Metal nanoclusters can exhibit catalytic properties distinct from those of the bulk phases.  It is desirable, but remains a challenge, to create dense ensembles of uniformly sized metal nanoclusters for catalytic studies.  Deposition of metal onto patterned substrates offers the intriguing possibility to self-assemble dense ensembles of nanoclusters with controlled sizes and composition.  Using this approach we have synthesized a new class of nanostructured gold model catalysts by depositing Au on single-layer graphene and boron nitride (BN) thin films formed on refractory metals.  These thin films are free of oxygen and defects, and exhibit superstructures that present periodic, identical traps on the potential energy surface for cluster nucleation.  Scanning tunneling microscopy combined with density functional theory (DFT) calculations suggests that Au forms large flexible bilayer islands on graphene/Ru(0001) but monodisperse clusters on BN/Rh(111).  At low coverage and low substrate temperature, predominantly monolayer Au clusters form exclusively in the pores of the BN nanomesh.  Even when warmed to room temperature at multi-layer equivalent Au coverages, the BN surface is still decorated by Au clusters at a high number density (1 cluster/~13 nm2).  CO and O2 are used to probe the catalytic activity of these Au nanostructures, which are characterized by infrared spectroscopies and temperature programmed desorption, with DFT calculations performed to elucidate the adsorption sites and energetics for CO and O2.  Our findings illustrate the importance of size to the reactivity of Au catalysts and the exciting possibility of corrugated thin films such as graphene and BN moir�s functioning as templates to form model nano-catalysts, including and beyond Au.

Nanostructured gold model catalysts on thin film substrates

248th National Meeting (2014)

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