OXYGEN ABSORBING AND RELEASING MATERIAL, CATALYST, EXHAUST GAS PURIFYING SYSTEM, AND EXHAUST GAS TREATMENT METHOD

The purpose of the present invention is to provide: an oxygen absorbing and releasing material comprising a ceria/zirconia-based composite oxide having improved HC and NOx purification performance; and a three-way catalyst capable of reducing a NOx discharge amount. To solve said problem, the present invention provides an oxygen absorbing and releasing material, which is a ceria/zirconia-based composite oxide, containing 0.1-20 mol% (exclusive of 20 mol%) of Gd2O3 and has an ionic conductivity of 2*10-5 S/cm or more at 400 DEG C. In addition to the above, an oxygen absorbing and releasing material is provided which is characterized in that a molar ratio of cerium to zirconium is 0.2-0.6 in terms of cerium/(cerium+zirconium), and an oxygen absorbing and releasing speed (OSC speed) Delta t50is 20.0 seconds or more or an oxygen absorbing and releasing amount (OSC amount) is 300 [mu]mol-O2/g or more. Furthermore, by applying the oxygen absorbing and releasing material to a catalyst, it ispossible to obtain a cata