Hydrogenation of nitrate (NO3-) in water has been investigated by using Cu-Pd exchanged zeolites in a gas-liquid co-current flow system. Cu-Pd/mordenites prepared by ion-exchange at 383 K were highly selective for the hydrogenation of NO3- with H-2 to N-2 and N2O 20 at 278-333 K. Among Cu-Pd/mordenites with various Cu/Pd ratios and loading amounts of metal, 1.2 wt.% Cu-0.5 wt.% Pd/mordenite (Cu/Pd = 4) were shown to display the highest selectivity for N2O (96%) at 278 K, with the generation of undesired by-product NH3 being suppressed. In addition, this catalyst was superior in the selectivity to other Cu-Pd/zeolites and Cu-Pd/gamma-Al2O3. The concentrations of NH3 formed 1.2 wt.% Cu-0.5 wt.% Pd/ mordenite at 278 K were only 1.4 and 2.0 ppm at near 100%-conversion for the initial concentrations of 100 and 200 ppm of NO3-, respectively. The product N2O being a greenhouse gas was hydrogenated entirely to N-2 with 5 wt.% Pd/AC placed at the gas phase of outlet of reactor. Kinetic study has determined the activation energy to be 27 W mol(-1) and the reaction order to be 0.5 with respect to the concentration of NO3-) also produced N2O. Hydrogenation of nitrite (NO2-) selectively over 1.2 wt.% Cu-0.5 wt.% Pd/mordenite, supporting that the hydrogenation of NO3- proceeds through NO2- as an intermediate. It was confirmed that 1.2 wt.% Cu-0.5 wt.% Pd/mordenite exhibited a robust stability both in its activity and against the dissolution of metals during reaction at 278-333 K. (c) 2006 Elsevier B.V. All rights reserved.