Use of palladium based catalysts in the hydrogenation of nitrates in drinking water: from powders to membranes

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