• Author: Benavidez, Angelica D.

    Department of Chemical & Nuclear Engineering and Center for Microengineered Materials, University of New Mexico, United States

  • Author: Kovarik, Libor

    Pacific Northwest National Laboratory, United States

  • Author: Genc, Arda

    FEI Company, USA NanoPort, United States

  • Author: Agrawal, Nitin

    Pacific Northwest National Laboratory, United States

  • Author: Larsson, Elin M.

    Chalmers University of Technology, Sweden

  • Author: Hansen, Thomas Willum

    Center for Electron Nanoscopy, Technical University of Denmark, Fysikvej, bygning 307, 2800, Kgs. Lyngby, Denmark

  • Author: Karim, Ayman M.

    Pacific Northwest National Laboratory, United States

  • Author: Datye, Abhaya K.

    Department of Chemical & Nuclear Engineering and Center for Microengineered Materials, University of New Mexico, United States

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In this Environmental Transmission Electron Microscopy (ETEM) study we examined the growth patterns of uniform distributions of nanoparticles (NPs) using model catalysts. Pt/SiO2 was heated at 550 °C in 560 Pa of O2 while Pd/carbon was heated in vacuum at 500 °C and in 300 Pa of 5%H2 in Argon at temperatures up to 600 °C. Individual NPs of Pd were tracked to determine the operative sintering mechanisms. We found anomalous growth of NPs occurred during the early stages of catalyst sintering wherein some particles started to grow significantly larger than the mean, resulting in a broadening of the particle size distribution (PSD). The abundance of the larger particles did not fit the log-normal distribution. We can rule out sample nonuniformity as a cause for the growth of these large particles, since images were recorded prior to heat treatments. The anomalous growth of these particles may help explain PSDs in heterogeneous catalysts which often show particles that are significantly larger than the mean, resulting in a long tail to the right. It has been suggested previously that particle migration and coalescence could be the likely cause for such broad size distributions. We did not detect any random migration of the NPs leading to coalescence. A directed migration process was seen to occur at elevated temperatures for Pd/carbon under H2. This study shows that anomalous growth of NPs can occur under conditions where Ostwald ripening is the primary sintering mechanism.
Original languageEnglish
JournalA C S Catalysis
Publication date2012
Volume2
Pages2349-2356
ISSN2155-5435
DOIs
StatePublished
CitationsWeb of Science® Times Cited: 9

Keywords

  • Catalyst sintering, Ostwald ripening, Particle size distributions, Pt/SiO2, Pd/carbon, Environmental TEM
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