KINDS OF CATIONS IN NAZSM-5 ZEOLITE

Dielectric properties of dehydrated and hydrated NaZSM-5 zeolites were measured in order to investigate behaviors of Na+ ions. Two loss peaks and an apparent conductivity loss were observed in the dehydrated state. In order to study characteristics of these losses observed, water vapor was gradually added to the dehydrated zeolite at 430.5 K, and the changes along with increasing water content were followed. The peak at the higher frequency side (Peak II) shifted to the higher frequency range with increasing water vapor pressure. The peak at the lower frequency side (Peak I), on the other hand, changed its peak position very little. Since the dielectric losses are caused by cation movements, and a water molecule adsorbs on the cation, it was judged from the results that there are at least two kinds of Na+ ions in NaZSM-5 zeolite, and the Na+ ion responsible for Peak II (Na II) is a more active site for water adsorption than the Na+ ion causing Peak I (Na I). The apparent conductivity loss was also affected by water adsorption. An activation energy of the conductivity process was determined and compared with those of relaxation processes for Na's I and II. From these results, it was concluded that both the conduction loss and Peak II was caused by Na II. The existence of two kinds of Na+ ions was confirmed by MAS-NMR measurements. © 1992.