Selective hydrogenation of diolefins in steam cracking petrol on catalysts based on a support metal in which an organic compound has been incorporated prior to loading into the reactor

A process for the selective hydrogenation of diolefins which comprises hydrogenating diolefins selectively in steam cracking petrol containing the diolefins and at least monoolefins and aromatics within a reactor at pressure of approximately 30 to 50 bar and temperature between 50.degree. and 180.degree. C. in the presence of a hydrogen-activated catalyst containing sulphur and at least one metal of group VIII of the periodic classification of elements deposited on a support, wherein prior to the use of the catalyst and prior to its activation by hydrogen, at least one pretreatment agent comprising an organic compound containing sulphur is incorporated into the catalyst out of the reactor, without reduction and in a liquid phase, and said pretreatment agent is added in an adequate quantity to incorporate 0.05 to 10% of sulphur, expressed in sulphur weight, into the catalyst mass.