The upstream portion of a reactor (1), contains, between the feeding area of the catalyst flow and the injection area of the charge to be cracked, at least one solid and attached packing element (6, 6′), that extends over all or part of the cross section of the reactor and consists of a network of cells through which pass the catalyst particles. This network makes it possible to create at least one step of division and recombination of the flow of catalyst particles, so as to redistribute the latter in a homogenous manner over the cross section of the reactor.