(641a) Selective Activation of Primary C-H Bonds of Propane on Pdo(101)

Achieving selective C-H bond cleavage is critical for developing catalytic processes that transform small alkanes to value-added products. In this talk, I will discuss our recent investigations that clarify the molecular-level origin for an exceptionally strong preference for propane to dissociate on the crystalline PdO(101) surface via primary C-H bond cleavage. From experiments using different propane isotopologues, we find that more than 90% of the adsorbed propane molecules that dissociate on PdO(101) during temperature programmed reaction spectroscopy react via cleavage of primary C-H bonds. Using reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations, we show that the adsorbed propane Ï?-complexes preferentially adopt geometries on PdO(101) in which only primary C-H bonds datively interact with the surface Pd atoms at low propane coverages and are thus activated under typical catalytic reaction conditions. We show that a propane molecule achieves maximum stability on PdO(101) by adopting a bidentate geometry in which a H-Pd dative bond forms at each CH₃ group. We also find that adsorbed propane molecules undergo a configurational change with increasing coverage, and begin to preferentially coordinate to the surface through the CH₂ group at sufficiently high coverage. Our results demonstrate that structural registry between the molecule and surface can strongly influence the selectivity of a metal oxide surface in activating alkane C-H bonds, and may thus provide guidance in designing catalysts capable of promoting selective alkane conversions.