Abstract:
Hydroxy! groups on rutile react with silicon tetrachloride to form hydrogen chloride and TiOSi
bonds. Nucleophilic attack of the silicon atom by oxide ions in the surface also occurs, and causes
the displacement of chlorine atoms which adsorb on titanium ion sites. Unreaclcd chlorine atoms
in the chemisorbed species are hydrolyzed by water to SiOH groups. The hydrogen chloride formed
adsorbs on remaining exposed rutile surface. In the presence of adsorbed ammonia or pyridine
the modified surface, after desorption of hydrogen chloride, exhibits Bronsted acidity which is
enhanced by the addition of water. Bronsted acidity was also observed for a rutile surface treated
with tin tetrachloride, hydrolyzed, and evacuated at 400 C to remove hydrogen chloride. The
similar reactions of silica and rutile surfaces with titanium tetrachloride followed by hydrolysis and
evacuation at 400 C conferred Bronsted acidity on silica but not on rutile. The modified silica surface
also contained Lewis acid sites.
