Abstract: The invention relates to a process for the preparation and activation of a catalyst, comprising a stage of fabricating a support consisting at least in part of at least one refractory oxide mineral, a stage of depositing on the support at least one metal from the platinum group, and a stage intended for forming on the support at least two metal halides of the Lewis acid type. Between the deposition of the metal halides of the Lewis acid type and the utilization of the catalyst in the reactor, the catalyst is subjected to an activation stage by being maintained in an acidic and nonoxidizing or reducing medium at a temperature between 300.degree. and 475.degree. C. so that its final content of a promoter metal of the zirconium, molybdenum tungsten or titanium type ranges from 0.15 to 1 percent, based on the weight of the support.