A process for the preparation of beads having a crosslinked inorganic matrix with a size controlled in the millimeter range, which comprises pouring a suspension comprising a precursor of the inorganic matrix and an alginate drop wise into a solution of a polyvalent cation salt with a pH of less than 3, to obtain a reaction medium, in which the alginate gels, and crosslinking the precursor of the inorganic matrix by a sol-gel process.