Cluster size effects on hydrazine decomposition on Irn/Al2O3/NiAl(1 1 0)

A series of planar model catalysts were prepared by deposition of size-selected Ir n + on Al2O3/NiAl(1 1 0), and hydrazine decomposition chemistry was used to probe their size-dependent chemical properties. Small Irn (n ⩽ 15) on Al2O3/NiAl(1 1 0) are able to induce hydrazine decomposition at temperatures well below room temperature, with significant activity first appearing at Ir7. Both activity and product branching are strongly dependent on deposited cluster size, with these small clusters supporting only the simplest decomposition mechanism: dehydrogenation and N2 desorption at low temperatures, followed by H2 recombinative desorption at temperatures above 300 K. For Ir15, we begin to see ammonia production, signaling the onset of a transition to clusters able to support more complex chemistry.