The reduction of NO by CO over H and Na forms of Ru exchanged mordenite has been studied with ruthenium content of 0.2, 1 and 3 wt.%. The catalysts were characterized with respect to X-ray diffraction, BET surface area, temperature programmed oxidation, and temperature programmed desorption of ammonia. These catalysts have been evaluated for their activity for NO-CO reaction using a steady state gas laboratory evaluation assembly. The catalysts show high activity for NO reduction and almost 100% conversion of NO to N-2 was observed below 400 degrees C. The activity was found to be a factor of ruthenium content, however, Ru-mordenite in Na form was observed to be relatively more active than Ru-mordenite in H form, probably due to the electron donation from sodium to ruthenium sites. New zeolite phases with improved hydrothermal stability, high surface area and reasonable cation exchange properties can be potential materials for catalytic reduction of NOx. Introduction of active metal ions through ion exchange insures their high dispersion in zeolite supports, which also offer tailoring possibilities for DeNOx catalysts. (c) 2006 Elsevier B.V. All rights reserved.