Nanostructured Cerium Oxide “Ecocatalysts”

Abstract

Catalysts based on cerium oxide are now used as effective oxidation systems in numerous environmental applications. Cerium oxide was introduced into the catalysis field relatively recently, in 1976, and not as a catalyst initially. Rather, it was chosen as the key oxygen-storage component of the three-way catalyst (TWC) used in automotive exhausts. Accordingly, ceria is used to extend the air/fuel ratio window in the exhaust gas, releasing or accepting oxygen, respectively, under fuel-rich or fuellean conditions, so that the noble metal catalyst operates at the desirable stoichiometric air/fuel ratio, at which it effectively converts all three gaseous pollutants—CO, hydrocarbons, and NO—to innocuous products. A solid solution of cerium and zirconium oxides is used in today's catalytic converters because of its higher oxygen-storage capacity (OSC) compared with pure ceria. In the years that followed the introduction of ceria into the catalytic converter, many additional merits of cerium oxide were realized, first as an active catalytic component of the TWC and subsequently as a catalyst and sorbent in various industrial applications. A review article by Trovarelli on ceria-based catalysts is a good recent compilation.