STRATEGIES IN CONTROLLING THE HOMOGENEITY OF ZIRCONIA SILICA AEROGELS- EFFECT OF PREPARATION ON TEXTURAL AND CATALYTIC PROPERTIES

We have used a sol-gel synthesis, followed by supercritical drying, to prepare zirconia-silica aerogels with different molecular ratios and varying degrees of homogeneity. Even at levels as low as 1-5 mol%, sil ica retards surface area loss and phase transformations that would nor mally occur in zirconia samples upon heat treatment. At 5 mol% silica, prehydrolysis of the silicon precursor tetraethylorthosilicate produc es mixed oxide gels whose textural properties, most notably surface ar ea and pore size distribution, vary with gel time in a manner that par allels pure zirconia aerogels. This evidence suggests that prehydrolys is effectively matches precursor reactivities and, in turn, produces h omogeneous mixed oxides. Choosing an alternate silicon precursor, tetr amethylorthosilicate, or chemically modifying the zirconium precursor by treatment with acetylacetone is also effective in matching precurso r reactivity. Well-mixed 95 mol% zirconia-5 mol% silica aerogels are m ore active in 1-butene isomerization than are poorly mixed samples or either single component aerogel. (C) 1994 Academic Press, Inc.