(509s) High Surface Area Indium Oxide And Mixed Indium-Tin-Oxide

High surface area In2O3 and mixed In-Sn-O (ITO) are desirable materials for catalysis, electroceramics and semiconductors. We have developed proprietary recipes for the synthesis of porous In2O3, SnO2 and In-Sn mixed oxides by dry decomposition of metal salts, non-alkoxide sol-gel and modified Pechini combustion methods. Calcination of dry In (III) acetate and In (III) formate powders in the temperature range 200C-300C resulted in BET surface areas of ~100 m2/g. By dissolving In (III) acetate or In (III) acac in acac (2,4-pentanedione) or anhydrous ethyleneglycol followed by the addition of aqueous acids as gelation agents and calcination at 350C-400C, materials with high surface areas well above 100 m2/g could be produced. Similarly, by dissolving In (III) acetate in 2-methoxyethanol and aging the solution for several days, surface areas of 150 m2/g were achieved after calcination at 250C-300C. The modified Pechini method is based on dissolving In (III) acetate in aqueous glyoxylic acid (OHC-COOH) or slurrying In (III) acetate or In (III) hydroxide in aq. glyoxylic acid or oxalic acid. BET surface areas >100 m2/g have been achieved after calcination at 300C-350C.

The non-alkoxide sol-gel method and the combustion synthesis using easily decomposable organic acids as dispersants are well suited for the preparation of mixed oxides. By dissolving In (III) acetate and Sn (IV) acetate in acac and gelation by aqueous ketoglutaric acid (acetone-1,3-dicarboxylic acid), 135 m2/g ITO was obtained (calcination at 400C). By dissolving In (III) acetate and Sn (IV) acetate in aqueous glyoxylic acid and calcining at 310C, ITO having surface areas >150 m2/g was produced. The novel glyoxylic acid method is more generally applicable for the synthesis of high surface area metal oxides and mixtures and has already been demonstrated for a variety of transition and main group metals including Sn, Mn, Fe, Co, Ce, Y.