A zirconium doped mesoporous silica has been used as a support of cobalt oxide (4-16 wt.% Co), and tested in the selective catalytic reduction (SCR) of NO with ammonia in an excess of oxygen. These catalysts exhibit maximum conversion of NO (88%) at low temperature (200degreesC), with an almost stoichiometric conversion of NH3 and minimal N2O formation. Moreover, the catalytic activity can be correlated to the presence of well dispersed Co2+/Co3+ species, as evidenced by different characterisation techniques, and their capacity to adsorb NO molecules.