Cluster size effects on hydrazine decomposition on Irn/Al2O3/NiAl(110)

A series of planar model catalysts were prepared by deposition of size-selected lr(n)(+) on Al2O3/NiAl(110), and hydrazine decomposition chemistry was used to probe their size-dependent chemical properties. Small Ir-n (n <= 15) on Al2O3/NiAl(110) are able to induce hydrazine decomposition at temperatures well below room temperature, with significant activity first appearing at Ir-7. Both activity and product branching are strongly dependent on deposited cluster size, with these small clusters supporting only the simplest decomposition mechanism: dehydrogenation and N-2 desorption at low temperatures, followed by H-2 recombinative desorption at temperatures above 300 K. For Ir-15, we begin to see ammonia production, signaling the onset of a transition to clusters able to support more complex chemistry. (c) 2005 Elsevier B.V. All rights reserved.