STUDY OF H-ZSM-5 ACIDITY BY H-1-NMR - BROAD-LINE AT 4 K AND HIGH-RESOLUTION MAS AT 300 K - BRONSTED ACIDITY SCALE AND COMPARISON WITH ETHERZEOLITES

The interaction of water molecules with the acidic OH groups of two H- ZSM-5 zeolites, with Si/Al values of 23 and 39, is quantitatively stud ied using H-1 NMR, broad-line at 4 K and magic angle spinning (MAS) at 300 K. The H-ZSM-5 are ranked on a scale of Bronsted acidity based on the ''acidity coefficient'', alpha(a), which is equal to the hydroxon ium ion concentration per Bronsted acid site when one water molecule i nteracts with each acidic OH group. The results are compared with thos e obtained for H-Y and H-mordenite zeolites.