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X-Ray Mapping of Bimetallic Catalysts in Mesoporous Silica

Published online by Cambridge University Press:  02 July 2020

Vicki J. Keast ,
Paul A. Midgley ,
Brian F.G. Johnson  and
John Meurig Thomas
Vicki J. Keast
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke St., Cambridge, CB2 3QZ, UK.
Paul A. Midgley
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke St., Cambridge, CB2 3QZ, UK.
Brian F.G. Johnson
Affiliation:
The University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, UK.
John Meurig Thomas
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke St., Cambridge, CB2 3QZ, UK.Davy-Faraday Research Laboratory, The Royal Institution of Great Britian, 21 Albemarle St, London, W1X 4BS, UK.
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The small electron probe available in a scanning transmission electron microscope (STEM), when combined with X-ray energy dispersive spectroscopy (XEDS), enables the acquisition of 2D compositional maps with high spatial resolution and sensitivity. In addition to the spectroscopic information available, images sensitive to atomic number (so called Z-contrast images) can be acquired simultaneously using high-angle annular dark field imaging (HAADF). These capabilities make the STEM an ideal tool to study elemental distributions in catalysts containing 1-2 nm sized metal clusters within a support of low atomic number. The material examined in this work comprises of mesoporous silica in a honeycomb structure with channels of ˜3 nm diameter (designated MCM-41) in which nano-clusters of the bimetallic Pd6Ru6 have been introduced into the channels using metal-cluster carbonyls as precursors. Details of the specimen preparation are similar to that outlined by Shepard et al. for a Cu-Ru bimetallic catalyst.

Fig. 1 shows (a) a bright-field (BF) image, (b) a HAADF image and (c-f) X-ray elemental maps acquired on a VG 603 STEM, operated at 300 keV with probe size of ˜1.4 nm (FWTM) and probe current of ˜0.6 nA.

Type
Compositional Imaging and Spectroscopy
Information
Microscopy and Microanalysis , Volume 5 , Issue S2: Proceedings: Microscopy & Microanalysis '99, Microscopy Society of America 57th Annual Meeting, Microbeam Analysis Society 33rd Annual Meeting, Portland, Oregon August 1-5, 1999 , August 1999 , pp. 622 - 623
Copyright
Copyright © Microscopy Society of America

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References

1.Williams, D.B.et.alMikrochimica Acta S15 (1998) 49.Google Scholar
2.Shepard, D.S.et.alChem. Eur. J. 4 (1998) 1214.3.0.CO;2-E>CrossRefGoogle Scholar
3. The Department of Materials Science and Engineering at Lehigh University is gratefully acknowledged for the use of the VG 603 STEM. Thanks to Shepard, D.S.and Hermans, S. for providing the specimens and the EPSRC is acknowledged for general support.Google Scholar