Abstract
Noble-metal nanocages with ultrathin (less than 2 nm) walls and well-defined facets have received great interest owing to their remarkable utilization efficiency of atoms and facet-dependent catalytic activities toward various reactions. Here, we report the synthesis of Ru-based octahedral nanocages covered by {111} facets, together with ultrathin walls in a face-centered cubic (fcc) structure rather than the hexagonal close-packed (hcp) of bulk Ru. The involvement of slow injection for the Ru(III) precursor, the introduction of KBr, and the use of elevated temperature were all instrumental to the formation of Pd@Ru core-shell octahedra with a conformal, uniform shell and a smooth surface. The {111} facets were well preserved during the selective removal of the Pd cores via wet etching, even when the Ru walls were only five atomic layers in thickness. Through in situ XRD, we demonstrated that the fcc structure of the Ru nanocages was stable up to 300 °C. We also used first-principles, self-consistent density functional theory calculations to study the adsorption and dissociation of N2 as a means to predict the catalytic performance toward ammonia synthesis. Our results suggested that the small proportions of Pd atoms left behind in the walls during etching could play a key role in stabilizing the adsorption of N2 as well as in reducing the activation energy barrier to N2 dissociation.
| Original language | English |
|---|---|
| Pages (from-to) | 9227-9237 |
| Number of pages | 11 |
| Journal | Chemistry of Materials |
| Volume | 29 |
| Issue number | 21 |
| DOIs | |
| State | Published - Nov 14 2017 |
Funding
This work was supported in part by a grant from the NSF (DMR 1506018) and start-up funds from the Georgia Institute of Technology. High-resolution imaging was performed at GT’s Institute of Electronics and Nanotechnology (IEN) facilities. Calculations were performed at supercomputing centers located at the Environmental Molecular Sciences Laboratory, which is sponsored by the DOE Office of Biological and Environmental Research at Pacific Northwest National Laboratory; the Center for Nanoscale Materials at Argonne National Laboratory, supported by DOE Contract DE-AC02-06CH11357; the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by DOE Contract DE-AC02-05CH11231; and the UW-Madison Center for High Throughput Computing (CHTC), supported by UW-Madison, the Advanced Computing Initiative, the Wisconsin Alumni Research Foundation, the Wisconsin Institutes for Discovery, and the National Science Foundation, and is an active member of the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy’s Office of Science. A portion of this research was completed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Z.D.H. gratefully acknowledges support from the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1650044 and the Georgia Tech-ORNL Fellowship.