Deuteration of Bronsted acid sites in zeolites and SAPOs results in in
-plane O-D bending modes that can be studied with FTi.r. spectroscopy.
A band maximum near 870 cm-1 and a shoulder near 890 cm-1 are related
to the high-frequency (HF) and low-frequency (LF) O-H or O-D stretchi
ng modes observed for zeolites Y and ZK-5 and for SAPO-17 and SAPO-34.
For mordenite, zeolite beta, ZSM-5, and SAPO-11, only one type of ben
ding mode is observed near 890 cm-1. Structure type and composition in
fluence the frequencies for these bands. Increasing the sodium content
of the samples results in a shift of the fundamentals to lower freque
ncies. Increasing the Si/Al ratio shifts the bands to slightly higher
frequencies. The in-plane bending modes are more sensitive to structur
al differences than are the corresponding stretching modes. The first
overtones of the O-D bending modes are observed near 1580 cm-1 for the
zeolites and near 1540 cm-1 for the SAPOs. Simulations of the inelast
ic neutron scattering spectra indicate that the in-plane bending modes
are localized modes, whereas the out-of-plane bending modes are coupl
ed to the lattice modes. The in-plane O-D bending modes are shifted to
higher frequencies due to Fermi resonance with the zeolite T-O lattic
e modes. The observed shift is 80 cm-1 for the zeolites and 110 cm-1 f
or the SAPOs.