Abstract
Zeolite β was prepared with different Si/Al atios by a hydrothermal method and dealuminated by leaching with dilute HCl. Samples of β from the various stages of H-β synthesis, and after leaching, were characterized by X-ray diffraction and IR and 27 Al MAS-NMR (MAS=magic angle spinning) spectroscopies. All the samples exhibited both Lewis and Bronsted acidities. The types of OH groups present, and also their distribution, are greatly affected by sample treatment. Five types of hydroxyl IR absorptions were found: those from strongly acidic bridging hydroxyl groups (3605 cm -1 ), OH groups bonded to extralattice aluminum (3660-3680 cm -1 ), internal SiOH at framework defects (3730 cm -1 ), and terminal SiOH groups (3745 cm -1 ) and a «very high frequency» (VHF) absorption (3782 cm -1 )
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