Thermal NH Bond Activation on Anionic and Cationic Platinum Clusters: Non‐Predetermined Reaction Pathways Indicate Transitions to a Bulk Surface Reactivity

Reactions of cationic and anionic platinum clusters Pt n +/− , n =1–5, with NH 3 are studied by FT‐ICR mass spectrometry and DFT calculations. With cationic clusters, radiative association of an intact NH 3 is the dominant reaction channel. On anionic clusters, NH 3 undergoes reductive elimination of molecular hydrogen, with nitride and hydride bound at remote sites of the cluster. Nitride assumes a bridge position, while hydride is bound atop a single platinum atom. On the [Pt n ,NH 3 ] − potential energy surface, for n =4 fifteen local minima and connecting transition states were identified with relevance to the hydrogen formation reaction, and 12 local minima were identified for n =5. These potential energy surfaces offer a rich variety of pathways, illustrating a key feature of a successful bulk catalyst: The variety of pathways helps the catalyst to work over a wide range of temperatures and pressures.