Silicalite characterization. 2. IR spectroscopy of the interaction of carbon monoxide with internal and external hydroxyl groups

In paper 1 we have shown that the structural properties of silicalites depend upon the preparation procedure. In particular Na- and Al-free sample (S) prepared following a specifically designed method is characterized by the presence of internal atomic-dimension defects (nanodefects and microcavities). On the basis of spectroscopic data and computer graphic simulations, it is shown that the microcavities derive from one or more missing [SiO 4 ] units and can contain up to four OH groups per missing tetrahedron