Basic sites on acidic SAPO-5, MAPO-5, and MAPO-36 molecular sieves

The acidic aluminophosphate molecular sieves possess weak basic sites, which can be detected by i.r. spectra of chemisorbed pyrrole. This is attributed to the special chemical composition of these materials: the high AI content but small amount of protons, which results in a relatively small Sanderson average electronegativity and, therefore, a relatively high negative charge on framework oxygen.