Paper SS-TuA2
Faceted Metal Surfaces: Surface Chemistry and Growth of Metallic Nanoclusters

Tuesday, November 1, 2011, 2:20 pm, Room 109

In this work, surface faceting is used to prepare a nanoscale model catalyst for surface reactions and a nanoscale template for growth of metallic nanoclusters. Faceting occurs when an initially planar surface converts to a “hill and valley” structure exposing new crystal faces of nanometer scale dimensions. Nanoscale three-sided pyramids exposing (311), (31-1) and (110) faces with tunable facet sizes are formed on an initially planar Ir(210) surface upon annealing in O₂ and a clean faceted Ir(210) surface can routinely be prepared in situ by heating in H₂. Surface reaction of NO+CO has been carried out on clean planar Ir(210) and clean faceted Ir(210) with varying facet size (5-14nm). Both planar and faceted Ir(210) favor reduction of NO by CO with high selectivity to N₂, which is accompanied by simultaneous oxidation of CO. The reaction is not only structure sensitive on faceted Ir(210) versus planar Ir(210) but also exhibits size effects on faceted Ir(210) for average facet size ranging from 5nm to 14nm without change in facet structure. Strong interaction between NO and CO at high NO exposure and 1ML CO pre-coverage results in “explosive” evolution of N₂ and CO₂ on planar Ir(210). Annealing Ru(11-20) in NO₂ leads to formation of ridge-like faceted surface exposing (10-11), (10-1-1), (01-11) and (01-1-1) faces. Faceted O/Ru(11-20) facilitates growth of nanoscale metallic clusters at room temperature which preferentially nucleate within valleys of the faceted surface.

Supported by DOE contract No. DE-FG02-93ER14331