Understanding the Thermal Stability of Palladium–Platinum Core–Shell Nanocrystals by In Situ Transmission Electron Microscopy and Density Functional Theory

Journal Article · Tue May 09 00:00:00 EDT 2017 · ACS Nano

DOI:https://doi.org/10.1021/acsnano.6b08692· OSTI ID:1398267

Vara, Madeline ^[1]; Roling, Luke T. ^[2]; Wang, Xue ^[3]; Elnabawy, Ahmed O. ^[2]; Hood, Zachary D. ^[4]; Chi, Miaofang ^[5]; Mavrikakis, Manos ^[2]; Xia, Younan ^[3]

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1. Georgia Inst. of Technology, Atlanta, GA (United States); Department of Chemical and Biological Engineering, University of Wisconsin—Madison
2. Univ. of Wisconsin-Madison, Madison, WI (United States)
3. Georgia Inst. of Technology, Atlanta, GA (United States)
4. Georgia Inst. of Technology, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Core–shell nanocrystals offer many advantages for heterogeneous catalysis, including precise control over both the surface structure and composition, as well as reduction in loading for rare and costly metals. Although many catalytic processes are operated at elevated temperatures, the adverse impacts of heating on the shape and structure of core–shell nanocrystals are yet to be understood. In this work, we used ex situ heating experiments to demonstrate that Pd@Pt_4L core–shell nanoscale cubes and octahedra are promising for catalytic applications at temperatures up to 400 °C. We also used in situ transmission electron microscopy to monitor the thermal stability of the core–shell nanocrystals in real time. Our results demonstrate a facet dependence for the thermal stability in terms of shape and composition. Specifically, the cubes enclosed by {100} facets readily deform shape at a temperature 300 °C lower than that of the octahedral counterparts enclosed by {111} facets. A reversed trend is observed for composition, as alloying between the Pd core and the Pt shell of an octahedron occurs at a temperature 200 °C lower than that for the cubic counterpart. Density functional theory calculations provide atomic-level explanations for the experimentally observed behaviors, demonstrating that the barriers for edge reconstruction determine the relative ease of shape deformation for cubes compared to octahedra. Furthermore, the opposite trend for alloying of the core–shell structure can be attributed to a higher propensity for subsurface Pt vacancy formation in octahedra than in cubes.

• Research Organization: Univ. of Wisconsin-Madison, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Contributing Organization: Center for Nanoscale Materials at Argonne National Laboratory; Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences; and the UW-Madison Center for High Throughput Computing (CHTC); the Environmental Molecular Sciences Laboratory; the National Energy Research Scientific Computing Center (NERSC)
• Grant/Contract Number: FG02-05ER15731
• OSTI ID: 1398267
• Journal Information: ACS Nano, Journal Name: ACS Nano Journal Issue: 5 Vol. 11; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
core−shell nanocrystal
density functional theory
electron microscopy
in situ heating
thermal stability