Paper SS+NS-WeM12
Nanostructured Gold Model Catalysts on Oxygen-Free Substrates

Wednesday, October 30, 2013, 11:40 am, Room 201 A

A new class of nanostructured gold model catalysts has been synthesized by depositing gold on single-layer graphene and boron nitride (BN) thin films formed on refractory metals. These thin films, which are oxygen-free and devoid of strong adsorption sites in themselves, develop moiré superstructures due to lattice mismatch with the metal substrates, which present periodic, identical traps on the potential energy surface for possible cluster nucleation. STM studies have shown that gold atoms forms two-dimensional (2-D) islands on graphene/Ru(0001) but small monodisperse clusters on BN/Rh(111). The electronic structures of these gold nanostructures have been characterized by electron energy loss spectroscopy (EELS) and angle resolved photoemission spectroscopy (ARPES), and the geometric structures have been studied by scanning tunneling microscopy (STM). CO and O₂ are used to probe the activity of these gold model catalysts. On 2-D gold islands, adsorbed CO molecules demonstrate a stretching frequency characteristic of anionic Au and can be titrated by O₂ molecules. On gold clusters on BN/Rh(111) substrates, both CO and O₂ chemisorption is demonstrated in temperature programmed desorption (TPD). Furthermore, density function theory (DFT) calculations have been used to elucidate the adsorption sites and adsorption configurations for CO and O₂ on the two different gold model catalysts. Our findings illustrate the critical importance of size to the reactivity of gold catalysts and the exciting possibility of corrugated thin films such as graphene and BN moirés functioning as templates to form model nano-catalysts.