A series of Ru-based additives were developed to simultaneously reduce the NO and CO emissions during the regeneration of spent fluid catalytic cracking (FCC) catalyst. The evaluation of the additives was performed in a bench-scale fluid-bed reactor, while the parameters under study were the catalytic support and the Ru loading. The additives' performance was compared to that of a commercial, Pt-based, CO promoter. It was found that different types of alumina supports affected the catalytic performance. The promotion of the alumina support with cerium (Ce) enhanced the CO oxidation but had no significant influence on the deNOx performance. Decreasing Ru loading improved NO reduction but inhibited CO oxidation. A combined performance of CO oxidation and NO reduction was achieved using a Ru(0.1%)/Ce(10%)alumina additive. Moreover, in the present work, the stability of the Ru-based additive was examined by submitting the best additive to a redox pretreatment. The presence of 02 inhibited, while the presence of CO improved, its NO reduction activity. This improvement was cumulative until 100% NO reduction was achieved and suggests that reduced Ru is the required active phase. Selected Ru-based additives were tested in a pilot plant scale FCCU. The pilot plant data showed that Ru/alumina exhibited an unstable performance and high levels of CO emissions. However, low Ru loadings on Ce-promoted alumina were more stable and efficient for reducing both NO and CO emissions. Pilot plant results also validated that submitting the additive in a reducing pretreatment further enhanced its performance.