Photocatalytic behaviour of mesoporous Au-Cu/TiO2-SiO2 for the selective CO oxidation in H2-rich stream under simulated sunlight irradiation

With the aim of developing sustainable and economic catalysts, Au doped-transition metals have gained great interest thanks to their abundance and affordability. Moreover, they have shown a synergistic effect in degradation of pollutants and CO oxidation reactions [1]. This fact can be understood considering that the incorporation of transition metals in a photoactive matrix, such as titania, may turn out in new energy levels between valence and conduction bands and therefore inducing a shift of light absorption towards the visible light region. In this work, Au-Cu (Au:Cu=1) nanoparticles were supported on a post-synthesis titania modified SBA-15 silica to be used in the preferential oxidation of CO in excess of hydrogen at room temperature and atmospheric pressure both in the dark and under simulated solar light irradiation (photo-CO-PROX) [2]. To study their textural, structural, chemical and optical properties, the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (HR-TEM), adsorption-desorption of N2 at -196 °C, 13C and 29Si solid state NMR, X-ray photoelectron spectroscopy (XPS) and DRUV-vis spectroscopy. The synthesized Au-Cu/TiO2-SiO2 materials showed an ordered mesoporous network with high surface area and narrow pore size distribution (4.3 nm), exhibiting the main peaks of anatase phase. Incorporation of AuCu bimetallic phase was investigated by HR-TEM, that revealed the presence of very small nanoparticles (< 4 nm) homogenously distributed on the support and interacting with titania as assessed by XPS measurements. The photocatalysts were tested in the photo-CO-PROX and, in spite of the low gold and copper loading (Au 1.5 wt% and Cu 0.5 wt%), they resulted highly active and selective, with CO conversion and CO2 selectivity values of about 80% under simulated sunlight irradiation, due both to the presence of titania incorporated in SBA-15 and to the synergistic effect of Cu when alloyed with Au.