Effects of H₂O₂ and SO₄²⁻ Species on the Crystalline Structure and Surface Properties of ZrO₂ Processed by Alkaline Precipitation

The preparation of ZrO 2 by alkaline hydrolysis of ZrOCl 2 ·8H 2 O, leads to an amorphous oxohydroxide precursor that upon calcination at temperatures higher than 350 °C produces a system with mixed crystallographic phases (monoclinic and tetragonal). Preparation of this material by the same procedure but adding different molar ratios of H 2 O 2 produces amorphous precursors (ZHP n ) developing, mainly, the tetragonal crystal phase at the same calcination temperatures. The molar fraction of the phases seems to be dependent on the H 2 O 2 molar ratio, thus indicating a direct relationship of this parameter with the crystallization behavior. At a surface level, preparation with H 2 O 2 seems to retain NH 4 + from the alkaline medium even after calcination at 500 °C for 2 h. The sulfation process of these ZHP n samples also modifies the structural properties; in this case, the crystallization process is delayed at higher temperatures, but with the same crystallographic features of the nonsulfated series, the tetragonal phase becoming stable for temperatures up to 800 °C.