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

Abstract

As a novel and rather convenient method, ultrasonic pretreatment was employed for the preparation of nanostructured Au/MnOx–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)/MnOx–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)/MnOx–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.