Diphosphine-Protected Au22 Nanoclusters on Oxide Supports Are Active for Gas-Phase Catalysis without Ligand Removal

Investigation of atomically precise Au nanoclusters provides a route to understand the roles of coordination; size, and ligand effects on Au catalysis. Herein, we explored the catalytic behavior of a newly synthesized Au-22(L-8)(6) nanocluster uncoordinated Au sites supported on TiO2, CeO2, and Al2O3. Stability of the supported Au-22 nanoclusters was probed structurally by in situ extended X-ray absorption fine structure (EXAFS) and high-angle annular dark,field scanning transmission electron microcopy (HAADF-STEM), and their ability to adsorb and oxidize CO was investigated by IR absorption spectroscopy and a temperature-programmed flow-reaction. Low-temperature CO oxidation activity was observed for the supported pristine Au-22(L-8)(6) nanoclusters without ligand, removal. Density functional theory (DFT) calculations confirmed that the eight uncoordinated Au sites In the intact Au-22(L-8)(6) nanoclusters can chemisorb both CO and O-2. Use of isotopically labeled O-2 demonstrated that the reaction pathway,occurs mainly through a redox mechanism consistent with the Observed, support-dependent activity trend of CeO2 > TiO2 > Al2O3. We conclude that the uncoordinated Au sites in the intact Au-22(L-8)(6) nanoclusters are capable of adsorbing CO, activating O-2, and catalyzing CO oxidation reaction. This work is the first clear demonstration of a ligand-protected intact Au nanoduster that is active for gas-phase catalysis without the need of ligand removal.