The activities of the Pd-Cu catalysts supported on various metal oxides for the reduction of nitrate and nitrite ions were compared at a constant pH. Among them, the catalysts supported on titania xerogel prepared by a glycothermal method showed the highest performance for nitrate reduction. For the reduction of nitrite ions, Pd-Cu/CeO2 showed the highest catalytic activity; however, significant dissolution of the components of the catalyst was observed during the reaction at a relatively low pH range. On the other hand, a single-component Pd catalyst supported on titania xerogel showed excellent activity for the reduction of nitrite ion and could be used at a wide range of pH. For these catalysts, the product selectivity for N-2 from nitrite ions was markedly improved by decreasing the partial pressure of H-2 in the feed. (C) 2011 Elsevier B.V. All rights reserved.