Perchlorate ions are present in both ground and surface waters in several regions of U.S. Due to the detrimental effect of perchlorate on human health it is of current urgency to remove perchlorate from the source water. Reduction of perchlorate by hydrogen gas has undisputed advantages in cost, ease in operation, and public acceptance. In the present. study, we attempted to remove perchlorate ions from dilute solutions using hydrogen gas assisted by metallic catalysts in a pressurized reactor. Results indicated that perchlorate ions could be reduced to chloride by molecular hydrogen gas. Among a total of 78 catalytic systems studied, 25 showed significant or observable perchlorate reduction. The reaction rate was dependent on the type of catalysts used. The maximum removal efficiency was about 20% in hours at an initial perchlorate concentration of 10 ppm in the presence of several commercial catalysts. However, metallic catalysts were able to achieve about 90% removal in 2 weeks at an initial Perchlorate concentration of 2 ppm. The most efficient system was the Ti-TiO2 surface with a removal efficiency of higher than 90% in 3 days at an initial Perchlorate concentration of only 1 ppm or 1000 ppb. Results clearly indicate the potential of perchlorate reduction by hydrogen molecules. (c) 2007 Elsevier B.V. All rights reserved.