The exposure of CoO/Al2O3 catalyst to CO at elevated temperatures leads, after reduction of CoO to cobalt metal, to the formation of filamentary carbon, on top of which a metal particle is situated. In this way a carbon-supported metal catalyst on an alumina base can be prepared. These catalysts were tested for CO oxidation, NO reduction and thiophene hydrodesulphurization and the activity was compared with that of untreated CoO/Al2O3 catalysts. In all reactions the CO-treated CoO/Al2O3 showed a higher activity. CO-treated CoO-MoO3/Al2O3, on which no filamentary carbon was formed, showed a "normal" deactivation behaviour.