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Abstract: A silica overlayer was prepared on gamma-alumina by a method of chemical vapor deposition (CVD) of silicon alkoxide using preadsorbed benzaldehyde and alpha-naphthaldehyde as a template. Infrared spectroscopy confirmed that the preadsorbed benzoate anion species remained after the deposition of silica, indicating that silica was deposited on the exposed surface of alumina. On the basis of the adsorption property of modified alumina, it is considered that the silica overlayer had a vacancy whose size was as large as the template molecule. Si-29 NMR spectroscopy showed that the Si species deposited using the template was Si(OAl)(1)(OSi)(1)(OH)(2) or Si(OAl)(2)(OSi)(1)(OH)(1), while the deposition without the template formed such a species as Si(OAl)(1)(OSi)(3) and Si(OAl)(1)(OSi)(2)(OH)(1) bonded via a two-dimensional siloxane network. Lack of activity for double-bond isomerization of 1- butene to 2-butene on the silica overlayer prepared using the template was consistent with the previous results that the two- dimensional network of siloxane on the alumina surface induced Bronsted acidity on the Al-O-Si-OH species. Both the adsorption and acidic properties on silica-deposited alumina using alpha- naphthaldehyde were different from those on the sample prepared using benzaldehyde, showing that the structure of the silica overlayer was controlled by the template molecules