VANADIA-SILICA AEROGELS FROM VANADYLACETYLACETONATE

For the preparation of vanadium pentoxide doped silica gels, vanadium( V) oxide trialkoxides are the precursors of choice [A.E. Stiegman H. E ckert, G. Plett, S.S. Kim, M. Anderson, A. Yavrouia, Chem. Mater. 5 (1 1) (1993) 1591; D.C.M. Dutoit, M. Schneider, P. Fabrizioli, A. Baiker. Chem. Mater. 8 (1996) 734] as they possess already the desired oxidat ion number. Ln vanadylacetylacetonate, the oxidation number of vanadiu m is only +4 instead of +5. However, vanadylacetylacetonate is less re active with water and thus easier to handle, less toxic and cheaper th an vanadium(V) oxide triisopropoxide. Gels were prepared using vanadyl acetylacetonate, tetramethoxysilane, methanol and water containing HCl or NH3 as catalyst. After supercritical drying with respect to CO2 an d heat treatment in air, vanadia doped silica aerogels show the same c olour change upon adsorption of water molecules as vanadium(V) oxide t riisopropoxide doped silica xerogels. Structural properties were inves tigated by N-2-absorption and SAXS measurements. (C) 1998 Elsevier Sci ence B.V. All rights reserved.