The activities and selectivities of four pairs of bimetallic catalysts (Pd-Cu, Pt-Cu, Rh-Cu and Ir-Cu) supported on activated carbon were studied in order to optimize the metals composition for the reduction of nitrate in water with hydrogen. The catalytic tests were carried out in a semi-batch reactor, working at room temperature and pressure. The activity of the catalysts is quite different depending on the copper content. The maximum activity for the catalysts with 11% of the noble metal was obtained for 1%Rh-0.6%Cu, 1%Pd-0.6%Cu, 1%Pt-0.3%Cu and 1%Ir-0.3%Cu, with nitrate conversions after 5h of reaction of 98%, 63%, 56%, and 55%, respectively. All these weight compositions correspond to an atomic ratio noble metal/copper close to 1. With the exception of the pair Ir-Cu, where the selectivity to ammonium is almost independent of the metals composition, for all the other cases it increases with the atomic copper content up to around 75%. The pair Rh-Cu was the most active among the bimetallic catalysts tested; however, significant amounts of ammonium are obtained. The nitrate conversions for the pairs Ir-Cu and Pt-Cu are similar but the former presents higher selectivities to ammonium. The pair Pd-Cu is the most selective in the transformation of nitrate to nitrogen. (C) 2009 Elsevier B.V. All rights reserved.