Hydrogenations of nitrate (NO3-) and nitrite (NO2-) in water were studied with 40-5000 ppm of the reactant at 333 K using a gas-liquid flow reactor over Pt-promoted Ni catalysts. Porous Ni was highly active for hydrogenation of NO3- to form NH3 exclusively, but rapid deactivation was observed during the reaction. It was found that the addition of a small amount of Pt to the porous Ni greatly enhanced the stationary activity. The loading amount of Pt was sensitive to the activity; 1 wt.% Pt-Ni exhibited the maximum activity. XPS measurements revealed that Pt suppressed the oxidation of the Ni-0 atoms on the surface. The kinetic equation, v = k[NO3-](0.8) PH20.8, was obtained for the hydrogenation of NO3 over 1 wt.% Pt-Ni. Results showed that 1 wt.% Pt-Ni was highly active and stable even for 5000 ppm of nitrate without the dissolutions of Pt and Ni. The product was mainly NH3 over Pt-Ni, independent of the concentration of NO3- or NO2-, the pressure of hydrogen or the reaction temperature. (c) 2005 Elsevier B.V. All rights reserved.