The K-doped Co-Mn-Al mixed oxide deN(2)O catalyst was prepared by calcination of Co-Mn-Al layered double hydroxide, subsequent impregnation with KNO3, and shaping into tablets of 5 mm x 5 mm. Tablets were tested for N2O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NOx/NH3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical-chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N2O conversion of 90 +/-+ 6% at 450 degrees C was kept (GHSV = 11 000 m(3) robed-3 h-1). The obtained kinetic data were applied in modeling of a fullscale reactor for the N2O emissions abatement and can be used for estimation of the amount of the catalyst necessary for obtaining required N2O conversion in the target plant.