Sol-gel synthesis of zirconia supports: Important properties for generating n-butane isomerization activity upon sulfate promotion

By studying zirconium oxide supports prepared by a variety of methods, we determined the characteristics required of a zirconia support for the generation of n-butane isomerization activity after sulfate impregnation, Using sol-gel chemistry and supercritical drying, we formed a zirconia aerogel and examined two different sulfate promotion points: (i) after drying the aerogel at 383 K and (ii) after calcination at 773 K, All sulfated aerogels, given the appropriate activation temperature, were active for n-butane isomerization, but had very different textural properties and activation behaviors depending on the sulfate introduction point, In addition, as the aerogel support after 773 K heat treatment was crystalline tetragonal, we demonstrated that crystalline zirconia can be impregnated with sulfate to give an active sample, in contrast to previous literature results. From a comparison of this calcined aerogel with other calcined supports prepared from preformed zirconia sols or commercially available zirconia, the hydroxyl content of the surface was shown to be the determining factor in whether a support could form an active sample from sulfate promotion, The sol-gel preparation of zirconia yielded materials with a high hydroxyl content, even after calcination, which allowed for successful sulfate impregnation. (C) 1995 Academic Press, Inc.