Gold Supported on Metal Oxides for Carbon Monoxide Oxidation

Au has been loaded (1% wt.) on different commercial oxide supports (CuO, La₂O₃, Y₂O₃, NiO) by three different methods: double impregnation (DIM), liquid-phase reductive deposition (LPRD), and ultrasonication (US). Samples were characterised by N₂ adsorption at −196 ℃, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray diffraction, and temperature programmed reduction. CO oxidation was used as a test reaction to compare the catalytic activities. The best results were obtained with Au loaded by DIM on the NiO support, with an activity of 7.2 × 10⁻⁴ mol_CO·g_Au⁻¹·s⁻¹ at room temperature. This is most likely related to the Au nanoparticle size being the smallest in this catalyst (average 4.8 nm), since it is well known that gold particle size determines the catalytic activity. Other samples, having larger Au particle sizes (in the 2–12 nm range, with average sizes ranging from 4.8 to 6.8 nm), showed lower activities. Nevertheless, all samples prepared by DIM had activities (from 1.1 × 10⁻⁴ to 7.2 × 10⁻⁴ mol_CO·g_Au⁻¹·s⁻¹, at room temperature) above those reported in the literature for gold on similar oxide supports. Therefore, this method gives better results than the most usual methods of deposition–precipitation or co-precipitation.