The distribution of acid sites of different acid strengths on zeolite Y with different Si/Al ratios prepared by secondary synthesis with (NH4)2SiF6 were studied by 20Si magic angle spinning (MAS) NMR, statistical calculation, and NH3-TPD temperature- desorption. The data correlated with the activities of the zeolites toward typical acid-ctalyzed reactions. The acid strength of the Al sites in zeolite Y framework depends on their local framework environment, i.e. the no. of next nearest Al neighbors. Changes in zeolite acidity and acid strength with Al content measured by NH3-TPD with the result of 29Si MAS NMR and the distribution of Al sites obtained from statistical calculation As the Al content decreases, the total acidity of zeolite Y decreases, but the strong acidity increases first and then decreases. The max. of the curve of the strong acidity is located at Al/(Al + Si) = 0.15. The catalytic activity of the zeolites toward isopropanol dehydration, which requires only weak acidity, and the total acidity vary similarly with Al content. The catalytic activity toward cumene cracking, which needs strong acidity, parallels that of the strong acidity.

Key words: AMMONIUM COMPOUND, ZEOLITE, ACID CATALYST, FLUORIDE, SILICON COMPOUNDS, ACID PROPERTY, CATALYTIC ACTIVITY, DEALUMINIZATION