Propane σ-Complexes on PdO(101): Spectroscopic Evidence of the Selective Coordination and Activation of Primary C-H Bonds

Abstract

Achieving selective C-H bond cleavage is critical for developing catalytic processes that transform small alkanes to value-added products. The present study clarifies 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. Using reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations, we show that adsorbed propane σ-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. These 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.

Keywords: CH bond activation; alkane; heterogeneous catalysis; palladium; palladium oxide.