Molecular-Level Structure-Function Relations in Gold Nanoparticle Catalysis

Coordinatively unsaturated corner and edge atoms have been hypothesized to have the highest activity of sites responsible for many catalytic reactions on a metal surface.  Recent studies have demonstrated the validity of this hypothesis in varied reaction systems. However, the separate quantification of different types of coordinatively unsaturated sites, and elucidation of their individual catalytic rates has remained a largely unresolved challenge when dealing with catalysis on metal surfaces. Such a quantification and understanding would permit catalyst optimization based on a detailed understanding of how the degree of coordinative unsaturation affects catalysis rate. In a heterogeneous gold nanoparticle system consisting of gold nanoparticles on a metal oxide support, the catalytic contributions of undercoordinated sites such as corner and edge atoms are investigated in a model reaction system.  It is demonstrated that the most undercoordinated sites, the corner atoms, are the most active atoms by over an order of magnitude as compared to uncoordinated edge atom sites, whereas terrace sites are completely inactive.  Results provide a unique perspective into coordinative unsaturation requirements for catalysis.