Process for the preparation of a solid catalyst system comprising the steps of generating an emulsion by dispersing a liquid clathrate in a solution wherein (i) the solution constitutes the continuous phase of the emulsion and (ii) the liquid clathrate constitutes in form of droplets the dispersed phase of the emulsion, solidifying said dispersed phase to convert said droplets to solid particles and optionally recovering said particles to obtain said catalyst system, wherein the liquid clathrate comprises a lattice being the reaction product of aluminoxane, an organometallic compound of a transition metal of Group 3 to 10 of the Periodic Table (IUPAC 2007) or of an actinide or lanthanide, and a further compound being effective to form with the aluminoxane and the organometallic compound the lattice, and a guest being an hydrocarbon compound, and the solution comprises a silicon fluid and a hydrocarbon solvent.