Palladium and platinum-based catalysts in the catalytic reduction of nitrate in water: effect of copper, silver, or gold addition

Supported bimetallic palladium and platinum catalysts promoted by metals of group 11 (Cu, Ag, and Au) were prepared by control surface deposition and tested in the liquid-phase reduction of nitrates. Whereas bimetallic catalysts promoted by gold are totally inactive, copper or silver deposition leads to bimetallic catalysts active for nitrate reduction. The promoting effect of the second metal can be related to its redox properties, confirming that nitrate reduction occurs through a bifunctionnal mechanism following (i) a direct redox mechanism between promoter and nitrate and (ii) a catalytic reaction between hydrogen, chemisorbed on the noble metal, and intermediate nitrite. TEM experiments, TPR, and FTIR of chemisorbed CO studies of the different systems have been used to evidence the metal-metal interaction and the localization of the promoter. The characterization results have been correlated with the catalytic behavior of the materials. (C) 2003 Elsevier Inc. All rights reserved.