THE EFFECT OF EXCHANGE DEGREE ON THE HETEROGENEITY OF ACID SITES IN DECATIONATED FAUJASITES

Adsorption microcalorimetry, TPD, thermal analysis, and IR spectroscop y are applied to evaluate the strength of acidity for faujasites with varying degrees of decationization. It is shown that acidity and catal ytic activity appear relatively slowly as the first half of the Na+ ca tions is removed, but after reaching a decationization level of 50%, b oth the number of acid sites and activity increase much more rapidly. To rationalize the observed acidity-exchange level profile, a model is developed that extends the shielding power of a single Na+ ion to sev eral neighboring AlO4 tetrahedra.