The preparation and characterization of a series of Pd–Sn catalysts deposited on acrylic resins bearing carboxylic functional groups and having different Sn contents and different reduction temperatures is reported. They are used for the hydrogenation of 100 ppm aqueous nitrate solutions. It is observed that a high COOH content in the support is important in the control of the selectivity of the catalysts limiting ammonia formation. A correlation between the buffering ability of the COOH/COO groups pending from the support surface and the amount of ammonia observed is observed. Powder X-ray diffraction analysis indicates the presence of Pd–Sn alloys of different composition depending on the reduction temperature. This affects the activity of the catalysts.