Ligand-protected gold nanoclusters, AunRm, with atomic precision and monodispersity have recently attracted much attention due to their well-defined structures and excellent catalytic performances in various reactions. The atomically precise Au nanoclusters are ideal model systems for understanding the structure-catalysis relationship of Au-based nanocatalysts. To elucidate how the organic ligands may affect the catalytic properties of gold catalysts, We compared two different AunRm nanoclusters supported on ceria for gas phase CO oxidation: thiolate ligands protected Au25(SR)18 (SR = -SCH2-CH2-Ph) with all surface Au atoms being coordinated and phosphine protected Au22(L8)6 (L8 = 1,8-bis(diphenylphosphino) octane) with coordination unsaturated (cus) Au atoms. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy (XAFS), and density functional theory (DFT) were employed to understand how the different ligands affect the activation of CO and O2 and thus the reaction mechanisms. The results clearly suggest that organic ligands can act as a double-edged sword for the AunRm nanoclusters in gas phase reactions when the surface Au atoms are fully coordinated: they are needed to keep the structural integrity of the nanocluster, yet they also block the surface Au sites from activating reactants and catalyzing the subsequent reaction steps. Furthermore, when the organic ligands are removed, the Au clusters would be ligated with the oxide support (inorganic ligand). The interface structure of the Au-oxide is of vital importance for Au catalysis yet is also the most difficult aspect to understand. We employed aberration-corrected electron microscopy and revealed the atomic structures of the interface between Au particles and ceria nanocubes and nanorods under oxidation and reduction conditions. The atomic level information of the interface structure provides unprecedented insights into the catalytic role of the inorganic ligands (oxide support) in the catalysis of Au nanoparticles. Acknowledgements: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Part of the work was conducted at the Center for Nanophase Materials Sciences, which is U. S. Department of Energy Office of Science User Facility.

Catalytic role of ligands in supported AunRm nanoclusters for gas phase reactions

251st National Meeting (2016)

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