The reaction between cerium compounds and H2O2 is pH dependent.

Under acidic conditions the ceric (IV) ion is reduced to the cerous (III) state.

Under alkaline conditions the addition of H2O2 to a solution of Ce(III) results in the oxidation of the metal ion to Ce(IV).  Oxidation of cerous compounds to ceric under acid conditions is possible using a solution of sodium perdisulphate with a silver catalyst.

Use is made of the reduction reaction in the purification of cerium compounds from their ores. The reaction occurs via a per-hydroxy compound, in ammoniacal solution.