Three transition metal nitrides, viz. VN, Mo2N, and W2N were synthesized and characterized; their catalytic activities for NO reduction with H-2 were evaluated. The as-prepared nitrides were pure in phase and ionic binding in nature. Their activities for NO reduction with H-2 ranked in the order of W2N > Mo2N > VN. Characterization by XRD, XPS, and H-2-TPR revealed that oxygen generated during NO dissociation was entirely captured by VN, and that VN acted as a reactant rather than a catalyst for NO reduction. Catalytic cycles could be established over the Mo2N and W2N catalysts; the nitrides catalyzed the dissociation of NO, while the oxygen generated during NO dissociation was partly reduced by H-2 and partly incorporated into the nitride lattice. Deactivation of the catalysts was due to the gradual oxidation of the nitrides. By regulating H-2 concentration in the feed, one can retain the active Mo2N and W2N phases by minimizing the presence of surface oxygen. (C) 2004 Elsevier B.V.All rights reserved.