THIN SILICA LAYER ON ALUMINA - EVIDENCE OF THE ACIDITY IN THE MONOLAYER

A thin silica layer on alumina was readily prepared by chemical vapor deposition of silicon methoxide; the structure of deposit silica and its relationship with the surface acidity were studied by characterization and test reactions. A silica monolayer was formed from the beginning of deposition until it covered the alumina surface almost completely. The silica monolayer on alumina possessed the Brønsted acid sites active for the isomerization of 1-butene and the dehydration of tert-butyl alcohol but inactive for the cumene cracking. The acid strength of the assumed species -Al-O-Si-OH was so weak as to catalyze only these facile reactions. Lack of strong Brønsted acidity of silanol attached to alumina was thereby confirmed. A fine distribution of acid strength due to the simple structure is suggested. © 1990 American Chemical Society.