Passivation of metal contaminants on cracking catalyst

A process for passivating a metal on fluidized cracking catalyst which has been contaminated with said metal due to the use of said catalyst in a fluidized cracking system, and wherein said catalyst is cycled between a cracking zone, in which said catalyst is contacted at an elevated temperature with a hydrocarbon feedstock containing said metal which deposits on said catalyst, and a regeneration zone, in which carbon is oxidized and thereby removed from said catalyst, said metal being included in the group comprising nickel, cobalt or iron, the total amount of all metals of said group contained in said feedstock comprising at least one part per million by weight of said feedstock, which process comprises contacting said catalyst, prior to the cycling of said catalyst to said cracking zone, with a gas comprising hydrogen at passivation conditions prior to contact with a hydrogen gas to effect at least partial reduction of said metal and contacting said partially reduced catalyst with a gas comprising hydrocarbons selected from the group consisting of hydrocarbons containing one, two or three carbon atoms at passivation reaction conditions selected so as to effect reduction of substantially all said metal to its metallic state and deactivation of said metal in its metallic state by carbonization.