Hydrothermal synthesis of manganese oxide nanorods as a highly active support for gold nanoparticles in CO oxidation and their stability at low temperature

Nanostructured mesoporous α-MnO 2 nanorods were synthesized via a simple hydrothermal process using MnSO 4 ·H 2 O and KMnO 4 as precursors. A series of Au/MnO 2 catalysts were prepared by a colloidal deposition (CD) method and were characterized by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and temperature programmed reduction of hydrogen (H 2 -TPR) analysis. The influence of the preparation conditions of the supports on the catalytic performance of Au/MnO 2 catalysts in CO oxidation has been investigated. The results show that the structure and properties of MnO 2 products were strongly dependent on the hydrothermal time. One can distinguish the aspect ratio of MnO 2 nanorods from SEM images. The obtained Au/MnO 2 catalysts with 1 wt% Au exhibits excellent performance with a complete CO conversion at 20 °C ( T 100% = 20 °C) and 50% CO conversion at −25 °C ( T 50% = −25 °C). Furthermore, H 2 -TPR studies reveal the superior activities have been attributed to the support unique reducibility and the interaction between Au and support. However, the U-shaped activity curves show a significant drop in CO conversion at low-temperature. With the help of temperature programmed desorption (CO 2 -TPD) and CO 2 static adsorption studies, it confirms that the deactivation of catalytic activity was attributed to the adsorbed CO 2 taking up the active sites, which can be desorbed by increasing the reaction temperature. One active Au/MnO 2 catalysts were prepared by a colloidal deposition method. The deactivation was studied by temperature programmed desorption of CO 2 analysis.