Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al ₂ O ₃ Nanoparticles

Journal Article · Fri Oct 23 00:00:00 EDT 2015 · ChemCatChem

DOI:https://doi.org/10.1002/cctc.201500784· OSTI ID:1786157

Sinkler, Wharton ^[1]; Sanchez, Sergio I. ^[1]; Bradley, Steven A. ^[1]; Wen, Jianguo ^[2]; Mishra, Bhoopesh ^[3]; Kelly, Shelly D. ^[1]; Bare, Simon R. ^[1]

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1. UOP LLC, a Honeywell Company Des Plaines IL 60017 USA
2. Electron Microscopy Center—Center for Nanoscale Materials, Nanoscience and Technology Division, Argonne National Laboratory Argonne IL 60439 USA
3. Physics Department, Illinois Institute of Technology Chicago IL 60016 USA

Abstract Aberration‐corrected (AC) STEM, AC TEM and in situ X‐ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ‐alumina support after reduction in hydrogen at 700 °C. STEM high‐angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two‐dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X‐ray absorption fine structure data are in good agreement with these observations. High‐resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through‐focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two‐dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel‐beam TEM mode of imaging may be advantageous because of the less pronounced beam‐induced structural rearrangements that occur when imaging with a fine STEM probe.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1786157
• Journal Information: ChemCatChem, Journal Name: ChemCatChem Vol. 7 Journal Issue: 22; ISSN 1867-3880
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: Germany
• Language: English