Cerium Zirconium Lanthanum Yttrium Solid Rare Earth Catalyst Automotive exhaust emission is a major cause of air pollution. Rare earth elements possess 4f orbitals without full electron occupancy and lanthanide contraction. This characteristic results in their unique chemical properties when they are used as catalysts or catalytic components.Rare earth elements possess 4f orbitals without full electron occupancy and lanthanide contraction. This characteristic results in their