Testing of the Lewis acidity of H-Y and HZSM-5 zeolites with 15N n.m.r. of adsorbed N 2O

Abstract

The Lewis acidity of H-Y and HZSM-5 zeolites has been studied using 15N n.m.r. of adsorbed N2O. It follows from 15N n.m.r. data that in H-Y zeolites a variety of Lewis acidic sites having different strengths of acidity is present. The number of the strongest Lewis sites is about 20–30 μmole/g, i.e., about 102 times less compared with the total quantity of extralattice aluminum atoms. The number of the “strong” and “weak” Lewis sites in H-Y zeolites depends on the types of treatment. The strong Lewis sites are found in the samples treated under shallow-bed conditions. The deep-bed treatment results in decreasing of the concentration of the strongest Lewis acidic sites. For HZSM-5 zeolites, the quantity of the strong Lewis acidic sites is the same order of magnitude as the number of the extralattice aluminum atoms.