Diphosphine-Protected Au22Nanoclusters 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 Au22(L8)6nanocluster (L = 1,8-bis(diphenylphosphino) octane) with in situ uncoordinated Au sites supported on TiO2, CeO2, and Al2O3. Stability of the supported Au22nanoclusters was probed structurally by in situ extended X-ray absorption fine structure (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (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 Au22(L8)6nanoclusters without ligand removal. Density functional theory (DFT) calculations confirmed that the eight uncoordinated Au sites in the intact Au22(L8)6nanoclusters can chemisorb both CO and O2. Use of isotopically labeled O2demonstrated 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 Au22(L8)6nanoclusters are capable of adsorbing CO, activating O2, and catalyzing CO oxidation reaction. This work is the first clear demonstration of a ligand-protected intact Au nanocluster that is active for gas-phase catalysis without the need of ligand removal.
Chemical Science Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Zili
Z
Wu
Department of Chemistry, University of California , Riverside, California 92521, United States.
Guoxiang
G
Hu
Department of Chemistry, University of California , Riverside, California 92521, United States.
De-En
DE
Jiang
Chemical Science Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
David R
DR
Mullins
Department of Chemistry, Brown University , Providence, Rhode Island 02912, United States.
Qian-Fan
QF
Zhang
Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Lawrence F
LF
Allard
Department of Chemistry, Brown University , Providence, Rhode Island 02912, United States.
Lai-Sheng
LS
Wang
Chemical Science Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Steven H
SH
Overbury
CO oxidation; Gold nanoclusters; ligands; oxide support; uncoordinated sites