On the catalytic nature of VN, Mo₂N, and W₂N nitrides for NO reduction with hydrogen

Three transition metal nitrides, viz. VN, Mo₂N, and W ₂N were synthesized and characterized; their catalytic activities for NO reduction with H₂ were evaluated. The as-prepared nitrides were pure in phase and ionic binding in nature. Their activities for NO reduction with H₂ ranked in the order of W₂N > Mo₂N > VN. Characterization by XRD, XPS, and H₂-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 H₂ and partly incorporated into the nitride lattice. Deactivation of the catalysts was due to the gradual oxidation of the nitrides. By regulating H₂ concentration in the feed, one can retain the active Mo₂N and W₂N phases by minimizing the presence of surface oxygen.