The catalytic behavior of mono- and bimetallic catalysts with Pd and/or Cu supported over gamma-Al2O3 in the reduction of aqueous nitrate and nitrite ions by hydrogen was investigated. The composition of the supported metal catalysts was analysed using secondary ion mass spectroscopy (SIMS) and X-ray diffraction (XRD) techniques. Surface enrichment of the bimetallic Pd-Cu particles in copper was revealed. Interactions of NO (possible intermediate in reduction of nitrate and nitrite ions) with H-2 over Pd were studied by thermal desorption spectroscopy (TDS) under high-vacuum conditions. The molecular mechanism of NO3- and NO2- reduction by H-2 as well as the role of Pd and Cu active sites are discussed.