Conclusions
The rare earth exchanged forms invariably show
the same structural patterns as that of the parent form.
Among different rare earth zeolites, only the ceriumexchanged
form shows diffuse reflectance spectra due
to the presence of interchangeable (Ce3+/Ce4+)
oxidation states. The strain in the framework
tetrahedra could be followed using the shift in the 27Al
and 29Si MAS-NMR peak positions. High field shifts
in the spectra of the rare earth samples are due the
perturbation owing to the presence of rare earth
cations in the extra-framework locations. 27Al MAS
NMR spectra show broadening in the case of LaNa-Y
and CeNa-Y. This is caused by a distribution of
chemical shifts due to aluminium atoms in the locality
of strained (due to vicinity of heavy or bulky cations)
and non-strained framework. Lanthanum exchanged
form shows remarkable properties compared to other
rare earth zeolites. This is reflected in the catalytic
activity of the sample and in the acid site amount
determination by NH3-TPD and thermodesorption of
2,6-DMP experiments and might be due to the
migration of La3+ ions from the large cages to the
small cages of the zeolite framework. The prepared
catalysts were effectively employed for the alkylation
of benzene with 1-octene. The rare earth zeolites
show better selectivity for the 2-phenyloctane
formation. The low activity of LaNa-Y could be
correlated to its low acid amount as evidenced by both
NH3-TPD and 2,6-DMP desorption studies. Time on
stream studies shows that the rare earth exchanged
zeolites exhibit better stability under the given
reaction conditions. Deactivation of the catalyst is due
to the blocking of the zeolite pores by the alkylation
products.