Homogeneous OH groups in dealuminated HY zeolite studied by IR spectroscopy

Abstract

The analysis of IR spectra of free OH groups in strongly dealuminated zeolite HY (Si/Al ≅ 100) restoring on desorption of ammonia or pyridine provides spectroscopic evidence for the homogeneity of SiO 1HAl groups. The same conclusion is obtained by analysis of the IR spectra of OH and OD groups interacting (by hydrogen-bonding) with nitrogen at 170 K. The homogeneity of OH groups in strongly dealuminated HY is explained by the presence of only (SiO) 3SiO 1HAl(OSi) 3 groups. By contrast, heterogeneous OH groups are found in non-dealuminated HY (Si/Al=2.56) containing three kinds of OH groups of various acid strength: (SiO)(AlO) 2SiO 1HAl(OSi) 3, (SiO) 2(AlO)SiO 1HAl(OSi) 3 and (SiO) 3SiO 1HAl(OSi) 3. Our dealuminated sample is the only known example of a zeolite with strongly acidic homogeneous hydroxyls. It may be a model catalyst for strongly acidic homogeneous OH groups or a model system for spectroscopic studies (IR, NMR etc.).