A series of Ir-based additives were developed to reduce the NO emissions during the regeneration of spent fluid catalytic cracking (FCC) catalyst. Catalytic additives were prepared using different catalytic supports and varying the metal loading. The evaluation of the additives' performance was initially carried out in a laboratory fluidized-bed reactor at 700 degreesC using a 2% O-2 in N-2 feed. The amounts of NO and CO emitted during regeneration in the presence of Ir-based additives were compared with those obtained when a commercial, Pt-based, CO promoter (1% CP-3) was used. All Ir-based additives exhibited high NO reduction ability in the bench scale reactor (up to 55%). The highest deNOx efficiency was measured when the additive was supported on a commercial alumina or on a stoichiometric spinel. The CO oxidation ability of Ir-based additives was, in general, lower than that over CP-3. Higher Ir loadings (0.1-1%) on alumina enhanced the CO oxidation, but inhibited the NO reduction. Addition of Ce on alumina improved the CO oxidation ability and, at the same time, maintained the NO emissions at low levels. Introducing CO into the O-2/N-2 feed enhanced the NO reduction performance. The combination of Ir-based additives and CP-3 resulted in the lowest NO and CO emissions. Selected Ir-based additives were tested in a pilot plant scale FCC unit. The pilot plant scale results were in good agreement with the corresponding bench scale experiments. Use of Ir additives in the pilot plant experiments led to up to 72% reduction of the NO emissions from the regenerator.