Infrared spectroscopic study of the bending modes of the bronsted acidic sites in deuterated zeolites

Deuteration of Bronsted acidic sites in zeolites gives observable infrared in-plane O-D bending modes. For zeolite Y and ZK-5, a maximum near 870 cm-1 with a shoulder near 890 cm-1 is observed. These signals are related to, respectively, the high-frequency and the low-frequency stretching modes. Mordenite, zeolite beta and ZSM-5 possess a single mode near 890 cm-1. The zeolite structure type and composition influences the position of the modes strongly. A large anharmonicity parameter, x(deltadelta)OD (-80 cm-1), is found due to Fermi resonance with the zeolite lattice mode