Cerium is the most abundant among the rare earth elements (REE). Its chemical states include the +3 cerous and +4 ceric states. The ceric state is the only non-trivalent rare earth ion stable in aqueous solutions. It is, therefore, strongly acidic and a strong oxidizer. The cerous state closely resembles the other trivalent rare earths.
The numerous commercial applications for Cerium include glass and glass polishing, phosphors, ceramics, catalysts and metallurgy.
In glass industry, it is the most efficient glass polishing agent for precision optical polishing. It is also used to decolorize glass by keeping iron in its Ferrous state. The ability of Cerium-doped glass to block out ultra violet light is utilized in the manufacturing of medical glassware and aerospace windows. It is also used to prevent polymers from darkening in sunlight and to suppress discoloration of television glass. It is applied to optical components to improve performance.
In phosphors, the role of Cerium is not as the emitting atom, but as a "sensitizer."
Cerium is also used in a variety of ceramics, including dental compositions and as a phase stabilizer in zirconia-based products.
Ceria plays several catalytic roles. In catalytic converters it acts as a stabilizer for the high surface area Alumina, as a promoter of the water-gas shift reaction, as an oxygen storage component and as an enhancer of the NOX reduction capability of Rhodium. Cerium is added to the dominant catalyst for the production of styrene from methylbenzene to improve styrene formation. It is used in FCC catalysts containing zeolites to provide both catalytic reactivity in the reactor and thermal stability in the regenerator.
In steel manufacturing, it is used to remove free Oxygen and Sulfur by forming stable oxysulfides and by tying up undesirable trace elements, such as Lead and Antimony.