The Ci(3)O(4) spinel catalyst was prepd. by pptn. from aq. soln., doped with Zn and K ions and used for decompn. of N(2)O both in stream of N(2) (2000 ppm) and in tail gases from HNO(3) prodn. (1450 ppm) in presence of H(2)O, O(2), and NO. inhibitors. The catalyst developed showed good activity and stability (conversion higher than 97%) when used for 500 h at 350 degrees C in an on-stream test. The N(2)O decompn. mechanism was confirmed by quantum chem. calcns.