Fj. Berry et al., The location of europium in Eu3+-exchanged zeolite-Y as determined by extended X-ray absorption fine structure (EXAFS) investigations at 77 K, J MAT CHEM, 10(9), 2000, pp. 2131-2136
Eu L-3-edge EXAFS has been used to investigate the location of Eu3+ cations
in an Eu3+-exchanged zeolite-Y, with a framework Si/Al molar ratio of 13.5
+/- 2.0, as a function of heat treatment up to 200 degrees C. All of the E
XAFS data were recorded from samples cooled to 77 K following ion-exchange
and heat treatment. The interpretation of the EXAFS data, in conjunction wi
th a geometrical modelling approach, for the sample subject only to ion-exc
hange at 60 degrees C is consistent with hydrated Eu3+ cations being direct
ly bound to framework oxygen atoms (O4) of free six-membered rings that bor
der the supercages of the zeolite-Y structure. The hydrated Eu3+ cations ar
e displaced from the high-symmetry SII sites. The coordination environment
of the Eu3+ cation in the sample heated to 100 degrees C is similar to that
in the as-exchanged sample. Heating of the Eu3+-exchanged zeolite-Y at 200
degrees C results in migration of the Eu3+ cations into the sodalite cages
where, as partially hydrated species, they are coordinated to three framew
ork oxygen atoms in such a way as to be displaced from SI' sites.