Photocatalyzed preferential oxidation of CO under simulated sunlight using Au–transition metal oxide–sepiolite catalysts

Abstract

In the present study a series of Au–transition metal oxides supported on a clay mineral such as sepiolite were tested in the preferential oxidation of CO in an excess of H₂ under simulated solar light irradiation and in the absence of light, at 30 °C and atmospheric pressure. Transition metal oxides (ZnO, Fe₂O₃, NiO, MnO₂, and Co₃O₄) were dispersed over the sepiolite surface where, subsequently, Au nanoparticles with an average particle size between 2 and 3 nm were successfully deposited–precipitated. The obtained photocatalysts were characterized by XRD, XRF, DRUV-Vis, N₂ adsorption–desorption and HRTEM in order to evaluate the optical, structural and chemical properties of the prepared samples. Despite the low amount of gold (nominal 1.0 wt%), the catalysts exhibited an outstanding behavior under light irradiation, with reaction rates between 4.5 and 5.2 mmol CO_ox g_cat⁻¹ h⁻¹ for the Au–NiSep, Au–CoSep and Au–ZnSep samples. These photocatalysts exhibited a high dispersion of the respective transition metal oxides over the sepiolite support and the presence of low-coordinated hemispherical gold nanoparticles. The superior photocatalytic efficiency of these samples was ascribed to the reduction of the electron–hole pair recombination of photogenerated charge carriers by the excitation of the localized surface plasmon resonance of the Au nanoparticles. The BET surface area and the gold particle size seemed to be relevant factors affecting the catalytic performance.