NITROGEN OXIDE PURIFYING CATALYST

PROBLEM TO BE SOLVED: To provide a nitrogen oxide purifying catalyst, a method of producing the same, a catalyst body for purifying a nitrogen oxide, and an exhaust gas purifying device, capable of sufficiently purifying NOx contained in an exhaust gas under a high-temperature environment and stably purifying NOx even in the coexistence of CO.SOLUTION: There are provided a nitrogen oxide purifying catalyst composed of a composite oxide particle, a method of producing the same, a catalyst body for purifying a nitrogen oxide which is obtained by supporting the catalyst on a base material, and an exhaust gas purifying device using the catalyst body. The composite oxide particle is composed of two phases, a crystal phase of an yttrium-barium composite oxide having a diffraction peak in a specific position and a crystal phase of an yttrium-iron composite oxide having a diffraction peak in a specific position, in a pattern of powder X-ray diffraction using CuKα1 rays.