Al-Pillared saponites. Part 1.—IR studies

Abstract

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 Brønsted and Lewis acidity. Lewis sites are evidenced in the parent Na-exchanged clay as well as in the pillared clays. Brønsted acid sites are not evidenced in the parent Na-exchanged saponite but Al-pillared saponites exhibit Brønsted acidity as shown by a pyridinium band at 1549 cm^–1. Brønsted acid sites have been related to OH groups at 3740–3720 cm^–1 and 3597–3594 cm^–1. The same wavenumbers are evidenced for ν(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 Brønsted sites occurs on the clay sheets during the pillaring process.