Infra-red study of the reactions of silicon, titanium and tin tetrachlorides with rutile

Abstract

Hydroxyl 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. Unreacted 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 Brønsted acidity which is enhanced by the addition of water. Brønsted 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 Brønsted acidity on silica but not on rutile. The modified silica surface also contained Lewis acid sites.