In this work, the role of the Pt-Cu interaction and the influence of the Pt metal loading in the catalytic reduction of nitrates in water have been studied, using Pt supported on CuMgAl mixed oxides catalysts in a continuous reactor. Following three Pt impregnation protocols different surface chemistries were obtained, as confirmed by BET, TPR, HRTEM, XRD and FTIR spectroscopy. In the first protocol, the presence of Cu and Pt-Cu alloy formation has been promoted, whereas the second protocol leads to separated Pt and Cu particles in close contact. The third protocol leads to the presence of Cu, Pt and Pt-Cu alloy particles. The different catalytic behaviors were related to the differences in the surface metal chemistry of the samples. Low ammonium formation was detected in all cases but nitrite concentrations need to be improved to fulfill the maximum admissible concentration of the EU legislation. It is concluded that: (i) the presence of Pt-Cu alloy particles leads to an increase in nitrogen selectivity, enhancing the nitrite reduction but showing lower nitrate conversion, and (ii) to maximize the nitrate conversion it is necessary to obtain mainly Pt particles interacting with Cu and Pt-Cu alloy particles. (C) 2011 Elsevier B.V. All rights reserved.