S
ets of ZSM-5 z
eolit
es with diff
er
ent distributions of Al atoms in th
e fram
ework w
er
e synth
esiz
ed from th
e mixtur
es of Si/Al
gel 25鈥?0, varying in th
e s
equ
enc
e of mixing and using Na-silicat
e or t
etra
ethoxy orthosilicat
e as th
e Si sourc
e, AlCl
3 or Al(NO
3)
3 as th
e Al sourc
e, NaCl or Na-silicat
e as th
e Na sourc
e, and t
etrapropylammonium hydroxid
e as th
e structur
e dir
ecting ag
ent. Th
e distribution of Al atoms in th
e ZSM-5 fram
ework b
etw
een singl
e Al atoms and Al pairs of Al鈥揙鈥?Si鈥揙)
2鈥揂l s
equ
enc
es was monitor
ed by th
e 29Si MAS NMR, Co(II) ion
exchang
e capacity and UV鈥搗is sp
ectroscopy of bar
e Co(II) ions in th
e d
ehydrat
ed z
eolit
es. Th
e r
esults show
ed that th
e distribution of Al atoms in th
e ZSM-5 fram
ework can b
e controll
ed in a wid
e rang
e of conc
entrations (6鈥?6% of Al atoms in Al pairs for th
e giv
en Si/Al) and Si/Al
prod 15鈥?7. From th
e analysis of both th
e initial g
els and crystallin
e products by th
e 13C,
27Al, and
29Si (SP and CP) MAS NMR and FTIR, it was conclud
ed that th
e el
ectrostatic and van d
er Waals int
eractions, gov
ern
ed mainly by th
e pr
es
enc
e of hydrophobic (TPA
+) and charg
ed (Na
+) cations and anions (Cl
鈥?/sup>, NO3鈥?/sup>) of different polarization ability and by the reactivity of alumosilicate species, control the incorporation of Al atoms into the framework of ZSM-5 in the Al pairs located in the rings of three cationic sites and distant not-cooperating single Al atoms in different rings. The high concentration of Al pairs in the zeolite can be reached by the increase of the positive charge of the central N atom of TPA+, which supports incorporation of the Al pair in its close vicinity or by the increase in relative concentration of entities containing Al pairs in the synthesis gel. The predominant incorporation of single Al atoms into the framework occurs in the presence of highly reactive q3 Al species containing an OH group or under the addition of Na+ ions to the synthesis mixture. Single AlO4鈥?/sup> balanced by Na+ ions can be located at each framework T site, not only in the vicinity of TPA+.
Keywords:
ef="http://pubs.acs.org/action/doSearch?action=search&searchText=ZSM%5C-5&qsSearchArea=searchText">ZSM-5; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=Al+distribution&qsSearchArea=searchText">Al distribution; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=single+Al+atoms&qsSearchArea=searchText">single Al atoms; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=Al+pairs&qsSearchArea=searchText">Al pairs; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=MAS+NMR&qsSearchArea=searchText">MAS NMR; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=Co%5C%28II%5C%29+vis+spectroscopy&qsSearchArea=searchText">Co(II) vis spectroscopy; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=zeolites&qsSearchArea=searchText">zeolites; ef="http://pubs.acs.org/action/doSearch?action=search&searchText=hydrothermal+synthesis&qsSearchArea=searchText">hydrothermal synthesis