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Hydroxyl groups in crystalline silicoaluminophosphate SAPO-34 have been investigated by diffuse reflectance IR spectroscopy. By carefully comparing the intensities of stretching vibrations with the appropriate combination and overtone bands the two types of bridged Si-OH-AI group were assigned to the fundamental stretching vibrations at 3625 and 3600 cm-'. Both types of group exhibited approximately the same acidic properties but differed in their localization. The bridged groups with v = 3600 cm-' were assumed to be localized in the hexagonal prisms, forming an H-bond with adjacent oxygen anions of the framework. In-plane and out-of-plane bending vibrations were observed for the first time in SAPOs.

Abstract--Two samples, obtained by pillaring a Wyoming montmorillonite with hydroxy aluminium and oligosilsesquioxane cations, were studied by stepwise thermal desorption of ammonia and by highly sensitive diffuse reflectance 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, BrSnsted acid sites with an acid strength comparable to that of bridging hydroxyls in zeolites were found in A1 samples but not on Si-montmorillonites. These sites were characterized by an overtone band at 7100 cm -~ and an activity for ethylene oligomerization at 300 K.

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