The location of europium in Eu3+-exchanged zeolite-Y as determined by extended X-ray absorption fine structure (EXAFS) investigations at 77 K

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 EXAFS data were recorded from samples cooled to 77 K following ion-exchange and heat treatment. The interpretation of the EXAFS data, in conjunction with a geometrical modelling approach, for the sample subject only to ion-exchange at 60 degrees C is consistent with hydrated Eu3+ cations being directly bound to framework oxygen atoms (O4) of free six-membered rings that border the supercages of the zeolite-Y structure. The hydrated Eu3+ cations are 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 framework oxygen atoms in such a way as to be displaced from SI' sites.