4.8 Article

Ir6 Clusters Compartmentalized in the Supercages of Zeolite NaY: Direct Imaging of a Catalyst with Aberration-Corrected Scanning Transmission Electron Microscopy

期刊

ACS CATALYSIS
卷 1, 期 11, 页码 1613-1620

出版社

AMER CHEMICAL SOC
DOI: 10.1021/cs2004104

关键词

hexairidium clusters; zeolite NaY; aberration-corrected scanning transmission electron microscopy; zeolite-encaged nanoclusters

资金

  1. Department of Energy (DOE) [DE-SC0005822, DE-FG02-03ER46057]
  2. University of California
  3. U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-98CH10886]
  4. DOE Office of Science, Materials Sciences
  5. U.S. Department of Energy (DOE) [DE-SC0005822, DE-FG02-03ER46057] Funding Source: U.S. Department of Energy (DOE)

向作者/读者索取更多资源

By use of the precursor Ir(CO)(2)(acac) (acac is acetylacetonate), a ship-in-a-bottle synthesis was used to prepare Ir-6(CO)(16) and, by decarbonylation, clusters well approximated as Ir-6 in the supercages of zeolite NaY. The samples were characterized by infrared and extended X-ray absorption fine structure (EXAFS) spectroscopies and imaged by aberration-corrected scanning transmission electron microscopy with a high-dose electron beam (similar to 10(8) e(-)/angstrom(2), 200 kV), and the catalyst performance was characterized by turnover frequencies for ethene hydrogenation at 298 K and atmospheric pressure. The images characterizing a sample with about 17% of the supercages occupied by decarbonylated nanoclusters indicated clusters well approximated as Ir-6, with diameters consistent with such clusters, and some of the images show the clusters with atomic resolution and indicating each of the 6 Ir atoms. The cluster size was confirmed by EXAFS spectra. Two bonding positions of the Ir6 clusters in the supercages were distinguished; 25% of the clusters were present at T5 sites and 75% at T6 sites. The results represent the first example of the application of high-dose electron beam conditions to image metal nanoclusters in a nanoporous material; the data are characterized by a high signal-to-noise ratio, and their interpretation does not require any image processing or simulations. These statements are based on images determined in the first 5 s of exposure of the catalyst to the electron beam; thereafter, the electron beam caused measurable deterioration of the zeolite framework and thereupon aggregation of the iridium clusters.

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