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%, silica retards surface area loss and phase transformations that would normally occur in zirconia samples upon heat treatment. At 5 mol% silica, prehydrolysis of the silicon precursor tetraethylorthosilicate produces mixed oxide gels whose textural properties, most notably surface area and pore size distribution, vary with gel time in a manner that parallels pure zirconia aerogels. This evidence suggests that prehydrolysis effectively matches precursor reactivities and, in turn, produces homogeneous mixed oxides. Choosing an alternate silicon precursor, tetramethylorthosilicate, or chemically modifying the zirconium precursor by treatment with acetylacetone is also effective in matching precursor reactivity. Well-mixed 95 mol% zirconia-5 mol% silica aerogels are more active in 1-butene isomerization than are poorly mixed samples or either single component aerogel. (C) 1994 Academic Press, Inc.