Title: Gold nano-particles supported on hematite and magnetite as highly selective catalysts for the hydrogenation of nitro-aromatics

Authors: Fernando Cárdenas-Lizana; Santiago Gómez-Quero; Lioubov Kiwi-Minsker; Mark A. Keane

Addresses: Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK; Group of Catalytic Reaction Engineering, Ecole Polytechnique Fédérale de Lausanne (GGRC-ISIC-EPFL), Lausanne, Switzerland. ' Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK. ' Group of Catalytic Reaction Engineering, Ecole Polytechnique Fédérale de Lausanne (GGRC-ISIC-EPFL), Lausanne, Switzerland. ' Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK

Abstract: The catalytic action of nano-sized Au particles supported on hematite (Fe2O3) and magnetite (Fe3O4) is compared in the continuous gas phase hydrogenation of p-chloronitrobenzene and m-dinitrobenzene. The catalysts were prepared by deposition-precipitation and have been characterised in terms of BET/pore volume, powder X-ray diffraction (XRD), temperature programmed reduction (TPR), H2 chemisorption, high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) measurements. XRD confirmed the formation Fe2O3, which was transformed into Fe3O4 during TPR to 673 K with a concomitant decrease in BET area and pore volume. Post-TPR to 423 K, Au/Fe2O3 exhibited well dispersed pseudo-spherical Au particles with mean diameter = 2.0 nm. HRTEM and XPS demonstrate the encapsulation of Au in the Fe3O4 matrix after TPR to 423 K, which inhibited hydrogenation rate. Thermal treatment to 673 K resulted in the segregation of Au on the Fe3O4 surface and the formation of nano-scale particles with mean diameter = 4.0 nm. Similar activities were recorded over both Au/Fe2O3 and Au/Fe3O4 with exclusive nitro-group reduction to yield p-chloroaniline and m-nitroaniline, a response that is discussed in terms of Au electronic character.

Keywords: gold nanoparticles; selective hydrogenation; p-chloronitrobenzene; p-chloroaniline; m-dinitrobenzene; m-nitroaniline; nanoscale supported gold; hematite; magnetite; Au/Fe2O3; Au/Fe3O4; temperature programmed reduction; HRTEM; XPS; catalysts; nitro-aromatics; nanotechnology.

DOI: 10.1504/IJNT.2012.044831

International Journal of Nanotechnology, 2012 Vol.9 No.1/2, pp.92 - 112

Published online: 09 Jan 2012 *

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