Abstract: A process is disclosed wherein a regenerator is operated in an incomplete mode of combustion to regenerate FCC catalyst to burn coke contained thereon in the presence of a CO oxidation promoter. The quantity of the CO oxidation promoter is regulated so that there is at least two and preferably at least three times the minimum quantity of CO oxidation promoter present than necessary to prevent temperature excursions in the dilute phase caused by afterburn combustion of CO to CO.sub.2. The regeneration zone is maintained in an incomplete mode of combustion defined by having a CO content greater than 1.0 percent and preferably from 1 to 10 percent.

Abstract: A regeneration zone for fluid catalytic cracking contains ammonia (NH.sub.3) when the regeneration zone is operated in a partial combustion mode as defined by a content of CO of between 1 and 6 percent by volume. If the ammonia is not removed from the regeneration zone off gass, the same will be passed to a CO combustion zone where, in the presence of oxygen, CO is oxidized to CO.sub.2 and some of the ammonia will undesirably be oxidized to NO.sub.x. This invention reduces the presence of ammonia in the feed gas to a CO combustion zone of an FCC process by the introduction of a NO.sub.x -containing gas to dilute phase of a regeneration zone or to a regeneration zone off gas. Ammonia, NO.sub.x and oxygen present in the regeneration zone off gas of the regeneration zone, will tend to react to produce nitrogen and water vapor, which then is passed to the CO combustion zone for CO oxidation to CO.sub.2. Where the addition of NO.sub.x is made at temperatures greater than 1700.degree. F.