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Jpc lett 10.1021jz300574u-gates presentation on Atomically Resolved Site-Isolated Catalyst on MgO
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Jpc lett 10.1021jz300574u-gates presentation on Atomically Resolved Site-Isolated Catalyst on MgO


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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.

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  • 1. Atomically ResolvedSite-Isolated Catalyst on MgO:Mononuclear Osmium DicarbonylsFormed from Os3(CO)12Ceren Aydin, Apoorva Kulkarni,Miaofang Chi, Nigel D. Browningand Bruce C. GatesUniversity of California, DavisJ. 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 Handlingair sensitivity  moisture & oxygen exclusion Characterizationintegrating information from complementary techniques(microscopy & spectroscopy)Proprietary and ConfidentialAmerican Chemical Society 2
  • 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 Proprietary and Confidential American Chemical Society 3
  • 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 hProprietary and ConfidentialAmerican Chemical Society 4
  • 5. IR Spectra of MgO-supported Intensity Analysis Osmium Species on STEM ImagesIR spectra show formation ofMgO- supported Os(CO)2 speciesstarting from Os3(CO)12Intensity analysis on STEM images showsfragmented osmium species located atop Mg atoms Proprietary and Confidential American Chemical Society 5
  • 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.Proprietary and ConfidentialAmerican Chemical Society 6
  • 7. Conclusions Precise synthesis of supported metal catalysts with uniform & well-definedstructures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 triosmiumcarbonyls in helium Proprietary and Confidential American Chemical Society 7
  • 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 Proprietary and Confidential American Chemical Society 8