(154b) Understanding Homogeneous Au Nanoparticle Reduction Catalysis Using Organic Ligands

In a homogeneous Au nanoparticle system, the existence of accessible surface area on calixarene-bound gold nanoparticles in solution has been measured by fluorescence previously using 2-napthalenethiol (2-NT) binding experiments. Because of the calixarene's size and steric bulk, it does not completely block reactants' access to the surface atoms, but instead creates pockets wherein the reactants are able to access the catalyst's active site. Catalytic performance of the homogeneous calixarene-modified Au nanoparticles is demonstrated using reduction reactions in solution with homogeneous and heterogeneous Au catalysts.  However, in these and other unsupported nanoparticle systems, it is often unclear and difficult to prove whether the gold nanoparticle surface versus leached gold atoms/ions are the actual catalytically-active species.  Here, in this contribution, we demonstrate a new method to determine whether catalysis is occurring on the Au nanoparticle surface in such systems.  This method relies on selective blocking of the nanoparticle surface with organic ligands.  Synthesis is used as a tool to enable comparative studies employing different surface organic ligands on the gold nanoparticles. Results provide a unique perspective into the identity of the catalyst’s active sites.