Structural characterization of Rh/pumice SMAD catalysts |
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| Authors: | A Balerna S Coluccia G Deganello A Longo A Martorana G Martra C Meneghini P Pertici G Pipitone E Pitzalis AM Venezia A Verrazzani G Vitulli |
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| Institution: | (1) Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, via E. Fermi 40, 00044 Frascati, Italy, IT;(2) Dipartimento di Chimica Inorganica, Fisica e dei Materiali, Università di Torino, via P. Giuria 7, 10125 Torino, Italy, IT;(3) Istituto di Chimica e Tecnologia dei Prodotti Naturali del CNR, via Ugo La Malfa 153, 90146 Palermo, Italy, IT;(4) Dipartimento di Chimica Inorganica, Università di Palermo, viale delle Scienze, 90128 Palermo, Italy, IT;(5) Centro CNR Macromolecole Stereordinate ed Otticamente Attive, Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56100 Pisa, Italy, IT |
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| Abstract: | The structure of Rh/pumice catalysts prepared by the SMAD (Solvated Metal Atoms Dispersion) technique at different metal loadings
has been investigated by EXAFS (Extended X-ray Absorption Fine Structure Spectroscopy), XPS (X-ray Photoelectron Spectroscopy),
SAXS (Small-Angle X-ray Scattering), WAXS (Wide-Angle X-ray Scattering) and TEM (Transmission Electron Microscopy). According
to EXAFS and XPS, a fraction of the Rh atoms is oxidised, but a noticeable part is also present as Rh
0. The Rh oxidation is attributed to the interaction of the Rh atoms with the hydroxyls of the support; after the formation
of the oxide, the nucleation of metallic rhodium becomes possible. The WAXS data do not show evidence of rhodium fcc crystallites; the metal-bearing particles are probably amorphous and/or very small, as results from the SAXS and TEM data
analysis. The disagreement between the latter two techniques, resulting in a small-angle determination of the average size
of the particles that is about half that of TEM in the catalyst with the higher Rh loading, is acknowledged and discussed.
Preliminary catalytic tests are described, demonstrating the suitability of using a low surface area support for the preparation
of SMAD catalysts.
Received 2 February 1999 |
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| Keywords: | PACS 61 10 Eq X-ray scattering (including small-angle scattering) - 61 10 Ht X-ray absorption spectroscopy: EXAFS NEXAFS XANES etc - 61 16 Bg Transmission reflection and scanning electron microscopy (including EBIC) |
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