Adsorption and Activation of n-Alkanes On a Pdo(101) Thin Film

The formation of palladium oxide (PdO) is thought to be responsible for the exceptional activity of supported Pd catalysts toward the complete oxidation of alkanes under oxygen-rich conditions. In this talk, I will discuss our recent investigations of the adsorption and activation of n-alkanes on a PdO(101) thin film that is prepared by oxidizing Pd(111) in ultrahigh vacuum (UHV) using an oxygen atom beam. We find that alkanes adsorb relatively strongly on the PdO(101) surface by forming σ-complexes along the rows of coordinatively unsaturated (cus) Pd atoms, and that this adsorbed state acts as the precursor for initial C-H bond cleavage. For example, propane and n-butane undergo facile C-H bond cleavage on PdO(101) below about 215 K in UHV. I will also discuss density functional theory calculations which show that dative bonding between the alkane and cus-Pd atoms weakens the coordinated C-H bonds, thereby lowering dissociation barriers significantly. Finally, I will discuss recent results on C-H bond selectivity in the initial activation of propane on PdO(101) as well as the activity of binary Pd-M oxides toward alkane activation.