AL-PILLARED SAPONITES .1. IR STUDIES

Al-Pillared saponites have been prepared from natural Na-exchanged Ballarat saponite. Acidic properties of these saponites have been studied by IR spectroscopy using pyridine as a probe molecule. Al-Pillared saponites exhibit both Bronsted and Lewis acidity. Lewis sites are evidenced in the parent Na-exchanged clay as well as in the pillared clays. Bronsted acid sites are not evidenced in the parent Na-exchanged saponite but Al-pillared saponites exhibit Bronsted acidity as shown by a pyridinium band at 1549 cm-1. Bronsted acid sites have been related to OH groups at 3740-3720 cm-1 and 3597-3594 cm-1. The same wavenumbers are evidenced for nu(OH) stretchings in acidified saponite and in Al-pillared saponites. It is assumed that an acidic attack of Si-O-Al linkages which may provide Bronsted sites occurs on the clay sheets during the pillaring process.