Effect of synthesis pH and Au loading on the CO preferential oxidation performance of Au/MnOx-CeO2 catalysts prepared with ultrasonic assistance

As a novel and rather convenient method, ultrasonic pretreatment was employed for the preparation of nanostructured Au/MnO_x-CeO₂ (Mn/Ce = 1:1) catalysts which were used for CO preferential oxidation. The effects of synthesis pH (7.0-11.0) and Au loading (0.5-5.0 wt.%) on the performance of these catalysts were systematically investigated. It is found that the Au(1.0)/MnO_x-CeO₂-10.0 with 1.0 wt.% Au prepared at pH = 10.0 exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest oxygen to CO₂ selectivity of 47.8% at 120 °C. The results of XRD, HR-TEM and XPS indicate that this catalyst possesses the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which facilitates CO oxidation. The H₂-TPR results reveal that the selectivity of oxygen to CO₂ is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the supports in the catalyst Au(1.0)/MnO_x-CeO₂-10.0 decreases its capability for H₂ dissociation, effectively inhibiting the hydrogen spillover, as a result, the selectivity of oxygen to CO₂ is remarkably increased.