STUDY OF THE NATURE OF ACID SITES OF MONTMORILLONITES PILLARED WITH ALUMINUM AND OLIGOSILSESQUIOXANE COMPLEX CATIONS .1. BRONSTED ACIDITY

Two samples, obtained by pillaring a Wyoming montmorillonite with hydr oxy aluminium and oligosilsesquioxane cations, were studied by stepwis e thermal desorption of ammonia and by highly sensitive diffuse reflec tance IR-spectroscopy. For both clays, the adsorption of ammonia shows a total number of acid sites equal to 0.35 meq/g, with acid strengths comparable to that of HY zeolites. By IR reflectance spectroscopy, Br onsted acid sites with an acid strength comparable to that of bridging hydroxyls in zeolites were found in Al samples but not on Si-montmori llonites. These sites were characterized by an overtone band at 7100 c m(-1) and an activity for ethylene oligomerization at 300 K.