title: Location of Framework Al Atoms in the Channels of ZSM-5: Effect of the (Hydrothermal) Synthesis.
abstract: (27) Al 3Q MAS NMR and UV/Vis spectroscopy with bare Co(II) ions as probes of Al pairs in the zeolite framework were employed to analyze the location of framework Al atoms in the channel system of zeolite ZSM-5. Furthermore, the effect of Na(+) ions together with tetrapropylammonium cation (TPA(+)) in the ZSM-5 synthesis gel on the location of Al in the channel system was investigated. Zeolites prepared using exclusively TPA(+) as a structure-directing agent (i.e., in the absence of Na(+) ions) led to 55-90% of Al atoms located at the channel intersection, regardless the presence or absence of Al pairs [Al-O-(Si-O)2 -Al sequences in one ring] in the zeolite framework. The presence of Na(+) ions in the synthesis gel did not modify the Al location at the channel intersection (55-95% of Al atoms) and led only to changes in i) the distribution of framework Al atoms between Al pairs (decrease) and single isolated Al atoms (increase), and ii) the siting of Al in distinguishable framework tetrahedral sites.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejskova 3, Prague 8, 182 23, Czech Republic.
authors.forename: Veronika
authors.initials: V
authors.lastname: Pashkova
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejskova 3, Prague 8, 182 23, Czech Republic.
authors.forename: Stepan
authors.initials: S
authors.lastname: Sklenak
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejskova 3, Prague 8, 182 23, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Klein
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejskova 3, Prague 8, 182 23, Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Urbanova
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, Dolejskova 3, Prague 8, 182 23, Czech Republic. dedecek@jh-inst.cas.cz.
authors.forename: Jiří
authors.initials: J
authors.lastname: Dědeček
keywords: NMR spectroscopy; aluminum; shape selectivity; structure elucidation; zeolites