Out-of-plane bending vibrations of bridging OH groups in zeolites: A new characteristic of the geometry and acidity of a broensted site

Abstract

Abstract Out-of-plane bending vibrations of bridging OH groups in zeolites were studied by diffuse-reflectance IR spectroscopy in the region of the combination bands of the out-of-plane bending and fundamental stretching vibrations (3800 - 4200 cm -1). Similar to the in-plane bending vibrations, the out-of-plane bending modes were found to be a very sensitive haracteristicof the bridging OH groups in zeolites. These frequencies increase with increasing acidity of the OH groups and with formation of H-complexes with adsorbed molecules.