Acidity of high-surface-area zirconia prepared from different precipitants

High-surface-area zirconia was obtained by digestion of hydrous oxide preci pitated with ammonia and sodium hydroxide, The acidity of digested and undi gested samples was compared by ammonia temperature-programmed desorption an d pyridine adsorption. Undigested zirconia showed only Lewis acid sites but digested samples have Bronsted sites as well. The acid strength of the dig ested samples was higher than that of undigested samples. This is attribute d to the smaller crystallite size, which results in a larger number of high ly uncoordinated zirconium ions. Samples prepared from sodium hydroxide con tained sodium ions in a surface layer that reduces the acidity of the sampl es. Copyright (C) 1999 John Wiley & Sons, Ltd.