Catalyst system and process for its manufacture. The catalyst system consists of a support on which the catalytically active product is deposited. The support has mechanical or physical properties which are advantageous for the operating conditions required, but a mediocre specific surface. The catalytically active product, a metal carbide, is obtained by coating the support in a suspension of a reducible compound of the metal in a solution of an organic compound, carbonisation of this compound, reduction of the metal compound and carbiding of the metal.; The carbide thus obtained has a high specific surface, the support preferably consists of silicon carbide prepared by carbonisation of a paste containing silicon, carbon and an organic resin. The invention applies to any form of catalyst, but in particular to the monolithic catalysts intended for the treatment of exhaust gases.