavebnictví; CI - Průmyslová chemie a chemické inženýrství (UFCH-W)
    Impakt faktor: 11.709, rok: 2015

    Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework AlFR Lewis acid sites are often found in their H-forms. The formation of AlFR Lewis sites in zeolites is a key issue regarding their selectivity in acid-catalyzed reactions. The local structures of AlFR Lewis sites in dehydrated zeolites and their precursors—“perturbed” AlFR atoms in hydrated zeolites—were studied by high-resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)3AlOH groups and are characterized by a broad 27Al NMR resonance (δi=59–62 ppm, CQ=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the 27Al MAS NMR spectrum. Dehydroxylation of (SiO)3AlOH occurs at mild temperatures and leads to the formation of AlFR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)3Al Lewis sites exhibit an extremely broad 27Al NMR resonance (δi≈67 ppm, CQ≈20 MHz, and η≈0.1).
    Trvalý link: http://hdl.handle.net/11104/0244084

     
     
Počet záznamů: 1  

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