GENERATION OF ACID SITES BY SIO2 DEPOSITION ON GROUPS IVB METAL-OXIDES

An ultra thin silica layer was prepared by chemical vapor deposition of Si(OCH3)4 onto titania and zirconia. The relationship between surface structure and acidity was studied by measurement of coverage, IR spectroscopy of probe molecules, and test reactions. Silica was deposited to form a 1 : 1 complex with the oxide cation (-MSi-), until more than 90% of monolayer coverage was obtained. The silica overlayer showed weak Brønsted acidity only sufficient to catalyze the isomerization of 1-butene and the dehydration of tert-butyl alcohol. The acidity could not be correlated with the difference in coordination number or valence of cations but seemed to correlate with the interaction between silica and metal oxide. © 1992.