The reactivity of bimetallic species PtMCH2+(M = Pt, Cu; Ag, An) toward NH3 has been explored by the relativistic density functional approach. Calculated results reveal that the hydrogenation reactivity of PtMCH2+(M = Cu, Ag, Au, Pt) strongly depends on their low energy reactive precursors. The coexistence of the closed- and open-triangular structures as precursors to distinct dehydrogenation channels for PtMCH2+(M = Cu, Ag, Au) make them exhibit similar reactivity. Predicted free energies of the reaction Delta G degrees and reaction barriers of the key steps reasonably agree with the experimental ratio of the product. (c) 2005 Elsevier B.V. All rights reserved.