Abstract: Passivation of vanadium accumulated on catalyst, e.g. crystalline zeolite hydrocarbon conversion catalyst in the rare earth and/or ammonia exchanged zeolite form, effectively minimizes the degrading characteristics of accumulated vanadium on the catalyst. The passivation is accomplished by impregnating or, preferable, precipitating, rare earths, e.g. lanthanum, onto the catalyst particles before and/or after vanadium accumulation. The process is also applicable to inert sorbent particles, e.g. those used for removing carbon and metals from contaminated hydrocarbons.