Oxides of nitrogen (NO.sub.x) emissions from an FCC regenerator are reduced by operating the regenerator in partial CO burn mode to produce flue gas with more CO than O.sub.2 and with NO.sub.x precursors. This flue gas is then enriched with controlled amounts of oxygen and charged over catalyst, preferably Group VIII noble metal on a support, to convert most NO.sub.x precursors to nitrogen. Flue gas may then be charged to a CO boiler. Eliminating more than 90% of NO.sub.x emissions is possible by operating the FCC regenerator in partial CO burn mode, then adding air and catalytically converting NO.sub.x precursors at substoichiometric conditions. Conversion of NO.sub.x, if formed in the regenerator, may be achieved as well.