The behavior of Cu or Sn promoted palladium catalysts supported on zirconia and titania for the hydrogenation of nitrate in drinking water is discussed. Catalysts are prepared either as powders (microspheres) or in the form of membranes deposited on commercial alumina tubes. The performance of the former in terms of activity and selectivity towards the formation of nitrogen in a batch reactor is presented as a function of the preparation procedure, the type of precursor, the Pd/Cu ratio and the type of promoter. The use of catalysts under diffusion controlled conditions allows to reduce significantly the amount of ammonia formed while retaining a high catalytic activity. Membrane catalysts are prepared by sol-gel and characterized by SEM, EDS and hydrogen permeability tests. Their reactivity is studied either in a recirculation reactor or in a continuous flow reactor and the effect of the initial pH, the residence time and the internal hydrogen pressure are reported. (C)2000 Elsevier Science B.V. All rights reserved.