Reactor modifications for NOx reduction from a fluid catalytic cracking regeneration vessel

A process for regenerating a spent catalyst having coke deposits thereon in a catalyst regeneration vessel having a dense phase and a dilute phase, wherein the process comprises the steps of: (a) contacting the spent catalyst with a primary oxygen-containing gas in the dense phase, thereby combusting the coke, resulting in the formation of a combustion gas comprising nitrogen oxides and carbon monoxide which further reacts, thus reducing a majority of the nitrogen oxides to form elemental nitrogen; and (b) contacting the combustion gas with a secondary oxygen-containing gas, and typically a shield gas, in the dilute phase, thereby oxidizing the remaining CO to CO2 without significant temperature rise in the dilute phase due to the after burn.