This presentation has been moved. To view this presentation, please visit http://pubs.acs.org/iapps/liveslides/pages/index.htm?mscNo=jz300574u Atomically Resolved Site-Isolated Catalyst on MgO: Mononuclear Osmium Dicarbonyls formed from Os3(CO)12 Abstract: Supported triosmium clusters, formed from Os3(CO)12 on MgO, were treated in helium at 548 K for 2 h, causing fragmentation of the cluster frame and the formation of mononuclear osmium dicarbonyls. The cluster breakup and the resultant fragmented species were characterized by infrared and X-ray absorption spectroscopies, and the fragmented species were imaged by scanning transmission electron microscopy. The spectra identify the surface osmium complexes as Os(CO)2{Osupport}n (n = 3 or 4) (where the braces denote support surface atoms). The images show site-isolated Os atoms in mononuclear osmium species on MgO. The intensity analysis on the images of the MgO(110) face showed that the Os atoms were located atop Mg columns. This information led to a model of the Os(CO)2 on MgO(110), with the distances approximated as those determined by EXAFS spectroscopy, which are an average over the whole MgO surface; the results imply that these complexes were located at Mg vacancies.

1. Atomically Resolved
Site-Isolated Catalyst on MgO:
Mononuclear Osmium Dicarbonyls
Formed from Os3(CO)12
Ceren Aydin, Apoorva Kulkarni,
Miaofang Chi, Nigel D. Browning
and Bruce C. Gates
University of California, Davis
J. Phys. Chem. Lett. 2012, 3, 1865-1871 1

2. Fundamental Understanding of Supported Catalysts
– Molecular Approach O
C
 Synthesis Os
well-defined organometallic precursors
uniform, highly crystalline supports
 Sample Handling
air sensitivity  moisture & oxygen exclusion
 Characterization
integrating information from complementary techniques
(microscopy & spectroscopy)
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3. HAADF-STEM Imaging of MgO-supported Osmium Species
flowing helium Os(CO)2{OMg}n ,
Os3(CO)12 + MgO Os3(CO)11{OMg}
1 bar, 548 K, 2 h n = 3 or 4
Images A, B
C
Images C, D, E
A
1 nm
B D E
1 nm 1 1 nm
nm 1 nm
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4. XANES and EXAFS Analysis of MgO-supported Osmium Species
XANES in flowing helium at
(a) 333 K
(b) 353 K
(c) 373 K
(d) 548 K for 2 h
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5. IR Spectra of MgO-supported Intensity Analysis
Osmium Species on STEM Images
IR spectra show formation of
MgO- supported Os(CO)2 species
starting from Os3(CO)12
Intensity analysis on STEM images shows
fragmented osmium species located atop Mg atoms
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6. Building a Structural Model Based on STEM, EXAFS, & IR
The composition of the surface species indicated by EXAFS and IR
spectra, Os(CO)2{Osupport}n (n = 3 or 4), shown on MgO(110) face as
evidenced from STEM images.
Fragmented osmium carbonyls are bonded at defect sites where the
topmost Mg atom in the atomic column is missing.
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7. Conclusions
 Precise synthesis of supported metal catalysts with uniform & well-defined
structures
Complementary characterization by microscopy (STEM) & spectroscopy
(XAS & IR) at atomic scale
 Tracking structural changes with spectroscopy
 Direct observation of location of fragmented osmium species on MgO
 Structural model suggested on basis of STEM, XAS, & IR data for MgO-
supported osmium dicarbonyls formed by fragmentation of triosmium
carbonyls in helium
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8. Acknowledgments
• Department of Energy (DOE), Basic Energy Sciences
Grant No. DE-FG02-03ER46057 and DE-FG02-04ER15513
• Beamline X-18B at the National Synchrotron Light Source (NSLS)
• Beamline 10-2 at the Stanford Synchrotron Radiation Lightsource (SSRL)
• Oak Ridge National Laboratory (ORNL)
Shared Research Equipment (ShaRE) User Facility
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