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

Abstract

High-surface-area zirconia was obtained by digestion of hydrous oxide precipitated with ammonia and sodium hydroxide. The acidity of digested and undigested samples was compared by ammonia temperature-programmed desorption and pyridine adsorption. Undigested zirconia showed only Lewis acid sites but digested samples have Bransted sites as well. The acid strength of the digested samples was higher than that of undigested samples. This is attributed to the smaller crystallite size, which results in a larger number of highly uncoordinated zirconium ions. Samples prepared from sodium hydroxide contained sodium ions in a surface layer that reduces the acidity of the samples.