CRYSTAL-STRUCTURES OF DEHYDRATED H CHABAZITE PRETREATED AT 320-DEGREES-C AND AT 600-DEGREES-C AFTER STEAMING

Two crystal structures of dehydrated NH4-exchanged chabazite crystals were studied by use of single-crystal X-ray diffraction methods after dehydration at 320 °C, and at 600 °C following a steaming period. No significant differences are observed between the two structures; there is no preference of the protons for a single oxygen species nor any indication of Al removal from the framework after steaming. A strong correlation between T-O-T bond angles and T-O distances in adjacent tetrahedra shows an identical slope with that of dehydrated H mordenite. The framework oxygens, all pointing either to the hexagonal prisms or to the centers of the framework eight-rings, prohibit the free vibration of OH bonds in the large cavity. This explains the 30 cm-1 decrease of the HF bands as compared to the value predicted from the framework composition. © 1979 American Chemical Society.