Monday, November 8, 2010: 9:45 AM
Topaz Room (Hilton)
In this study we investigated the molecular adsorption and dissociation of n-butane on a PdO(101) thin film using temperature-programmed reaction spectroscopy (TPRS) experiments and density functional theory (DFT) calculations. We observe that n-butane adsorbs on PdO(101) in a molecular state that is more strongly-bound than n-butane physisorbed on Pd(111). We show that this molecularly adsorbed state of n-butane corresponds to to a σ-complex that forms on the rows of coordinatively unsaturated (cus) Pd atoms of the oxide surface. During TPRS, the n-butane layer undergoes facile C-H bond cleavage below about 215 K and the resulting fragments are completely oxidized by the surface upon continued heating. The evolution of product yields with increasing n-butane coverage as well as site blocking experiments provide strong evidence that the n-butane σ-complex serves as the precursor to initial C-H bond cleavage. Our DFT results further demonstrate that dative bonding between alkane molecules and cus-Pd atoms serves to activate C-H bonds on PdO(101), and suggest that adsorbed σ-complexes play a general role as precursors in alkane activation on transition metal oxide surfaces.