Nanostructured iron oxidecatalysts with gold for the oxidation of carbon monoxide

Abstract

A commercial iron oxide support is compared with Fe₂O₃ samples prepared by decomposition of iron nitrate, at 300 °C and 500 °C and heating times varying from 30 min to 96 h in N₂. Different methods were used for gold deposition, namely double impregnation (DIM), liquid phase reductive deposition (LPRD) and ultrasonication (US). Samples were characterised by N₂ adsorption at −196 °C, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed reduction. CO oxidation was used as a test reaction to compare the catalytic activities. The best results were obtained for the sample produced by decomposition of nitrate at 300 °C for 1 h, which showed the largest surface area and highest amount of hydroxylated iron species. Increasing the calcination time and/or the temperature produced less active samples. Although LPRD materials showed the smallest gold nanoparticle sizes (1–12 nm), the best catalytic results were obtained for the DIM materials. This is most likely related to the oxidation state of gold (Au⁺) found in the DIM catalysts, in contrast with LPRD and US materials, where metallic gold (Au⁰) is present. Other samples showed lower activities. Nevertheless, all samples prepared by DIM had better catalytic activity than the Au/Fe₂O₃ World Gold Council reference catalyst.