Redox Behavior of Ceria−Zirconia Solid Solutions Modified by the Chemical Filing Process

Abstract

In the ceria−zirconia system, two kinds of preparation methods using oxalic acid or hydrazine monohydrate have been investigated to improve oxygen release and storage properties at low temperatures. These processes consist of a reduction process and surface modification. The redcutants were carbon particles produced by thermal decomposition of oxalate or a mixture of hydrazine and hydrogen produced by decomposition of hydrazine monohydrate, and the surface modification was carried out by the calcination of the obtained powders with ammonium chloride in air at 1273 K for 1 h. Cerium and zirconium chlorides produced on the surface of the solid solutions vaporized to form a chemically filed surface. As a result of the treatment, the ceria−zirconia solid solutions released a larger amount of oxygen at lower temperatures. The oxygen storage capacity of the samples measured by a pulse technique also increased after the treatment. The redox properties of the chemically filed samples have been maintained even after reduction and reoxidation aging at 1273 K for many times, indicating thermal durability of the redox activity of the catalysts.