A system is provided for passivating metals, such as vanadium, deposited on a catalyst during a conversion reaction. Spent catalyst particles containing the metal deposits are introduced into a regenerator, and passivating particles containing the passivating materials are also introduced into the regenerator. The passivating particles and the catalyst particles are separated after they have exited from the regenerator. At least a portion of the separated passivating particles are recycled to the regenerator, and the regenerated, separated catalyst particles are reintroduced into a reaction zone, such as a riser conversion zone.