Cerium

About Cerium

Cerium is the lanthanide that breaks the rule. Most of the f-block sticks rigidly to +3, but cerium can lose a fourth electron from its 4f¹ shell to give Ce⁴⁺, and that one quirk turns it into the most chemically interesting member of the family. Ceric ammonium nitrate (CAN) is the workhorse one-electron oxidant in synthetic organic chemistry — it cleaves PMB ethers, deprotects acetals, oxidizes hydroquinones to quinones, and initiates radical cyclizations, all in aqueous acetonitrile at room temperature. In automotive three-way catalysts, ceria stores oxygen on the lean cycle (Ce³⁺ → Ce⁴⁺) and releases it on the rich cycle, smoothing the air–fuel ratio so platinum-group metals can simultaneously oxidize CO and reduce NOₓ — without ceria, modern emissions standards are not reachable. Ceria slurries are also the final-stage chemical-mechanical polishing abrasive for silicon wafers and gorilla-glass smartphone covers, where the planarity tolerance is angstroms. Cerium is more abundant than copper in the crust and accounts for almost half the rare-earth content of bastnäsite ore.