SIO- DEFECTS IN AS-SYNTHESIZED PURE-SILICA AND ALUMINOSILICATE SODALITES

The existence and distribution of Si-O- defects in pure-silica and alu minosilicate sodalites prepared from nonaqueous media containing ethyl ene glycol are investigated by Na-23 MAS NMR and XPS techniques. The o verall results of this study demonstrate that Si-O- defects are predom inantly present in the surface/near surface of pure-silica sodalite cr ystals and thus are not uniformly distributed. By contrast, the isomor phous substitution of Si by Al in the sodalite framework is found to p roduce nearly defect-free aluminosilicate sodalites.