SAPO-37 - THE IMPLICATIONS OF STRUCTURE FLEXIBILITY ON ACIDITY

When tetrapropylammonium cations are removed from the alpha cavities o f SAPO 37, but tetramethylammonium cations are still in the beta-cages , a shift in the vibrational frequency of hydroxy groups to lower freq uencies, with the corresponding appearance of stronger acid sites is o bserved; this is a consequence of the increase of the T-O-T' angle dim ensions owing to the presence of the bulky tetramethylammonium cations .