1996 Volume 17 Issue 8 Pages 489-494
In order to prepare hydroxyl-free or Lewis acid surfaces, silica, titania and HZSM-5 zeolite were first dehydrated and then exposed to dry chlorine at high temperatures. The silica chlorinated at 973 K and the titanic at 873 K had no hydroxyl and were Lewis acidic. However, some oxygen atoms of hydroxyls on the silica and titania had remained as bridge oxygens. When adsorbed pyridine was outgassed at moderate temperatures, the bridge oxygen atoms were converted to hydroxyls. On the chlorination of HZSM-5, 3750 cm-1 peak due to external silanol disappeared at 823 K while 3618 cm-1 peak assigned to hydroxyl associated with framework aluminum atom was eliminated at 973 K. The former was restored when the adsorbed pyridine was outgassed at moderate temperatures. All the chlorinated samples showed no activity against the Friedel-Crafts type alkylation of benzene and naphthalene at room temperature which proceeded easily on chlorinated aluminas. However, the hydroxyl-free surfaces seem likely to be available to prepare new functional surfaces.
