Removal of nitrates and nitrites from drinking water by catalytic hydrogenation over zeolite-supported Pt-Sn catalysts was studied. Bimetallic Pt-Sn/HZSM-5 catalysts were characterized by temperature-programmed reduction (TPR), H-2 chemisorption, X-ray photoelectron spectroscopy (XPS) and Sn-119 Mossbauer spectroscopy. The characterization techniques showed a significant decrease in the H/Pt ratio, upon tin addition, tin surface enrichment, the formation of PtSn alloys and platinum catalysis of the tin reduction. The Pt-Sn/HZSM-5 catalyst, clearly showed high catalytic activity for the reduction of nitrate to form N-2. In the bimetallic catalyst, the role of tin is to reduce nitrate or, nitrite according to a redox process, while the platinum maintains tin in the metallic state. (c) 2005 Elsevier B.V. All rights reserved.