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In-situ TEM Catalysis

One of the most exciting and promising areas of TEM-based research is the in-situ observation of materials interacting with gaseous environments. This research includes studies into the effect of gaseous overpressures on the shape, structure, defects, and electronic activity of a material.  It is perhaps most critical to the study of catalysis because it allows researchers to observe on the atomic scale how catalysts respond to their environment while they are active.

Right: Microstructural changes as a function of the gas environment of an Fe catalyst, shown in sequential high-resolution transmission electron micrographs:

  • (A to C) Size evolution of Fe catalysts after 60 min under H2 (A), He (B), and Ar (C) at 500°C and 500 mtorr.
  • (D to F) Series of images from the same two Fe catalyst particles held at 500°C, as the gas overpressure changes from (D) 500 mtorr He to (E) 500 mtorr Ar to (F) 500 mtorr He.
  • (G to I) Series of images from a larger Fe catalyst particle along a 110 zone axis:
  • (G) Image taken in 500 mtorr He at 500°C, showing very strong {111} facets. The inset diffractogram confirms the zone axis orientation.
  • (H) After the introduction of Ar, local degradation of the facets begins.
  • (I) With further time at 500°C in the Ar environment, the facet has been completely removed.

For all cases, the H2O with base pressure of 10-2 mtorr is present. Arrows in (H) and (I) indicate the gradual defaceting features over time.

Reference: A.R. Harutyunyan, G. Chen,T.M. Paronyan, E.M. Pigos, O.A. Kuznetsov, K. Hewaparakrama, S.M. Kim, D. Zakharov, E.A. Stach, G.U. Sumanasekera. “Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity,” Science 326 (2009) pp. 116–120. Abstract

Image Copyright © 2009, American Association for the Advancement of Science